Hydroxyapatite-polymer biocomposites for bone regeneration: A review of current trends

Biochemical, toxicological, and microbiological assessment of calcined poultry manure for potential use as bone scaffold material

The biosafety of thermally calcined poultry manure as a hydroxyapatite source for potential use as bone-making material was investigated in this study. In vitro assays were used to determine the sensitivity of the antioxidant properties to the thermal calcination temperature used to process the poultry manure (750, 800, and 850 °C ). The effect of the extract of both calcined poultry manure (local) and analytical grade hydroxyapatite (foreign) at various concentrations of 100%-25 % inclusion at (100 mg/kg) body weight intubation for 21 days on kidney, liver, and serum of animal model used was assessed. The results show that the thermally calcined poultry manure-derived hydroxyapatite generally possessed good antioxidant properties with the poultry manure treated at 750 °C having the most promising antioxidant properties compared to those treated at 800 and 850 °C , and hence a more likely improved anti-toxicity potential. The various blends of the analytical high-grade hydroxyapatite and thermally calcined poultry manure hydroxyapatite samples are safe compared to the normal control rats with regards hepatic function and renal function parameters with the equal blend of analytical high grade and thermally calcined poultry manure-derived hydroxyapatite (1:1) possessing the lowest activity concentrations. In addition, the enzymatic (glutathione peroxidase) and non-enzymatic (reduced glutathione) antioxidant concentrations of the experimental animals administered the varied compositions of the analytical high grade and thermally calcined poultry manure-derived hydroxyapatite, were lower when compared to normal control rats. The microbiological evaluation suggests that the calcined poultry manure inclusion at various concentrations could not pose a negative effect on various pathology in the liver, kidney, and blood.

Fabrication of 3D microfibrous composite polycaprolactone/hydroxyapatite scaffolds loaded with piezoelectric poly (lactic acid) nanofibers by sequential near-field and conventional electrospinning for bone tissue engineering

Near-field electrospinning (NFES) has recently gained considerable interest in fabricating tissue engineering scaffolds. This technique combines the advantages of both 3D printing and electrospinning. It allows for the production of fibers with smaller resolution and the ability to make regular structures with suitable pores. In this study, a microfibrous composite scaffold of polycaprolactone (PCL)/hydroxyapatite (HA) was prepared by NFES in the first step. The microfibrous scaffold had a fiber spacing of 414.674 ± 24.9 μm with an average fiber diameter of 94.695 ± 16.149 μm. However, due to the large fiber spacing, the surface area was insufficient for cell adhesion. Therefore, the hybrid scaffold was prepared by adding aligned and random electrospun poly (L-lactic acid) (PLLA) nanofibers to the microfibrous scaffold. Cellular studies showed that cell adhesion to the hybrid scaffold increased by 334 % compared to the microfibrous scaffold. These nanofibers also exhibited piezoelectric properties, which helped stimulate bone regeneration. Aligned nanofibers in the hybrid scaffold enhanced alkaline phosphatase activity and the intensity of alizarin red staining 1.5 and 1.6 times, respectively, compared to the microfibrous scaffold. Furthermore, the elastic modulus and ultimate tensile strength increased by 268 % and 130 %, respectively, by adding aligned nanofibers to the microfibrous scaffold. Therefore, the hybrid microfibrous composite scaffold of PCL/HA containing aligned electrospun PLLA nanofibers with improved properties showed the potential for bone regeneration.

Osteoblast and osteoclast activity on collagen-based 3D printed scaffolds enriched with strontium-doped bioactive glasses and hydroxyapatite nanorods for bone tissue engineering

Bone tissue engineering (BTE) aims to promote bone regeneration by means of the synergistic effect of biomaterials, cells, and other factors, as potential alternative to conventional treatments for bone fractures. To this aim, a composite material was developed, based on collagen type I, strontium-enriched mesoporous bioactive glasses, and hydroxyapatite nanorods as bioactive and biomimetic components. Nanostructured scaffolds were 3D printed and subsequently chemically crosslinked with genipin to improve mechanical properties and stability. The developed nanostructured system was maintained in culture until 3 weeks with a co-culture of human bone cells to provide anex vivomodel of bone microenvironment and examine the cellular crosstalk and signaling pathways through paracrine cell activities. Human osteoblasts (OBs), derived from trabecular bone, and human osteoclast precursors (OCs), isolated from buffy coat samples were involved, with OBs seeded on the scaffold and OC precursors seeded in a transwell device. When compared to the material without inorganic components, the bioactive and biomimetic scaffold positively influenced cell proliferation and cell metabolic activity, boosting alkaline phosphatase activity of OBs, and reducing OC differentiation. Thus, the bioactive and biomimetic system promoted an enhanced cellular response, highlighting its potential application in BTE.

Dual-functional Hydroxyapatite scaffolds for bone regeneration and precision drug delivery

Addressing infected bone defects remains a significant challenge in orthopedics, requiring effective infection control and bone defect repair. A promising therapeutic approach involves the development of dual-functional engineered biomaterials with drug delivery systems that combine antibacterial properties with osteogenesis promotion. The Hydroxyapatite composite scaffolds offer a one-stage treatment, eliminating the need for multiple surgeries and thereby streamlining the process and reducing treatment time. This review delves into the impaired bone repair mechanisms within pathogen-infected and inflamed microenvironments, providing a theoretical foundation for treating infectious bone defects. Additionally, it explores composite scaffolds made of antibacterial and osteogenic materials, along with advanced drug delivery systems that possess both antibacterial and bone-regenerative properties. By offering a comprehensive understanding of the microenvironment of infectious bone defects and innovative design strategies for dual-function scaffolds, this review presents significant advancements in treatment methods for infectious bone defects. Continued research and clinical validation are essential to refine these innovations, ensuring biocompatibility and safety, achieving controlled release and stability, and developing scalable manufacturing processes for widespread clinical application.

Use of Zebrafish (Danio rerio) for Biosafety Evaluation of Strontium Nanostructured Hydroxyapatite

Despite the numerous studies on biocompatibility with nano-biomaterials, the biological effects of strontium-substituted HA nanoparticles (nSrHA) need to be better understood. So, we conducted an embryotoxicity test using zebrafish (Danio rerio) according to the OECD 236 guideline, a model that represents a viable alternative that bridges the gap between in vitro and mammalian models. Zebrafish embryos were exposed for 120 h to microspheres containing nSrHA nanoparticles with low and high crystallinity, synthesized at temperatures of 5°C (nSrHA5) and 90°C (nSrHA90). We evaluated lethality, developmental parameters, and reactive oxygen species (ROS) production. The larval behavior was assessed at 168 hpf to determine if the biomaterials affected motor responses and anxiety-like behavior. The results showed that the survival rate decreased significantly for the nSrHA5 group (low crystalline particles), and an increase in ROS was also observed in this group. However, none of the biomaterials caused morphological changes indicative of toxicity during larval development. Additionally, the behavioral tests did not reveal any alterations in all experimental groups, indicating the absence of neurotoxic effects from exposure to the tested biomaterials. These findings provide valuable insights into the biosafety of modified HA-based nanostructured biomaterials, making them a promising strategy for bone tissue repair. As the use of hydroxyapatite-based biomaterials continues to grow, it is crucial to ensure rigorous control over the quality, reliability, and traceability of these materials.

Insights into the Dual Anticancer and Antibacterial Activities of Composites Based on Silver Camphorimine Complexes

Hydroxyapatite (HAp) is a widely used biocompatible material in orthopedic composite preparations. However, HAp composites that exhibit both anticancer and antibacterial activities through bioactive coordination complexes are relatively rare. To explore orthopedic applications, we blended several silver camphorimine compounds with HAp to create [Ag(I)] composites. All compounds [Ag(NO3)(L)n] (n = 1,2) based on camphorimine (LA), camphor sulfonimine (LB) or imine bi-camphor (LC) ligands demonstrated significant cytotoxic activity (IC50 = 0.30-2.6 μgAg/mL) against osteosarcoma cancer cells (HOS). Based on their structural and electronic characteristics, four complexes (1-4) were selected for antibacterial evaluation against Escherichia coli, Burkholderia contaminans, Pseudomonas aeruginosa, and Staphylococcus aureus. All complexes (1-4) revealed combined anticancer and antibacterial activities; therefore, they were used to prepare [Ag(I)]:HAp composites of 50:50% and 20:80% weight compositions and the activities of the composites were assessed. Results showed that they retain the dual anticancer and antibacterial characteristics of their precursor complexes. To replicate the clinical context of bone-filling applications, hand-pressed surfaces (pellets) were prepared. It is worth highlighting that no agglutination agent was necessary for the pellet's consistency. The biological properties of the so-prepared pellets were assessed, and the HOS cells and bacteria spreading on the pellet's surface were analyzed by SEM. Notably, composite 4B, derived from the bicamphor (LC) complex [Ag(NO3)(OC10H14N(C6H4)2NC10H14O)], exhibited significant anticancer activity against HOS cells and antibacterial activity against P. aeruginosa, fostering potential clinical applications on post-surgical OS treatment.

