Fluoride-amorphous calcium phosphate and biomimetic nano-hydroxyapatite for enamel remineralization: An in-vitro study of surface microhardness and composition

AIM

Fluoride-Amorphous Calcium Phosphate and Biomimetic Nano-Hydroxyapatite for Enamel Remineralization; An In-Vitro Study of Surface Microhardness and Composition.

MATERIAL AND METHODS

Ninety-six extracted human premolars with sound buccal surface were divided using a randomization computer-generating software into four groups; Group I (control) sound untreated enamel, Group II (demineralized) demineralized to create white spot lesions, Group III (biom-n-HA) demineralized and then treated with biomimetic nanohydroxyapatite cream, and Group IV (F-ACP) demineralized and then treated using Fluoride-Amorphous Calcium Phosphate varnish. Each group was divided into two subgroups; subgroup "A" evaluated for mineral content using energy dispersive x-ray spectroscopy (EDX) and for surface microhardness using the Vickers microhardness test and Subgroup "B" evaluated for white spot lesion depth using a polarized light microscope (PLM).

RESULTS

The highest microhardness (VHN) was found in the (F-ACP) group (mean=428.61±54.43) and then in the (Biom-n-HA) group (mean=408.11±70.16) followed by the (Control) group (mean=402.13±53.40) with no significant difference between them and finally in the significantly different (Demineralized) group (mean=256.99±45.83). The weight percentage of Ca (30.29±1.04 and 33.44±1.07) and Ca/P ratio (1.87±0.06 and 2.03±0.05) were significantly different between Group III and Group IV respectively. PLM measurements in Group II (198.83μm), Group III (60.17μm), and Group IV (26.33μm) were significantly different.

CONCLUSIONS

Both the (Biom-n-HA) cream and the (F-ACP) varnish showed promising results for enamel remineralization. The increased enamel surface microhardness was consistent with the mineral content and the changes in the birefringence.

Evaluation of incipient enamel-carious-like lesion treated with hydroxyapatite-chitosan nanocomposite hydrogel

BACKGROUND

Non-invasive restoration of tooth enamel is a topic of high relevance in dental material science. Multiple approaches have been proposed to reach optimum reconstruction results. The current study was performed to evaluate the cross-sectional microhardness besides mineral quality and content in artificially induced carious enamel after treatment with hydroxyapatite-chitosan (HAp-CS) nanocomposite gel.

METHODS

Artificially carious lesions were induced by immersion of teeth in acidic carboxymethyl cellulose gel (pH 4.95-5) for 24- and 72-hours periods. Two different compositions of HAp-CS nanocomposite hydrogel were prepared with two different ratios 50/50 (%) and 70/30 (%), respectively. Additionally, sodium fluoride gel (1000 ppm concentration) was prepared and used as reference. Gels were applied to carious lesions twice/day for 3 min/each. After 45 days of application, surface morphology, energy dispersive x-ray spectroscopy, micro-Raman analysis in addition to cross-sectional microhardness were evaluated. Statistical analysis was performed using two-way ANOVA and Tukey's post hoc statistical tests.

RESULTS

Surface morphological evaluation of treated surfaces showed obliteration of surface irregularities. Groups demineralized for 24 hours and treated with 70/30 (HAp-CS) showed highest significant cross-sectional-microhardness (P ≤ 0.05). Evaluated subsurface cross-sectional microhardness showed better mineral quality for groups demineralized for 24 hours and treated with HAp-CS nanocomposite gels.

CONCLUSIONS

Nanocomposite gel with 70/30 (HAp-CS) could efficiently improve cross-sectional microhardness and both minerals composition and quality for lesions demineralized for 24 hours. More severely induced lesions, as demineralized for 72 hours, need more powerful agent compositions and/or prolonged application protocols for improvement.

Biomimetic dentin remineralization using eggshell derived nanohydroxyapatite with and without carboxymethyl chitosan - An in vitro study

The objective of this study was to evaluate the synergistic effect of eggshell-derived nanohydroxyapatite (EnHA) and carboxymethyl chitosan (CMC) in remineralizing artificially induced dentinal lesions. EnHA and CMC were synthesized using simple chemical processes and characterized using FTIR, XRD, HRSEM-EDX, TEM, DLS and TGA/DTA analyses. A total of 64 pre-demineralized coronal dentin specimens were randomly subjected to following treatments (n = 16):artificial saliva (AS), EnHA, CMC, and EnHA-CMC, followed by pH cycling for 7 days. HRSEM-EDX, Vickers-indenter, and micro-Raman analyses were used to assess surface-topography, microhardness, and chemical analysis, respectively. All tested materials demonstrated non-cytotoxicity when assessed on hDPSCs using MTT assay. FTIR, XRD and thermal analyses confirmed the characteristics of both EnHA and CMC. EnHA showed irregular rod-shaped nanoparticles (30-70 nm) with the presence of Ca,P,Na, and Mg ions. Dentin treated with EnHA-CMC exhibited complete tubular occlusion and highest microhardness whereas the AS group revealed the least mineral deposits (p < 0.05). No significant differences were observed between EnHA and CMC groups (p > 0.05). In addition, molecular conformation analysis revealed peak intensities in collagen's polypeptide chains in dentin treated with CMC and EnHA-CMC, whereas other groups showed poor collagen stability. The results highlighted that EnHA-CMC aided in rapid and effective biomineralization, suggesting its potential as a therapeutic solution for treating dentin caries.

Deterioration phenomenon of Pb-contaminated aqueous solution remediation and enhancement mechanism of nano-hydroxyapatite-assisted biomineralization

Modern metallurgical and smelting activities discharge the lead-containing wastewater, causing serious threats to human health. Bacteria and urease applied to microbial-induced carbonate precipitation (MICP) and enzyme-induced carbonate precipitation (EICP) are denatured under high Pb2+ concentration. The nano-hydroxyapatite (nHAP)-assisted biomineralization technology was applied in this study for Pb immobilization. Results showed that the extracellular polymers and cell membranes failed to secure the urease activity when subjected to 60 mM Pb2+. The immobilization efficiency dropped to below 50% under MICP, whereas it due to a lack of extracellular polymers and cell membranes dropped to below 30% under EICP. nHAP prevented the attachment of Pb2+ either through competing with bacteria and urease or promoting Ca2+/Pb2+ ion exchange. Furthermore, CO32- from ureolysis replaced the hydroxyl (-OH) in hydroxylpyromorphite to encourage the formation of carbonate-bearing hydroxylpyromorphite of higher stability (Pb10(PO4)6CO3). Moreover, nHAP application overcame an inability to provide nucleation sites by urease. As a result, the immobilization efficiency, when subjected to 60 mM Pb2+, elevated to above 80% under MICP-nHAP and to some 70% under EICP-nHAP. The findings highlight the potential of applying the nHAP-assisted biomineralization technology to Pb-containing water bodies remediation.

Development of a multifunctional nano-hydroxyapatite platform (nHEA) for advanced treatment of severely infected full-thickness skin wounds

The treatment of full-thickness skin injuries complicated by severe infection is hampered by the lack of comprehensive solutions that can regulate the various stages of wound healing. Consequently, there is an urgent need for a multifunctional dressing capable of multi-level regulation. In this study, we propose a novel solution by covalently integrating ε-poly-l-lysine-grafted gallic acid (EG) and in situ bioreduced silver nanoparticles (AgNPs) onto nano-hydroxyapatite (nHAP), thereby developing a multi-layered, multifunctional nanoplatform (nHEA). Cell experiments have shown that, compared to nHAP and nHAP loaded only with EG (nHEG), the addition of AgNPs to nHEA confers excellent antibacterial properties while maintaining optimal biocompatibility. The incorporation of EG onto nHEG and nHEA imparts antioxidation, anti-inflammatory, and pro-angiogenic functions, and the release of Ca2+ and EG further enhances fibroblast migration and collagen secretion. In a rat model of full-thickness skin injury with severe infection, nHEA demonstrates remarkable antibacterial and anti-inflammatory effects, along with promoting collagen remodeling and regeneration. Together, both cell experiments and animal studies confirm the significant potential of this innovative multifunctional nanoplatform in the treatment of full-thickness skin injuries with severe infection. STATEMENT OF SIGNIFICANCE: Treating infected full-thickness skin injuries poses a longstanding challenge due to the lack of comprehensive solutions that can regulate different stages of wound healing. This study introduces a novel multifunctional nanoplatform, nHEA, developed by covalently integrating ε-poly-l-lysine grafted with gallic acid (EG) and in situ bioreduced AgNPs onto nano-hydroxyapatite (nHAP). Cell experiments reveal that the integration of AgNPs enhances nHEA's antibacterial performance while maintaining optimal biocompatibility. The inclusion of EG bestows antioxidant, inflammation-regulating, and angiogenetic properties upon nHEA, and the release of Ca2+ and EG stimulates the migration and collagen secretion of fibroblast cells. Consequently, nHEA exhibits superior antibacterial and inflammation-regulating efficacy, and stimulates collagen remodeling and regeneration in vivo, making it a promising treatment for severely infected skin injuries.

Biochar and nano-hydroxyapatite combined remediation of soil surrounding tailings area: Multi-metal(loid)s fixation and soybean rhizosphere soil microbial improvement

The soil near tailings areas is relatively barren and contaminated by multi-metal(loid)s, seriously threatening the safety of crop production. Here, biochar and nano-hydroxyapatite (nHAP) were combined to improve the sterilized and unsterilized polymetallic contaminated soil, and soil incubation and soybean pot experiments were designed. Results showed that biochar and nHAP not only increased soil C, N, and P but also effectively reduced multi-metal bioavailability, wherein the combined application of the two amendments had the best effect on metal immobilization. The synergistic effect of the two amendments decreased the acid-soluble contents of Co, Cu, Fe, and Pb in rhizosphere soils up to 86.75%, 80.69%, 89.09%, and 96.70%, respectively. The ameliorant reduced the accumulation of metal(loid)s in soybean plants, and rhizosphere microorganisms inhibited the migration of soil metals to plants. Additionally, biochar and nHAP regulated the rhizosphere soil microbial community. The rhizosphere soil of the sterilization group tended to prioritize the restoration of the original dominant bacteria. As, Pb, Fe, Urease, OM, TN, and TP were the critical environmental variables affecting rhizosphere soil bacterial communities. Therefore, combining biochar and nHAP is an environmentally friendly strategy to reduce polymetallic mobility in tailings soil and crops and improve soil microbial community structure.

