Comparison of in vivo dissolution processes in hydroxyapatite and silicon-substituted hydroxyapatite bioceramics

Evaluation of resorption rate-controlled calcium carbonate ceramics as a substitute bone material

Artificial bone, primarily composed of calcium carbonate, demonstrates a higher resorption rate than calcium phosphate-based counterparts, suggesting potential for early bone replacement. Animal experiments using porous calcium carbonate ceramics have demonstrated bone formation superior to commercially available artificial bone after short-term implantation. Long-term implantation has yielded suboptimal results owing to resorption of both newly formed bone and implantation material. We prepared calcium carbonate ceramics added with silica (Si-CaCO3) to regulate the resorption rate. After 12 weeks of implantation, Si-CaCO3 ceramics exhibited bone formation comparable to that of β-tricalcium phosphate (β-TCP) but less variability in the distribution of bone formation within the tissue. An in vitro dissolution test, serving as an indicator of in vivo resorption rate, revealed that Si-CaCO3 ceramics exhibited an intermediate dissolution rate between high-purity calcium carbonate and β-TCP ceramics. Silica doping in CaCO3 ceramics presents an effective approach for aligning material resorption with bone formation and growth.

Silicate-substituted bovine-derived hydroxyapatite as a bone substitute in regenerative dentistry

Hydroxyapatite, renowned for its biocompatibility and osteoconductive properties, plays a fundamental role in bone regeneration owing to its resemblance to natural bone mineral, thus offering considerable potential for advancing tissue engineering strategies. In this article, the innovative integration of silicon ions into biogenic (bovine-derived) hydroxyapatite (SiBHA) via a tailored sol-gel process is reported. The resultant SiBHA scaffolds exhibited an interconnected microporous structure with a total porosity of 70% and pore dimensions ranging from 120 to 650 µm. Fourier-transform infrared spectroscopy and X-ray diffraction studies validated the effective incorporation of silicon ions into the BHA lattice, with energy-dispersive X-ray and inductively-coupled plasma mass spectrometry further confirming a Ca/P molar ratio for SiBHA between 1.63 and 1.74. Moreover, SiBHA scaffolds demonstrated commendable chemical and thermal stability. Of note, SiBHA scaffolds were found to display significantly enhanced mechanical properties, including compressive strength and Young's modulus, compared to the control BHA scaffolds. In vitro assessments highlighted the capacity of SiBHA scaffolds to foster cell viability, proliferation, and osteogenic differentiation of Saos-2 cells. Immunohistochemical analysis revealed a significant increase in osteonectin expression, a key bone matrix protein, after 14 days of incubation under osteogenic conditions. These findings highlight the biocompatibility and therapeutic potential of SiBHA scaffolds, suggesting their suitability as biomaterials for dental bone regeneration applications.

Effect of silver ion and silicate group on the antibacterial and antifungal properties of nanosized hydroxyapatite

Hydroxyapatite is one of the most widely used materials in biomedical applications in reparative and regenerative medicine. Doping of nanosized hydroxyapatite improves its bioactive properties, and thus, the synthesis of different types of nanohydroxyapatite with antimicrobial activity is a perspective route of modern materials science. In this study, undoped hydroxyapatite (HAp), hydroxyapatite doped with silver (HAp with 0.1, 0.5 and 1 mol% Ag+ ions), and silicate-substituted hydroxyapatite doped with silver (Si-HAp with 0.1, 0.5 and 1 mol% Ag+ ions) nanoparticles (NPs) were synthesized by microwave-assisted hydrothermal technique and sintered at 450 °C. The structural properties and composition of obtained hydroxyapatite NPs were investigated using X-ray powder diffraction (XRPD), Fourier-transformed infrared spectroscopy (FT-IR), and Energy-dispersive X-ray spectroscopy (EDS). The morphology of synthesized nanosized powders was detected using the high-resolution transmission electron microscopy (HRTEM) technique. The results of XRPD for all synthesized nanosized powders confirmed the presence of hydroxyapatite crystal structure. The FT-IR spectra confirmed the presence of functional groups characteristic of the hydroxyapatite structure. The EDS analysis of obtained materials has shown the presence of Ca, P, O, Si, and Ag elements. Significant differences in size and morphology of the obtained particles were found using HRTEM. The particles have an elongated, rod-like shape with subtle differences. Moreover, HAp doped with 1 mol% Ag+ ions and Si-HAp doped with 1 mol% Ag+ ions nanosized powders showed antibacterial activity in comparison to pure hydroxyapatite both against gram-positive and gram-negative bacterial strains (Klebsiella pneumoniae, Pseudomonas aeruginosa, Staphylococcus epidermidis, Staphylococcus aureus, Enterococcus faecalis). These two types of hydroxyapatite NPs also demonstrated antifungal activity against reference strains of Candida albicans, Candida kruzei, and Candida tropicalis, with stronger activity observed for Si-HAp doped with silver.

Dental Applications of Ion-Substituted Hydroxyapatite: A Review of the Literature

Hydroxyapatite (HA) forms an essential constituent of human teeth and bone. Its distinctive characteristic features, such as bioactivity and osteoconductivity, make it an ideal candidate to be used as an implant coating in restorative dentistry and maxillofacial surgery for bone regeneration. However, low fracture toughness and brittleness are a few of the inherent features of HA, which limit its application in load-bearing areas. The potential of HA to engage its lattice structure with either partial or complete substitution with external ions has become an increasing area of research as this phenomenon has the potential to enhance the biological and functional properties of the material. Consequently, this review aimed to highlight the role of various substituted ions in dental applications. Data indicate that the newly formed HA-substituted biomaterials demonstrate enhanced remineralization and antimicrobial activity along with improved hardness. Ion-substituted HA offers a promising strategy for future clinical research as these materials may be incorporated into various dental products for therapeutic treatments.