Microstructural, Fluid Dynamic, and Mechanical Characterization of Zinc Oxide and Magnesium Chloride-Modified Hydrogel Scaffolds

Scaffolds for the filling and regeneration of osteochondral defects are a current challenge in the biomaterials field, and solutions with greater functionality are still being sought. The novel approach of this work was to obtain scaffolds with biologically active additives possessing microstructural, permeability, and mechanical properties, mimicking the complexity of natural cartilage. Four types of scaffolds with a gelatin/alginate matrix modified with hydroxyapatite were obtained, and the relationship between the modifiers and substrate properties was evaluated. They differed in the type of second modifier used, which was hydrated MgCl2 in two proportions, ZnO, and nanohydroxyapatite. The samples were obtained by freeze-drying by using two-stage freezing. Based on microstructural observations combined with X-ray microanalysis, the microstructure of the samples and the elemental content were assessed. Permeability and mechanical tests were also performed. The scaffolds exhibited a network of interconnected pores and complex microarchitecture, with lower porosity at the surface (15 ± 7 to 29 ± 6%) and higher porosity at the center (67 ± 8 to 75 ± 8%). The additives had varying effects on the pore sizes and permeabilities of the samples. ZnO yielded the most permeable scaffolds (5.92 × 10-11 m2), whereas nanohydroxyapatite yielded the scaffold with the lowest permeability (1.18 × 10-11 m2), values within the range reported for trabecular bone. The magnesium content had no statistically significant effect on the permeability. The best mechanical parameters were obtained for ZnO samples and those containing hydrated MgCl2. The scaffold's properties meet the criteria for filling osteochondral defects. The developed scaffolds follow a biomimetic approach in terms of hierarchical microarchitecture and mechanical parameters as well as chemical composition. The obtained composite materials have the potential as biomimetic scaffolds for the regeneration of osteochondral defects.

Application of Bioactive Materials for Osteogenic Function in Bone Tissue Engineering

Bone tissue defects present a major challenge in orthopedic surgery. Bone tissue engineering using multiple versatile bioactive materials is a potential strategy for bone-defect repair and regeneration. Due to their unique physicochemical and mechanical properties, biofunctional materials can enhance cellular adhesion, proliferation, and osteogenic differentiation, thereby supporting and stimulating the formation of new bone tissue. 3D bioprinting and physical stimuli-responsive strategies have been employed in various studies on bone regeneration for the fabrication of desired multifunctional biomaterials with integrated bone tissue repair and regeneration properties. In this review, biomaterials applied to bone tissue engineering, emerging 3D bioprinting techniques, and physical stimuli-responsive strategies for the rational manufacturing of novel biomaterials with bone therapeutic and regenerative functions are summarized. Furthermore, the impact of biomaterials on the osteogenic differentiation of stem cells and the potential pathways associated with biomaterial-induced osteogenesis are discussed.

Osteogenic potential of adipose stem cells on hydroxyapatite-functionalized decellularized amniotic membrane

Amniotic membrane (AM) is an attractive source for bone tissue engineering because of its low immunogenicity, contains biomolecules and proteins, and osteogenic differentiation properties. Hydroxyapatite is widely used as bone scaffolds due to its biocompatibility and bioactivity properties. The aim of this study is to design and fabricate scaffold based on hydroxyapatite-coated decellularized amniotic membrane (DAM-HA) for bone tissue engineering purpose. So human amniotic membranes were collected from healthy donors and decellularized (DAM). Then a hydroxyapatite-coating was created by immersion in 10X SBF, under variable parameters of pH and incubation time. Hydroxyapatite-coating was characterized and the optimal sample was selected. Human adipose-derived mesenchymal stem cell behaviors were assessed on control, amniotic membrane, and coated amniotic membrane. The results of the SEM, MTT assay, and Live-Dead staining showed that DAM and DAM-HA support cell adhesion, viability and proliferation. Osteogenic differentiation was evaluated by assessment of alkaline phosphatase activity and expression of osteogenic markers. Maximum gene expression values compared to control occurred in 14 days for alkalin phosphatase, while the highest values for osteocalcin and osteopontin in 21 days. These gene expression values in DAM and DAM-HA for alkalin phosphatase is 6.41 and 8.47, for osteocalcin is 3.95 and 5.94 and for osteopontin is 5.59 and 9.9 respectively. The results of this study indicated DAM supports the survival and growth of stem cells. Also, addition of hydroxyapatite component to DAM promotes osteogenic differentiation while maintaining viability. Therefore, hydroxyapatite-coated decellularized amniotic membrane can be a promising choice for bone tissue engineering applications.

Synthetic composites versus calcium phosphate cements in bone regeneration: A narrative review

BACKGROUND

When the natural process of bone remodeling is disturbed, the need arises for a stimulant material in order to enhance the formation of a new healthy and strong osseous tissue to replace the damaged one. Recent studies have reported synthetic biomaterials to be a very good option for supporting bone regeneration.

STUDY DESIGN

Narrative review.

OBJECTIVE

This review aims to provide a brief presentation of two of the most recently developed synthetic biomaterials, i.e. calcium phosphate cements and synthetic composites, that are currently being used in bone regeneration with promising results.

METHODS

Literature searches using broad terms such as "bone regeneration," "biomaterials," "synthetic composites" and "calcium phosphate cements" were performed using PubMed. The osteal cells state of the art was explored by searching topic-specific full text keywords using Google Scholar.

CONCLUSIONS

Synthetic polymers such as PCL (poly-ε-caprolactone) and PLGA (poly lactic-co-glycolic acid) can improve the effectiveness of biomaterials like HA (hydroxyapatite) and BG (bioglass). Calcium phosphate, although being a suitable material for stimulating bone regeneration, needs an adjuvant in order to be effective in larger bone defects.

Surface functionalization of hydroxyapatite nanoparticles for biomedical applications

This review completely covers the various aspects of hydroxyapatite (HAp) nanoparticles and their role in different biological situations, and provides the surface and interface contents on (i) hydroxyapatite nanoparticles and their hybridization with organic molecules, (ii) surface designing of hydroxyapatite nanoparticles to provide their biocompatibility and photofunction, and (iii) coating technology of hydroxyapatite nanoparticles. In particular, we summarized how the HAp nanoparticles interact with the different ions and molecules and highlighted the potential for hybridization between HAp nanoparticles and organic molecules, which is driven by the interactions of the HAp nanoparticle surface ions with several functional groups of biological molecules. In addition, we highlighted the studies focusing on the interfacial interactions between the HAp nanoparticles and proteins for exploring the enhanced biocompatibility. Such studies focus on how these interactions affect the hydration layers and protein adsorption. However, the hydration layer state involves diverse molecular interactions that can alter the shape of the adsorbed proteins, thereby affecting cell adhesion and spreading on the surfaces. We also summarized the relationship between the surface properties of the HAp nanoparticles and the hydration layer. Furthermore, we spotlighted the cytocompatible photoluminescent probes that can be developed by designing HAp/organic nanohybrid structures. We then emphasized the importance of photofunctionalization in theranostics, which involves the integration of diagnostics and therapy based on the surface design of the HAp nanoparticles. Furthermore, the coating techniques using HAp nanoparticles and HAp nanoparticle/polymer composites were outlined for fusing base biomaterials with biological tissues. The advantages of HAp/biocompatible polymer composite coatings include the ability to effectively cover porous or irregularly shaped surfaces while controlling the thickness of the coating layer, and the addition of HAp nanoparticles to the polymer matrix improves the mechanical properties, increases the roughness, and forms the morphologies that mimic bone nanostructures. Therefore, the fundamental design of hydroxyapatite nanoparticles and their surfaces was suggested from various aspects for biomedical applications.

In vivo evaluation of bioactivity of alginate/chitosan based osteoplastic nanocomposites loaded with inorganic nanoparticles

The influence of two nanostructured osteoplastic materials with different compositions: i) alginate (Alg) matrix, loaded with Zn2+ ions and nanostructured hydroxyapatite (HA) - S1/HA-Zn, and ii) chitosan (CS) matrix loaded with brushite nanoparticles (NPs, dicalcium phosphate dihydrate, DCPD) - S2/DCPD on the healing of an experimental femoral diaphysis defect was investigated. The structure of cellular elements and the lacunar tubular system of the regenerated bone tissue were studied by electron microscopy. Osteogenic cells on the surface and inside S1/HA-Zn formed bone tissue. On the 30th day, the latter had a reticulofibrous and later lamellar structure. On the 30th day, the S2/DCPD biomaterial was integrated mainly into connective tissue and, starting from the 90th day, into the bone tissue, which was formed only on its outer surface. Thus, it has been proven that both biomaterials contribute to the healing of bone wounds. The regenerative potential of the new bone tissue formation of S1/HA-Zn prevails over that of S2/DCPD.