Uncovering nano-bonechar for attenuating fluoride in naturally contaminated soil

Fluoride ion (F-) is one of the major geogenic contaminants in water and soil. Excessive consumption of these geogenic contaminants poses serious health impacts on humans and plants. In this study, a novel carbonaceous material, nano-bonechar, was synthesized from cow bones and applied as a soil amendment at rates of 0, 0.5, 1, and 2% to remediate and revitalize naturally F--contaminated soil. The results revealed that the nano-bonechar significantly reduced the mobility and bioavailability of F- by 90% in the contaminated soil, and improved the soil quality by increasing the soil water holding capacity, soil organic matter, and the bioavailable contents of PO43-, Ca2+, and Na+. Subsequently, the pot experiment results showed a significant reduction in the uptake of F- by 93% in Zea mays plants. Moreover, the nano-bonechar application improved the plant's growth, as indicated by the higher fresh and dry weights, root and shoot lengths, and total content of PO43-, Ca2+, and K+ than those of un-amended soil. The F-immobilization in soil was mainly due to the presence of the hydroxyapatite [Ca10(PO4)6(OH)2] mineral in the nano-bonechar. Ion exchange between OH- (of nano-bonechar) and F- (of soil), and the formation of insoluble fluorite (CaF2) contributed to the attenuation of F- mobility in the soil. It is concluded that nano-bonechar, due to its size and enrichment in hydroxyapatite, could successfully be utilized for the rapid remediation and revitalization of F--contaminated agricultural soil.

An injectable and photocurable methacrylate-silk fibroin/nano-hydroxyapatite hydrogel for bone regeneration through osteoimmunomodulation

Tissue engineering has emerged as a promising approach for addressing bone defects. Most of the traditional 3D printing materials predominantly relying on polymers and ceramics. Although these materials exhibit superior osteogenic effects, their gradual degradation poses a limitation. Digital light processing (DLP) 3D bioprinting that uses natural biomaterials as bioinks has become one of the promising strategies for bone regeneration. In this study, we introduce a hydrogel biomaterial derived from silk fibroin (SF). Notably, we present the novel integration of nano-hydroxyapatite (nHA) into the hydrogel, forming a composite hydrogel that rapidly cross-links upon initiation. Moreover, we demonstrate the loading of nHA through non-covalent bonds in SilMA. In vitro experiments reveal that composite hydrogel scaffolds with 10 % nHA exhibit enhanced osteogenic effects. Transcriptomic analysis indicates that the composite hydrogel promotes bone regeneration by inducing M2 macrophage polarization. Furthermore, rat femoral defect experiments validate the efficacy of SilMA/nHA10 in bone regeneration. This study synthesis of a simple and effective composite hydrogel bioink for bone regeneration, presenting a novel strategy for the future implementation of digital 3D printing technology in bone tissue engineering.

Effects of Hydroxyapatite-Containing Toothpastes on Some Caries-Related Variables: A Randomised Clinical Trial

OBJECTIVES

This randomised clinical trial was designed and carried out with the aim to evaluate the capacity of fluoride-substituted hydroxyapatite (HAF) toothpaste to modulate oral microflora composition and biofilm acidogenicity in schoolchildren.

METHODS

In all, 610 children (4 to 5 and 6 to 7 years) were enrolled. Four toothpastes were randomly administered during 24 months: 2 contained fluoride-substituted hydroxyapatite (HAF1000 and HAF1450; 1000 and 1450 ppmF) and magnesium-, strontium-, and carbonate-substituted hydroxyapatite in a chitosan matrix, and 2 were monofluorophosphate fluoridated toothpastes (F1000 and F1450; 1000 and 1450 ppmF). Caries lesions were assessed by International Caries Detection and Assessment System scores, supragingival plaque was sampled from the approximal sites between primary molars using sterile Gracey curettes for microbiological analysis, and plaque pH curves after sucrose challenge were assessed at baseline and reevaluated after 1 year and after 2 years. The minimum and maximum pH decrease was calculated for caries-free patients and participants with a caries lesion(s) at baseline and at the end of the experimental period (24 months). Differences amongst measurements were analysed with 1-way analysis of variance.

RESULTS

During the trial, the minimum pH value increased statistically significantly in all groups; in HAF1000 and HAF1450, the increase was greatest. At the end of trial, in the 2 HAF groups all primary cariogenic bacteria were statistically significantly lower with respect to F groups (P = .03 for Streptococcus mutans and sobrinus, for Lactobacillus casei, and for Lactobacillus fermentum).

CONCLUSIONS

The trial provides robust but still inconclusive evidence on the efficacy of HAF toothpastes compared to traditional fluoridated toothpastes to reduce caries risk factors and to prevent caries lesions.

Designing bioinspired multifunctional nanoplatforms to support wound healing and skin regeneration: Mg-hydroxyapatite meets melanins

Melanin is a multifunctional biological pigment that recently emerged as endowed with anti-inflammatory, antioxidant, and antimicrobial properties and with high potentialities in skin protection and regenerative medicine. Here, a biomimetic magnesium-doped nano-hydroxyapatite (MgHA) was synthesized and decorated with melanin molecules starting from two different monomeric precursors, i.e. 5,6-dihydroxyindole-2-carboxylic acid (DHICA) and dopamine (DA), demonstrating to be able to polymerize on the surface of MgHA nanostructures, thus leading to a melanin coating. This functionalization was realized by a simple and green preparation method requiring mild conditions in an aqueous medium and room temperature. Complementary spectroscopy and electron imaging analyses were carried out to define the effective formation of a stable coating, the percentage of the organic compounds, and the structural properties of resulting melanin-coated nanostructures, which showed good antioxidant activity. The in vitro interaction with a cell model, i.e. mouse fibroblasts, was investigated. The excellent biocompatibility of all bioinspired nanostructures was confirmed from a suitable cell proliferation. Finally, the enhanced biological performances of the nanostructures coated with melanin from DHICA were confirmed by scratch assays. Jointly our findings indicated that low crystalline MgHA and melanin pigments can be efficiently combined, and the resulting nanostructures are promising candidates as multifunctional platforms for a more efficient approach for skin regeneration and protection.

Simultaneous Coating of Electrospun Nanofibers with Bioactive Molecules for Stem Cell Osteogenesis In Vitro

OBJECTIVE

Mesenchymal stem cells (MSCs) are widely recognized as a promising cell type for therapeutic applications due to their ability to secrete and regenerate bioactive molecules. For effective bone healing, it is crucial to select a scaffold that can support, induce, and restore biological function. Evaluating the scaffold should involve assessing MSC survival, proliferation, and differentiation. The principal aim of this investigation was to formulate composite nanofibrous scaffolds apt for applications in bone tissue engineering.

MATERIALS AND METHODS

In this experimental study, nanofibrous scaffolds were fabricated using Poly-L-lactic acid (PLLA) polymer. The PLLA fibers' surface was modified by integrating collagen and hydroxyapatite (HA) nanoparticles.

RESULTS

The findings demonstrated that the collagen- and nanohydroxyapatite-modified electrospun PLLA scaffold positively influenced the attachment, growth, and osteogenic differentiation of MSCs.

CONCLUSION

Coating the nanofiber scaffold with collagen and nanoparticle HA significantly enhanced the osteogenic differentiation of MSCs on electrospun PLLA scaffolds.

Study on a co-hybrid nano-hydroxyapatite with lignin derivatives and alendronate and the reinforce effect for poly(lactide-co-glycolide)

A novel co-hybrid nano-apatite (n-HA) by introducing lignin derivatives (LDs) and alendronate (ALE) was designed to reinforce poly(lactide-co-glycolide) (PLGA). The effect of different addition methods and contents of LDs, lignin derivatives sorts of lignosulfonate (LS), alkali lignin (AL) and carboxymethyl lignin (CML), and the addition order of ALE on the dispersion of hybrid n-HA, and reinforce effective for PLGA were investigated by FTIR, XRD, TEM, TGA, XPS, N2 adsorption/desorption, zeta potential, dispersion experiments, universal testing machine, SEM, DSC and POM. The results showed that the addition order could regulate the growth of n-HA crystal planes by binding with Ca2+, and co-hybrid HA by LDs and ALE possessed better dispersion owing to the synergistic effect. Moreover, 10 wt% LS-ALE-n-HA displayed the best reinforce effect, and the tensile strength of composite was 24.43 % higher than that of PLGA, even 15 wt% LS-ALE-n-HA was added, it still exhibited reinforce effect for PLGA. In vitro soaking in simulated body fluid (SBF) results indicated that LS-ALE-n-HA delayed tensile strength reduce of PLGA and promoted bone-like apatite deposition. The cell proliferation results demonstrated that the hybrid n-HA by the introduction of ALE endowed PLGA with better cell adhesion and proliferation.

Dual scaffold delivery of miR-210 mimic and miR-16 inhibitor enhances angiogenesis and osteogenesis to accelerate bone healing

Angiogenesis is critical for successful bone repair, and interestingly, miR-210 and miR-16 possess counter-active targets involved in both angiogenesis and osteogenesis: miR-210 acts as an activator by silencing EFNA3 & AcvR1b, while miR-16 inhibits both pathways by silencing VEGF & Smad5. It was thus hypothesized that dual delivery of both a miR-210 mimic and a miR-16 inhibitor from a collagen-nanohydroxyapatite scaffold system may hold significant potential for bone repair. Therefore, this systems potential to rapidly accelerate bone repair by directing enhanced angiogenic-osteogenic coupling in host cells in a rat calvarial defect model at a very early 4 week timepoint was assessed. In vitro, the treatment significantly enhanced angiogenic-osteogenic coupling of human mesenchymal stem cells, with enhanced calcium deposition after just 10 days in 2D and 14 days on scaffolds. In vivo, these dual-miRNA loaded scaffolds showed more than double bone volume and vessel recruitment increased 2.3 fold over the miRNA-free scaffolds. Overall, this study demonstrates the successful development of a dual-miRNA mimic/inhibitor scaffold for enhanced in vivo bone repair for the first time, and the possibility of extending this 'off-the-shelf' platform system to applications beyond bone offers immense potential to impact a myriad of other tissue engineering areas. STATEMENT OF SIGNIFICANCE: miRNAs have potential as a new class of bone healing therapeutics as they can enhance the regenerative capacity of bone-forming cells. However, angiogenic-osteogenic coupling is critical for successful bone repair. Therefore, this study harnesses the delivery of miR-210, known to be an activator of both angiogenesis and osteogenesis, and miR-16 inhibitor, as miR-16 is known to inhibit both pathways, from a collagen-nanohydroxyapatite scaffold system to rapidly enhance osteogenesis in vitro and bone repair in vivo in a rat calvarial defect model. Overall, it describes the successful development of the first dual-miRNA mimic/inhibitor scaffold for enhanced in vivo bone repair. This 'off-the-shelf' platform system offers immense potential to extend beyond bone applications and impact a myriad of other tissue engineering areas.

