The effect of calcium phosphate ceramic composition and structure on in vitro behavior. I. Dissolution

Effect of a synthetic hydroxyapatite-based bone grafting material compared to established bone substitute materials on regeneration of critical-size bone defects in the ovine scapula

Lately, the potential risk of disease transmission due to the use of bovine-derived bone substitutes has become obvious, demonstrating the urgent need for a synthetic grafting material with comparable bioactive behaviour and properties. Therefore, the effect of a synthetic hydroxyapatite (HA) (Osbone®) bone grafting material on bone regeneration was evaluated 2 weeks, 1 month, and 3, 6, 12 and 18 months after implantation in critical-size bone defects in the ovine scapula and compared to that of a bovine-derived HA (Bio-Oss®) and β-tricalcium phosphate (TCP) (Cerasorb® M). New bone formation and the biodegradability of the bone substitutes were assessed histomorphometrically. Hard tissue histology and immunohistochemical analysis were employed to characterize collagen type I, alkaline phosphatase, osteocalcin, as well as bone sialoprotein expression in the various cell and matrix components of the bone tissue to evaluate the bioactive properties of the bone grafting materials. No inflammatory tissue response was detected with any of the bone substitute materials studied. After 3 and 6 months, β-TCP (Cerasorb® M) showed superior bone formation when compared to both HA-based materials (3 months: β-TCP 55.65 ± 2.03% vs. SHA 49.05 ± 3.84% and BHA 47.59 ± 1.97%; p ≤ 0.03; 6 months: β-TCP 62.03 ± 1.58%; SHA: 55.83 ± 2.59%; BHA: 53.44 ± 0.78%; p ≤ 0.04). Further, after 12 and 18 months, a similar degree of bone formation and bone-particle contact was noted for all three bone substitute materials without any significant differences. The synthetic HA supported new bone formation, osteogenic marker expression, matrix mineralization and good bone-bonding behaviour to an equal and even slightly superior degree compared to the bovine-derived HA. As a result, synthetic HA can be regarded as a valuable alternative to the bovine-derived HA without the potential risk of disease transmission.

Obtaining Polyvinylpyrrolidone Fibers Using the Electroforming Method with the Inclusion of Microcrystalline High-Temperature Phosphates

The results of the synthesis of microcrystalline calcium phosphates such as hydroxoapatite, pyrophosphate, and tricalcium phosphate are presented herein. The influence of the addition of polyvinylpyrrolidone (PVP) on the phase characteristics of the resulting high-temperature ceramic sample is considered. The X-ray results show that hydroxyapatite (HAp) consists of a Ca5(PO4)3(OH) phase, while the sample with the addition of polyvinylpyrrolidone contains β-Ca3(PO4)2 (65.5%) and β-Ca2P2O7 (34.5%) phases calcium phosphates (CPs). IR spectroscopy was used to characterize the compositions of the samples. An important characteristic of the obtained samples is the elemental Ca/P ratio, which was determined via energy-dispersive analysis. The data obtained are consistent with the composition of dental enamel apatites, namely, in the CPs (1.27) and HAp (1.40). SEM was used to study the morphology of the surfaces of hydroxyapatite particles. Polyvinylpyrrolidone polymer fibers were obtained using the electroforming method with the inclusion of CPs in the composition. The fibers were oriented randomly, and nanoscale hydroxyapatite particles were incorporated into the fiber structure. Solubility data of the HAp, CPs, and Fibers in a physiological solution at room temperature and human body temperature were obtained. The solubility of the resulting HAp turned out to be higher than the solubility of the CPs. In turn, the concentration of Ca2+ in a physiological solution of PVP composite fibers with the inclusion of CPs was lower than that in powdered CPs.

The development of non-resorbable bone allografts: Biological background and clinical perspectives

Bone grafts are typically categorized into four categories: autografts, allografts, xenografts, and synthetic alloplasts. While it was originally thought that all bone grafts should be slowly resorbed and replaced with native bone over time, accumulating evidence has in fact suggested that the use of nonresorbable xenografts is favored for certain clinical indications. Thus, many clinicians take advantage of the nonresorbable properties/features of xenografts for various clinical indications, such as contour augmentation, sinus grafting, and guided bone regeneration, which are often combined with allografts (e.g., human freeze-dried bone allografts [FDBAs] and human demineralized freeze-dried bone allografts [DFDBAs]). Thus, many clinicians have advocated different 50/50 or 70/30 ratios of allograft/xenograft combination approaches for various grafting procedures. Interestingly, many clinicians believe that one of the main reasons for the nonresorbability or low substitution rates of xenografts has to do with their foreign animal origin. Recent research has indicated that the sintering technique and heating conducted during their processing changes the dissolution rate of hydroxyapatite, leading to a state in which osteoclasts are no longer able to resorb (dissolve) the sintered bone. While many clinicians often combine nonresorbable xenografts with the bone-inducing properties of allografts for a variety of bone augmentation procedures, clinicians are forced to use two separate products owing to their origins (the FDA/CE does not allow the mixture of allografts with xenografts within the same dish/bottle). This has led to significant progress in understanding the dissolution rates of xenografts at various sintering temperature changes, which has since led to the breakthrough development of nonresorbable bone allografts sintered at similar temperatures to nonresorbable xenografts. The advantage of the nonresorbable bone allograft is that they can now be combined with standard allografts to create a single mixture combining the advantages of both allografts and xenografts while allowing the purchase and use of a single product. This review article presents the concept with evidence derived from a 52-week monkey study that demonstrated little to no resorption along with in vitro data supporting this novel technology as a "next-generation" biomaterial with optimized bone grafting material properties.

β-Tricalcium Phosphate as Alveolar Bone Grafting in Cleft Lip/Palate: A Systematic Review

The aim of this systematic review is to describe and identify the prospects of β-Tricalcium Phosphate (β-TCP) as an alveolar bone grafting (ABG) material in cleft lip/palate (CL/P) or alveolar bone cleft defects. A systematic review protocol based on the Preferred Reporting Items for Systematic Reviews and Meta-Analyses 2020 (PRISMA 2020) was drafted. The literature search was conducted using MEDLINE/PubMed, Web of Science/ISI Web of Knowledge, Scopus, and the Cochrane Library, with English as the inclusion criterion and no publication year limits. The keywords yielded a total of 5824 publications. After removing duplicates and non-English articles, there were 3196 suitable articles available for evaluation. Subsequently, 1315 studies remained after reviewing titles and abstracts. Furthermore, 85 full articles were assessed for eligibility. After reading the complete texts of those papers, 20 were eventually selected that matched the inclusion requirements. Thirteen out of the twenty studies included in this systematic review were deemed to have a low risk of bias; one had a high risk of bias; and six had a moderate risk of bias due to not reporting randomization. β-TCP, when used as an ABG material, is biocompatible, visible, practical, offers a less invasive procedure, and does not interfere with orthodontic treatment. Synthetic β-TCP for ABG can be an alternative to autologous bone grafts under certain terms and conditions. The efficacy of β-TCP for ABG in CL/P or alveolar bone cleft defects can be enhanced through a tissue engineering approach that combines β-TCP with growth factors, mesenchymal stem cells, or other graft materials, along with modifications to β-TCP's physical properties.