Design, clinical applications and post-surgical assessment of bioresorbable 3D-printed craniofacial composite implants

This study details the design, fabrication, clinical trials' evaluation, and analysis after the clinical application of 3D-printed bone reconstruction implants made of nHAp@PLDLLA [nanohydroxyapatite@poly(L-lactide-co-D,L-lactide)] biomaterial. The 3D-printed formulations have been tested as bone reconstruction Cranioimplants in 3 different medical cases, including frontal lobe, mandibular bone, and cleft palate reconstructions. Replacing one of the implants after 6 months provided a unique opportunity to evaluate the post-surgical implant obtained from a human patient. This allowed us to quantify physicochemical changes and develop a spatial map of osseointegration and material degradation kinetics as a function of specific locations. To the best of our knowledge, hydrolytic degradation and variability in the physicochemical and mechanical properties of the biomimetic, 3D-printed implants have not been quantified in the literature after permanent placement in the human body. Such analysis has revealed the constantly changing properties of the implant, which should be considered to optimize the design of patient-specific bone substitutes. Moreover, it has been proven that the obtained composition can produce biomimetic, bioresorbable and bone-forming alloplastic substitutes tailored to each patient, allowing for shorter surgery times and faster patient recovery than currently available methods.

Calcium Orthophosphate (CaPO4) Containing Composites for Biomedical Applications: Formulations, Properties, and Applications

The goal of this review is to present a wide range of hybrid formulations and composites containing calcium orthophosphates (abbreviated as CaPO4) that are suitable for use in biomedical applications and currently on the market. The bioactive, biocompatible, and osteoconductive properties of various CaPO4-based formulations make them valuable in the rapidly developing field of biomedical research, both in vitro and in vivo. Due to the brittleness of CaPO4, it is essential to combine the desired osteologic properties of ceramic CaPO4 with those of other compounds to create novel, multifunctional bone graft biomaterials. Consequently, this analysis offers a thorough overview of the hybrid formulations and CaPO4-based composites that are currently known. To do this, a comprehensive search of the literature on the subject was carried out in all significant databases to extract pertinent papers. There have been many formulations found with different material compositions, production methods, structural and bioactive features, and in vitro and in vivo properties. When these formulations contain additional biofunctional ingredients, such as drugs, proteins, enzymes, or antibacterial agents, they offer improved biomedical applications. Moreover, a lot of these formulations allow cell loading and promote the development of smart formulations based on CaPO4. This evaluation also discusses basic problems and scientific difficulties that call for more investigation and advancements. It also indicates perspectives for the future.

Synthesis of a new potassium-substituted lead fluorapatite and its structural characterization

Prismatic crystals of partially potassium substituted lead fluorapatite Pb5.09Ca3.78K1.13(PO4)6F0.87 were grown through a solid-state reaction. The structural study conducted by single-crystal X-ray diffraction revealed that the compound crystallizes in the hexagonal P63/m space group, with unit cell parameters a = b = 9.7190(5) Å, c = 7.1700(6) Å and V = 587.37(7) Å3(Z = 1), as well as final values amounting to R and wR of 0.0309 and 0.0546, respectively. The structural refinement demonstrated that Pb occupies both the (6h) and (4f) structural sites of hexagonal fluorapatite, K occupies the (6h) site, and Ca is placed on the (4f) site. Powder X-ray diffraction study indicated the absence of additional phases or impurities. Chemical analysis using atomic absorption spectrometry and energy-dispersive X-ray spectroscopy confirmed the expected chemical formula. The electrical conductivity measured over a wide temperature range was found to be governed by the ion mobility mechanism in the tunnel along the c axis (probably attributed to the fluorine ion located there). We, therefore, could infer from the analysis of the complex impedance spectra that the electrical conductivity of our apatite depends essentially on the temperature and frequency, which produces a relaxation phenomenon and semiconductor-like behavior. Moreover, the strong absorption in the UV-Visible region was substantiated through studies of the optical properties of the developed sample. Fluorescence spectra exhibited emissions in the orange regions when excited at 375 nm. The findings of the phenomena resulting from the emission and conduction of the apatite in question suggest its potential for application in various technological fields such as photovoltaic cells, optoelectronics, photonics, LED applications, catalysis and batteries.

Designer Micro-/Nanocrumpled MXene Multilayer Coatings Accelerate Osteogenesis and Regulate Macrophage Polarization

Effective tissue regeneration and immune responses are essential for the success of biomaterial implantation. Although the interaction between synthetic materials and biological systems is well-recognized, the role of surface topographical cues in regulating the local osteoimmune microenvironment─specifically, their impact on host tissue and immune cells, and their dynamic interactions─remains underexplored. This study addresses this gap by investigating the impact of surface topography on osteogenesis and immunomodulation. We fabricated MXene/hydroxyapatite (HAP)-coated surfaces with controlled 2.5D nano-, submicro-, and microscale topographical patterns using our custom bottom-up patterning method. These engineered surfaces were employed to assess the behavior of osteoblast precursor cells and macrophage polarization. Our results demonstrate that MXene/HAP-coated surfaces with microscale crumpled topography significantly influence osteogenic activity and macrophage polarization: these surfaces notably enhanced osteoblast precursor cell spreading, proliferation, and differentiation and facilitated a shift in macrophages toward an anti-inflammatory, prohealing M2 phenotype. The observed cell responses indicate that the physical cues from the crumpled topographies, combined with the chemical cues from the MXene/HAP coatings, synergistically create a favorable osteoimmune microenvironment. This study presents the first evidence of employing MXene/HAP-multilayer coated surfaces with finely crumpled topography to concurrently facilitate osteogenesis and immunomodulation for improved implant-to-tissue integration. The tunable topographic patterns of these coatings coupled with a facile and scalable fabrication process make them widely applicable for various biomedical purposes. Our results highlight the potential of these multilayer coatings with controlled topography to improve the in vivo performance and fate of implants by modulating the host response at the material interface.

Genetically engineered bacteriophages as novel nanomaterials: applications beyond antimicrobial agents

Bacteriophages, also known as phages, are viruses that replicate in bacteria and archaea. Phages were initially discovered as antimicrobial agents, and they have been used as therapeutic agents for bacterial infection in a process known as "phage therapy." Recently, phages have been investigated as functional nanomaterials in a variety of areas, as they can function not only as therapeutic agents but also as biosensors and tissue regenerative materials. Phages are nontoxic to humans, and they possess self-assembled nanostructures and functional properties. Additionally, phages can be easily genetically modified to display specific peptides or to screen for functional peptides via phage display. Here, we demonstrated the application of phage nanomaterials in the context of tissue engineering, sensing, and probing.

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.

3D-printed nanohydroxyapatite/methylacrylylated silk fibroin scaffold for repairing rat skull defects

The repair of bone defects remains a major challenge in the clinic, and treatment requires bone grafts or bone replacement materials. Existing biomaterials have many limitations and cannot meet the various needs of clinical applications. To treat bone defects, we constructed a nanohydroxyapatite (nHA)/methylacrylylated silk fibroin (MASF) composite biological scaffold using photocurable 3D printing technology. In this study, scanning electron microscopy (SEM) was used to detect the changes in the morphological structure of the composite scaffold with different contents of nanohydroxyapatite, and FTIR was used to detect the functional groups and chemical bonds in the composite scaffold to determine the specific components of the scaffold. In in vitro experiments, bone marrow mesenchymal stem cells from SD rats were cocultured with scaffolds soaking solution, and the cytotoxicity, cell proliferation, Western blot analysis, Quantitative real-time PCR analysis, bone alkaline phosphatase activity and alizarin red staining of scaffolds were detected to determine the biocompatibility of scaffolds and the effect of promoting proliferation and osteogenesis of bone marrow mesenchymal stem cells in vitro. In the in vivo experiment, the skull defect was constructed by adult SD rats, and the scaffold was implanted into the skull defect site. After 4 weeks and 8 weeks of culture, the specific osteogenic effect of the scaffold in the skull defect site was detected by animal micro-CT, hematoxylin and eosin (HE) staining and Masson's staining. Through the analysis of the morphological structure of the scaffold, we found that the frame supported good retention of the lamellar structure of silk fibroin, when mixed with nHA, the surface of the stent was rougher, the cell contact area increased, and cell adhesion and lamellar microstructure for cell migration and proliferation of the microenvironment provided a better space. FTIR results showed that the scaffold completely retained the β -folded structure of silk fibroin, and the scaffold composite was present without obvious impurities. The staining results of live/dead cells showed that the constructed scaffolds had no significant cytotoxicity, and thw CCK-8 assay also showed that the constructed scaffolds had good biocompatibility. The results of osteogenic induction showed that the scaffold had good osteogenic induction ability. Moreover, the results also showed that the scaffold with a MASF: nHA ratio of 1: 0.5 (SFH) showed better osteogenic ability. The micro-CT and bone histometric results were consistent with the in vitro results after stent implantation, and there was more bone formation at the bone defect site in the SFH group.This research used photocurable 3D printing technology to successfully build an osteogenesis bracket. The results show that the constructed nHA/MASF biological composite material, has good biocompatibility and good osteogenesis function. At the same time, in the microenvironment, the material can also promote bone defect repair and can potentially be used as a bone defect filling material for bone regeneration applications.