Effect of Physicochemical Surface Properties of Silicon-Substituted Hydroxyapatite on Angiogenesis

Synthetic hydroxyapatite (HA) is a widely studied bioceramic for bone tissue engineering (BTE) due to its similarity to the mineral component of bone. As bone mineral contains various ionic substitutions that play a crucial role in bone metabolism, the bioactivity of HA can be improved by adding small amounts of physiologically relevant ions into its crystal structure, with silicate-substituted HA (Si-HA) showing particularly promising results. Nevertheless, it remains unclear how distinct material characteristics influence the bioactivity due to the intertwined nature of surface properties. A coculture methodology was optimized and applied for in vitro quantification of the biological response. Initially, HA and Si-HA samples were produced and characterized. To compare the bioactivity of the samples, a method was developed to measure interactions in an increasingly complex environment, first including fibronectin (FN) adsorption and subsequently cell adhesion in mono and coculture using primary human osteoblasts (hOBs) and human dermal microvascular endothelial cells (HDMECs), with and without FN precoating. An experimental set-up was designed to assess to what extent different surface features of the samples contribute to the induced biological response. An 8-nm gold sputter coating was applied to eradicate the electrochemical differences and polishing and abrading was used to reduce the differences in surface topographies. Overall, 1.25 wt% Si-HA exhibited most nanoscale variations in surface potential. In terms of bioactivity, 1.25 wt% Si-HA samples induced the highest osteoblast attachment and vessel formation. Additionally, in vitro vessel formation was established on Si-HA surfaces using a hOB:HDMEC cell ratio of 70:30 and a methodology was established that enabled the assessment of the relative effect of topographical and electrochemical features induced by silicon substitution in the HA lattice on their bioactivity. It was found that the difference in the amount of protein attached to HA and 1.25 wt% Si-HA after 2 h was affected by topographical differences. Conversely, electrochemical differences induced different vessel-like structure formation in coculture with a FN precoating. Without an FN precoating, both topographical and electrochemical differences dictated the differences in angiogenic response. Overall, 1.25 wt% Si-HA surface features appear to induce the most favorable protein adsorption and cell adhesion in mono and coculture with and without FN precoating.

Biological Surface Layer Formation on Bioceramic Particles for Protein Adsorption

In the biomedical fields of bone regenerative therapy, the immobilization of proteins on the bioceramic particles to maintain their highly ordered structures is significantly important. In this review, we comprehensively discussed the importance of the specific surface layer, which can be called "non-apatitic layer", affecting the immobilization of proteins on particles such as hydroxyapatite and amorphous silica. It was suggested that the water molecules and ions contained in the non-apatitic layer can determine and control the protein immobilization states. In amorphous silica particles, the direct interactions between proteins and silanol groups make it difficult to immobilize the proteins and maintain their highly ordered structures. Thus, the importance of the formation of a surface layer consisting of water molecules and ions (i.e., a non-apatitic layer) on the particle surfaces for immobilizing proteins and maintaining their highly ordered structures was suggested and described. In particular, chlorine-containing amorphous silica particles were also described, which can effectively form the surface layer of protein immobilization carriers. The design of the bio-interactive and bio-compatible surfaces for protein immobilization while maintaining the highly ordered structures will improve cell adhesion and tissue formation, thereby contributing to the construction of social infrastructures to support super-aged society.

Control of Biological Surface States on Chlorine-Doped Amorphous Silica Particles and Their Effective Absorptive Ability for Antibody Protein

Amorphous silica particles (ASPs) have low biotoxicity and are used in foodstuffs; however, the adsorption states of proteins on their surfaces have not yet been clarified. If the adsorption states can be clarified and controlled, then a wide range of biological and medical applications can be expected. The conventional amorphous silica particles have the problem of protein adsorption due to the strong interaction with their dense silanol groups and denaturation. In this study, the surfaces of amorphous silica particles with a lower silanol group density were modified with a small amount of chlorine during the synthesis process to form a specific surface layer by adsorbing water molecules and ions in the biological fluid, thereby controlling the protein adsorption state. Specifically, the hydration state on the surface of the amorphous silica particles containing trace amounts of chlorine was evaluated, and the surface layer (especially the hydration state) for the adsorption of antibody proteins while maintaining their steric structures was evaluated and discussed. The results showed that the inclusion of trace amounts of chlorine increased the silanol groups and Si-Cl bonds in the topmost surface layer of the particles, thereby inducing the adsorption of ions and water molecules in the biological fluid. Then, it was found that a novel surface layer was formed by the effective adsorption of Na and phosphate ions, which would change the proportion of the components in the hydration layer. In particular, the proportion of the free water component increased by 21% with the doping of chlorine. Antibody proteins were effectively adsorbed on the particles doped with trace amounts of chlorine, and their steric adsorption states were evaluated. It was found that the proteins were clearly adsorbed and maintained the steric state of their secondary structure. In the immunoreactivity tests using streptavidin and biotin, biotin bound to the chlorine-doped particles showed efficient reactivity. In conclusion, this study is the first to discover the surface layer of the amorphous silica particles to maintain the steric structures of adsorbed proteins, which is expected to be used as a carrier particle for antibody test kits and immunochromatography.

Enhanced Release of Calcium Ions from Hydroxyapatite Nanoparticles with an Increase in Their Specific Surface Area

Synthetic calcium phosphates, e.g., hydroxyapatite (HAP) and tricalcium phosphate (TCP), are the most commonly used bone-graft materials due to their high chemical similarity to the natural hydroxyapatite-the inorganic component of bones. Calcium in the form of a free ion or bound complexes plays a key role in many biological functions, including bone regeneration. This paper explores the possibility of increasing the Ca2+-ion release from HAP nanoparticles (NPs) by reducing their size. Hydroxyapatite nanoparticles were obtained through microwave hydrothermal synthesis. Particles with a specific surface area ranging from 51 m2/g to 240 m2/g and with sizes of 39, 29, 19, 11, 10, and 9 nm were used in the experiment. The structure of the nanomaterial was also studied by means of helium pycnometry, X-ray diffraction (XRD), and transmission-electron microscopy (TEM). The calcium-ion release into phosphate-buffered saline (PBS) was studied. The highest release of Ca2+ ions, i.e., 18 mg/L, was observed in HAP with a specific surface area 240 m2/g and an average nanoparticle size of 9 nm. A significant increase in Ca2+-ion release was also observed with specific surface areas of 183 m2/g and above, and with nanoparticle sizes of 11 nm and below. No substantial size dependence was observed for the larger particle sizes.