Effects of Diatomite Contents on Microstructure, Microhardness, Bioactivity and Biocompatibility of Gradient Bioceramic Coating Prepared by Laser Cladding

Biometallic materials are widely used in medicine because of excellent mechanical properties. However, biometallic materials are limited in the application of biomaterials due to their lack of bioactivity. To solve this problem, a gradient bioceramic coating doped with diatomite (DE) was successfully fabricated on the surface of Ti6Al4V alloy by using the broadband-laser cladding process to improve the bioactivity of metal materials. As well as the DE contents on the microstructure, microhardness, bioactivity and biocompatibility were investigated. The experimental results demonstrate that the addition of moderate amounts of DE is effective in reducing the number of cracks. The X-ray diffraction (XRD) results reveal that the bioceramic coating doped with DE mainly consists of CaTiO3, hydroxyapatite (HA), tricalcium phosphate (TCP) and silicate, and that the amount of HA and TCP in the coating reached maximum when the bioceramic coating was doped with 10wt% DE. The bioceramic coating doped with 10wt% DE has favorable ability to deposit bone-like apatite. These results indicate that the addition of DE can improve cracking sensibility, bioactivity and biocompatibility of the coating.

Development of root resorption during orthodontic tooth movement after cleft repair using different grafting materials in rats

OBJECTIVE

The aim of the present study was to investigate the influence of three grafting materials for cleft repair on orthodontic tooth movement in rats.

MATERIALS AND METHODS

Artificial alveolar clefts were created in 21 Wistar rats and were repaired 4 weeks later using autografts, human xenografts and synthetic bone substitute (beta-tricalcium phosphate/hydroxyapatite [β-TCP/HA]). A further 4 weeks later, the first molar was moved into the reconstructed maxilla. Microfocus computed tomography (μCT) was performed six times (T0-T5) to assess the tooth movement and root resorption. After 8 weeks, the affected reconstructed jaw was resected for histopathological investigation.

RESULTS

Total distances reached ranged from 0.82 ± 0.72 mm (β-TCP/HA) to 0.67 ± 0.27 mm (autograft). The resorption was particularly determined at the mesiobuccal root. Descriptive tooth movement slowed and root resorption increased slightly. However, neither the radiological changes during tooth movement (µCT T1 vs. µCT T5: autograft 1.85 ± 0.39 mm³ vs. 2.38 ± 0.35 mm³, p = 0.30; human xenograft 1.75 ± 0.45 mm³ vs. 2.17 ± 0.26 mm³, p = 0.54; β-TCP/HA: 1.52 ± 0.42 mm³ vs. 1.88 ± 0.41 mm³, p = 0.60) nor the histological differences after tooth movement (human xenograft: 0.078 ± 0.05 mm²; β-TCP/HA: 0.067 ± 0.049 mm²; autograft: 0.048 ± 0.015 mm²) were statistically significant.

CONCLUSION

The autografts, human xenografts or synthetic bone substitute used for cleft repair seem to have a similar effect on the subsequent orthodontic tooth movement and the associated root resorptions.

CLINICAL RELEVANCE

Development of root resorptions seems to have a secondary role in choosing a suitable grafting material for cleft repair.

A Narrative Review of u-HA/PLLA, a Bioactive Resorbable Reconstruction Material: Applications in Oral and Maxillofacial Surgery

The advent of bioresorbable materials to overcome limitations and replace traditional bone-reconstruction titanium-plate systems for bone fixation, thus achieving greater efficiency and safety in medical and dental applications, has ushered in a new era in biomaterial development. Because of its bioactive osteoconductive ability and biocompatibility, the forged composite of uncalcined/unsintered hydroxyapatite and poly L-lactic acid (u-HA/PLLA) has attracted considerable interest from researchers in bone tissue engineering, as well as from clinicians, particularly for applications in maxillofacial reconstructive surgery. Thus, various in vitro studies, in vivo studies, and clinical trials have been conducted to investigate the feasibility and weaknesses of this biomaterial in oral and maxillofacial surgery. Various technical improvements have been proposed to optimize its advantages and limit its disadvantages. This narrative review presents an up-to-date, comprehensive review of u-HA/PLLA, a bioactive osteoconductive and bioresorbable bone-reconstruction and -fixation material, in the context of oral and maxillofacial surgery, notably maxillofacial trauma, orthognathic surgery, and maxillofacial reconstruction. It simultaneously introduces new trends in the development of bioresorbable materials that could used in this field. Various studies have shown the superiority of u-HA/PLLA, a third-generation bioresorbable biomaterial with high mechanical strength, biocompatibility, and bioactive osteoconductivity, compared to other bioresorbable materials. Future developments may focus on controlling its bioactivity and biodegradation rate and enhancing its mechanical strength.

Evaluation of different grafting materials for alveolar cleft repair in the context of orthodontic tooth movement in rats

To minimize the postoperative risks posed by grafting autologous transplants for cleft repair, efforts are being made to improve grafting materials for use as potential alternatives. The aim of this study was to compare the bone graft quality of different bone substitutes including the gold standard autografts during the healing processes after cleft repair in the context of orthodontic treatment. In 21 Wistar rats, a complete, continuity-interrupting cleft was created. After 4 weeks, cleft repair was performed using autografts from the hips’ ischial tuberosity, human xenografts, or synthetic bone substitutes [beta-tricalcium phosphate (β-TCP)/hydroxyapatite (HA)]. After another 4 weeks, the first molar movement was initiated in the reconstructed jaw for 8 weeks. The bone remodeling was analyzed in vivo using micro-computed tomography (bone mineral density and bone volume fraction) and histology (new bone formation). All the grafting materials were statistically different in bone morphology, which changed during the treatment period. The β-TCP/HA substitute demonstrated less resorption compared to the autologous and xenogeneic/human bone, and the autografts led to a stronger reaction in the surrounding bone. Histologically, the highest level of new bone formation was found in the human xenografts, and the lowest was found in the β-TCP/HA substitute. The differences between the two bone groups and the synthetic materials were statistically significant. Autografts were confirmed to be the gold standard in cleft repair with regard to graft integration. However, parts of the human xenograft seemed comparable to the autografts. Thus, this substitute could perhaps be used as an alternative after additional tissue-engineered modification.

eIF2α-ATF4 Pathway Activated by a Change in the Calcium Environment Participates in BCP-Mediated Bone Regeneration