Trends in bioactivity: inducing and detecting mineralization of regenerative polymeric scaffolds

Due to limitations of biological and alloplastic grafts, regenerative engineering has emerged as a promising alternative to treat bone defects. Bioactive polymeric scaffolds are an integral part of such an approach. Bioactivity importantly induces hydroxyapatite mineralization that promotes osteoinductivity and osseointegration with surrounding bone tissue. Strategies to confer bioactivity to polymeric scaffolds utilize bioceramic fillers, coatings and surface treatments, and additives. These approaches can also favorably impact mechanical and degradation properties. A variety of fabrication methods are utilized to prepare scaffolds with requisite morphological features. The bioactivity of scaffolds may be evaluated with a broad set of techniques, including in vitro (acellular and cellular) and in vivo methods. Herein, we highlight contemporary and emerging approaches to prepare and assess scaffold bioactivity, as well as existing challenges.

Advances in amelioration of plasma electrolytic oxidation coatings on biodegradable magnesium and alloys

Magnesium and its alloys are considered excellent materials for biodegradable implants because of their good biocompatibility and biodegradability as well as their mechanical properties. However, the rapid degradation rate severely limits their clinical applications. Plasma electrolytic oxidation (PEO), also known as micro-arc oxidation (MAO), is an effective surface modification technique. However, there are many pores and cracks on the coating surface under conventional PEO process. The corrosive products tend to penetrate deeply into the substrate, reducing its corrosion resistance and the biocompatibility, which makes PEO-coated Mg difficult to meet the long-term needs of in vivo implants. Hence, it is necessary to modify the PEO coating. This review discusses the formation mechanism and the influential parameters of PEO coatings on Mg. This is followed by a review of the latest research of the pretreatment and typical amelioration of PEO coating on biodegradable Mg alloys in the past 5 years, including calcium phosphate (Ca-P) coating, layered double hydroxide (LDH)-PEO coating, ZrO2 incorporated-PEO coating, antibacterial ingredients-PEO coating, drug-PEO coating, polymer-PEO composite coating, Plasma electrolytic fluorination (PEF) coating and self-healing coating. Meanwhile, the improvements of morphology, corrosion resistance, wear resistance, biocompatibility, antibacterial abilities, and drug loading abilities and the preparation methods of the modified PEO coatings are deeply discussed as well. Finally, the challenges and prospects of PEO coatings are discussed in detail for the purpose of promoting the clinical application of biodegradable Mg alloys.

Chemical-physical behavior of Hydroxyapatite: A modeling approach

Hydroxyapatite (HAp) is a ceramic composed of calcium phosphate, frequently employed as a bone substitute material due to its biocompatibility and bioactivity. Over the past century, there has been substantial attention in fields such as orthopedics and plastic surgery. Remarkably, synthetic HAp exhibits properties akin to those found in natural bone and teeth. Computational theoretical chemistry focuses on numerically computing molecular electronic structures and interactions. As chemistry education evolves, it's imperative to acknowledge the increasing significance of computational tools in research. Density Functional Theory (DFT) stands out as the most widely adopted method in contemporary computational chemistry. In this study, we synthesized Hydroxyapatite (HAp) via the double decomposition method using synthetic sources. The synthesized materials underwent thorough characterization, including X-ray Diffraction (XRD), UV-visible spectroscopy, and Fourier Transform Infrared (FTIR) spectroscopy under various conditions. Additionally, we performed quantum mechanical computations on the HAp molecule using density functional theory. Our results were then compared with experimental data. Our experimental findings highlight the successful synthesis of HAp, particularly under specific temperature conditions. Moreover, the quantum chemistry calculations exhibited excellent agreement with the experimental results, especially in terms of spectroscopic characterizations.

Towards a sustainable chitosan-based composite scaffold derived from Scylla serrata crab chitosan for bone tissue engineering

Bone tissue engineering offers a novel therapy for repairing bone defects or fractures. However, it is becoming increasingly challenging because an ideal scaffold should possess a similar porous structure, high biocompatibility, and mechanical properties that match those of natural bone. To fabricate such a scaffold, biodegradable polymers are often preferred due to their degradability and tailored structure. This study involved the isolation of chitosan from crab shells (Scylla serrata) waste to use as a biomaterial in combination with hydroxyapatite (HAP) and collagen I (COL I) to mimic the extracellular matrix (ECM) composition of bone. After being cast and freeze-dried, it resulted in an interconnected porous scaffold with a porosity of 51.44% ± 2.28% and a pore diameter of 109.88 μm ± 49.84 μm. The swelling ratio of the crab scaffold was measured at 358.31% ± 25.23%, 363.04% ± 1.56%, and 370.11% ± 3.7% at 1, 3, and 6 h, respectively. Consequently, the scaffold exhibited a degradation ratio of 8.17% ± 2.59%, 21.62% ± 5.43%, 22.59% ± 14.23%, and 23.12% ± 6.28% over the course of 1 to 4 weeks. It demonstrated excellent biocompatibility with MG-63 osteosarcoma cells. Although the compression strength was lower than 2-12 MPa, the crab scaffold can still be applied effectively for non-load-bearing bone defects. Crab shell waste emerges as a promising source of chitosan for tissue engineering applications.

Polymethylmethacrylate-hydroxyapatite antibacterial and antifungal activity against oral bacteria: An in vitro study

Objective

Reconstruction of alveolar bone defects resulting from aging, trauma, ablative surgery or pathology, remains a significant clinical challenge. The objective of this study was to investigate the antibacterial and antifungal activities of mixed polymethylmethacrylate-hydroxyapatite (PMMA-HA) against oral microorganisms. Our findings could provide valuable insights into the prospective application of PMMA-HA as a synthetic bone graft material to manage alveolar bone defects via tissue engineering.

Methods

HA powder was obtained from the Center for Ceramics in Indonesia and PMMA granules were obtained from HiMedia Laboratories; these were prepared in 20:80, 30:70, and 40:60 ratios. The antibacterial diffusion method was then performed against Staphylococcusaureus, Aggregatibacter actinomycetemcomitans, Porphyromonas gingivalis, and Fusobacterium nucleatum, while the antifungal diffusion method was used to test against Candida albicans. Standardized protocols were used for microbial culturing and inhibition zones were measured with digital calipers. Statistical analyses included one-way ANOVA and Kruskal-Wallis tests, supplemented by post-hoc Tukey HSD tests.

Results

A PMMA-HA scaffold with a 20:80 ratio demonstrated the highest antibacterial activity against S. aureus, A. actinomycetemcomitans, P. gingivalis, and F. nucleatum. This was followed by the 30:70 and 40:60 ratios in terms of antibacterial activity. Statistical significance was achieved with p < 0.05 in comparison to controls. However, none of the PMMA-HA ratios showed antifungal activity against C. albicans.

Conclusion

PMMA-HA scaffolds have significant activity against bacteria, but not against fungi.

Balancing beauty and science: a review of facial implant materials in craniofacial surgery

Facial reconstruction and augmentation, integral in facial plastic surgery, address defects related to trauma, tumors infections, and congenital skeletal deficiencies. Aesthetic considerations, including age-related facial changes, involve volume loss and diminished projection, often associated with predictable changes in the facial skeleton. Autologous, allogeneic, and alloplastic implants are used to address these concerns. Autologous materials such as bone, cartilage, and fat, while longstanding options, have limitations, including unpredictability and resorption rates. Alloplastic materials, including metals, polymers, and ceramics, offer alternatives. Metals like titanium are biocompatible and used primarily in fracture fixation. Polymers, such as silicone and polyethylene, are widely used, with silicone presenting migration, bony resorption, and visibility issues. Polyethylene, particularly porous polyethylene (MedPor), was reported to have one of the lowest infection rates while it becomes incorporated into the host. Polyether-ether-ketone (PEEK) exhibits mechanical strength and compatibility with imaging modalities, with custom PEEK implants providing stable results. Acrylic materials, like poly-methylmethacrylate (PMMA), offer strength and is thus mostly used in the case of cranioplasty. Bioceramics, notably hydroxyapatite (HaP), offer osteoconductive and inductive properties, and HaP granules demonstrate stable volume retention in facial aesthetic augmentation. Combining HaP with other materials, such as PLA, may enhance mechanical stability. 3D bioprinting with HaP-based bioinks presents a promising avenue for customizable and biocompatible implants. In conclusion, various materials have been used for craniofacial augmentation, but none have definitively demonstrated superiority. Larger randomized controlled trials are essential to evaluate short- and long-term complications comprehensively, potentially revolutionizing facial balancing surgery.