Investigation of Surface Layers on Biological and Synthetic Hydroxyapatites Based on Bone Mineralization Process

In this review, the current status of the influence of added ions (i.e., SiO₄^4-, CO₃^2-, etc.) and surface states (i.e., hydrated and non-apatite layers) on the biocompatibility nature of hydroxyapatite (HA, Ca₁₀(PO₄)₆(OH)₂) is discussed. It is well known that HA is a type of calcium phosphate with high biocompatibility that is present in biological hard tissues such as bones and enamel. This biomedical material has been extensively studied due to its osteogenic properties. The chemical composition and crystalline structure of HA change depending on the synthetic method and the addition of other ions, thereby affecting the surface properties related to biocompatibility. This review illustrates the structural and surface properties of HA substituted with ions such as silicate, carbonate, and other elemental ions. The importance of the surface characteristics of HA and its components, the hydration layers, and the non-apatite layers for the effective control of biomedical function, as well as their relationship at the interface to improve biocompatibility, has been highlighted. Since the interfacial properties will affect protein adsorption and cell adhesion, the analysis of their properties may provide ideas for effective bone formation and regeneration mechanisms.

Halloysite nanoclay reinforced hydroxyapatite porous scaffold for hard tissue regeneration

Hydroxyapatite (HAP), a natural constituent of bone tissue is commonly used for the clinical treatment of bone defects due to its similar structure with bone and excellent biocompatibility. However, the processing exertion, poor osteoinductive capability and poor mechanical strength of HAP needs further addressing for its immense implementation in tissue engineering. Different approaches have been reported to escalate the mechanical hardness and osteogenic potential of HAP. In the present work, halloysite nanoclay (HNC) and sericin protein were used for better mechanical and osteogenic properties, respectively. Halloysite nanoclay (HNC, 1.0-4.0%) was used to reinforce hydroxyapatite (HAP) and the mechanical strength of nanocomposite scaffolds were evaluated. After surface modification of nanocomposite scaffolds with 1.0% silk sericin protein; physical properties like microstructure, porosity, swelling ratio and degradation rate were evaluated. Cell morphology, cytocompatibility and alkaline phosphatase (ALP) activity were assessed using MG 63 osteoblast cell lines. HAP reinforced with 4% HNC (HAP@4) showed a significant increase (199 MPa) in young modulus as compared to pure HAP. HAP reinforced with 2% HNC (HAP@2) and 4% HNC (HAP@4) showed a significant decrease in porosity as well as degradation rate than pure HAP but no significant difference was observed in swelling ratio. The scanning electron microscope (SEM) images of the scaffolds showed porous architecture. Remarkably, the incorporation of HNC in HAP enhanced the cytocompatibility as well as ALP activity in comparison to pure HAP. Overall, these results suggested that halloysite nanoclay reinforced HAP scaffold could be an auspicious alternative for bone tissue regeneration.

Improving Biocompatibility for Next Generation of Metallic Implants

The increasing need for joint replacement surgeries, musculoskeletal repairs, and orthodontics worldwide prompts emerging technologies to evolve with healthcare's changing landscape. Metallic orthopaedic materials have a shared application history with the aerospace industry, making them only partly efficient in the biomedical domain. However, suitability of metallic materials in bone tissue replacements and regenerative therapies remains unchallenged due to their superior mechanical properties, eventhough they are not perfectly biocompatible. Therefore, exploring ways to improve biocompatibility is the most critical step toward designing the next generation of metallic biomaterials. This review discusses methods of improving biocompatibility of metals used in biomedical devices using surface modification, bulk modification, and incorporation of biologics. Our investigation spans multiple length scales, from bulk metals to the effect of microporosities, surface nanoarchitecture, and biomolecules such as DNA incorporation for enhanced biological response in metallic materials. We examine recent technologies such as 3D printing in alloy design and storing surface charge on nanoarchitecture surfaces, metal-on-metal, and ceramic-on-metal coatings to present a coherent and comprehensive understanding of the subject. Finally, we consider the advantages and challenges of metallic biomaterials and identify future directions.

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.

3D Printed Strontium and Zinc Doped Hydroxyapatite Loaded PEEK for Craniomaxillofacial Implants

In this study, Strontium (Sr) and Zinc (Zn) doped-HA nanoparticles were synthesized and incorporated into polyetheretherketone (PEEK) up to 30 wt.% and processed by a novel approach i.e., fused deposition modelling (FDM) 3D printing for the production of patient specific cranial implants with improved bioactivity and the required mechanical performance. Filaments were produced via extrusion and subsequently 3D-printed using FDM. To further improve the bioactivity of the 3D-printed parts, the samples were dip-coated in polyethylene glycol-DOPA (PEG-DOPA) solution. The printing quality was influenced by filler loading, but was not significantly influenced by the nature of doped-HA. Hence, the printing conditions were optimized for each sample. Micro-CT and Scanning Electron Microscopy (SEM) showed a uniform distribution of bioceramic particles in PEEK. Although agglomeration of particles increased with increase in filler loadings. Differential Scanning Calorimetry (DSC) showed that the melting point and crystallinity of PEEK increased with an increase in doped-HA loading from 343 °C to 355 °C and 27.7% to 34.6%, respectively. Apatite formation was confirmed on the 3D-printed samples after immersion in simulated body fluid (SBF) for 7, 14 and 28 days via SEM, X-ray diffraction (XRD) and Fourier Transform Infrared Spectroscopy (FTIR). The tensile strength and impact strength decreased from 75 MPa to 51 MPa and 14 kJ/m2 to 4 kJ/m2, respectively, while Young's modulus increased with increasing doped-HA content from 2.8 GPa to 4.2 GPa. However, the tensile strengths of composites remained in the range of human cortical bone i.e., ≥50 MPa. In addition, there was a slight increase in mechanical strength after 28 days immersion which was attributed to apatite formation. Water contact angle showed that the hydrophilicity of the samples improved after coating the 3D-printed samples with PEG-DOPA. Hence, based on the results, the 3D-printed PEEK nanocomposites with 20 wt.% doped-HA is selected as the best candidate for the 3D-printing of craniomaxillofacial implants.