Biphasic calcium phosphate (BCP) ceramic is a classic bone void filler and a common basis of new materials for bone defect repair. However, the specific mechanism of BCP in osteogenesis has not been fully elucidated. Endoplasmic reticulum stress (ERs) and the subsequent PERK-eIF2α-ATF4 pathway can be activated by various factors, including trauma and intracellular calcium changes, and therefore worth exploring as a potential mechanism in BCP-mediated bone repair. Herein, a rat lateral femoral epicondyle defect model in vivo and a simulated BCP-mediated calcium environment in vitro were constructed for the analysis of BCP-related osteogenesis and the activation of ERs and the eIF2α-ATF4 pathway. An inhibitor of eIF2α dephosphorylation (salubrinal) was also used to explore the effect of the eIF2α-ATF4 pathway on BCP-mediated bone regeneration. The results showed that the ERs and eIF2α-ATF4 pathway activation were observed during 4 weeks of bone repair, with a rapid but brief increase immediately after artificial defect surgery and a re-increase after 4 weeks with the resorption of BCP materials. Mild ERs and the activated eIF2α induced by the calcium changes mediated by BCP regulated the expression of osteogenic-related proteins and had an important role during the defect repair. In conclusion, the eIF2α-ATF4 pathway activated by a change in the calcium environment participates in BCP-mediated bone regeneration. eIF2α-ATF4 and ERs could provide new directions for further studies on new materials in bone tissue engineering.

Preparation of Absorption-Resistant Hard Tissue Using Dental Pulp-Derived Cells and Honeycomb Tricalcium Phosphate

In recent years, there has been increasing interest in the treatment of bone defects using undifferentiated mesenchymal stem cells (MSCs) in vivo. Recently, dental pulp has been proposed as a promising source of pluripotent mesenchymal stem cells (MSCs), which can be used in various clinical applications. Dentin is the hard tissue that makes up teeth, and has the same composition and strength as bone. However, unlike bone, dentin is usually not remodeled under physiological conditions. Here, we generated odontoblast-like cells from mouse dental pulp stem cells and combined them with honeycomb tricalcium phosphate (TCP) with a 300 μm hole to create bone-like tissue under the skin of mice. The bone-like hard tissue produced in this study was different from bone tissue, i.e., was not resorbed by osteoclasts and was less easily absorbed than the bone tissue. It has been suggested that hard tissue-forming cells induced from dental pulp do not have the ability to induce osteoclast differentiation. Therefore, the newly created bone-like hard tissue has high potential for absorption-resistant hard tissue repair and regeneration procedures.

In-vitroassessment of β-tricalcium phosphate/bredigite-ciprofloxacin (CPFX) scaffolds for bone treatment applications

In the present study, β-tricalcium phosphate (β-TCP) scaffolds with various amounts of bredigite (Bre) were fabricated by the space holder method. The effect of bredigite content on the structure, mechanical properties,in vitrobioactivity, and cell viability was investigated. The structural assessment of the composite scaffolds presented interconnected pores with diameter of 300-500 μm with around 78%-82% porosity. The results indicated that the compressive strength of the scaffolds with 20% bredigite (1.91 MPa) was improved in comparison with scaffolds with 10% bredigite (0.52 MPa), due to the reduction of the average pore and grain sizes. Also, the results showed that the bioactivity and biodegradability of β-TCP/20Bre were better than that of β-TCP/10Bre. Besides, in this study, the release kinetics of ciprofloxacin (CPFX) loaded β-TCP/Bre composites as well as the ability of scaffolds to function as a sustained release drug carrier was investigated. Drug release pattern of β-TCP/bredigite-5CPFX scaffolds exhibited the rapid burst release of 43% for 3 h along with sustained release (82%) for 32 h which is favorable for bone infection treatment. Antibacterial tests revealed that the antibacterial properties of β-TCP/bredigite scaffolds are strongly related to the CPFX concentration, wherein the scaffold containing 5% CPFX showed the most significant zone of inhibition (33 ± 0.5 mm) againstStaphylococcus aureus. The higher specific surface areas of nanostructure β-TCP/bredigite scaffolds containing CPFX lead to an initial rapid release followed by constant drug delivery. MTT assay showed that the cell viability of β-TCP/bredigite scaffold loading with up to 1%-3% CPFX (95 ± 2%), is greater than for scaffolds containing 5% CPFX (84 ± 2%). In Overall, it may suggested that β-TCP/bredigite containing 1%-3% CPFX possesses great cell viability and antibacterial activity and be employed as bactericidal biomaterials and bone infection treatment.

Electrodeposited Hydroxyapatite-Based Biocoatings: Recent Progress and Future Challenges

Hydroxyapatite has become an important coating material for bioimplants, following the introduction of synthetic HAp in the 1950s. The HAp coatings require controlled surface roughness/porosity, adequate corrosion resistance and need to show favorable tribological behavior. The deposition rate must be sufficiently fast and the coating technique needs to be applied at different scales on substrates having a diverse structure, composition, size, and shape. A detailed overview of dry and wet coating methods is given. The benefits of electrodeposition include controlled thickness and morphology, ability to coat a wide range of component size/shape and ease of industrial processing. Pulsed current and potential techniques have provided denser and more uniform coatings on different metallic materials/implants. The mechanism of HAp electrodeposition is considered and the effect of operational variables on deposit properties is highlighted. The most recent progress in the field is critically reviewed. Developments in mineral substituted and included particle, composite HAp coatings, including those reinforced by metallic, ceramic and polymeric particles; carbon nanotubes, modified graphenes, chitosan, and heparin, are considered in detail. Technical challenges which deserve further research are identified and a forward look in the field of the electrodeposited HAp coatings is taken.

Histological and Radiological Features of a Four-Phase Injectable Synthetic Bone Graft in Guided Bone Regeneration: A Case Report

BACKGROUND AND OBJECTIVE

Injectable synthetic bone grafts (ISBG) are widely used biomaterials for regeneration purposes. The aim of this case report was to examine the efficacy of ISBG in the management of buccal fenestration in the case of a 25-year-old female.

CASE REPORT

After a traumatic tooth extraction, the defect was filled with ISBG and covered with a resorbable membrane. The ISBG showed easy handling and the patient had no complications during healing. Six months after augmentation, a bone biopsy was taken during implant bed preparation. The histological results showed good integration of ISBG into the newly formed bone and no signs of tissue inflammation. Additionally, a CBCT (cone beam computed tomography) analysis was performed to support the histological results.

CONCLUSION

The use of the examined ISBG led to successful treatment of the buccal fenestration defect.