Cell-Laden 3D Printed GelMA/HAp and THA Hydrogel Bioinks: Development of Osteochondral Tissue-like Bioinks

Osteochondral (OC) disorders such as osteoarthritis (OA) damage joint cartilage and subchondral bone tissue. To understand the disease, facilitate drug screening, and advance therapeutic development, in vitro models of OC tissue are essential. This study aims to create a bioprinted OC miniature construct that replicates the cartilage and bone compartments. For this purpose, two hydrogels were selected: one composed of gelatin methacrylate (GelMA) blended with nanosized hydroxyapatite (nHAp) and the other consisting of tyramine-modified hyaluronic acid (THA) to mimic bone and cartilage tissue, respectively. We characterized these hydrogels using rheological testing and assessed their cytotoxicity with live-dead assays. Subsequently, human osteoblasts (hOBs) were encapsulated in GelMA-nHAp, while micropellet chondrocytes were incorporated into THA hydrogels for bioprinting the osteochondral construct. After one week of culture, successful OC tissue generation was confirmed through RT-PCR and histology. Notably, GelMA/nHAp hydrogels exhibited a significantly higher storage modulus (G') compared to GelMA alone. Rheological temperature sweeps and printing tests determined an optimal printing temperature of 20 °C, which remained unaffected by the addition of nHAp. Cell encapsulation did not alter the storage modulus, as demonstrated by amplitude sweep tests, in either GelMA/nHAp or THA hydrogels. Cell viability assays using Ca-AM and EthD-1 staining revealed high cell viability in both GelMA/nHAp and THA hydrogels. Furthermore, RT-PCR and histological analysis confirmed the maintenance of osteogenic and chondrogenic properties in GelMA/nHAp and THA hydrogels, respectively. In conclusion, we have developed GelMA-nHAp and THA hydrogels to simulate bone and cartilage components, optimized 3D printing parameters, and ensured cell viability for bioprinting OC constructs.

Deciphering load attenuation mechanisms of the dentin-enamel junction: Insights from a viscoelastic constitutive model

A considerable material discontinuity between the enamel and dentin might jeopardize the tooth's mechanical durability over time without the attenuation of the dentin-enamel junction (DEJ). However, the critical loading transmission mechanism at the DEJ remains understudied. This study aimed to define the extent and effective width of the DEJ, along with its mechanical competence. The presence of DEJ interphase layer was identified using a motif analysis based on the ion beam-transmission electron microscopy coupled with nanoindentation modulus mapping. For each region, nanoindentation load-displacement curves were recorded and mathematically analyzed using an appropriate viscoelastic constitutive model. The time-course of indenter penetration (creep) behavior of the tooth tissues can be mathematically approximated by the Kelvin-Voigt model in series, which determined the visco-contribution to the overall mechanical responses. Therefore, the elastic-plastic contribution can be distinguished from the overall mechanical responses of the tooth after subtracting the visco-contributions. During the loading period, the enamel behavior was dominated by elastic-plastic responses, while both the dentin and DEJ showed pronounced viscoelastic responses. The instantaneous modulus of the DEJ, which was measured by eliminating viscoelastic behavior from the raw load-displacement curve, was almost double that of the dentin. The DEJ was stiffer than the dentin, but it exhibited large viscoelastic motion even at the initial loading stage. This study revealed that the load attenuation competence of the DEJ, which involves extra energy expenditure, is mainly associated with its viscoelasticity. The mathematical analysis proposed here, performed on the nanoindentation creep behavior, could potentially augment the existing knowledge on hard-tissue biomechanics. STATEMENT OF SIGNIFICANCE: In this study, we undertake a rigorous mechanical characterization of the dentin-enamel junction (DEJ) using an advanced nanoindentation technique coupled with a pertinent viscoelastic constitutive model. Our approach unveils the substantial viscoelastic contribution of the DEJ during the initial indentation loading phase and offers an elaborate delineation of the DEJ interphase layer through sophisticated image analysis. These insights significantly augment our understanding of tooth durability. Importantly, our innovative mathematical analysis of creep behavior introduces a novel approach with profound implications for future research in the expansive field of hard-tissue biomechanics. The pioneering methodologies and findings presented in this work hold substantial potential to invigorate progress in biomaterials research and fuel further explorations into the functionality of biological tissues.

Progress in microsphere-based scaffolds in bone/cartilage tissue engineering

Bone/cartilage repair and regeneration have been popular and difficult issues in medical research. Tissue engineering is rapidly evolving to provide new solutions to this problem, and the key point is to design the appropriate scaffold biomaterial. In recent years, microsphere-based scaffolds have been considered suitable scaffold materials for bone/cartilage injury repair because microporous structures can form more internal space for better cell proliferation and other cellular activities, and these composite scaffolds can provide physical/chemical signals for neotissue formation with higher efficiency. This paper reviews the research progress of microsphere-based scaffolds in bone/chondral tissue engineering, briefly introduces types of microspheres made from polymer, inorganic and composite materials, discusses the preparation methods of microspheres and the exploration of suitable microsphere pore size in bone and cartilage tissue engineering, and finally details the application of microsphere-based scaffolds in biomimetic scaffolds, cell proliferation and drug delivery systems.

Applications of Polydopamine in Implant Surface Modification

There is great clinical demand for orthopedic and dental implant surface modification methods to prevent osseointegration failure and improve implant biological functions. Notably, dopamine (DA) can be polymerized to form polydopamine (PDA), which is similar to the adhesive proteins secreted by mussels, to form a stable bond between the bone surface and implants. Therefore, PDA has the potential to be used as an implant surface modification material with good hydrophilicity, roughness, morphology, mechanical strength, biocompatibility, antibacterial activity, cellular adhesion, and osteogenesis. In addition, PDA degradation releases DA into the surrounding microenvironment, which is found to play an important role in regulating DA receptors on both osteoblasts and osteoclasts during the bone remodeling process. Furthermore, the adhesion properties of PDA suggest its use as an intermediate layer in assisting other functional bone remodeling materials, such as nanoparticles, growth factors, peptides, and hydrogels, to form "dual modifications." The purpose of this review is to summarize the recent progress in research on PDA and its derivatives as orthopedic and dental implant surface modification materials and to analyze the multiple functions of PDA.

Flavonoid-Loaded Biomaterials in Bone Defect Repair

Skeletons play an important role in the human body, and can form gaps of varying sizes once damaged. Bone defect healing involves a series of complex physiological processes and requires ideal bone defect implants to accelerate bone defect healing. Traditional grafts are often accompanied by issues such as insufficient donors and disease transmission, while some bone defect implants are made of natural and synthetic polymers, which have characteristics such as good porosity, mechanical properties, high drug loading efficiency, biocompatibility and biodegradability. However, their antibacterial, antioxidant, anti-inflammatory and bone repair promoting abilities are limited. Flavonoids are natural compounds with various biological activities, such as antitumor, anti-inflammatory and analgesic. Their good anti-inflammatory, antibacterial and antioxidant activities make them beneficial for the treatment of bone defects. Several researchers have designed different types of flavonoid-loaded polymer implants for bone defects. These implants have good biocompatibility, and they can effectively promote the expression of angiogenesis factors such as VEGF and CD31, promote angiogenesis, regulate signaling pathways such as Wnt, p38, AKT, Erk and increase the levels of osteogenesis-related factors such as Runx-2, OCN, OPN significantly to accelerate the process of bone defect healing. This article reviews the effectiveness and mechanism of biomaterials loaded with flavonoids in the treatment of bone defects. Flavonoid-loaded biomaterials can effectively promote bone defect repair, but we still need to improve the overall performance of flavonoid-loaded bone repair biomaterials to improve the bioavailability of flavonoids and provide more possibilities for bone defect repair.