Research progress on the biological modifications of implant materials in 3D printed intervertebral fusion cages

Anterior spine decompression and reconstruction with bone grafts and fusion is a routine spinal surgery. The intervertebral fusion cage can maintain intervertebral height and provide a bone graft window. Titanium fusion cages are the most widely used metal material in spinal clinical applications. However, there is a certain incidence of complications in clinical follow-ups, such as pseudoarticulation formation and implant displacement due to nonfusion of bone grafts in the cage. With the deepening research on metal materials, the properties of these materials have been developed from being biologically inert to having biological activity and biological functionalization, promoting adhesion, cell differentiation, and bone fusion. In addition, 3D printing, thin-film, active biological material, and 4D bioprinting technology are also being used in the biofunctionalization and intelligent advanced manufacturing processes of implant devices in the spine. This review focuses on the biofunctionalization of implant materials in 3D printed intervertebral fusion cages. The surface modifications of implant materials in metal endoscopy, material biocompatibility, and bioactive functionalizationare summarized. Furthermore, the prospects and challenges of the biofunctionalization of implant materials in spinal surgery are discussed. Fig.a.b.c.d.e.f.g As a pre-selected image for the cover, I really look forward to being selected. Special thanks to you for your comments.

Effect of silicon-doped calcium phosphate cement on angiogenesis based on controlled macrophage polarization

Vascularization is an important early indicator of osteogenesis involving biomaterials. Bone repair and new bone formation are associated with extensive neovascularization. Silicon-based biomaterials have attracted widespread attention due to their rapid vascularization. Although calcium phosphate cement (CPC) is a mature substitute for bone, the application of CPC is limited by its slow degradation and insufficient promotion of neovascularization. Calcium silicate (CS) has been shown to stimulate vascular endothelial proliferation. Thus, CS may be added to CPC (CPC-CS) to improve the biocompatibility and neovascularization of CPC. In the early phase of bone repair (the inflammatory phase), macrophages accumulate around the biomaterial and exert both anti- and pro-inflammatory effects. However, the effect of CPC-CS on macrophage polarization is not known, and it is not clear whether the effect on neovascularization is mediated through macrophage polarization. In the present study, we explored whether silicon-mediated macrophage polarization contributes to vascularization by evaluating the CPC-CS-mediated changes in the immuno-environment under different silicate ion contents both in vivo and in vitro. We found that the silicon released from CPC-CS can promote macrophage polarization into the M2 phenotype and rapid endothelial neovascularization during bone repair. Dramatic neovascularization and osteogenesis were observed in mouse calvarial bone defects implanted with CPC-CS containing 60% CS. These findings suggest that CPC-CS is a novel biomaterial that can modulate immune response, promote endothelial proliferation, and facilitate neovascularization and osteogenesis. Thus, CPC-CS shows potential as a bone substitute material.

From tissue retrieval to electron tomography: nanoscale characterization of the interface between bone and bioactive glass

The success of biomaterials for bone regeneration relies on many factors, among which osseointegration plays a key role. Biogran (BG) is a bioactive glass commonly employed as a bone graft in dental procedures. Despite its use in clinical practice, the capability of BG to promote osseointegration has never been resolved at the nanoscale. In this paper, we present the workflow for characterizing the interface between newly formed bone and BG in a preclinical rat model. Areas of bone-BG contact were first identified by backscattered electron imaging in a scanning electron microscope. A focused ion beam in situ lift-out protocol was employed to prepare ultrathin samples for transmission electron microscopy analysis. The bone-BG gradual interface, i.e. the biointerphase, was visualized at the nanoscale with unprecedented resolution thanks to scanning transmission electron microscopy. Finally, we present a method to view the bone-BG interface in three dimensions using electron tomography.

Spongostan™ Leads to Increased Regeneration of a Rat Calvarial Critical Size Defect Compared to NanoBone® and Actifuse

Bone substitute materials are becoming increasingly important in oral and maxillofacial surgery. Reconstruction of critical size bone defects is still challenging for surgeons. Here, we compared the clinically applied organic bone substitute materials NanoBone^® (nanocrystalline hydroxyapatite and nanostructured silica gel; n = 5) and Actifuse (calcium phosphate with silicate substitution; n = 5) with natural collagen-based Spongostan™ (hardened pork gelatin containing formalin and lauryl alcohol; n = 5) in bilateral rat critical-size defects (5 mm diameter). On topological level, NanoBone is known to harbour nanopores of about 20 nm diameter, while Actifuse comprises micropores of 200–500 µm. Spongostan™, which is clinically applied as a haemostatic agent, combines in its wet form both nano- and microporous topological features by comprising 60.66 ± 24.48 μm micropores accompanied by nanopores of 32.97 ± 1.41 nm diameter. Micro-computed tomography (µCT) used for evaluation 30 days after surgery revealed a significant increase in bone volume by all three bone substitute materials in comparison to the untreated controls. Clearly visual was the closure of trepanation in all treated groups, but granular appearance of NanoBone^® and Actifuse with less closure at the margins of the burr holes. In contrast, transplantion of Spongostan™ lead to complete filling of the burr hole with the highest bone volume of 7.98 ccm and the highest bone mineral density compared to all other groups. In summary, transplantation of Spongostan™ resulted in increased regeneration of a rat calvarial critical size defect compared to NanoBone and Actifuse, suggesting the distinct nano- and microtopography of wet Spongostan™ to account for this superior regenerative capacity. Since Spongostan™ is a clinically approved product used primarily for haemostasis, it may represent an interesting alternative in the reconstruction of defects in the maxillary region.