Surface topography and spectrophotometric assessment of white spot lesions restored with nano-hydroxyapatite-containing universal adhesive resin: an in-vitro study

BACKGROUND

White spot lesion (WSL) is a main shortcoming accompanied by orthodontic treatment. It impairs the esthetic, surface hardness, and surface texture of enamel. So, this study was conducted to analyze the surface characteristics and color change of white spot lesions treated with nano-hydroxyapatite (nHA)-enriched universal adhesive resin.

MATERIALS AND METHODS

Eighty sound human permanent molars crowns were sectioned into two halves, producing 160 specimens. 16 specimens were left untreated, and 144 specimens were artificially-demineralized to generate WSLs. The specimens were classified according to the treatment approach applied as follows: I; Sound enamel, Group II; artificially-created WSLs, Group III; ICON resin-restored WSLs, Group IV; Universal adhesive resin-restored WSLs, Group V; 0.5 wt% nHA-containing universal adhesive resin-restored WSLs, Group VI; 1 wt% nHA-containing universal adhesive resin- restored WSLs, and Group VII; 3 wt% nHA-containing universal adhesive resin-restored WSLs, Group VIII; 5 wt% nHA-containing universal adhesive resin-restored WSLs, Group IX; 7 wt% nHA-containing universal adhesive resin-restored WSLs, and Group X; 10 wt% nHA-containing universal adhesive resin-restored WSLs. Some surface characteristics and color changes were assessed. Data was collected and analyzed statistically using ANOVA and the Tukey test at p < 0.05.

RESULTS

Surface microhardness of WSLs was significantly improved with all investigated ratios of nHA-containing universal adhesive (p < 0.0001), with the highest mean belonging to 10 wt% nHA-containing universal adhesive resin treated WSLs. All ratios of nHA-containing universal adhesive resin significantly reduced the surface roughness of WSLs (p < 0.0001). The investigated ratios of 1, 3, 5, 7, and 10 wt% nHA-containing universal adhesive resin treatment approach could mask the WSLs significantly (p < 0.0001).

CONCLUSIONS

Nano-hydroxyapatite-containing universal adhesive is a promising contemporary approach for the management of WSLs, coupled both the remineralizing concept and the minimally invasive resin infiltration.

Acceptance and awareness of southeastern and western private practice pediatric dentists of fluoride-free toothpastes: a survey study

The American Academy of Pediatric Dentistry (AAPD) affirms that the use of fluoride, as an adjunct in the prevention of caries, is safe and effective. The AAPD encourages dentists, other healthcare providers, and parents to optimize fluoride exposures to reduce the risk of caries and to enhance the remineralization of affected teeth. However, there is resistance amongst patients towards fluoride overexposure and despite there being research on other effective remineralizing agents, most pediatric dentists primarily cater their practice to fluoride-based products. The objective of the study is to survey pediatric dentists' acceptance and awareness of fluoride-free remineralizing agents. A listserv of the southeastern and western private practice pediatric dentists was obtained from the AAPD consisting of 6490 email addresses. A questionnaire consisting of 15 questions was sent to each address using Qualtrics. Different trends in fluoride-free acceptance and awareness were seen based on region of practice, region of training and age of practitioner. Region of practice, residency training and age can be contributing factors toward fluoride-free remineralizing agent opinion. The data gathered trends towards western-trained pediatric dentists are more likely to recommend a fluoride-free toothpaste than a southeastern-trained dentist.

Printing tissue-engineered scaffolds made of polycaprolactone and nano-hydroxyapatite with mechanical properties appropriate for trabecular bone substitutes

BACKGROUND

Bone tissue engineering, based on three-dimensional (3D) printing technology, has emerged as a promising approach to treat bone defects using scaffolds. The objective of this study was to investigate the influence of porosity and internal structure on the mechanical properties of scaffolds.

METHODS

We fabricated composite scaffolds (which aimed to replicate trabecular bone) from polycaprolactone (PCL) reinforced with 30% (wt.) nano-hydroxyapatite (nHAp) by extrusion printing. Scaffolds with various porosities were designed and fabricated with and without an interlayer offset, termed as staggered and lattice structure, respectively. Mechanical compressive testing was performed to determine scaffold elastic modulus and yield strength. Linear regression was used to evaluate mechanical properties as a function of scaffold porosity.

RESULTS

Different relationships between mechanical properties and porosities were noted for the staggered and lattice structures. For elastic moduli, the two relationships intersected (porosity = 55%) such that the lattice structure exhibited higher moduli with porosity values greater than the intersection point; vice versa for the staggered structure. The lattice structure exhibited higher yield strength at all porosities. Mechanical testing results also indicated elastic moduli and yield strength properties comparable to trabecular bone (elastic moduli: 14-165 MPa; yield strength: 0.9-10 MPa).

CONCLUSIONS

Taken together, this study demonstrates that scaffolds printed from PCL/30% (wt.) nHAp with lattice and staggered structure offer promise for treating trabecular bone defects. This study identified the effect of porosity and internal structure on scaffold mechanical properties and provided suggestions for developing scaffolds with mechanical properties for substituting trabecular bone.

An investigation on the fabrication and characterization of friction stir processed nano-HAp reinforced AZ91D magnesium matrix surface composite for bio-implants

In the present research, friction stir processed (FSPed) nano-hydroxyapatite reinforced AZ91D magnesium matrix surface composite has been developed with improved ultimate tensile strength (UTS) and biological performance, which are needed for the bio-implants. Nano-hydroxyapatite reinforcement with varying proportions (5.8%, 8.3%, and 12.5%) was introduced into the AZ91-D parent material (PM) by the grooving method with different grooves of 0.5, 1 & 1.5 mm of width and 2 mm depth machined on the surface of the PM. Taguchi's L-9 orthogonal array was employed to optimize the processing variables for enhancing the UTS of the developed composite material. The optimum parameters were discovered to be the tool rotational speed of 1000 rpm, transverse speed of 50 mm/min, and 12.5% reinforcement concentration. The results revealed that the tool rotational speed contributes the highest effect (43.69%) on UTS, followed by the reinforcement percentage (37.49%) and transverse speed (18.31%). The FSPed samples at the optimized parameter setting confirmed the enhancement of 30.17% and 31.86% in UTS and micro-hardness, respectively, compared to the PM. Cytotoxicity of the optimized sample was also found superior compared to the other FSPed samples. The optimized FSPed composite's grain size was 6.88 times smaller than the AZ91D parent matrix material. The improved mechanical and biological performances of the composites are attributed to the significant grain refinement and proper dispersion of the nHAp reinforcement in the matrix.

Application of nano-hydroxyapatite matrix graft in inter-vertebral fusion therapy: a meta-analysis

OBJECTIVE

Nano-hydroxyapatite and its composites(nHA) have been widely used as grafts in inter-vertebral fusion. However, the safety and efficacy of the graft in inter-vertebral fusion is controversial. This meta-analysis aimed at evaluating the safety and efficacy of nHA and non-hydroxyapatite grafts (noHA) (autologous bone, etc.) in inter-body fusion.

MATERIALS AND METHODS

A comprehensive search was performed in electronic database as follows: PubMed, EMBASE, the Cochrane Library, Web of Science, and China National Knowledge Internet (CNKI) from inception until October 2022. Clinical studies on the effect of nHA and noHA in spinal fusion were collected. Analysis of outcome indicators using RevMan 5.4 statistical software.

RESULTS

The meta-analysis showed that the operation time of patients who underwent inter-body fusion with nHA grafts was less than that of patients who underwent noHA (p < 0.05). Compared with the noHA group, the nHA group can achieve similar clinical effects in the fusion rate(OR = 1.29,95%CI: 0.88 to 1.88,p = 0.19),Subsidence rate(OR = 1.2,95%CI:0.44 to 3.28,p = 0.72), inter-vertebral space height(SMD = 0.04,95%CI:-0.08 to 0.15,p = 0.54),Cobb angle(SMD = 0.21,95%CI: 0.18 to 0.6,p = 0.21),Blood loss(SMD = -36.58,95%CI: -81.45 to 8.29,p = 0.11),operative time in 12 months(SMD = -5.82,95%CI: -9.98 to -1.67,p = 0.006) and in the final follow-up(SMD = -0.38,95%CI: -0.51 to -0.26,p < 0.00001),ODI(SMD = 0.68,95%CI: -0.84 to 2.19,p = 0.38), VAS(SMD = 0.17,95%CI: -0.13 to 0.48,p = 0.27) and adverse events(OR = 0.98,95%CI: 0.66 to 1.45,p = 0.92), and the differences are not statistically significant.

CONCLUSION

This meta-analysis suggests that nHA matrix grafts are similar to noHA grafts in the safety and efficacy of spinal reconstruction, and are an ideal material for inter-vertebral bone grafting.

Micro-Raman spectroscopy analysis of dentin remineralization using eggshell derived nanohydroxyapatite combined with phytosphingosine

The aim of this study was to assess the remineralization efficacy of chicken eggshell-derived nano-hydroxyapatite (CEnHAp) combined with phytosphingosine (PHS) on artificially induced dentinal lesions. PHS was commercially procured whereas CEnHAp was synthesized using microwave-irradiation method and characterized using X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), high-resolution scanning electron microscopy-energy-dispersive X-ray spectroscopy (HRSEM-EDX), and transmission electron microscopy (TEM). A total of 75 pre-demineralized coronal dentin specimens were randomly treated with one of the following test agents (n = 15 each): artificial saliva (AS), casein phosphopeptide-amorphous calcium phosphate (CPP-ACP), CEnHAp, PHS, and CEnHAp-PHS under pH cycling for 7, 14, and 28 days. Vickers microhardness indenter, HRSEM-EDX, and micro-Raman spectroscopy methods were used to assess the mineral changes in the treated dentin samples. Data were submitted to Kruskal-Wallis and Friedman's two-way analyses of variance (p < 0.05). HRSEM and TEM analysis depicted irregular spherical structure of the prepared CEnHAp with a particle size of 20-50 nm. The EDX analysis confirmed the presence of Ca, P, Na and Mg ions. The XRD pattern showed the characteristic crystalline peaks for hydroxyapatite and calcium carbonate that are present in the prepared CEnHAp. Dentin treated with CEnHAp-PHS revealed highest microhardness values along with complete tubular occlusion compared to other groups at all test time intervals (p < 0.05). Specimens treated with CEnHAp showed increased remineralization than those treated with CPP-ACP followed by PHS and AS groups. The intensity of mineral peaks, as observed in the EDX and micro-Raman spectra, confirmed these findings. Further, the molecular conformation of the collagen's polypeptide chains, and amide-I and CH₂ peaks attained peak intensities in dentin treated with CEnHAp-PHS and PHS whereas other groups revealed poor stability of collagen bands. Microhardness, surface topography, and micro-Raman spectroscopy analyses revealed that dentin treated with CEnHAp-PHS have an improved collagen structure and stability as well as highest mineralization and crystallinity.