Dextrose, maltose and starch guide crystallization of strontium-substituted hydroxyapatite: A comparative study for bone tissue engineering application

The influence of carbohydrates on the crystallization of metal-substituted hydroxyapatite predicts its relevance to natural bone growth. This study demonstrates the role of carbohydrates in the crystallization of strontium-substituted hydroxyapatite (SHAP). The increasing order of hydroxyl groups, dextrose (monosaccharide) < maltose (disaccharide) < starch (polysaccharide), coordinated with Ca2+/Sr2+ and thus guided SHAP crystallization, with crystal size reduced from 35 to 19 nm, lattice volume increased from 518 to 537 Å3, and residual carbohydrates increased from 1.8 to 20.2 %. The variation in residual carbohydrates is due to their interaction with apatite and/or aqueous insolubility. Compared to pure SHAP, the starch-SHAP with higher residual starch showed increased water uptake from 1.23 ± 0.18 to 4.26 ± 0.21 % and degradation from 0.22 ± 0.06 to 1.53 ± 0.14 %, but decreased microhardness from 0.73 ± 0.12 to 0.38 ± 0.01 GPa and protein affinity from 4.82 ± 0.01 to 0.81 ± 0.01 μg/mg. However, its microhardness value was bone-like, and the reduced protein adsorption was masked by the rich osteogenic behaviour. In vitro cellular response demonstrated that the residual carbohydrate and strontium augmented osteocompatibility, proliferation, differentiation and biomineralization. The result concludes that carbohydrates drive SHAP crystallization, and starch-SHAP replicates natural bone.

Recent Advances in Bioengineering Bone Revascularization Based on Composite Materials Comprising Hydroxyapatite

The natural healing process of bone is impaired in the presence of tumors, trauma, or inflammation, necessitating external assistance for bone regeneration. The limitations of autologous/allogeneic bone grafting are still being discovered as research progresses. Bone tissue engineering (BTE) is now a crucial component of treating bone injuries and actively works to promote vascularization, a crucial stage in bone repair. A biomaterial with hydroxyapatite (HA), which resembles the mineral makeup of invertebrate bones and teeth, has demonstrated high osteoconductivity, bioactivity, and biocompatibility. However, due to its brittleness and porosity, which restrict its application, scientists have been prompted to explore ways to improve its properties by mixing it with other materials, modifying its structural composition, improving fabrication techniques and growth factor loading, and co-cultivating bone regrowth cells to stimulate vascularization. This review scrutinizes the latest five-year research on HA composite studies aimed at amplifying vascularization in bone regeneration.

Bioinspired gradient scaffolds for osteochondral tissue engineering

Repairing articular osteochondral defects present considerable challenges in self-repair due to the complex tissue structure and low proliferation of chondrocytes. Conventional clinical therapies have not shown significant efficacy, including microfracture, autologous/allograft osteochondral transplantation, and cell-based techniques. Therefore, tissue engineering has been widely explored in repairing osteochondral defects by leveraging the natural regenerative potential of biomaterials to control cell functions. However, osteochondral tissue is a gradient structure with a smooth transition from the cartilage to subchondral bone, involving changes in chondrocyte morphologies and phenotypes, extracellular matrix components, collagen type and orientation, and cytokines. Bioinspired scaffolds have been developed by simulating gradient characteristics in heterogeneous tissues, such as the pores, components, and osteochondrogenesis-inducing factors, to satisfy the anisotropic features of osteochondral matrices. Bioinspired gradient scaffolds repair osteochondral defects by altering the microenvironments of cell growth to induce osteochondrogenesis and promote the formation of osteochondral interfaces compared with homogeneous scaffolds. This review outlines the meaningful strategies for repairing osteochondral defects by tissue engineering based on gradient scaffolds and predicts the pros and cons of prospective translation into clinical practice.

Enzymatically cross-linked hyaluronic acid hydrogels as in situ forming carriers of platelet-rich plasma: Mechanical properties and bioactivity levels evaluation

New studies have shown the great potential of the combination of in situ enzymatically cross-linked hydrogels based on tyramine derivative of hyaluronic acid (HA-TA) with platelet-rich plasma (PRP) and platelet lysate in regenerative medicine. This study describes how the presence of PRP and platelet lysate affects the kinetics of gelation, viscoelastic properties, swelling ratio, and the network structure of HA-TA hydrogels and how the encapsulation of PRP in hydrogels affects the bioactivity of released PRP determined as the ability to induce cell proliferation. The properties of hydrogels were tuned by a degree of substitution and concentration of HA-TA derivatives. The addition of platelet derivatives to the reaction mixture slowed down the cross-linking reaction and reduced elastic modulus (G') and thus cross-linking efficiency. However, low-swellable hydrogels (7-190%) suitable for soft tissue engineering with G' 200-1800 Pa were prepared with a gelation time within 1 min. It was confirmed that tested cross-linking reaction conditions are suitable for PRP incorporation because the total bioactivity level of PRP released from HA-TA hydrogels was ≥87% and HA-TA content in the hydrogels and thus mesh size (285-482 nm) has no significant effect on the bioactivity level of released PRP.

Regenerative Engineering of a Biphasic Patient-Fitted Temporomandibular Joint Condylar Prosthesis

Regenerative medicine approaches to restore the mandibular condyle of the temporomandibular joint (TMJ) may fill an unmet patient need. In this study, a method to implant an acellular regenerative TMJ prosthesis was developed for orthotopic implantation in a pilot goat study. The scaffold incorporated a porous, polycaprolactone-hydroxyapatite (PCL-HAp, 20wt% HAp) 3D printed condyle with a cartilage-matrix-containing hydrogel. A series of material characterizations was used to determine the structure, fluid transport, and mechanical properties of 3D printed PCL-HAp. To promote marrow uptake for cell seeding, a scaffold pore size of 152 ± 68 μm resulted in a whole blood transport initial velocity of 3.7 ± 1.2 mm·s-1 transported to the full 1 cm height. The Young's modulus of PCL was increased by 67% with the addition of HAp, resulting in a stiffness of 269 ± 20 MPa for etched PCL-HAp. In addition, the bending modulus increased by 2.06-fold with the addition of HAp to 470 MPa for PCL-HAp. The prosthesis design with an integrated hydrogel was compared with unoperated contralateral control and no-hydrogel group in a goat model for 6 months. A guide was used to make the condylectomy cut, and the TMJ disc was preserved. MicroCT assessment of bone suggested variable tissue responses with some regions of bone growth and loss, although more loss may have been exhibited by the hydrogel group than the no-hydrogel group. A benchtop load transmission test suggested that the prosthesis was not shielding load to the underlying bone. Although variable, signs of neocartilage formation were exhibited by Alcian blue and collagen II staining on the anterior, functional surface of the condyle. Overall, this study demonstrated signs of functional TMJ restoration with an acellular prosthesis. There were apparent limitations to continuous, reproducible bone formation, and stratified zonal cartilage regeneration. Future work may refine the prosthesis design for a regenerative TMJ prosthesis amenable to clinical translation.

Electrochemical and Structural Characterization of Lanthanum-Doped Hydroxyapatite: A Promising Material for Sensing Applications

In the quest to find powerful modifiers of screen-printed electrodes for sensing applications, a set of rare earth-doped Ca_10-xRE_x(PO₄)₆(OH)₂ (RE = La, Nd, Sm, Eu, Dy, and Tm and x = 0.01, 0.02, 0.10, and 0.20) hydroxyapatite (HAp) samples were subjected to an in-depth electrochemical characterization using electrochemical impedance spectroscopy and cyclic and square wave voltammetry. Among all of these, the inorganic phosphates doped with lanthanum proved to be the most reliable, revealing robust analytical performances in terms of sensitivity, repeatability, reproducibility, and reusability, hence paving the way for their exploitation in sensing applications. Structural data on La-doped HAp samples were also provided by using different techniques, including optical microscopy, X-ray diffraction, Rietveld refinement from X-ray data, Fourier transform infrared, and Raman vibrational spectroscopies, to complement the electrochemical characterization.

Biomechanical Characteristics and Analysis Approaches of Bone and Bone Substitute Materials

Bone has a special structure that is both stiff and elastic, and the composition of bone confers it with an exceptional mechanical property. However, bone substitute materials that are made of the same hydroxyapatite (HA) and collagen do not offer the same mechanical properties. It is important for bionic bone preparation to understand the structure of bone and the mineralization process and factors. In this paper, the research on the mineralization of collagen is reviewed in terms of the mechanical properties in recent years. Firstly, the structure and mechanical properties of bone are analyzed, and the differences of bone in different parts are described. Then, different scaffolds for bone repair are suggested considering bone repair sites. Mineralized collagen seems to be a better option for new composite scaffolds. Last, the paper introduces the most common method to prepare mineralized collagen and summarizes the factors influencing collagen mineralization and methods to analyze its mechanical properties. In conclusion, mineralized collagen is thought to be an ideal bone substitute material because it promotes faster development. Among the factors that promote collagen mineralization, more attention should be given to the mechanical loading factors of bone.