Hydroxyapatite Based Materials for Bone Tissue Engineering: A Brief and Comprehensive Introduction

Hydroxyapatite (HA) is widely used in bone tissue engineering for its bioactivity and biocompatibility, and a growing number of researchers are exploring ways to improve the physical properties and biological functions of hydroxyapatite. Up to now, HA has been used as inorganic building blocks for tissue engineering or as nanofillers to blend with polymers, furthermore, various methods such as ion doping or surface modification have been also reported to prepare functionalized HA. In this review, we try to give a brief and comprehensive introduction about HA-based materials, including ion-doped HA, HA/polymer composites and surface modified HA and their applications in bone tissue engineering. In addition, the prospective of HA is also discussed. This review may be helpful for researchers to get a general understanding about the development of hydroxyapatite based materials.

Bio-surface coated titanium scaffolds with cancellous bone-like biomimetic structure for enhanced bone tissue regeneration

In view of the fact that titanium (Ti)-based implants still face the problem of loosening and failure of the implants caused by the slow biological response, the low osseointegration rate and the implant bacterial infection in clinical application, we designed a cancellous bone-like biomimetic Ti scaffold using the template accumulated by sugar spheres as a pore-forming agent. And based on a modified surface mineralization process and mussel-like adhesion mechanism, a silicon-doped calcium phosphate composite coating (Van-pBNPs/pep@pSiCaP) with Vancomycin (Van)-loaded polydopamine (pDA)-modified albumin nanoparticles (Van-pBNPs) and cell adhesion peptides (GFOGER) was constructed on the surface of Ti scaffold for mimicking the extracellular matrix (ECM) microenvironment of natural bone matrix to induce greater tissue regeneration. The in vitro study demonstrated that this porous Ti scaffold with functional bio-surface could distinctly facilitate cell early adhesion and spreading, and activate the expression of α2β1 integrin receptor on the cell membrane through promoting the formation of focal adhesions (FAs) in bone marrow stromal cells (BMSCs), thus mediating greater osteogenic cell differentiation. And it could also effectively inhibit the adhesion and growth of Staphylococcus epidermidis, exhibiting good antibacterial properties. Moreover, the Van-pBNPs/pep@pSiCaP-Ti scaffolds showed enhanced in vivo bone-forming ability due to the contributions of bioactive chemical components and the natural cancellous bone-like macrostructure. This work offers a promising structural and functional bio-inspired strategy for designing metal implants with desirable ability of osteoinduction synergistically with antibacterial efficacy for promoting bone regeneration and infection prevention simultaneously. STATEMENT OF SIGNIFICANCE: This manuscript describes a new method for making porous Ti scaffolds with a natural cancellous bone-like structure. Besides, a functional bio-surface was constructed on the bionic structure, mimicking some of the functions of the collagen-rich organic matrix and inorganic CaP nanocrystallites of native ECM of bone in chemical components and biological activities. This interconnected inter-pore opening structure encouraged the migration of cells among open macro-pores within the scaffold. In addition, the functionalized surface not only improved early cell adhesion, spreading, stimulated greater osteogenic differentiation of bone-forming cells, but also endowed the scaffold with excellent antibacterial effect. The biomimetic metal implant with multiple biomedical functions designed in this study has a great clinical application potential. This study represents a feasible method for the preparation of biomimetic structure of metal implants and the improvement of their surface biological activity.

Bioinorganic supplementation of calcium phosphate-based bone substitutes to improve in vivo performance: a systematic review and meta-analysis of animal studies

Supplementation of CaP-based bone graft substitutes with bioinorganics such as strontium, zinc or silicon is an interesting approach to increase the biological performance in terms of bone regenerative potential of calcium phosphate (CaP)-based bone substitutes. However, the in vivo efficacy of this approach has not been systematically analyzed, yet. Consequently, we performed a systematic review using the available literature regarding the effect of bioinorganic supplementation in CaP-based biomaterials on new bone formation and material degradation in preclinical animal bone defect models and studied this effect quantitatively by performing a meta-analysis. Additional subgroup analyses were used to study the effect of different bioinorganics, animal model, or phase category of CaP-based biomaterial on bone formation or material degradation. Results show that bioinorganic supplementation increases new bone formation (standardized mean difference [SMD]: 1.43 SD, confidence interval [CI]: 1.13-1.73). Additional subgroup analysis showed that strontium, magnesium and silica significantly enhanced bone formation, while zinc did not have any effect. This effect of bioinorganic supplementation on new bone formation was stronger for DCPD or β-TCP and biphasic CaPs than for HA or α-TCP (p < 0.001). In general, material degradation was slightly hindered by bioinorganic supplementation (mean difference [MD]: 0.84%, CI: 0.01-1.66), with the exception of strontium that significantly enhanced degradation. Overall, bioinorganic supplementation represents an effective approach to enhance the biological performance of CaP-based bone substitutes.