Negatively charged nano-hydroxyapatite can be used as a phosphorus fertilizer to increase the efficacy of wollastonite for soil cadmium immobilization

Improper application of phosphorus (P) fertilizer during soil cadmium (Cd) immobilization reduces the efficiency of fertilizer and Cd remediation. In this study, we synthesized three types of nano-hydroxyapatite (NHAP) with different surface charges as slow-release P fertilizers during Cd immobilization. We also evaluated the effects of wollastonite application with or without NHAP addition, in comparison with triple superphosphate (TSP) or bulk hydroxyapatite, on Cd accumulation in Amaranthus tricolor L. The results showed that adding wollastonite significantly reduced P availability (23.5%) in the soil, but it did not inhibit plant P uptake. In wollastonite-amended soil, the application of negatively/positively charged NHAP significantly increased plant biomass by 643-865% and decreased Cd uptake by 74.8-75.1% compared to the unamended soil as well as showed greater efficiency than those with TSP. This was ascribed to the increased soil pH (from 3.94 to 6.52-6.63) and increased abundance of organic acids (including citric acid, malic acid, lactic acid, and acetic acid) secreted by plants. In addition, the P-preferring bacterial class Bacteroidia was specific to soils amended with both wollastonite and NHAP-. These results suggest that NHAP- may be an appropriate P fertilizer for soil Cd immobilization using wollastonite.

In vitro release of silver ions and expression of osteogenic genes by MC3T3-E1 cell line cultured on nano-hydroxyapatite and silver/strontium-coated titanium plates

Attempts are ongoing to improve the surface properties of dental implants by application of different coatings, aiming to enhance osseointegration, and decrease the adverse effects of titanium and its alloys used in dental implants. Coating of implant surface with hydroxyapatite (HA) is one suggested strategy for this purpose due to its high biocompatibility and similar structure to the adjacent bone. This study aimed to quantify the release of silver ions and expression of osteogenic genes by MC3T3-E1 cells cultured on nano-HA and silver/strontium (Ag/Sr)-coated titanium plates via the electrochemical deposition method. Plates measuring 10 × 10 × 0.9 mm were fabricated from Ti-6Al-4 V alloy, and polished with silicon carbide abrasive papers before electrochemical deposition to create a smooth, mirror-like surface. After applying homogenous nano-HA coatings with/without silver/strontium on the surface of the plates, the composition of coatings was confirmed by energy-dispersive X-ray spectroscopy (EDS), and their morphological properties were analyzed by scanning electron microscopy (SEM). The coated specimens were then immersed in simulated body fluid (SBF), and the concentration of released sliver ions was quantified by spectroscopy at 7-14 days. The MC3T3-E1 osteoblastic cell line was cultured in osteogenic medium for 7-14 days, and after RNA extraction and cDNA synthesis, the expression of runt-related transcription factor 2 (RUNX2), osteocalcin (OCN), and osteopontin (OPN); osteogenic genes was quantified by polymerase chain reaction (PCR) using SYBR Green Master Mix kit. The expression of genes and the released amount of silver ions were compared between the two groups using the Mann-Whitney U test. The two groups were not significantly different regarding silver ion release at 14 days (P > 0.05). However, silver ion release was significantly higher from nano-HA coatings with silver/strontium at 7 days (P = 0.03). The difference in expression of RUNX2 (P = 0.04), OPN (P = 0.04), and OCN (P = 0.03) genes was also significant between nano-HA coating groups with and without silver/strontium at 7 days, and the expressions were higher in nano-HA with silver/strontium group, but this difference was not significant at 14 days. Addition of silver and strontium to specimens coated with nano-HA increased the release of silver ions within the non-toxic range, and enhanced the expression of osteogenic genes particularly after 7 days.

3D printed polylactic acid/gelatin-nano-hydroxyapatite/platelet-rich plasma scaffold for critical-sized skull defect regeneration

BACKGROUND

Three-dimensional (3D) printing is a capable approach for the fabrication of bone tissue scaffolds. Nevertheless, a purely made scaffold such as polylactic acid (PLA) may suffer from shortcomings and be restricted due to its biological behavior. Gelatin, hydroxyapatite and platelet-rich plasma (PRP) have been revealed to be of potential to enhance the osteogenic effect. In this study, it was tried to improve the properties of 3D-printed PLA scaffolds by infilling them with gelatin-nano-hydroxyapatite (PLA/G-nHA) and subsequent coating with PRP. For comparison, bare PLA and PLA/G-nHA scaffolds were also fabricated. The printing accuracy, the scaffold structural characterizations, mechanical properties, degradability behavior, cell adhesion, mineralization, systemic effect of the scaffolds on the liver enzymes, osteocalcin level in blood serum and in vivo bone regeneration capability in rat critical-sized calvaria defect were evaluated.

RESULTS

High printing accuracy (printing error of < 11%) was obtained for all measured parameters including strut thickness, pore width, scaffold density and porosity%. The highest mean ultimate compression strength (UCS) was associated with PLA/G-nHA/PRP scaffolds, which was 10.95 MPa. A slow degradation rate was observed for all scaffolds. The PLA/G-nHA/PRP had slightly higher degradation rate, possibly due to PRP release, with burst release occurred at week 4. The MTT results showed that PLA/G-nHA/PRP provided the highest cell proliferation at all time points, and the serum biochemistry (ALT and AST level) results indicated no abnormal/toxic influence caused by scaffold biomaterials. Superior cell adhesion and mineralization were obtained for PLA/G-nHA/PRP. Furthermore, all the developed scaffolds showed bone repair capability. The PLA/G-nHA/PRP scaffolds could better support bone regeneration than bare PLA and PLA/G-nHA scaffolds.

CONCLUSION

The PLA/G-nHA/PRP scaffolds can be considered as potential for hard tissue repair.

Nano-hydroxyapatite modified biochar: Insights into the dynamic adsorption and performance of lead (II) removal from aqueous solution

Adsorption of lead as Pb(II) using biochar is an environmentally sustainable approach to remediate this kind of pollution affecting wastewater. In this study, rice straw biochar (BC) was modified by combination with nano-hydroxy-apatite (HAP), resulting in a material designated as BC@nHAP, with enhanced adsorption performance. Based on Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) analyses, it was evidenced that, after modification, HAP greatly enhanced surface functional groups (i.e., -COOH and/or -OH) of raw biochar's surface. Batch tests showed that the maximum sorption capacity of BC (63.03 mg g^-1) was improved due to the modification, reaching 335.88 mg g^-1 in BC@nHAP. Pseudo-second order (PSO) kinetics fitted well the adsorption data (R² = 0.99), as well as the Langmuir isotherm model (showing an adsorption value of 335.88 mg g^-1 for q_e). The results of thermodynamic calculations showed that the adsorption was primarily governed by chemisorption process. FTIR spectroscopy and XPS spectrum after adsorption further confirmed that the adsorption mechanisms were ion exchange with Pb²⁺ and surface complexation by -OH and -COOH. In addition, BC@nHAP revealed a brilliant regeneration capability. The maximum adsorption capacity by BC@nHAP was higher than that of raw biochar or other previously reported adsorbents. Therefore, BC@nHAP could be seen as a new sorbent material with high potential for real-scale heavy metal removal from wastewater, and specifically as a capable candidate new sorbent for Pb(II) removal from wastewater, which has clear implications as regard preservation of environmental quality and public health.

Synthesis of nano hydroxyapatite from Hypopthalmichthys molitrix (silver carp) bone waste by two different methods: a comparative biophysical and in vitro evaluation on osteoblast MG63 cell lines

More than a thousand tonnes of fish bone wastes can be transformed into biomedical products annually. Alkaline hydrolysis and thermal calcification were used to create nanosized hydroxyapatite (HAp) crystals from Silver carp bone wastes. Biophysical tests were used to determine the nano size and chemical composition of synthesised hydroxyapatite. Alkaline hydrolysis hydroxyapatite (AH-HAp) was 58.3 nm, while Thermal calcination hydroxyapatite (TC-HAp) was 64.3 nm in size, confirmed by Atomic Force Microscopy. Energy Dispersive X-ray Analysis studies showed Ca/P (Calcium phosphate) ratio of AH-HAp to be 1.65, whereas TC-HAp as 1.45, confirming AH-HAp to be organically rich along with a similar Ca/P ratio as natural HAp. Fourier Transform Infrared Spectroscopy spectra indicated HAp formation from both procedures, however AH-HAp had superior crystallinity than TC-HAp confirmed from X-Ray Diffraction spectra. MG63 osteoblast cell lines showed 91% cell viability in cytotoxicity studies and 70.1% proliferation efficiency in Alkaline Phosphatase assay, which was higher than TC-HAp. The present study shows that HAp produced via alkaline hydrolysis has better biocompatibility which enhances its applicability as a biomaterial, than HAp synthesized through thermal calcination, which tends to incinerate organic moieties.