Improved Bone Regeneration in Rabbit Bone Defects Using 3D Printed Composite Scaffolds Functionalized with Osteoinductive Factors

Large critical size bone defects are complicated to treat, and in many cases, autografts become a challenge due to size and availability. In such situations, a synthetic bone implant that can be patient-specifically designed and fabricated with control over parameters such as porosity, rigidity, and osteogenic cues can act as a potential synthetic bone substitute. In this study, we produced photocuring composite resins with poly(trimethylene carbonate) containing high ratios of bioactive ceramics and printed porous 3D composite scaffolds to be used as bone grafts. To enhance the overall surface area available for cell infiltration, the scaffolds were also filled with a macroporous cryogel. Furthermore, the scaffolds were functionalized with osteoactive factors: bone morphogenetic protein and zoledronic acid. The scaffolds were evaluated in vitro for biocompatibility and for functionality in vivo in critical bone defects (∼8 mm) in two clinically relevant rabbit models. These studies included a smaller study in rabbit tibia and a larger study in the rabbit cranium. It was observed that the bioactive molecule-functionalized 3D printed porous composite scaffolds provide an excellent conductive surface inducing higher bone formation and improved defect healing in both critical size long bones and cranial defects. Our findings provide strong evidence in favor of these composites as next generation synthetic bone substitutes.

Effect of Honeycomb β-TCP Geometrical Structure on Bone Tissue Regeneration in Skull Defect

The effect of the geometric structure of artificial biomaterials on skull regeneration remains unclear. In a previous study, we succeeded in developing honeycomb β-tricalcium phosphate (β-TCP), which has through-and-through holes and is able to provide the optimum bone microenvironment for bone tissue regeneration. We demonstrated that β-TCP with 300-μm hole diameters induced vigorous bone formation. In the present study, we investigated how differences in hole directions of honeycomb β-TCP (horizontal or vertical holes) influence bone tissue regeneration in skull defects. Honeycomb β-TCP with vertical and horizontal holes was loaded with BMP-2 using Matrigel and Collagen gel as carriers, and transplanted into skull bone defect model rats. The results showed that in each four groups (Collagen alone group, Matrigel alone group, Collagen + BMP group and Matrigel + BMP-2), vigorous bone formation was observed on the vertical β-TCP compared with horizontal β-TCP. The osteogenic area was larger in the Matrigel groups (with and without BMP-2) than in the Collagen group (with and without BMP-2) in both vertical β-TCP and horizontal β-TCP. However, when BMP-2 was added, the bone formation area was not significantly different between the Collagen group and the Matrigel group in the vertical β-TCP. Histological finding showed that, in vertical honeycomb β-TCP, new bone formation extended to the upper part of the holes and was observed from the dura side to the periosteum side as added to the inner walls of the holes. Therefore, we can control efficient bone formation by creating a bone microenvironment provided by vertical honeycomb β-TCP. Vertical honeycomb β-TCP has the potential to be an excellent biomaterial for bone tissue regeneration in skull defects and is expected to have clinical applications.

The degradation behavior of calcium-rich hydroxyapatite foams in vitro

Hydroxyapatite (HA) is a well-known regenerative biomaterial. However, the slow degradation rate of HA is still an obstacle in clinical applications. In this study, we concentrated on investigating the degradation behavior of the calcium-rich HA foams, which had a demonstrated effect on blood differentiation in previous studies. The HA foams were processed by an emulsion method and were infiltrated with calcium nitrate to create a calcium carbonate second phase, heterogeneously distributed on and under the surface of the foam. During the 28-day solubility test, the calcium carbonate phase contributed to enhanced Ca²⁺ ion release into the saline compared to phase pure HA foams. Both types of foams were biocompatible as demonstrated by human endothelial cell culture on their surface. The release of calcium ions, the degradation behavior, and the endothelial cell differentiation behavior suggest this biphasic ceramic is a candidate for bone marrow in vitro culture and a possible bone substitute material.

Spatial Presentation of Tissue-Specific Extracellular Matrix Components along Electrospun Scaffolds for Tissue Engineering the Bone-Ligament Interface

The bone-ligament interface transitions from a highly organized type I collagen rich matrix to a nonmineralized fibrocartilage region and finally to a mineralized fibrocartilage region that interfaces with the bone. Therefore, engineering the bone-ligament interface requires a biomaterial substrate capable of maintaining or directing the spatially defined differentiation of multiple cell phenotypes. To date the appropriate combination of biophysical and biochemical factors that can be used to engineer such a biomaterial substrate remain unknown. Here we show that microfiber scaffolds functionalized with tissue-specific extracellular matrix (ECM) components can direct the differentiation of MSCs toward the phenotypes seen at the bone-ligament interface. Ligament-ECM (L-ECM) promoted the expression of the ligament-marker gene tenomodulin (TNMD) and higher levels of type I and III collagen expression compared to functionalization with commercially available type I collagen. Functionalization of microfiber scaffolds with cartilage-ECM (C-ECM) promoted chondrogenesis of MSCs, as evidenced by adoption of a round cell morphology and increased SRY-box 9 (SOX9) expression in the absence of exogenous growth factors. Next, we fabricated a multiphasic scaffold by controlling the spatial presentation of L-ECM and C-ECM along the length of a single electrospun microfiber construct, with the distal region of the C-ECM coated fibers additionally functionalized with an apatite layer (using simulated body fluid) to promote endochondral ossification. These ECM functionalized scaffolds promoted spatially defined differentiation of MSCs, with higher expression of TNMD observed in the region functionalized with L-ECM, and higher expression of type X collagen and osteopontin (markers of endochondral ossification) observed at the end of the scaffold functionalized with C-ECM and the apatite coating. Our results demonstrate the utility of tissue-specific ECM derived components as a cue for directing MSC differentiation when engineering complex multiphasic interfaces such as the bone-ligament enthesis.

Role of Magnesium and the Effect of Surface Roughness on the Hydroxyapatite-Forming Ability of Zirconia Induced by Biomimetic Aqueous Solution Treatment

Zirconia is a well-known bioceramic for dental and orthopedic applications due to its mechanical and aesthetic properties. However, it lacks sufficient bioactivity to bond with the living bone. This study was aimed to induce bioactivity to tetragonal zirconia polycrystal (3Y-TZP) by simple biomimetic aqueous solution treatment. First, hydrofluoric acid (HF) etching was performed to enhance the surface roughness of the 3Y-TZP surface. Then, the samples were treated with two types of aqueous solutions containing calcium and phosphate ions (Ca-P solutions); one solution additionally contained magnesium (Mg) ions and the other without Mg ions. Finally, hydroxyapatite (HAp)-forming ability was evaluated by the conventional simulated body fluid (SBF) test, and the effect of Mg ions on the adhesive strength of the HAp layer to the roughened 3Y-TZP surface was also investigated. The results concluded that there were no noticeable differences in the effect of Mg ions on the HAp-forming ability, and both types of solution treatments resulted in dense HAp formation in 1 day SBF immersion. However, incorporation of Mg ions in one of the Ca-P solutions significantly improved the adhesive strength of the HAp layer to the HF-etched 3Y-TZP substrate compared to the Ca-P solution with no Mg ions.