Oyster shell-derived nano-hydroxyapatite and proanthocyanidin pretreatment on dentinal tubule occlusion and permeability before and after acid challenge-an in vitro study

This in vitro study evaluated the dentinal tubule occlusion (TO), depth of penetration (DoP), and dentin permeability (DP) of oyster shell-derived nanohydroxyapatite (os-nHAp) with and without 15% proanthocyanidin (PA) pretreatment. os-nHAp was synthesized via the precipitation method and it was characterized. The morphology and particle size of os-nHAp were analyzed using a high-resolution transmission electron microscope (HRTEM). Cytotoxicity of os-nHAp, PA/os-nHAp, and casein phosphopeptide-amorphous calcium phosphate (CPP-ACP) was assessed by (3-(4,5-dimethythiazol-2-yl) 2,5-diphenyl tetrazolium bromide (MTT) assay using human osteosarcoma (MG-63) cell line. One hundred and ninety-seven dentin discs of 3 mm thickness were prepared from the crown portion of extracted human teeth. The dentinal surfaces of the discs were etched for 2 min with 6% citric acid to simulate dentin hypersensitivity. Five discs were randomly selected and the patency of dentinal tubules was confirmed using a scanning electron microscope (SEM). The remaining 192 discs were divided into four groups (n = 48) depending on the type of remineralization as follows: group 1: os-nHAp, group 2: PA/os-nHAp, group 3: CPP-ACP, and group 4: no treatment. The remineralization protocol was followed for 21 days. Out of the 48 dentin discs in each group, 32 discs were used to evaluate dentinal tubule occlusion (TO) and depth of penetration (DoP) using SEM. The remaining 16 discs were subjected to an assessment of dentin permeability (DP) using a hydraulic conductance model. TO, DoP and DP were evaluated after remineralization and acid challenge. Characterization studies confirmed the presence of pure phase apatite. HRTEM confirmed the nanometric particle size of os-nHAp. MTT assay results showed that all the tested materials exhibited >80% cell viability when tested up to a concentration of 100 µg/mL. The results demonstrated a significantly higher mean percentage of TO, DoP, and lesser mean DP after remineralization in groups 1, 2, and 3 (p < 0.05). After the acid challenge, group 3 showed a significant reduction in TO and DoP, and increased DP (p < 0.05). However, no such changes were observed in groups 1 and 2. Within the limitations of this study, it can be concluded that os-nHAp and PA/os-nHAp could serve as potential and durable therapeutic agents in the treatment of dentin hypersensitivity.

A Novel Hydroxyapatite/Vitamin B12 Nanoformula for Treatment of Bone Damage: Preparation, Characterization, and Anti-Arthritic, Anti-Inflammatory, and Antioxidant Activities in Chemically Induced Arthritic Rats

The usage of nanomaterials for rheumatoid arthritis (RA) treatment can improve bioavailability and enable selective targeting. The current study prepares and evaluates the in vivo biological effects of a novel hydroxyapatite/vitamin B₁₂ nanoformula in Complete Freund's adjuvant-induced arthritis in rats. The synthesized nanoformula was characterized using XRD, FTIR, BET analysis, HERTEM, SEM, particle size, and zeta potential. We synthesized pure HAP NPs with 71.01% loading weight percentages of Vit B12 and 49 mg/g loading capacity. Loading of vitamin B₁₂ on hydroxyapatite was modeled by Monte Carlo simulation. Anti-arthritic, anti-inflammatory, and antioxidant effects of the prepared nanoformula were assessed. Treated arthritic rats showed lower levels of RF and CRP, IL-1β, TNF-α, IL-17, and ADAMTS-5, but higher IL-4 and TIMP-3 levels. In addition, the prepared nanoformula increased GSH content and GST antioxidant activity while decreasing LPO levels. Furthermore, it reduced the expression of TGF-β mRNA. Histopathological examinations revealed an improvement in joint injuries through the reduction of inflammatory cell infiltration, cartilage deterioration, and bone damage caused by Complete Freund's adjuvant. These findings indicate that the anti-arthritic, antioxidant, and anti-inflammatory properties of the prepared nanoformula could be useful for the development of new anti-arthritic treatments.

Additive Manufacturing of Bioceramic Implants for Restoration Bone Engineering: Technologies, Advances, and Future Perspectives

Treating bone defects is highly challenging because they do not heal on their own inside the patients, so implants are needed to assist in the reconstruction of the bone. Bioceramic implants based on additive manufacturing (AM) are currently emerging as promising treatment options for restoration bone engineering. On the one hand, additively manufactured bioceramic implants have excellent mechanical properties and biocompatibility, which are suitable for bone regeneration. On the other hand, the designable structure and adjustable pores of additively manufactured bioceramic implants allow them to promote suitable cell growth and tissue climbing. Herein, this review unfolds to introduce several frequently employed AM technologies for bioceramic implants. After that, advances in commonly used additively manufactured bioceramic implants, including bioinert ceramic implants, bioactive ceramic implants, and bioceramic/organic composite implants, are categorized and summarized. Finally, the future perspectives of additively manufactured bioceramic implants, in terms of mechanical performance improvement, innovative structural design, biological property enhancement, and other functionalization approaches, are proposed and forecasted. This review is believed to provide some fundamental understanding and cutting-edge knowledge for the additive manufacturing of bioceramic implants for restoration bone engineering.

The Impact of Hydroxyapatite Sintering Temperature on Its Microstructural, Mechanical, and Biological Properties

Hydroxyapatite (HA), the principal mineral of bone tissue, can be fabricated as an artificial calcium phosphate (CaP) ceramic and potentially used as bioceramic material for bone defect treatment. Nevertheless, the production method (including the applied sintering temperature) of synthetic hydroxyapatite directly affects its basic properties, such as its microstructure, mechanical parameters, bioabsorbability, and osteoconductivity, and in turn influences its biomedical potential as an implantable biomaterial. The wide application of HA in regenerative medicine makes it necessary to explain the validity of the selection of the sintering temperature. The main emphasis of this article is on the description and summarization of the key features of HA depending on the applied sintering temperature during the synthesis process. The review is mainly focused on the dependence between the HA sintering temperature and its microstructural features, mechanical properties, biodegradability/bioabsorbability, bioactivity, and biocompatibility.

Biodegradable Cements for Bone Regeneration

Bone cements such as polymethyl methacrylate and calcium phosphates have been widely used for the reconstruction of bone. Despite their remarkable clinical success, the low degradation rate of these materials hampers a broader clinical use. Matching the degradation rate of the materials with neo bone formation remains a challenge for bone-repairing materials. Moreover, questions such as the mechanism of degradation and how the composition of the materials contribute to the degradation property remain unanswered. Therefore, the review provides an overview of currently used biodegradable bone cements such as calcium phosphates (CaP), calcium sulfates and organic-inorganic composites. The possible degradation mechanism and clinical performance of the biodegradable cements are summarized. This paper reviews up-to-date research and applications of biodegradable cements, hoping to provide researchers in the field with inspirations and references.

Application of the neuropeptide NPVF to enhance angiogenesis and osteogenesis in bone regeneration

The brain-bone regulatory system regulates skeletal homeostasis via bioactive neuropeptides, yet the underlying mechanism remains elusive. Here, we report the role of the neuropeptide VF (NPVF, VPNLPQRF-NH2) in enhancing both angiogenesis and osteogenesis in a rat skeletal system and the potential pathways involved. An in vitro study revealed that NPVF not only promotes migration and angiogenesis of human umbilical vein endothelial cells (HUVECs) by activating NPFFR1, which leads to upregulation of miR-181c-3p and downregulation of Argonaute1 (AGO1), but also mediates osteogenic differentiation of bone mesenchymal stem cells (BMSCs) via the Wnt/β-catenin signaling pathway. To improve the stability and bioavailability and thus efficacy of NPVF as a promoter of in vivo bone regeneration, we genetically engineered amyloid-NPVF-fusion proteins and utilized them as self-assembling nanofiber coatings to treat bone defects in a rat calvarial defect model. We found that a porous hydroxyapatite scaffold loaded with the NPVF peptide-fused amyloid coating substantially enhanced angiogenesis and site-specific fresh bone in-growth when implanted in calvarial defects. Taken together, our work uncovered a previously undefined crosstalk between the brain and bone by unveiling the role of NPVF in bone tissue and demonstrated a viable method for promoting bone tissue repairs based upon self-assembling NPVF-containing protein coatings.