Preparation and characterization of diatomite and hydroxyapatite reinforced porous polyurethane foam biocomposites

Porous three-dimensional (3D) polyurethane-based biocomposites were produced utilizing diatomite and hydroxyapatite as fillers. Diatomite and Hydroxyapatite (HA) were utilized to reinforce the morphological, chemical, mechanical, and thermal properties of polyurethane foam (PUF). Diatomite and Hydroxyapatite were added into polyurethane at variable percentages 0, 1, 2, and 5. The mechanical properties of PUF were analyzed by the compression test. According to the compression test results, the compressive strength of the polyurethane foam is highest in the reinforced foam at 1% by weight hydroxyapatite compared to other reinforced PUFs. Scanning electron microscopy (SEM) images presented structural differences on foam by adding fillers. Functional groups of PUF were defined by Fourier Transform Infrared Spectroscopy (FTIR) and the thermal behavior of PUF was studied with Thermogravimetric Analysis (TGA). The obtained results revealed that PUF/HA biocomposites indicated higher thermal degradation than PUF/Diatomite biocomposites.

A review of the latest insights into the mechanism of action of strontium in bone

Interest in strontium (Sr) has persisted over the last three decades due to its unique mechanism of action: it simultaneously promotes osteoblast function and inhibits osteoclast function. While this mechanism of action is strongly supported by in vitro studies and small animal trials, recent large-scale clinical trials have demonstrated that orally administered strontium ranelate (SrRan) may have no anabolic effect on bone formation in humans. Yet, there is a strong correlation between Sr accumulation in bone and reduced fracture risk in post-menopausal women, suggesting Sr acts via a purely physiochemical mechanism to enhance bone strength. Conversely, the local administration of Sr with the use of modified biomaterials has been shown to enhance bone growth, osseointegration and bone healing at the bone-implant interface, to a greater degree than Sr-free materials. This review summarizes current knowledge of the main cellular and physiochemical mechanisms that underly Sr's effect in bone, which center around Sr's similarity to calcium (Ca). We will also summarize the main controversies in Sr research which cast doubt on the 'dual-acting mechanism'. Lastly, we will explore the effects of Sr-modified bone-implant materials both in vitro and in vivo, examining whether Sr may act via an alternate mechanism when administered locally.

Production of High Silicon-Doped Hydroxyapatite Thin Film Coatings via Magnetron Sputtering: Deposition, Characterisation, and In Vitro Biocompatibility

In recent years, it has been found that small weight percent additions of silicon to HA can be used to enhance the initial response between bone tissue and HA. A large amount of research has been concerned with bulk materials, however, only recently has the attention moved to the use of these doped materials as coatings. This paper focusses on the development of a co-RF and pulsed DC magnetron sputtering methodology to produce a high percentage Si containing HA (SiHA) thin films (from 1.8 to 13.4 wt.%; one of the highest recorded in the literature to date). As deposited thin films were found to be amorphous, but crystallised at different annealing temperatures employed, dependent on silicon content, which also lowered surface energy profiles destabilising the films. X-ray photoelectron spectroscopy (XPS) was used to explore the structure of silicon within the films which were found to be in a polymeric (SiO2; Q4) state. However, after annealing, the films transformed to a SiO44−, Q0, state, indicating that silicon had substituted into the HA lattice at higher concentrations than previously reported. A loss of hydroxyl groups and the maintenance of a single-phase HA crystal structure further provided evidence for silicon substitution. Furthermore, a human osteoblast cell (HOB) model was used to explore the in vitro cellular response. The cells appeared to prefer the HA surfaces compared to SiHA surfaces, which was thought to be due to the higher solubility of SiHA surfaces inhibiting protein mediated cell attachment. The extent of this effect was found to be dependent on film crystallinity and silicon content.

Incorporating silica-coated graphene in bioceramic nanocomposites to simultaneously enhance mechanical and biological performance

The applications of a variety of bioactive ceramics such as hydroxyapatite (HA) in orthopedics are limited by their insufficient mechanical properties, especially poor fracture toughness. Thus, further extending the clinical applications of these materials warrants the enhancement of their mechanical properties. Although the reinforcement of ceramics by 2D nanomaterials has been well recognized, integrated structural, mechanical, and functional considerations have been neglected in the design and synthesis of such composite materials. Herein, we report the first use of silica-coated reduced graphene oxide (S-rGO) hybrid nanosheets to create bioceramic-based composites with simultaneously enhanced mechanical and biological properties. In the representative HA-based bioceramic systems prepared by spark plasma sintering, S-rGO incorporation was found to be more effective for increasing the Young's modulus, hardness, and fracture toughness than the incorporation of uncoated reduced GO (rGO). Furthermore, when assessed with osteoblast-like MG-63 cells, such novel materials led to faster cell proliferation and higher cell viability and alkaline phosphatase activity than are generally observed with pure HA; additionally, cells demonstrate stronger affinity to S-rGO/HA than to rGO/HA composites. The S-rGO/bioceramic composites are therefore promising for applications in orthopedic tissue engineering, and this research provides valuable insights into the fabrication of silica-coated hybrid nanosheet-reinforced ceramics.

Silicon substituted hydroxyapatite/VEGF scaffolds stimulate bone regeneration in osteoporotic sheep

Silicon-substituted hydroxyapatite (SiHA) macroporous scaffolds have been prepared by robocasting. In order to optimize their bone regeneration properties, we have manufactured these scaffolds presenting different microstructures: nanocrystalline and crystalline. Moreover, their surfaces have been decorated with vascular endothelial growth factor (VEGF) to evaluate the potential coupling between vascularization and bone regeneration. In vitro cell culture tests evidence that nanocrystalline SiHA hinders pre-osteblast proliferation, whereas the presence of VEGF enhances the biological functions of both endothelial cells and pre-osteoblasts. The bone regeneration capability has been evaluated using an osteoporotic sheep model. In vivo observations strongly correlate with in vitro cell culture tests. Those scaffolds made of nanocrystalline SiHA were colonized by fibrous tissue, promoted inflammatory response and fostered osteoclast recruitment. These observations discard nanocystalline SiHA as a suitable material for bone regeneration purposes. On the contrary, those scaffolds made of crystalline SiHA and decorated with VEGF exhibited bone regeneration properties, with high ossification degree, thicker trabeculae and higher presence of osteoblasts and blood vessels. Considering these results, macroporous scaffolds made of SiHA and decorated with VEGF are suitable bone grafts for regeneration purposes, even in adverse pathological scenarios such as osteoporosis. STATEMENT OF SIGNIFICANCE: For the first time, the in vivo behavior of scaffolds made of silicon substituted hydroxyapatites (SiHA) has been evaluated under osteoporosis conditions. In order to optimize the bone regeneration properties of these bioceramics, 3D macroporous scaffolds have been manufactured by robocasting and implanted in osteoporotic sheep. Our experimental design shed light on the important issue of the biological response of nano-sized bioceramics vs highly crystalline bioceramics, as well as on the importance of coupling vascularization and bone growth processes by decorating SiHA scaffolds with vascular endothelial growth factor.