Preliminary studies of the effect of doping of chromium oxide in SiO2-CaO-P2O5 bioceramics for bone regeneration applications

Bioceramics of composition xCr₂O₃∙(43-x) CaO∙42SiO₂∙15P₂O₅ (x varying from 0 to 8 mol%) have been synthesized in the laboratory by using sol-gel technique. The morphology and structure has been determined by using Powder X-ray Diffraction, Fourier Transform Infrared and Raman spectroscopy and Field Emission Scanning Electron Microscopy. The in vitro bio mineralization behavior has been assessed by immersion in simulated body fluid for 7 days. The results obtained in our studies have indicated excellent hydroxyapatite formation ability of our samples. Drug delivery property of synthesized samples has been checked by using UV-spectroscopy of antibiotic 'gentamicin'. The in vitro drug release profile was fitted best in the Higuchi model with the highest value of coefficient of determination (R² = 0.9970). Antimicrobial properties have been evaluated from minimum inhibitory concentration and time kill assay values. The cellular response has been investigated by using human osteosarcoma MG 63 cell line. Also to check charge on the synthesized samples, Zeta potential studies have been conducted and it has been observed that samples carry negative charge when immersed in simulated body fluid. Negative surface charge provide suitable environment for cell adhesion and proliferation. Experiments have been undertaken to explore suitable composition with an objective of development of suitable implant material for bone regeneration applications.

Repair of Critical-Sized Long Bone Defects Using Dipyridamole-Augmented 3D-Printed Bioactive Ceramic Scaffolds

There are over two million long bone defects treated in the United States annually, of which ~5% will not heal without significant surgical intervention. While autogenous grafting is the standard of care in simple defects, a customized scaffold for large defects in unlimited quantities is not available. Recently, a three-dimensionally (3D)-printed bioactive ceramic (3DPBC) scaffold has been successfully utilized in the of repair critical-sized (CSD) long bone defects in vivo. In this study, 3DPBC scaffolds were augmented with dipyridamole (DIPY), an adenosine A2A receptor (A_2A R) indirect agonist, because of its known effect to enhance bone formation. CSD full thickness segmental defects (~11 mm × full thickness) defects were created in the radial diaphysis in New Zealand white rabbits (n = 24). A customized 3DPBC scaffold composed of β-tricalcium phosphate was placed into the defect site. Groups included scaffolds that were collagen-coated (COLL), or immersed in 10, 100, or 1,000 μM DIPY solution. Animals were euthanized 8 weeks post-operatively and the radii/ulna-scaffold complex retrieved en bloc, for micro-CT, histological, and mechanical analysis. Bone growth was assessed exclusively within scaffold pores and evaluated by microCT and advanced reconstruction software. Biomechanical properties were evaluated utilizing nanoindentation to assess the newly regenerated bone for elastic modulus (E) and hardness (H). MicroCT reconstructions illustrated bone in-growth throughout the scaffold, with an increase in bone volume dependent on the DIPY dosage. The histological evaluation did not indicate any adverse immune response while revealing progressive remodeling of bone. These customized biologic 3DPBC scaffolds have the potential of repairing and regenerating bone. © 2019 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 37:2499-2507, 2019.

Sic Parvis Magna: Manganese-Substituted Tricalcium Phosphate and Its Biophysical Properties

Succeeding in the substitution of pharmaceutical compounds with ions deliverable with the use of resorbable biomaterials could have far-reaching benefits for medicine and economy. Calcium phosphates are known as excellent accommodators of foreign ions. Manganese, the fifth most abundant metal on Earth was studied here as an ionic dopant in β-tricalcium phosphate (β-TCP) ceramics. β-TCP containing different amounts of Mn²⁺ ions per Mn_xCa_3-x(PO₄)₂ formula (x = 0, 0.001, 0.01, and 0.1) was investigated for a range of physicochemical and biological properties. The results suggested the role of Mn²⁺ as a structure booster, not breaker. Mn²⁺ ions increased the size of coherent X-ray scattering regions averaged across all crystallographic directions and also lowered the temperature of transformation of the hydroxyapatite precursor to β-TCP. The particle size increased fivefold, from 20 to 100 nm, in the 650-750 °C region, indicating that the reaction of formation of β-TCP was accompanied by a considerable degree of grain growth. The splitting of the antisymmetric stretching mode of the phosphate tetrahedron occurred proportionally to the Mn²⁺ content in the material, while electron paramagnetic resonance spectra suggested that Mn²⁺ might substitute for three out of five possible calcium ion positions in the unit cell of β-TCP. The biological effects of Mn-free β-TCP and Mn-doped β-TCP were selective: moderately proliferative to mammalian cells, moderately inhibitory to bacteria, and insignificant to fungi. Unlike pure β-TCP, β-TCP doped with the highest concentration of Mn²⁺ ions significantly inhibited the growth of all bacterial species tested: Staphylococcus aureus, Salmonella typhi, Escherichia coli, Pseudomonas aeruginosa, and Enterococcus faecalis. The overall effect against the Gram-positive bacteria was more intense than against the Gram-negative microorganisms. Meanwhile, β-TCP alone had an augmentative effect of the viability of adipose-derived mesenchymal stem cells (ADMSCs) and the addition of Mn²⁺ tended to reduce the extent of this augmentative effect, but without imparting any toxicity. For all Mn-doped β-TCP concentrations except the highest, the cell viability after 72 h incubation was significantly higher than that of the negative control. Assays evaluating the effect of Mn²⁺-containing β-TCP formulations on the differentiation of ADMSCs into three different lineages-osteogenic, adipogenic, and chondrogenic-demonstrated no inhibitory or adverse effects compared to pure β-TCP and powder-free positive controls. Still, β-TCP delivering the lowest amount of Mn²⁺ seemed most effective in sustaining the differentiation process toward all three phenotypes, indicating that the dose of Mn²⁺ in β-TCP need not be excessive to be effective.

[Study on tailoring the nanostructured surfaces of cuttlefish bone transformed hydroxyapatite porous ceramics and its effect on osteoblasts]

Objective

To investigate the formation of nanostructure on cuttlefish bone transformed hydroxyapatite (CB-HA) porous ceramics and the effects of different nanostructures on the osteoblasts adhesion, proliferation, and alkaline phosphatase (ALP) expression.

Methods

The cuttlefish bone was shaped as plate with diameter of 10 mm and thickness of 2 mm, filled with water, and divided into 4 groups. The CB-HA in groups 1-4 were mixed with different phosphorous solutions and then placed in an oven at 120℃ for 24 hours. In addition, the samples in group 4 were further sintered at 1 200℃ for 3 hours to remove nanostructure as controls. The chemical composition of CB-HA were analyzed by X-ray diffraction spectroscopy, Fourier transform infrared spectrum, and inductively coupled plasma (ICP). The physical structure was analyzed using scanning electron microscopy, specific surface tester, and porosity tester. The MC3T3-E1 cells of 4th generation were co-cultured with 4 groups of CB-HA. After 1 day, the morphology of the cells was observed under scanning electron microscopy. After 1, 3, and 7 days, the cell proliferation was analyzed by MTT assay. After 7 and 14 days, the ALP expression was measured by pNPP method.