Nano-hydroxyapatite-evoked immune response synchronized with controllable immune adjuvant release for strengthening melanoma-specific growth inhibition

Concerns about the potential systematic toxicity limit the extensive application of traditional therapeutic drugs for melanoma therapy, nano-hydroxyapatite (nHA) with good biocompatibility and anti-tumor ability could be an alternative choice. In this study, nHA was employed as an anti-tumor biomaterial due to its tumor-specific toxicity. Meanwhile, granulocyte-macrophage colony-stimulating factor (GM-CSF) served as the immune adjuvant to activate the immune response. The delivery platform was fabricated by co-encapsulation of both nHA and GM-CSF into a biocompatible thermosensitive PLGA-PEG-PLGA hydrogel. The results showed that the bio-activities of nHA and GM-CSF could be well-maintained within the hydrogel. Interestingly, the addition of nHA could attenuate the burst release of GM-CSF due to possible protein absorption capacity of nHA, which is beneficial for GM-CSF sustainable release at the tumor site, achieving boosted and prolonged anti-tumor immunity. The in vitro and in vivo data demonstrated that nHA/GM-CSF hydrogel exhibited greater potency to inhibit tumor growth via enhanced CD8⁺ T-cell response compared with hydrogel and nHA hydrogel groups, contributed by the synergistic effects of nHA and GM-CSF. Overall, the strategy combining nHA and immune adjuvant shows great promise, which largely broadens the choice of combinational therapies for melanoma. STATEMENT OF SIGNIFICANCE: Nano-hydroxyapatite (nHA) has been confirmed to specifically inhibit melanoma tumor growth and induce immune response. However, its antitumor efficiency and immunity-evoking capacity are limited. In this study, granulocyte-macrophage colony-stimulating factor (GM-CSF) was introduced to serve as the immune adjuvant. Both of them were encapsulated into a biocompatible thermosensitive PLGA-PEG-PLGA hydrogel. The addition of nHA could attenuate the burst release of GM-CSF due to the interaction with nHA, which is beneficial for GM-CSF sustainable release at tumor site, achieving boosted and prolonged anti-tumor immunity. Anti-tumor immune response could be activated due to the release of tumor-associated antigen and tumor debris induced by the specifically tumor inhibition effect of nHA and GM-CSF. The combination of nHA and GM-CSF could play synergistic inhibiting effect on tumor growth via boosting and prolonging anti-tumor immunity.

Development and in vitro assessment of a bi-layered chitosan-nano-hydroxyapatite osteochondral scaffold

An innovative approach was developed to engineer a multi-layered chitosan scaffold for osteochondral defect repair. A combination of freeze drying and porogen-leaching out methods produced a porous, bioresorbable scaffold with a distinct gradient of pore size (mean = 160-275 μm). Incorporation of 70 wt% nano-hydroxyapatite (nHA) provided additional strength to the bone-like layer. The scaffold showed instantaneous mechanical recovery under compressive loading and did not delaminate under tensile loading. The scaffold supported the attachment and proliferation of human mesenchymal stem cells (MSCs), with typical adherent cell morphology found on the bone layer compared to a rounded cell morphology on the chondrogenic layer. Osteogenic and chondrogenic differentiation of MSCs preferentially occurred in selected layers of the scaffold in vitro, driven by the distinct pore gradient and material composition. This scaffold is a suitable candidate for minimally invasive arthroscopic delivery in the clinic with potential to regenerate damaged cartilage and bone.

Nano-Hydroxyapatite Bone Scaffolds with Different Porous Structures Processed by Digital Light Processing 3D Printing

The morphologies and structures of the scaffold have a significant influence on their mechanical and biological properties. In this work, different types of porous structures: Triply periodic minimal surface-Schwarz primitive (P), body-centered cubic, and cubic pore-shaped (CPS) hydroxyapatite scaffolds with ~70% porosity were fabricated through digital light processing (DLP) 3D printing technology. The compressive properties and in vitro cell evaluations such as cell proliferation and attachment morphology of these scaffolds were systematically compared. The results showed that the CPS scaffolds exhibited the highest compressive strength (~22.5 MPa) and modulus (~400 MPa). In addition, the CPS scaffolds also performed the most active cell metabolisms as compared to other two structures, which may account for the larger pore size and smaller curvature of the substrate. This study provides a general guidance for the fabrication and selection of porous bone scaffolds processed by DLP 3D printing.

Nano-hydroxyapatite incorporated quince seed mucilage bioscaffolds for osteogenic differentiation of human adipose-derived mesenchymal stem cells

In this study, the therapeutic hydrocolloid quince seed mucilage (QSM) from Cydonia oblonga Miller fruit is enriched with needle-like nano-hydroxyapatite (nHAp) crystals to fabricate a novel biomimetic osteogenic bioscaffold. The molecular weight (M_w) of water-based extracted QSM was measured with GPC (8.67 × 10⁵ g/mol), and the composite blend was prepared at a ratio of 1:1 (w/w) QSM_aq and nHAp. The porous bioscaffolds were manufactured by the freeze-drying method, and evaluated in-depth with advanced analyses. The XRD, ATR-FTIR, SEM-EDX, and elemental mapping analyses revealed a uniform coated semi-crystalline structure with no covalent bindings between QSM and nHAp. Moreover, due to the hydrocolloid backbone, a supreme swelling ratio (w/w, 6523 ± 190%) with suitable pore size (208.12 ± 99.22 μm) for osteogenic development was obtained. Further, the cytocompatible bioscaffolds were evaluated for osteogenic differentiation in vitro using human adipose-derived mesenchymal stem cells (hAMSCs). The immuno/histochemical (I/HC) staining revealed that the cells with the spherical morphology invaded the pores of the prepared bioscaffolds. Also, relatively early up-regulated osteogenic markers were observed by the qRT-PCR analyses. Overall, it is believed that the QSM-nHAp bioscaffolds might be favorable in non-load bearing applications, especially in the cranio-maxillofacial region, due to their regenerative, bendable, and durable features.

Boron Nano-hydroxyapatite Composite Increases the Bone Regeneration of Ovariectomized Rabbit Femurs

Osteoporosis is a systemic metabolic disease defined by a decreased bone mineral density, microarchitectural deterioration, and an increased incidence of fragility fractures that may lead to morbidity and mortality. Boron may stimulate new bone formation and regeneration, when combined with nano-hydroxyapatite. We questioned whether injecting boron-containing nano-hydroxyapatite composites with hyaluronan increased the bone mineral density and new bone formation in osteoporotic rabbit femurs. The regenerative effects of injectable boron-containing nano-hydroxyapatite composites from 6 to 12 weeks, which may prevent osteoporotic femoral fractures, were assessed. Boron-containing (10 μg/ml) nano-hydroxyapatite composites were injected into the intramedullary femoral cavity with hyaluronan. These significantly increased the histomorphometric new bone surface to the total bone surface ratio at 6 and 9 weeks. The micro-tomographic bone volume to the total volume ratio and bone mineral density in osteoporotic rabbit femurs increased when compared to the hyaluronan (p = 0.004, p = 0.004, p = 0.004, p = 0.01, respectively) and the sham-control (p = 0.01, p = 0.004, p = 0.01, p = 0.037, respectively) groups. The boron-containing group had a higher bone mineralization and new bone formation compared to the nano-hydroxyapatite group, although the difference was not statistically significant. These findings reveal that intramedullary injection of boron-containing nano-hydroxyapatite with hyaluronan increases new bone formation and mineralization in ovariectomized rabbit femurs. Boron-containing nano-hydroxyapatite composites are promising tissue engineering biomaterials that may have regenerative potential in preventing primary and/or secondary femoral fractures in osteoporosis patients.

The sorption and short-term immobilization of lead and cadmium by nano-hydroxyapatite/biochar in aqueous solution and soil

In this study, the composite materials using different ratios of biochar (BC) to nano-hydroxyapatite (nHAP) were prepared for the remediation of lead (Pb) and cadmium (Cd) contaminated water and soil. The sorption and the immobilization experiments indicated a higher sorption capacity and immobilization efficiency of Pb compared to those of Cd. The characteristics of XRD, FTIR, SEM, and XPS manifested that dissolution-precipitation, cation exchange, complexation, and cation-π interaction were the main four mechanisms for the sorption of Pb²⁺ and Cd²⁺ using composite material PC1 (nHAP/BC = 1/1). From semi-quantitative analysis, the mineral effect accounted for the majority of the immobilization of Pb and Cd. Due to obvious Pb-precipitates in the sorbed material, dissolution-precipitation primarily affected the sorption of Pb using PC1, while the immobilization of Cd was mainly attributable to cation exchange. Such results corresponded to the stable Pb-precipitates and unstable Cd-compounds in soil, among which the latter was prone to be released into the environment. The sorption capacity in aqueous solutions and the immobilization efficiencies in the soil for both Pb and Cd increased with the addition of nHAP, which were linearly correlated to the nHAP proportion in the composite materials. In future practical applications, the percentages of composite materials can be designed according to the specific pollutant concentration. This study sheds light on the explicit immobilization mechanisms for Pb and Cd in aqueous solutions to better understand their behaviors in the soil remediated by relevant materials.

Enhanced bone formation in rat critical-size tibia defect by a novel quercetin-containing alpha-calcium sulphate hemihydrate/nano-hydroxyapatite composite

We developed an innovative method to include quercetin into alpha-calcium sulphate hemihydrate/nano-hydroxyapatite (α-CSH/n-HA), to prepare a novel quercetin-containing α-CSH/n-HA composite (Q-α-CSH/n-HA). The physicochemical properties, and ability of Q-α-CSH/n-HA to promote cell proliferation, migration, and osteogenic differentiation of bone marrow stem cells (BMSCs) in vitro were examined. Further, the potential of Q-α-CSH/n-HA to promote bone defect repair was studied using a Sprague-Dawley rat model of critical tibial defects. Imaging was conducted by radiography and micro-CT, and bone defect repairs were observed by histopathological staining. Addition of quercetin clearly increased the porosity of the degraded composite, which elevated the cell proliferation rate, migration ability, osteogenesis differentiation, and mineralisation of BMSCs. Further, quercetin-containing composite increased the expression levels of OSX, RUNX2, OCN, ALP, BMP-2, OPN, BSP, SMAD2, and TGF-β in BMSCs, while it downregulated TNF-α. X-ray and micro-CT imaging showed that the quercetin-containing composite significantly enhanced bone defect repair and new bone in formation. Haematoxylin and eosin, Goldner, and Safranin O staining also showed that quercetin significantly increased new bone generation and promoted composite degradation and absorption. Moreover, immunofluorescence assay revealed that quercetin significantly increased the number of RUNX2/OSX/OCN-positive cells. Overall, our data demonstrate that Q-α-CSH/n-HA has excellent biocompatibility, bone conductivity, and osteo-induction performance in vitro and mediates enhanced overall repair effects and bone reconstruction in vivo, indicating that it is a promising artificial bone graft to promote bone regeneration.

Anti-caries evaluation of a nano-hydroxyapatite dental lotion for use after toothbrushing: An in situ study

OBJECTIVES

The aim of this randomized, double-blind, two-arm crossover in situ study was to investigate whether nano-hydroxyapatite (nanoHAP) dental lotion (Apagard Deep Care) applied immediately after tooth-brushing with nanoHAP toothpaste (Apagard M-plus) enhances the remineralization promotion and the demineralization inhibition efficacies of nanoHAP toothpastes.