Animal Origin Bioactive Hydroxyapatite Thin Films Synthesized by RF-Magnetron Sputtering on 3D Printed Cranial Implants

Ti6Al4V cranial prostheses in the form of patterned meshes were 3D printed by selective laser melting in an argon environment; using a CO2 laser source and micron-sized Ti6Al4V powder as the starting material. The size and shape of prostheses were chosen based on actual computer tomography images of patient skull fractures supplied in the framework of a collaboration with a neurosurgery clinic. After optimizations of scanning speed and laser parameters, the printed material was defect-free (as shown by metallographic analyses) and chemically homogeneous, without elemental segregation or depletion. The prostheses were coated by radio-frequency magnetron sputtering (RF-MS) with a bioactive thin layer of hydroxyapatite using a bioceramic powder derived from biogenic resources (Bio-HA). Initially amorphous, the films were converted to fully-crystalline form by applying a post-deposition thermal-treatment at 500 °C/1 h in air. The X-ray diffraction structural investigations indicated the phase purity of the deposited films composed solely of a hexagonal hydroxyapatite-like compound. On the other hand, the Fourier transform infrared spectroscopic investigations revealed that the biological carbonatation of the bone mineral phase was well-replicated in the case of crystallized Bio-HA RF-MS implant coatings. The in vitro acellular assays, performed in both the fully inorganic Kokubo’s simulated body fluid and the biomimetic organic–inorganic McCoy’s 5A cell culture medium up to 21 days, emphasized both the good resistance to degradation and the biomineralization capacity of the films. Further in vitro tests conducted in SaOs-2 osteoblast-like cells showed a positive proliferation rate on the Bio-HA RF-MS coating along with a good adhesion developed on the biomaterial surface by elongated membrane protrusions.

TiO2 doped chitosan/hydroxyapatite/halloysite nanotube membranes with enhanced mechanical properties and osteoblast-like cell response for application in bone tissue engineering

The current therapeutic strategies for healing bone defects commonly suffer from the occurrence of bacterial contamination on the graft, resulting in nonunion in the segmental bone defects and the requirement for secondary surgery to remove or sterilize the primary graft. A membrane with enhanced anti-bacterial efficacy, mechanical strength and osteoconductivity would represent an improvement in the therapeutic strategy for guided bone regeneration. The present study aims to optimize the content of halloysite nanotubes (HNTs) and TiO₂ in the polymer matrix of chitosan (CTS) with a constant amount of nano-hydroxyapatite (5%) with the objective of mimicking the mechanical and biological microenvironment of the natural bone extracellular matrix with enhanced anti-bacterial efficacy. HNTs are a low-cost alternative to MWNCTs for enhancing the mechanical properties and anti-bacterial efficacy of the composite. From the first stage of the study, it was concluded that the membranes possessed enhanced mechanical properties and optimum biological properties at 7.5% (w/w) loading of HNTs in the composite. In the second stage of this investigation, we studied the effect of the addition of TiO₂ nanoparticles (NPs) and TiO₂ nanotubes (NTs) in small amounts to the CTS/n-HAP/HNT nanocomposite at 7.5% HNT loading, with an aim to augment the anti-bacterial efficacy and osteoconductivity of this mechanically strong membrane. The study revealed a significant enhancement in the anti-bacterial efficacy, osteoblast-like MG-63 cell proliferation and ALP expression with the addition of TiO₂ NTs. The CHH-TiT membrane successfully inhibited the S. aureus and E. coli growth within 16 hours and simultaneously assisted the enhanced proliferation of osteoblast-like cells on its surface. The study supports the potential exploitation of CHH-TiT (7.5% HNT & 0.2% TiO₂ NT) membranes as a template for guided bone tissue regeneration.

This two-stage study aims to optimize the amount of halloysite nanotubes and TiO₂ in a chitosan/nano-hydroxyapatite composite to tailor the mechanical and biological properties for application in bone tissue engineering.

Biofunctionalization of metallic implants by calcium phosphate coatings

Metallic materials have been extensively applied in clinical practice due to their unique mechanical properties and durability. Recent years have witnessed broad interests and advances on surface functionalization of metallic implants for high-performance biofunctions. Calcium phosphates (CaPs) are the major inorganic component of bone tissues, and thus owning inherent biocompatibility and osseointegration properties. As such, they have been widely used in clinical orthopedics and dentistry. The new emergence of surface functionalization on metallic implants with CaP coatings shows promise for a combination of mechanical properties from metals and various biofunctions from CaPs. This review provides a brief summary of state-of-art of surface biofunctionalization on implantable metals by CaP coatings. We first glance over different types of CaPs with their coating methods and in vitro and in vivo performances, and then give insight into the representative biofunctions, i.e. osteointegration, corrosion resistance and biodegradation control, and antibacterial property, provided by CaP coatings for metallic implant materials.