Results

X-ray diffraction spectrum showed that the four nanostructures of CB-HA were made of hydroxyapatite. The infrared absorption spectrum showed that the infrared absorption peak of CB-HA was consistent with hydroxyapatite. ICP showed that the ratio of calcium to phosphorus of all CB-HA was 1.68-1.76, which was consistent with hydroxyapatite. Scanning electron microscopy observation showed that the nanostructure on the surface of CB-HA in groups 1-3 were large, medium, and small cluster-like structures, respectively, and CB-HA in group 4 had no obvious nanostructure. There were significant differences in the specific surface areas between groups ( P<0.05). There was no significant difference in the porosity between groups ( P>0.05). Compared with group 4, groups 1-3 have more pores with pore size less than 50 nm. After co-cultured with osteoblasts, scanning electron microscopy observation and MTT assay showed that the cells on groups 2 and 3 adhered and proliferated better and had more ALP expression than that on groups 1 and 4 ( P<0.05).

Conclusion

The size of cluster-like nanostructure on the surface of CB-HA can be controlled by adjusting the concentration of ammonium ions in the phosphorous solution, and the introduction of small-sized cluster-like nanostructure on the surface of CB-HA can significantly improve the cell adhesion, proliferation, and ALP expression of the material which might be resulted from the enlarged surface area.

The 3D Printing of Calcium Phosphate with K-Carrageenan under Conditions Permitting the Incorporation of Biological Components-A Method

Critical-size bone defects are a common clinical problem. The golden standard to treat these defects is autologous bone grafting. Besides the limitations of availability and co-morbidity, autografts have to be manually adapted to fit in the defect, which might result in a sub-optimal fit and impaired healing. Scaffolds with precise dimensions can be created using 3-dimensional (3D) printing, enabling the production of patient-specific, 'tailor-made' bone substitutes with an exact fit. Calcium phosphate (CaP) is a popular material for bone tissue engineering due to its biocompatibility, osteoconductivity, and biodegradable properties. To enhance bone formation, a bioactive 3D-printed CaP scaffold can be created by combining the printed CaP scaffold with biological components such as growth factors and cytokines, e.g., vascular endothelial growth factor (VEGF), bone morphogenetic protein-2 (BMP-2), and interleukin-6 (IL-6). However, the 3D-printing of CaP with a biological component is challenging since production techniques often use high temperatures or aggressive chemicals, which hinders/inactivates the bioactivity of the incorporated biological components. Therefore, in our laboratory, we routinely perform extrusion-based 3D-printing with a biological binder at room temperature to create porous scaffolds for bone healing. In this method paper, we describe in detail a 3D-printing procedure for CaP paste with K-carrageenan as a biological binder.

Enhancing the Cell-Biological Performances of Hydroxyapatite Bioceramic by Constructing Silicate-Containing Grain Boundary Phases via Sol Infiltration

Hydroxyapatite (HA) is well-known as one of the excellent bone repair biomaterials because of its chemical similarity with biological apatite. However, weak bioactivity obstructs its application. Although the bioactivity of HA bioceramic could be enhanced by the incorporation of bioactive glass (BG), the dramatic decrease of its mechanical property is consistently a disturbance to the reliable efficacy of traditional modified HA bioceramic. In this study, HA bioceramic was modified by infiltration of BG sol and formation of silicate-containing grain boundary phases during subsequent sintering. The phase compositions, microstructure, mechanical performance, in vitro degradation behaviors, and osteogenesis of the bioceramic were investigated. The modified HA bioceramic exhibited an interesting phenomenon in which the HA grains were uniformly enveloped by the small silicate-containing grains in the boundaries of HA grains. The microporosity of modified HA bioceramics was up to 25.27% ± 0.01%, much higher than that of unmodified HA bioceramic (1.74% ± 0.27%). The compressive strength of the modified HA bioceramic via BG sol infiltration was much higher than that of the HA bioceramic modified by BG via mechanical blending method, though slightly lower than that of the blank. Moreover, mouse bone mesenchymal stem cells (mBMSCs) cultured on modified bioceramic displayed better adhesion morphology and proliferation, and had an enhanced expression of osteogenesis-related genes. This study offers a new strategy to improve the bioactivity of HA bioceramic without obvious deterioration in mechanical strength.

A comparative study of the dissolubility of pure and silicon substituted hydroxyapatite from density functional theory calculations

Introduction of silicon into hydroxyapatite (HA) is one of the effective ways to modulate the bioactivity of HA-based biomaterials. The bulk and surface structures of silicate-substituted HA (Si-HA) were characterized by using density functional theory calculations. The energetically favorable structures were identified from a number of candidate structures. Particular attention was paid to the surface structures of Si-HA, whose bioactivity is closely relevant to their surface atoms. Compared to the surface of pure HA, the Si-HA surface has similar surface energy but different charge distribution. Under the implicit solvent model, the exposed calcium/oxygen atoms become more positive/negative in net charge, resulting in a considerable change in the surface electrostatic potential at van der Waals distances. However, changes in the dissolution of surface calcium ions are not remarkable, as depicted by their activation energy leaving from the surface. Our calculations reveal that the surface structures and properties of HA were changed to some extent by silicate substitution, which provides some hints for understanding the experimentally observed changes in bioactivity and biodegradability of Si-HA that still remain controversial in many aspects.

Calcium and phosphate ions as simple signaling molecules with versatile osteoinductivity

Due to the continually increasing clinical need to heal large bone defects, synthetic bone graft substitutes have become ever more necessary with calcium phosphates (CaP) widely used due to their similarity to the mineral component of bone. In this research, different concentrations of calcium ions (Ca²⁺), phosphate ions (P_i), or their combination were provided to mesenchymal stem cells (MSCs) to evaluate their influence on proliferation and differentiation. The results suggest that 1-16 mM Ca²⁺ and 1-8 mM P_i is osteoinductive, but not cytotoxic. Furthermore, three distinct calcium phosphates (i.e. monobasic, dibasic, and hydroxyapatite) with different dissolution rates were investigated for their Ca²⁺ and P_i release. These biomaterials were then adjusted to release ion concentrations within the established therapeutics window for which MSC bioactivity was assessed. These findings suggest that CaP-based biomaterials can be leveraged to achieve Ca²⁺ and P_i dose-dependent osteoinduction for bone regenerative engineering applications.