METHODS

64 sound enamel blocks and 64 blocks bearing artificially-produced initial caries were produced from human permanent molar teeth. During each treatment period, lasting 14 days per arm, two blocks, one sound and one lesion-bearing, were exposed to either 5% nanoHAP-containing or placebo dental lotion after tooth-brushing with 5% nanoHAP toothpaste, via an intra-oral appliance worn by 30 adults in each of the study groups. Baseline and post-test mineral loss were quantified using transverse microradiography (TMR). One-sided t-test of one group mean was used for intragroup comparison, while two-sided t-test of two independent means was used to compare the two dental lotions.

RESULTS

Pairwise comparison (baseline vs. post-test) indicated significant (p<.001) remineralization by nanoHAP toothpaste in both groups. However, when compared against each other, there was a significantly (p<.001) greater percentage of remineralization with nanoHAP lotion [58.4(±1.8)%] than with placebo lotion [37.7(±2.2)%]. TMR examination showed absolute demineralization inhibition in sound enamel blocks exposed to either lotions.

CONCLUSIONS

Toothpaste containing 5% nanoHAP effectively remineralized initial caries and inhibited demineralization of healthy enamel; however, the application of a dental lotion containing 5% nanoHAP after brushing resulted in superior remineralization compared to a placebo lotion.

CLINICAL SIGNIFICANCE

Dental lotion containing 5% nanohydroxyapatite used immediately after toothbrushing with 5% nanohydroxyapatite toothpaste can serve as an adjunct to enhance the clinical benefits of the toothpaste.

Nano-hydroxyapatite accelerates vascular calcification via lysosome impairment and autophagy dysfunction in smooth muscle cells

Vascular calcification (VC) is a common characteristic of aging, diabetes, chronic renal failure, and atherosclerosis. The basic component of VC is hydroxyapatite (HAp). Nano-sized HAp (nHAp) has been identified to play an essential role in the development of pathological calcification of vasculature. However, whether nHAp can induce calcification in vivo and the mechanism of nHAp in the progression of VC remains unclear. We discovered that nHAp existed both in vascular smooth muscle cells (VSMCs) and their extracellular matrix (ECM) in the calcified arteries from patients. Synthetic nHAp had similar morphological and chemical properties as natural nHAp recovered from calcified artery. nHAp stimulated osteogenic differentiation and accelerated mineralization of VSMCs in vitro. Synthetic nHAp could also directly induce VC in vivo. Mechanistically, nHAp was internalized into lysosome, which impaired lysosome vacuolar H⁺-ATPase for its acidification, therefore blocked autophagic flux in VSMCs. Lysosomal re-acidification by cyclic-3′,5′-adenosine monophosphate (cAMP) significantly enhanced autophagic degradation and attenuated nHAp-induced calcification. The accumulated autophagosomes and autolysosomes were converted into calcium-containing exosomes which were secreted into ECM and accelerated vascular calcium deposit. Inhibition of exosome release in VSMCs decreased calcium deposition. Altogether, our results demonstrated a repressive effect of nHAp on lysosomal acidification, which inhibited autophagic degradation and promoted a conversion of the accumulated autophagic vacuoles into exosomes that were loaded with undissolved nHAp, Ca²⁺, Pi and ALP. These exosomes bud off the plasma membrane, deposit within ECM, and form calcium nodules. Vascular calcification was thus accelerated by nHAP through blockage of autophagic flux in VSMCs.

•

We first demonstrated that nHAp was internalized into the vascular cell in human calcified aorta.

•

Nano-HAp impairs lysosomal acidification and degradation, and causesblockage of autophagy flux in VSMCs.

•

The accumulated autophagosomes and autolysosomes induced by nHAp in VSMCs are converted into exosomes which promote calcification development.

Development of a hydroxyapatite nanoparticle-based gel for enamel remineralization -A physicochemical properties and cell viability assay analysis

Nano-hydroxyapatite (nHA) was synthesized from abalone mussel shells (Haliotis asinina) using a precipitation method, and gel HA-Abalone was developed using the carbomer materials with concentrations of 0, 10, 20, 30, and 40 wt%. The specimens used were 25 freshly extracted caries-free premolar teeth, and the treatment was done twice a day for 14 days. Gel HA-Abalone 20 wt%, with a crystallite size of 14.70±1.21 nm, was the best concentration to achieve the best remineralization (~863 VHN) of the superficial layer. Based on the results of cell viability assay on gel HA-Abalone 20 wt%, the growth of NIH/3T3 cells was inhibited beginning at a gel concentration of 1,000 µg/mL, and the half maximal inhibitory concentration (IC₅₀) value was 1,497 µg/mL. Based on to the one-way analysis of variance (ANOVA), the result reflected statistically significant differences in the average of the cell viability and enamel surface microhardness values (p<0.05).

[Research Progress in Biomimetic Synthesis of Nano-Hydroxyapatite in Bone Tissue Engineering]

Nano hydroxyapatite (nHAp), a main component of the inorganic composition of human bones and teeth, is widely used in bone tissue engineering, bone defect repair and replacement, for example, for its biocompatibility, bioactivity, bioaffinity and the ability to induce bone regeneration. Nano hydroxyapatite contains calcium and phosphorus, elements that can be replaced through the normal metabolic channels of the human body. Therefore, after implantation, it can be partially or completely absorbed and replaced by human tissues and can effectively assist bone regeneration, which makes it an ideal material for bone repair. However, traditional nHAp material is brittle and hard to be degraded in human body. In addition, nHAp has poor stability due to its high surface energy and tendency for agglomeration, which causes rapid attenuation of its mechanical strength and limits its clinical application. At present, the mechanical properties and biocompatibility of nHAp can be effectively improved by loading the related growth factors, proteins, peptides and other bioactive molecules, so as to better meet the biological requirements of bone repair materials. However, the traditional physicochemical modification methods are complicated and may interfere with the bioactivity of nHAp. It is simple to biomimetically synthesize nanomaterials by direct utilization of the molecular recognition and self-assemble capabilities of biomolecules or living microorganisms. Furthermore, the properties of the synthesized nanomaterials are stable, and the method has been extensively studied in recent years. Due to the unique crystaline structure and physicochemical properties of nHAp, results of a large number of studies have shown that its affinity with biological molecules can be used to produce bioactive nHAp by biomimetic synthesis methods. Biomimetically synthesized nHAp is expected to become the mainstream bone tissue engineering scaffold material. Analyzing and summarizing the biomimetic synthetic process and the characteristics of different nHAp materials will facilitate further development of bone defect repair materials with better mechanical and biological properties. Herein we reviewed methods of biomimetic synthesis of nHAp based on different biomolecular templates. Furthermore, we also discussed applications of biomimetic synthesized nHAp in bone tissue engineering, which can used as reference information for further research and development of new-generation bone repair biomaterials.

Nano-hydroxyapatite coated TiO2 nanotubes on Ti-19Zr-10Nb-1Fe alloy promotes osteogenesis in vitro

Titanium and titanium alloys have broad applications in orthopedic implants due to their excellent mechanical properties and biocompatibility. The biological activity of the metallic implants can be improved by implementing a nano-hydroxyapatite (nano-HA) coating, while it is still challenging to synthesize uniform and stable nano-HA on the metallic materials. The characterization results confirmed that the nanotube array with a diameter of 87 ± 21 nm and a length of 8.1 ± 1.3 μm is achieved by using double anodic oxidation, and then microsphere-like nano-HA crystals are formed on the TiO₂ nanotube arrays. Through X-ray diffraction (XRD) and Fourier Transform Infrared Spectrometer (FT-IR) analysis, it is determined that the chemical composition of the coating is hydroxyapatite. in vitro cell experiments, compared to the TZNF metal surface, the TZNF-NTs/HA is beneficial to the proliferation and adhesion of osteoblasts, and the activity of ALP was 6.93 ± 0.47 DEA unit and the content of OCN was 7.04 ± 0.51 ng/L. In terms of the expression of osteogenic gene information as osterix, osteopontin, and osteonectin, the mRNA levels of TZNF-NTs/HA were 2.6-fold, 1.6-fold, and 4.3-fold higher than that of TZNF samples, respectively, at 14 days. The results suggested that the introduction of nano-HA improves osteoblast differentiation and local factor production, as well as indicates the potential for improved implant osseointegration.

Effects of nanocrystalline hydroxyapatite concentration and skeletal site on bone and cartilage formation in rats

Most fractures heal by a combination of endochondral and intramembranous ossification dependent upon strain and vascularity at the fracture site. Many biomaterials-based bone regeneration strategies rely on the use of calcium phosphates such as nano-crystalline hydroxyapatite (nHA) to create bone-like scaffolds. In this study, nHA was dispersed in reactive polymers to form composite scaffolds that were evaluated both in vitro and in vivo. Matrix assays, immunofluorescent staining, and Western blots demonstrated that nHA influenced mineralization and subsequent osteogenesis in a dose-dependent manner in vitro. Furthermore, nHA dispersed in polymeric composites promoted osteogenesis by a similar mechanism as particulated nHA. Scaffolds were implanted into a 2-mm defect in the femoral diaphysis or metaphysis of Sprague-Dawley rats to evaluate new bone formation at 4 and 8 weeks. Two formulations were tested: a poly(thioketal urethane) scaffold without nHA (PTKUR) and a PTKUR scaffold augmented with 22 wt% nHA (22nHA). The scaffolds supported new bone formation in both anatomic sites. In the metaphysis, augmentation of scaffolds with nHA promoted an intramembranous healing response. Within the diaphysis, nHA inhibited endochondral ossification. Immunohistochemistry was performed on cryo-sections of the bone/scaffold interface in which CD146, CD31, Endomucin, CD68, and Myeloperoxidase were evaluated. No significant differences in the infiltrating cell populations were observed. These findings suggest that nHA dispersed in polymeric composites induces osteogenic differentiation of adherent endogenous cells, which has skeletal site-specific effects on fracture healing. STATEMENT OF SIGNIFICANCE: Understanding the mechanism by which synthetic scaffolds promote new bone formation in preclinical models is crucial for bone regeneration applications in the clinic where complex fracture cases are seen. In this study, we found that dispersion of nHA in polymeric scaffolds promoted in vitro osteogenesis in a dose-dependent manner through activation of the PiT1 receptor and subsequent downstream Erk1/2 signaling. While augmentation of polymeric scaffolds with nHA enhanced intramembranous ossification in metaphyseal defects, it inhibited endochondral ossification in diaphyseal defects. Thus, our findings provide new insights into designing synthetic bone grafts that complement the skeletal site-specific fracture healing response.