Vancomycin-Loaded, Nanohydroxyapatite-Based Scaffold for Osteomyelitis Treatment: In Vivo Rabbit Toxicological Tests and In Vivo Efficacy Tests in a Sheep Model

The treatment for osteomyelitis consists of surgical debridement, filling of the dead space, soft tissue coverage, and intravenous administration of antimicrobial (AM) agents for long periods. Biomaterials for local delivery of AM agents, while providing controllable antibiotic release rates and simultaneously acting as a bone scaffold, may be a valuable alternative; thus, avoiding systemic AM side effects. V-HEPHAPC is a heparinized nanohydroxyapatite (nHA)/collagen biocomposite loaded with vancomycin that has been previously studied and tested in vitro. It enables a vancomycin-releasing profile with an intense initial burst, followed by a sustained release with concentrations above the Minimum Inhibitory Concentration (MIC) for MRSA. In vitro results have also shown that cellular viability is not compromised, suggesting that V-HEPHAPC granules may be a promising alternative device for the treatment of osteomyelitis. In the present study, V-HEPHAPC (HEPHAPC with vancomycin) granules were used as a vancomycin carrier to treat MRSA osteomyelitis. First, in vivo Good Laboratory Practice (GLP) toxicological tests were performed in a rabbit model, assuring that HEPHAPC and V-HEPHAPC have no relevant side effects. Second, V-HEPHAPC proved to be an efficient drug carrier and bone substitute to control MRSA infection and simultaneously reconstruct the bone cavity in a sheep model.

Recent advances on bioactive baghdadite ceramic for bone tissue engineering applications: 20 years of research and innovation (a review)

Various artificial bone graft substitutes based on ceramics have been developed over the last 20 years. Among them, calcium-silicate-based ceramics, which are osteoconductive and can attach directly to biological organs, have received great attention for bone tissue engineering applications. However, the degradation rate of calcium-silicate and bone formation is often out of balance, resulting in stress shielding (osteopenia). A new strategy to improve the drawbacks of these ceramics is incorporating trace elements such as Zn, Mg, and Zr into their lattice structures, enhancing their physical and biological properties. Recently, baghdadite (Ca₃ZrSi₂O₉) ceramic, one of the most appealing calcium-silicate-based ceramics, has demonstrated high bioactivity, biocompatibility, biodegradability, and cell interaction. Because of its physical, mechanical, and biological properties and ability to be shaped using various fabrication techniques, baghdadite has found high potential in various biomedical applications such as coatings, fillers, cement, scaffolds, and drug delivery systems. Undoubtedly, there is a high potential for this newly developed ceramic to contribute significantly to therapies to provide a tremendous clinical outcome. This review paper aims to summarize and discuss the most relevant studies performed on baghdadite-based ceramics and composites by focusing on their behavior in vivo and in vitro.

Advancement in "Garbage In Biomaterials Out (GIBO)" concept to develop biomaterials from agricultural waste for tissue engineering and biomedical applications

Presently on a global scale, one of the major concerns is to find effective strategies to manage the agricultural waste to protect the environment. One strategy that has been drawing attention among the researchers is the development of biocompatible materials from agricultural waste. This strategy implies successful conversion of agricultural waste products (e.g.: cellulose, eggshell etc.) into building blocks for biomaterial development. Some of these wastes contain even bioactive compounds having biomedical applications. The replacement and augmentation of human tissue with biomaterials as alternative to traditional method not only bypasses immune-rejection, donor scarcity, and maintenance; but also provides long term solution to damaged or malfunctioning organs. Biomaterials development as one of the key challenges in tissue engineering approach, resourced from natural origin imparts better biocompatibility due to closely mimicking composition with cellular microenvironment. The "Garbage In, Biomaterials Out (GIBO)" concept, not only recycles the agricultural wastes, but also adds to biomaterial raw products for further product development in tissue regeneration. This paper reviews the conversion of garbage agricultural by-products to the biocompatible materials for various biomedical applications.

Graphical abstract

The agro-waste biomass processed, purified, modified, and further utilized for the fabrication of biomaterials-based support system for tissue engineering applications to grow living body parts in vitro or in vivo.

Chitosan/Xanthan membrane containing hydroxyapatite/Graphene oxide nanocomposite for guided bone regeneration

OBJECTIVE

To develop a chitosan-xanthan (CX) membrane associated with Hydroxyapatite (HA) and different concentrations of graphene oxide (GO).

METHODOLOGY

The CX complex was associated with the hydroxyapatite-graphene oxide (HAGO) nanocomposite in different concentrations. The experimental groups were:1) CX; 2) Chitosan-Xanthan/Hydroxyapatite (CXHA); 3) Chitosan-Xanthan/Hydroxyapatite-Graphene Oxide 0.5% (CXHAGO 0.5%); 4) CXHAGO 1.0%; 5) CXHAGO 1.5%. The membranes characterizations were performed by X-ray diffraction (XRD), Fourier Transform Infrared Spectroscopy (FTIR), Raman spectroscopy, Scanning Electron Microscopy (SEM), Contact angle, Tensile Strength, in vitro Bioactivity and the in vitro Cell viability (MTT test). The data was submitted to the Normality and Homogeneity tests. In vitro Indirect Cytotoxicity assay data was statistically analyzed by two-way ANOVA and Tukey's test (α = 0.05). Tensile Strength and Contact Angle data were statistically analyzed by one-way ANOVA followed by Tukey's test (α = 0.05).

RESULTS

XRD, FTIR and Raman spectroscopy confirmed the characteristic bands of the CX polymeric complex, the phosphate bands related to HA, and the presence of GO. SEM images demonstrated the non-porous and homogeneous surface of membranes. The contact angle test showed the hydrophilic characteristic of all membranes (p > 0.05). CX showed tensile strength significantly higher than other membranes. The apatite deposition was observed in all membranes after performing the bioactivity test. The cell viability of CXHAGO 1.0% and CXHAGO 1.5% was significantly higher than CX.

CONCLUSION

The addition of HAGO reduced the mechanical strength of membranes, but improved its cell viability. It demonstrated the potential of CXHAGO membranes to be used in guided bone regeneration therapies.

Multifunctional Scaffolds Based on Emulsion and Coaxial Electrospinning Incorporation of Hydroxyapatite for Bone Tissue Regeneration

Tissue engineering is nowadays a powerful tool to restore damaged tissues and recover their normal functionality. Advantages over other current methods are well established, although a continuous evolution is still necessary to improve the final performance and the range of applications. Trends are nowadays focused on the development of multifunctional scaffolds with hierarchical structures and the capability to render a sustained delivery of bioactive molecules under an appropriate stimulus. Nanocomposites incorporating hydroxyapatite nanoparticles (HAp NPs) have a predominant role in bone tissue regeneration due to their high capacity to enhance osteoinduction, osteoconduction, and osteointegration, as well as their encapsulation efficiency and protection capability of bioactive agents. Selection of appropriated polymeric matrices is fundamental and consequently great efforts have been invested to increase the range of properties of available materials through copolymerization, blending, or combining structures constituted by different materials. Scaffolds can be obtained from different processes that differ in characteristics, such as texture or porosity. Probably, electrospinning has the greater relevance, since the obtained nanofiber membranes have a great similarity with the extracellular matrix and, in addition, they can easily incorporate functional and bioactive compounds. Coaxial and emulsion electrospinning processes appear ideal to generate complex systems able to incorporate highly different agents. The present review is mainly focused on the recent works performed with Hap-loaded scaffolds having at least one structural layer composed of core/shell nanofibers.

3D Bioprinted Hydroxyapatite or Graphene Oxide Containing Nanocellulose-Based Scaffolds for Bone Regeneration

Bone tissue is usually damaged after big traumas, tumors, and increasing aging-related diseases such as osteoporosis and osteoarthritis. Current treatments are based on implanting grafts, which are shown to have several inconveniences. In this regard, tissue engineering through the 3D bioprinting technique has arisen to manufacture structures that would be a feasible therapeutic option for bone regenerative medicine. In this study, nanocellulose-alginate (NC-Alg)-based bioink is improved by adding two different inorganic components such as hydroxyapatite (HAP) and graphene oxide (GO). First, ink rheological properties and biocompatibility are evaluated as well as the influence of the sterilization process on them. Then, scaffolds are characterized. Finally, biological studies of embedded murine D1 mesenchymal stem cells engineered to secrete erythropoietin are performed. Results show that the addition of both HAP and GO prevents NC-Alg ink from viscosity lost in the sterilization process. However, GO is reduced due to short cycle autoclave sterilization, making it incompatible with this ink. In addition, HAP and GO have different influences on scaffold architecture and surface as well as in swelling capacity. Scaffolds mechanics, as well as cell viability and functionality, are promoted by both elements addition. Additionally, GO demonstrates an enhanced bone differentiation capacity.