Cleaning effect of osteoconductive powder abrasive treatment on explanted human implants and biofilm-coated titanium discs

The aim of this study is to test the cleaning effect and surface modification of a new implant surface treatment on explanted dental implants and titanium discs. It is a modified air powder abrasive (APA) treatment applied using osteoconductive powders. Twenty-eight in vitro Ca-precipitated organic film-coated titanium discs and 13 explanted dental implants were treated. In a 2-step approach, 3 powders were used: hydroxylapatite (HA) and biomimetic calcium phosphate (BioCaP), which are osteoconductive, and erythritol, which is not. APA treatment was applied. (Air pressure: 2.4 bar; water flow for cleaning: 41.5 ml/min, for Coating 1: 2.1 ml/min, and for Coating 2: 15.2 ml/min.) The test groups were as follows: Group 1: HA cleaning + BioCaP Coating 1; Group 2: HA cleaning + BioCaP Coating 2; Group 3: erythritol cleaning + BioCaP Coating 1; Group 4: erythritol cleaning + BioCaP Coating 2; Group 5: HA cleaning; Group 6: erythritol cleaning; and control: no powder. Cleaned areas were calculated by point counting method. Surface changes and chemical content were evaluated using light microscopy, scanning electron microscopy, and energy-dispersive X-ray spectroscopy. Cleaning effect between groups was compared by a pairwise Student's t test. The significance level was fixed at p < .05. Cleaning effect on the discs was 100% in all test groups and 5% in the control. Powder particles in varying size and shape were embedded on the surface. All HA- or CaP-treated surfaces showed Ca and P content but no surface damage. Calcified biofilm remnants were removed from the implant surface by the test groups, whereas in control groups, they remained. APA treatment with CaP and HA powders under clinically applicable pressure settings gives positive results in vitro; therefore, they could be promising when used in vivo.

Bone regeneration using composite non-demineralized xenogenic dentin with beta-tricalcium phosphate in experimental alveolar cleft repair in a rabbit model

Background

Alveolar cleft repair is performed via bone grafting procedure to restore the dental arch continuity. A suitable bone substitute materials should possess osteoinductive and osteoconductive properties, to promote new bone formation, along with a slowly resorbable scaffold that is subsequently replaced with functionally viable bone. Calcium phosphate biomaterials have long proved their efficacy as bone replacement materials. Dentin in several forms has also demonstrated its possibility to be used as bone graft replacement material in several studies. The purpose of this study was to evaluate bone regeneration pattern and quantify bone formation after grafting pre-established experimental alveolar clefts defects model in rabbits using composite xenogenic dentin and β-TCP in comparison to β-TCP alone.

Methods

Unilateral alveolar cleft defects were created in 16 New Zealand rabbits according to previously described methodology. Alveolar clefts were allowed 8 weeks healing period. 8 defects were filled with β-TCP, whereas 8 defects filled with composite xenogenic dentin with β-TCP. Bone regeneration of the healed defects was compared at the 8 weeks after intervention. Quantification of bone formation was analyzed using micro-computed tomography (µCT) and histomorphometric analysis.

Results

µCT and histomorphometric analysis revealed that defects filled with composite dentin/β-TCP showed statistically higher bone volume fraction, bone mineral density and percentage residual graft volume when compared to β-TCP alone. An improved surgical handling of the composite dentin/β-TCP graft was also noted.

Conclusions

Composite xenogenic dentin/β-TCP putty expresses enhanced bone regeneration compared to β-TCP alone in the reconstruction of rabbit alveolar clefts defects.

Biomimetic Materials and Fabrication Approaches for Bone Tissue Engineering

Various strategies have been explored to overcome critically sized bone defects via bone tissue engineering approaches that incorporate biomimetic scaffolds. Biomimetic scaffolds may provide a novel platform for phenotypically stable tissue formation and stem cell differentiation. In recent years, osteoinductive and inorganic biomimetic scaffold materials have been optimized to offer an osteo-friendly microenvironment for the osteogenic commitment of stem cells. Furthermore, scaffold structures with a microarchitecture design similar to native bone tissue are necessary for successful bone tissue regeneration. For this reason, various methods for fabricating 3D porous structures have been developed. Innovative techniques, such as 3D printing methods, are currently being utilized for optimal host stem cell infiltration, vascularization, nutrient transfer, and stem cell differentiation. In this progress report, biomimetic materials and fabrication approaches that are currently being utilized for biomimetic scaffold design are reviewed.

In vitro degradation of calcium phosphates: Effect of multiscale porosity, textural properties and composition

The capacity of calcium phosphates to be replaced by bone is tightly linked to their resorbability. However, the relative importance of some textural parameters on their degradation behavior is still unclear. The present study aims to quantify the effect of composition, specific surface area (SSA), and porosity at various length scales (nano-, micro- and macroporosity) on the in vitro degradation of different calcium phosphates. Degradation studies were performed in an acidic medium to mimic the osteoclastic environment. Small degradations were found in samples with interconnected nano- and micropores with sizes below 3µm although they were highly porous (35-65%), with maximum weight loss of 8wt%. Biomimetic calcium deficient hydroxyapatite, with high SSA and low crystallinity, presented the highest degradation rates exceeding even the more soluble β-TCP. A dependence of degradation on SSA was indisputable when porosity and pore sizes were increased. The introduction of additional macroporosity with pore interconnections above 20µm significantly impacted degradation, more markedly in the substrates with high SSA (>15m²/g), whereas in sintered substrates with low SSA (<1m²/g) it resulted just in a linear increase of degradation. Up to 30 % of degradation was registered in biomimetic substrates, compared to 15 % in β-TCP or 8 % in sintered hydroxyapatite. The incorporation of carbonate in calcium deficient hydroxyapatite did not increase its degradation rate. Overall, the study highlights the importance of textural properties, which can modulate or even outweigh the effect of other features such as the solubility of the compounds.

STATEMENT OF SIGNIFICANCE

The physicochemical features of calcium phosphates are crucial to tune biological events like resorption during bone remodeling. Understanding in vitro resorption can help to predict the in vivo behavior. Besides chemical composition, other parameters such as porosity and specific surface area have a strong influence on resorption. The complexity of isolating the contribution of each parameter lies in the close interrelation between them. In this work, a multiscale study was proposed to discern the extent to which each parameter influences degradation in a variety of calcium phosphates, using an acidic medium to resemble the osteoclastic environment. The results emphasize the importance of textural properties, which can modulate or even outweigh the effect of the intrinsic solubility of the compounds.

Synthesis of β-tricalcium phosphate

Ceramics play a key role in several biomedical applications. One of them is bone grafting, which is used for treating bone defects caused by injuries or osteoporosis. Calcium-phosphate based ceramic are preferred as bone graft biomaterials in hard tissue surgery because their chemical composition is close to the composition of human bone. They also have a marked bioresorbability and bioactivity. In this work, we have developed methods for synthesis of β-tricalcium phosphate apatite (β-TCP). These products were characterized by different techniques such as X-ray diffraction, infrared spectroscopy, scanning electron microscopy and chemical analysis.