Insights into the adsorption mechanism of tannic acid by a green synthesized nano-hydroxyapatite and its effect on aqueous Cu(II) removal

The polyphenolic tannic acid (TA) has been widely used in the stabilization and surface modification of nanomaterials. The interaction mechanism of TA with the biogenic nano-hydroxyapatite (nHAP) and its environmental importance, however, are poorly understood. This study explored the adsorption of TA using the green synthesized, eggshell-derived nHAP and implications of this process for the removal of aqueous Cu(II) via batch adsorption experiments, Raman spectroscopy, Fourier transform infrared spectroscopy (FTIR), and X-ray photoelectron spectroscopy (XPS) investigations. TA adsorption by nHAP was a complex pH-dependent process and significantly correlated with TA molecule speciation and amphoteric properties of nHAP via multiple adsorption modes including surface complexation, electrostatic attraction, and hydrogen bond. The maximum TA adsorption amount was found to be 94.8 mg/g for less crystalline nHAP with lower calcination temperature. In the ternary Cu-TA-nHAP systems, TA promoted Cu(II) adsorption at pH < 5 and reduced Cu(II) uptake at pH > 5. Further studies of the effects of ionic strength and addition sequences, as well as Raman, FTIR, and XPS analyses revealed Cu(II) adsorption on nHAP was mainly dominated by inner-sphere surface complexation. These results can shed light on not only the utility of biogenic nHAP for TA and Cu(II) adsorption but also the evaluation of the effect of TA on the environmental behavior of heavy metals.

A novel nano-hydroxyapatite/synthetic polymer/bone morphogenetic protein-2 composite for efficient bone regeneration

BACKGROUND

Efficient bone regeneration using recombinant human bone morphogenetic protein-2 (BMP-2) is needed to reduce side effects caused by high-dose BMP-2 use. The composite material of polylactic acid-polyethene glycol (PLA-PEG) for sustained release and an osteogenic nano-hydroxyapatite (nHAp) can contribute to efficient bone regeneration by BMP-2.

STUDY DESIGN

An experimental in vitro and in vivo study.

PURPOSE

The objective of this study is to investigate the effectiveness of a novel composite material of PLA-PEG and nHAp as a carrier for BMP-2.

METHODS

The release kinetics of BMP-2 from the composites was investigated by ELISA. Thirty-six male Sprague-Dawley rats underwent posterolateral spinal fusion on L4-L5 with three different doses of BMP-2 (0 µg [control], 3 µg [low dose], and 10 µg [high dose]). Weekly µCT results and histology and a manual palpation test at 8 weeks postoperatively were used for assessment of the spinal fusion.

RESULTS

ELISA demonstrated the sustained release of BMP-2 until day 21. µCT and manual palpation test demonstrated a solid fusion in 91.6% (11/12) of specimens in both the low- and high-dose groups. N mice in the control group attained bony fusion (0%, 0/9). nHAp was resorbed between 2 and 4 weeks postoperatively, and regenerated fusion mass at 8 weeks postoperatively consisted of only newly formed bone.

CONCLUSIONS

The nHAp/PLA-PEG composite enabled efficient bone regeneration with low-dose BMP-2. The sustained release of BMP-2 by PLA-PEG and the osteogenic and biodegradable scaffold of nHAp might contribute to efficient bone regeneration.

CLINICAL SIGNIFICANCE

This novel composite material has potential in clinical applications (spinal fusion, large bone defect and non-union) by enabling efficient bone formation by BMP-2.

Bioinspired mineral-polymeric hybrid hyaluronic acid/poly (γ-glutamic acid) hydrogels as tunable scaffolds for stem cells differentiation

Aiming at the difficulty of integrated repair of osteochondral tissue, we designed a hybrid hydrogel scaffold that mimicked the microenvironment of osteochondral niches. Besides, the nano-hydroxyapatite (nHAP) was specially introduced into the hydrogel for its natural ability to promote bone regeneration. The hydrogel also exhibited good toughness (7500 KJ/m³), strength (1000 kPa), viscoelasticity, and in vitro cell experiments showed that hydrogels had quite good cytocompatibility (near 100 % viability). The results of the three-dimensional (3D) cell culture also proved that the survival rate of the cells in the hybrid hydrogels doped with nHAP and dispersion were the highest. In vitro RT-qPCR experiments proved that after being cultured in hydrogel scaffolds doped with nHAP, bone mesenchymal stem cells (BMSCs) could express genes related to osteoblasts and chondrocytes. As a result, this hydrogel provides a general for developing alternative materials applicable for stem cells differentiation and even osteochondral tissue engineering.

A new cancellous bone material of silk fibroin/cellulose dual network composite aerogel reinforced by nano-hydroxyapatite filler

Composites materials comprised of biopolymeric aerogel matrices and inorganic nano-hydroxyapatite (n-HA) fillers have received considerable attention in bone engineering. Although with significant progress in aerogel-based biomaterials, the brittleness and low strengths limit the application. The improvements in toughness and mechanical strength of aerogel-based biomaterials are in great need. In this work, an alkali urea system was used to dissolve, regenerate and gelate cellulose and silk fibroin (SF) to prepare composite aerosol. A dual network structure was shaped in the composite aerosol materials interlaced by sheet-like SF and reticular cellulose wrapping n-HA on the surface. Through uniaxial compression, the density of the composite aerogel material was close to the one of natural bone, and mechanical strength and toughness were high. Our work indicates that the composite aerogel has the same mechanical strength range as cancellous bone when the ratio of cellulose, n-HA and SF being 8:1:1. In vitro cell culture showed HEK-293T cells cultured on composite aerogels had high ability of adhesion, proliferation and differentiation. Totally, the presented biodegradable composite aerogel has application potential in bone tissue engineering.

ATR-FTIR, EDS and SEM evaluations of enamel structure after treatment with hydrogen peroxide bleaching agents loaded with nano-hydroxyapatite particles

Background

Tooth whitening is one of the most requested dental treatments, but it still presents some side effects. Indeed, the bleaching agent can generate patients’ discomfort and dental hard tissue damages, not achieving an efficient and long-lasting treatment with optimum whitening effect. To overcome these limitations, the bleaching agents containing nano-hydroxyapatite can represent a reliable solution to avoid these detrimental effects.

Methods

In this study, human third molars were treated with commercial bleaching agents, containing nano-hydroxyapatite (nHA) and 6% (at-home treatment), 12% and 18% (in-office treatments) of hydrogen peroxide (HP), named respectively G1, G2 and G3. The results were evaluated descriptively and analytically using Attenuated Total Reflectance-Fourier Transform Infrared Spectroscopy (ATR-FTIR), Scanning Electron Microscopy (SEM) and Energy Dispersive X-ray spectroscopy (EDS), comparing the treated groups with a commercial gel containing 10% carbamide peroxide (CONV) and with a non-treated control group (CTRL).

Results

ATR-FTIR analysis revealed a similar composition in carbonates and phosphates for CTRL, G1 and G2 groups, which showed no significant differences in their spectral profiles; an increased amount of organic matter was found in G3, while CONV displayed an intermediate behavior. SEM analysis did not highlight significant changes in the enamel microstructure of G1 and CONV when compared to CTRL; the pattern observed in G2 presented a slight increase of enamel irregularities, while G3 displayed a partial removal of the aprismatic layer and microporosities. No evident effects due to nHA were observed in the structure of the hydroxyapatite component of G1, G2 and CONV, if compared to CTRL, while G3 showed a slight loss of crystallinity. In all groups, EDS identified slight changes in the concentration of chemical elements O and Ca, while the Ca/P ratio was similar when compared to CTRL.

Conclusion

The obtained results suggest that the application of the tested commercial bleaching agents, with a concentration of HP up to 12%, does not alter the morphological and chemical composition of the enamel surface and maintains its crystallinity.

3D printing PCL/nHA bone scaffolds: exploring the influence of material synthesis techniques

Background

It is known that a number of parameters can influence the post-printing properties of bone tissue scaffolds. Previous research has primarily focused on the effect of parameters associated with scaffold design (e.g., scaffold porosity) and specific scaffold printing processes (e.g., printing pressure). To our knowledge, no studies have investigated variations in post-printing properties attributed to the techniques used to synthesize the materials for printing (e.g., melt-blending, powder blending, liquid solvent, and solid solvent).

Methods

Four material preparation techniques were investigated to determine their influence on scaffold properties. Polycaprolactone/nano-hydroxyapatite 30% (wt.) materials were synthesized through melt-blending, powder blending, liquid solvent, and solid solvent techniques. The material printability and the properties of printed scaffolds, in terms of swelling/degradation, mechanical strength, morphology, and thermal properties, were examined and compared to one another using Kruskal-Wallis nonparametric statistical analysis.

Results

Material prepared through the liquid solvent technique was found to have limited printability, while melt-blended material demonstrated the highest degree of uniformity and lowest extent of swelling and degradation. Scaffolds prepared with powder-blended material demonstrated the highest Young’s modulus, yield strength, and modulus of resilience; however, they also demonstrated the highest degree of variability. The higher degree of inhomogeneity in the material was further supported by thermal gravimetric analysis. While scaffolds printed from melt-blended, powder-blended, and solid solvent materials demonstrated a high degree of micro-porosity, the liquid solvent material preparation technique resulted in minimal micro-porosity.

Conclusions

Study results indicate that specific techniques used to prepare materials influence the printing process and post-printing scaffold properties. Among the four techniques examined, melt-blended materials were found to be the most favorable, specifically when considering the combination of printability, consistent mechanical properties, and efficient preparation. Techniques determined to be favourable based on the properties investigated should undergo further studies related to biological properties and time-dependent properties beyond 21-days.

Supplementary Information

The online version contains supplementary material available at 10.1186/s40824-021-00204-y.

Influence of different carrier materials on biphasic calcium phosphate induced bone regeneration

OBJECTIVES

Biphasic calcium phosphate (BCP) is a bioceramic material successfully used in alloplastic bone augmentation. Despite many advantages, a disadvantage of BCP seems to be a difficult application and position instability. The aim of this study was to determine how different carrier materials influence BCP-induced quantitative and qualitative bone regeneration.