The Bone Building Blues: Self-hardening copper-doped calcium phosphate cement and its in vitro assessment against mammalian cells and bacteria

A blue calcium phosphate cement with optimal self-hardening properties was synthesized by doping whitlockite (β-TCP) with copper ions. The mechanism and the kinetics of the cement solidification process were studied using energy dispersive X-ray diffraction and it was found out that hardening was accompanied by the phase transition from TCP to brushite. Reduced lattice parameters in all crystallographic directions resulting from the rather low (1:180) substitution rate of copper for calcium was consistent with the higher ionic radius of the latter. The lower cationic hydration resulting from the partial Ca→Cu substitution facilitated the release of constitutive hydroxyls and lowered the energy of formation of TCP from the apatite precursor at elevated temperatures. Addition of copper thus effectively inhibited the formation of apatite as the secondary phase. The copper-doped cement exhibited an antibacterial effect, though exclusively against Gram-negative bacteria, including E. coli, P. aeruginosa and S. enteritidis. This antibacterial effect was due to copper ions, as demonstrated by an almost negligible antibacterial effect of the pure, copper-free cement. Also, the antibacterial activity of the copper-containing cement was significantly higher than that of its precursor powder. Since there was no significant difference between the kinetics of the release of copper from the precursor TCP powder and from the final, brushite phase of the hardened cement, this has suggested that the antibacterial effect was not solely due to copper ions, but due to the synergy between cationic copper and a particular phase and aggregation state of calcium phosphate. Though inhibitory to bacteria, the copper-doped cement increased the viability of human glial E297 cells, murine osteoblastic K7M2 cells and especially human primary lung fibroblasts. That this effect was also due to copper ions was evidenced by the null effect on viability increase exhibited by the copper-free cements. The difference in the mechanism of protection of dehydratases in prokaryotes and eukaryotes was used as a rationale for explaining the hereby evidenced selectivity in biological response. It presents the basis for the consideration of copper as a dually effective ion when synergized with calcium phosphates: toxic for bacteria and beneficial for the healthy cells.

In vitro evaluation of hydroxyapatite coatings with (002) crystallographic texture deposited by micro-plasma spraying

Hydroxyapatite (HA) coatings are usually deposited on the metallic implant to increase the biocompatibility and protect the bloodstream from harmful metal ions. Atmospheric plasma spray (APS) is known as a cost effective deposition method. However, the low crystallinity of APS deposited coating accelerates its dissolution in body fluid. We used micro-plasma spray (MPS) to develop chemically stable HA coatings, and performed APS as reference. Results showed that MPS deposited coatings exhibited (002) crystallographic texture while the reference sample did not. The texture intensity and crystallinity were improved by shortening stand-off distance. These suggested that different formation procedures of HA coatings were involved and three mechanisms were proposed by sketching typical splats. To evaluate the chemical stability of the coatings in a physiological environment, in vitro experiments were performed in Hanks' solution. Well crystallized (~100%) HA coating with the strongest crystallographic texture exhibited superior stability up to 14days. Crystals with (002) orientation was more stable than that with (211) orientation. Hence columnar structure with nanopores emerged on the coating surface after incubation, and this may facilitate the future osteoblast growth. Furthermore, HA coating with weak and no crystallographic texture induced apatite layer. However, vertical cracks and cleavage at coating-apatite interface may cause coating separation.

In vitro characterisation of a sol-gel derived in situ silica-coated silicate and carbonate co-doped hydroxyapatite nanopowder for bone grafting

Design and synthesis of materials with better properties and performance are essential requirements in the field of biomaterials science that would directly improve patient quality of life. For this purpose, in situ silica-coated silicate and carbonate co-doped hydroxyapatite (Sc/S.C.HA) nanopowder was synthesized via the sol-gel method. Characterisation of the prepared nanopowder was carried out by XRD, FTIR, TEM, SEM, EDX, ICP, zeta potential, acid dissolution test, and cell culture test. The substitution of the silicate and carbonate ions into hydroxyapatite structure was confirmed by FTIR analysis. XRD analysis showed that silica is an amorphous phase, which played a role in covering the surface of the S.C.HA nanoparticles as confirmed by acid dissolution test. Low thickness and low integrity of the amorphous silica surface layer facilitated ions release from S.C.HA nanoparticles into physiological saline solution. Zeta potential of the prepared nanopowder suspended in physiological saline solution was -27.3±0.2mV at pH7.4. This negatively charged surface, due to the presence of amorphous silica layer upon the S.C.HA nanoparticles, not only had an accelerating effect on in vitro biomineralization of apatite, but also had a positive effect on cell attachment.

Development of Sr-incorporated biphasic calcium phosphate bone cement

To follow the design strategy of traditional biphasic calcium phosphate (BCP) ceramic, in the present study, strontium-doped biphasic calcium phosphate bone cement (Sr-BCPC) composites comprising Sr-β-tricalcium phosphate (TCP)/Sr-hydroxyapatite (HAP) had been prepared for the first time using Sr _x -β-TCP/tetracalcium phosphate (TTCP) as a cement powder and diluted phosphoric acid as a cement liquid. The phase composition, setting time, compressive strength, washout resistance, in vitro degradation rate, microstructure evolutions, hydration dynamics and cytotoxicity of Sr-BCPC at various Sr contents were intensively investigated. It was found that the final cement product was composed of entangled Sr-HAP nano-needles and cobblestone-like Sr-β-TCP sub-micron particles, and the weight percentages in the final cement product after hydration in simulated body fluid for 24 h were in the ranges of 60 wt%-70 wt% Sr-HAP and 30 wt%-40 wt% Sr-β-TCP, respectively. Sr and the concentration of Sr exhibit significant effects on the phase compositions, compressive strength, setting time, in vitro degradation rate and cytotoxicity of the biphasic bone cement. In particular, the degradation rate increased considerably with the increase of the Sr-β-TCP phase. It is anticipated that the introduction of the 'biphasic' design into calcium phosphate bone cements is an effective strategy to improve their degradation properties.

N, Camargo NHA, Dallabrida AL, da Costa BD, Gil OG, Cambra-Moo O, Rodríguez MA, Canillas M. An in vivo study on bone formation behavior of microporous granular calcium phosphate

This study was developed based on in vivo investigation of microporous granular biomaterials based on calcium phosphates.

A microstructural study of the degradation and calcium release from hydroxyapatite-calcium oxide ceramics made by infiltration

Hydroxyapatite pellets, partially densified in a low-temperature heat treatment, were infiltrated with calcium nitrate solution followed by in-situ precipitation of Ca(OH)₂ and CaCO₃. The infiltrated bodies were then densified to high relative density and the calcium carbonate transformed to calcium oxide during sintering and resulted in biphasic hydroxyapatite-CaO ceramics. This work investigated the influence of the infiltration on surface morphology, weight change, and microstructural-level degradation caused by exposure to saline at pH=7.4 and a temperature of 20°C. The CaO rendered the materials more susceptible to degradation, and released calcium into the saline faster than single phase, calcium deficient hydroxyapatite (HA) that were used as a control. In consequence, these ceramics could be used to release calcium into the culture microenvironments of bone tissue or bone marrow cells next to a scaffold surface.