MATERIALS AND METHODS

A total of 70 critical size defects were set in the frontal bone of 14 domestic pigs (5 each) and filled randomly with either BCP alone (BCP), BCP in combination with nano-hydroxyapatite (BCP + NHA), BCP embedded in native porcine type I/III collagen blocks (BCP + C), autologous bone (AB), or were left empty (ED). Specimens were harvested after 4 and 8 weeks and were evaluated histologically as well as histomorphometrically.

RESULTS

Significantly lowest rate of new bone formation was found in ED (p = < 0.001) and BCP + NHA groups (p = 0.05). After 8 weeks, the highest percentage of new bone formation was observed in the BCP + C group. Fibrous matrix was detected highest in BCP alone. The lowest residual bone substitute material was found in BCP + C after 8 weeks.

CONCLUSIONS

BCP-induced bone regeneration is indeed affected by different carrier types. Surface morphology and bioactive characteristics influence osseointegration and new bone formation in vivo. The combination of type I/III collagen seems most suitable for qualitative and quantitative bone regeneration.

CLINICAL RELEVANCE

Stabilization of granular bone substitutes using type I/III collagen might be an alternative to granulates alone, indicating excellent volume stability, satisfactory plasticity, and easy application.

The osteogenic differentiation of human dental pulp stem cells in alginate-gelatin/Nano-hydroxyapatite microcapsules

Background

Microcapsule is considered as a promising 3D microenvironment for Bone Tissue Engineering (BTE) applications. Microencapsulation of cells in an appropriate scaffold not only protected the cells against excess stress but also promoted cell proliferation and differentiation. Through the current study, we aimed to microcapsulate the human Dental Pulp Stem Cells (hDPSCs) and evaluated the proliferation and osteogenic differentiation of those cells by using MTT assay, qRT-PCR, Alkaline phosphatase, and Alizarine Red S.

Results

The SEM results revealed that Alg/Gel microcapsules containing nHA showed a rough and more compact surface morphology in comparison with the Alg/Gel microcapsules. Moreover, the microencapsulation by Alg/Gel/nHA could improve cell proliferation and induce osteogenic differentiation. The cells cultured in the Alg/Gel and Alg/Gel/nHA microcapsules showed 1.4-fold and 1.7-fold activity of BMP-2 gene expression more in comparison with the control group after 21 days. The mentioned amounts for the BMP-2 gene were 2.5-fold and 4-fold more expression for the Alg/Gel and Alg/Gel/nHA microcapsules after 28 days. The nHA, addition to hDPSCs-laden Alg/Gel microcapsule, could up-regulate the bone-related gene expressions of osteocalcin, osteonectin, and RUNX-2 during the 21 and 28 days through the culturing period, too. Calcium deposition and ALP activities of the cells were observed in accordance with the proliferation results as well as the gene expression analysis.

Conclusion

The present study demonstrated that microencapsulation of the hDPSCs inside the Alg/Gel/nHA hydrogel could be a potential approach for regenerative dentistry in the near future.

Graphical abstract

Effect of different remineralizing agents on the initial carious lesions - A comparative study

Objectives

This study aimed to assess and compare the effectiveness of three different remineralizing agents (Tricalcium phosphate paste, Fluoride varnish, and Nano-hydroxyapatite gel) using the DIAGNOdent device.

Material and Methods

The present clinical study was carried out on 90 initial carious lesions detected by ICDAS caries diagnostic criteria and then take the baseline record by DIAGNOdent device. The selected initial carious lesions were randomly classified into three groups according to treatment modalities (30 lesions in each group) according to remineralizing agents: group A (TCP), group B (fluoride varnish) and group C (nano-hydroxyapatite gel). The remineralizing agents were applied for four minutes once weekly for four weeks. At the fifth week, the DIAGNOdent scores of initial carious lesions were recorded to evaluate the effect of remineralizing agents. A paired t-test was used to compare between baseline date and follow up of DIAGNOdent scores. A one-way ANOVA test was used to compare DIAGNOdent scores among the three groups. Post- Hoc Tukey test was used to determine the significant difference between every two groups.

Results

There were statistically significant differences among the three groups at follow up (p = 0.001). Within each group, there was a significant difference between baseline and follow up scores (p = 0.000 for the three groups). Multiple comparisons between every two groups showed a highly statistically significant difference at follow up records between nano-hydroxyapatite versus TCP and fluoride varnish on pit and fissure caries (p = 0.039 and p = 0.007 respectively) and the nano-hydroxyapatite was the best of them.

Conclusion

The present study concluded that the three remineralizing agents were effective in the treatment of initial carious lesion and the most effective remineralizing agent was nano-hydroxyapatite.

Effect of high concentration nano-hydroxyapatite serum on shear bond strength of metal brackets following three different enamel surface preparation methods: An in vitro study

OBJECTIVE

White spot lesion (WSL) is one of the most important complications of fixed orthodontic treatment. Many methods have been studied to prevent this problem. This study is aimed to investigate the effect of high concentration nano-hydroxyapatite (nHAP) on shear bond strength (SBS) of metal brackets and Adhesive Remnant Index (ARI) score in different preparation methods.

MATERIAL AND METHODS

Sixty human premolars, which were extracted for orthodontic reasons were included in this in vitro study. The teeth were randomly divided into 4 groups of 15 each: one control group and three nHAP groups. After applying nHAP for 2 to 3 minutes daily for 10 days, the groups 2 to 4 underwent sandblasting using 50μm aluminium oxide and 30 seconds etching, 60 and 30 seconds etching, respectively, and the brackets were then bonded to the teeth. After debonding, SBS and ARI scores were recorded. Data were analysed using the ANOVA test and posthoc test for pairwise comparisons.

RESULTS

No significant difference was observed in SBS between the control group and the nHAP groups. The sandblasted teeth showed significantly higher SBS than the 30 seconds etching after nHAP application (P=0.02). The teeth etched for 60 seconds showed a significantly higher ARI score than the 30 seconds etched teeth with (P=0.003) or without (P<0.001) nHAP application.

CONCLUSIONS

The use of nHAP before bracket bonding can be considered as a caries preventive method since it did not compromise the SBS. Sixty seconds etching is recommended for less likely damage to the enamel after debonding.

Alkali treatment facilitates functional nano-hydroxyapatite coating of 3D printed polylactic acid scaffolds

Autografting is currently the gold standard for treatment of bone defects, but has shown disadvantages in the limited volume of and donor site morbidity associated with harvested bone. Customized bone scaffolds that mimic the mechanical and biological properties of native bone are needed to augment the currently limited bone regeneration strategies. To achieve this goal, a repeated cross-hatch structure with uniform cubic pores was designed and 3D printed using polylactic acid (PLA) via fused deposition modeling (FDM). PLA surfaces were modified by wet chemical (alkali) treatment for either 1 h (1hAT) or 6 h (6hAT), followed by coating with nano-hydroxyapatite (nHA). Our hypotheses were that: (i) 6-hour (but not 1-hour) alkali treatment would enhance nHA coating, (ii) the nHA coating on the 6-hour alkali-treated surface would increase hydrophilicity and cell attachment/proliferation, and (iii) stiffness, but not effective Young's modulus, would be reduced by 6-hour alkali treatment. The effects of AT and nHA coating on scaffold morphology was observed by scanning electron microscopy and quantified using a custom MATLAB script. Chemical composition and hydrophilicity were evaluated via energy dispersive X-ray spectroscopy and Fourier transform infrared spectroscopy, and water contact angle analyses, respectively. Mechanical testing and in vitro cell culture were further employed to analyze compressive properties, and cell attachment and proliferation, respectively. As expected, 6hAT led to reduced strut width and stiffness, while improving the nHA coating and hydrophilicity. Interestingly, PLA/6hAT but not PLA/6hAT/nHA demonstrated a reduction in effective modulus compared to PLA and PLA/nHA scaffolds. From in vitro experiments, the combined PLA/6hAT/nHA modification resulted in the greatest extent of cell attachment but not proliferation. These results collectively demonstrate that the PLA/6hAT/nHA scaffold exhibits properties that may prove beneficial for cancellous bone regeneration.

Preparation and characterisation of a gellan gum-based hydrogel enabling osteogenesis and inhibiting Enterococcus faecalis

Infections are the leading cause of failure of osteogenic material implantation. Antibiotic treatment, treatment with bone cement, or collagen sponge placement can result in drug resistance and difficulties in operation. To address this, gellan gum (GG) was selected in this study and prepared as an injectable hydrogel containing chlorhexidine (CHX) and nanohydroxyapatite (nHA) that overcomes these intractable problems. Scanning electron microscopy and micro-computed tomography revealed a three-dimensional polymeric network of the hydrogel. The hydrogel had excellent biocompatibility, as detected by cell counting kit-8 and Live/Dead assay. Bone marrow mesenchymal stem cells could be encapsulated into the network, showing that the structure was suitable for cell growth. Additionally, loading the hydrogel with nHA improved its mechanical, biodegradable, and osteogenic properties. Quantitative alkaline phosphatase and Alizarin Red S staining validated its osteogenic ability. Furthermore, antibacterial activity assessment showed that the hydrogel loaded with 50 μg/mL CHX inhibited Enterococcus faecalis in a concentration-dependent manner. Thus, we report an injectable GG-based hydrogel with superior antibacterial effect against E. faecalis and osteogenesis, which holds promise for treating infectious bone defects caused by refractory periradicular periodontitis.

Combination of nano-hydroxyapatite and curcumin in a biopolymer blend matrix: Characteristics and drug release performance of fibrous composite material systems

The design of appropriate materials is required for biomedical applications (e.g. drug delivery systems) in improving people's health care processes. This study focused on the incorporation of nanosized hydroxyapatite (n-HA) with different ratios (ranging from 0.1 wt% to 0.5 wt%) into the poly (ε-caprolactone)/ poly (ethylene oxide) (PCL/PEO) blend matrix loaded or unloaded with curcumin. Composite fibrous material systems were successfully fabricated by the electrospinning technique without the occurrence of bead defects. In addition to the morphological and physicochemical properties of the material systems obtained, the in vitro curcumin release performance was investigated. Further, anti-cancer activity against breast cancer cell line (MCF-7) was examined by MTT assay. Fourier transform infrared spectroscopy and X-ray diffraction characterizations of the fabricated fibrous materials exhibited the interaction of PCL/PEO, n-HA, and curcumin. The 0.3 wt% n-HA incorporated fibrous materials showed a much slower curcumin release manner along with the highest cytotoxicity against MCF-7 cells. The findings obtained from this research are expected to contribute to the appropriate design of nanofiber-based composite materials not only for drug delivery systems but also for the fabrication of biomaterials toward different biomedical applications.