Hierarchically designed bone scaffolds: From internal cues to external stimuli

Bone tissue engineering utilizes three critical elements - cells, scaffolds, and bioactive factors - to recapitulate the bone tissue microenvironment, inducing the formation of new bone. Recent advances in materials development have enabled the production of scaffolds that more effectively mimic the hierarchical features of bone matrix, ranging from molecular composition to nano/micro-scale biochemical and physical features. This review summarizes recent advances within the field in utilizing these features of native bone to guide the hierarchical design of materials and scaffolds. Biomimetic strategies discussed in this review cover several levels of hierarchical design, including the development of element-doped compositions of bioceramics, the usage of molecular templates for in vitro biomineralization at the nanoscale, the fabrication of biomimetic scaffold architecture at the micro- and nanoscale, and the application of external physical stimuli at the macroscale to regulate bone growth. Developments at each level are discussed with an emphasis on their in vitro and in vivo outcomes in promoting osteogenic tissue development. Ultimately, these hierarchically designed scaffolds can complement or even replace the usage of cells and biological elements, which present clinical and regulatory barriers to translation. As the field progresses ever closer to clinical translation, the creation of viable therapies will thus benefit from further development of hierarchically designed materials and scaffolds.

Rapid Fabrication, Microstructure, and in Vitro and in Vivo Investigations of a High-Performance Multilayer Coating with External, Flexible, and Silicon-Doped Hydroxyapatite Nanorods on Titanium

A high-performance multilayer coating with external, flexible, and silicon-doped hydroxyapatite (Si-HA) nanorods was designed using bionics. Plasma electrolytic oxidation (PEO) and the microwave hydrothermal (MH) method were used to rapidly deposit this multilayer coating on a titanium (Ti) substrate, applied for 5 and 10 min, respectively. The bioactive multilayer coating was composed of four layers, and the outermost layer was an external growth layer that consisted of many Si-HA nanorods with a single-crystal structure. The Si-HA nanorods exhibited good flexibility, likely because of their complete single-crystal structures, smooth surfaces, and suitable diameters and lengths. This multilayer coating with a high surface energy was superhydrophilic and exhibited good in vitro bioactivities, such as good apatite formation ability, good cell spreading, and high osteogenic gene expression levels. After implantation in the tibia of rabbits for 16 weeks, almost no soft tissues were formed at the MH treated PEO implant-bone interface. A direct bone contact interface was formed by a bridging effect of the flexible Si-HA nanorods, which further produced a high implant-bone interface bonding strength. The current results demonstrated that the bioactive multilayer layers with the flexible Si-HA nanorods displayed a very good osseointegration ability, showing promising applications in the biomedical field.

Dual Doping of Silicon and Manganese in Hydroxyapatites: Physicochemical Properties and Preliminary Biological Studies

Silicated hydroxyapatite powders enriched with small amounts of manganese (Mn²⁺) cations were synthesized via two different methods: precipitation in aqueous solution and the solid-state method. The source of Mn²⁺ ions was manganese acetate, while silicon was incorporated using two different reagents: silicon acetate and sodium metasilicate. Powder X-ray diffraction (PXRD) analysis showed that the powders obtained via the precipitation method consisted of single-phase nanocrystalline hydroxyapatite. In contrast, samples obtained via the solid-state method were heterogenous and contaminated with other phases, (i.e., calcium oxide, calcium hydroxide, and silicocarnotite) arising during thermal treatment. The transmission electron microscope (TEM) images showed powders obtained via the precipitation method were nanosized and elongated, while solid-state synthesis produced spherical microcrystals. The phase identification was complemented by Fourier transform infrared spectroscopy (FTIR). An in-depth analysis via solid-state nuclear magnetic resonance (ssNMR) was carried out, using phosphorus ³¹P single-pulse Bloch decay (BD) (³¹P BD) and cross-polarization (CP) experiments from protons to silicon-29 nuclei (¹H → ²⁹Si CP). The elemental measurements carried out using wavelength-dispersive X-ray fluorescence (WD-XRF) showed that the efficiency of introducing manganese and silicon ions was between 45% and 95%, depending on the synthesis method and the reagents. Preliminary biological tests on the bacteria Allivibrio fisheri (Microtox®) and the protozoan Spirostomum ambiguum (Spirotox) showed no toxic effect in any of the samples. The obtained materials may find potential application in regenerative medicine, bone implantology, and orthopedics as bone substitutes or implant coatings.

Osseointegration and current interpretations of the bone-implant interface

Complex physical and chemical interactions take place in the interface between the implant surface and bone. Various descriptions of the ultrastructural arrangement to various implant design features, ranging from solid and macroporous geometries to surface modifications on the micron-, submicron-, and nano- levels, have been put forward. Here, the current knowledge regarding structural organisation of the bone-implant interface is reviewed with a focus on solid devices, mainly metal (or alloy) intended for permanent anchorage in bone. Certain biomaterials that undergo surface and bulk degradation are also considered. The bone-implant interface is a heterogeneous zone consisting of mineralised, partially mineralised, and unmineralised areas. Within the meso-micro-nano-continuum, mineralised collagen fibrils form the structural basis of the bone-implant interface, in addition to accumulation of non-collagenous macromolecules such as osteopontin, bone sialoprotein, and osteocalcin. In the published literature, as many as eight distinct arrangements of the bone-implant interface ultrastructure have been described. The interpretation is influenced by the in vivo model and species-specific characteristics, healing time point(s), physico-chemical properties of the implant surface, implant geometry, sample preparation route(s) and associated artefacts, analytical technique(s) and their limitations, and non-compromised vs compromised local tissue conditions. The understanding of the ultrastructure of the interface under experimental conditions is rapidly evolving due to the introduction of novel techniques for sample preparation and analysis. Nevertheless, the current understanding of the interface zone in humans in relation to clinical implant performance is still hampered by the shortcomings of clinical methods for resolving the finer details of the bone-implant interface. STATEMENT OF SIGNIFICANCE: Being a hierarchical material by design, the overall strength of bone is governed by composition and structure. Understanding the structure of the bone-implant interface is essential in the development of novel bone repair materials and strategies, and their long-term success. Here, the current knowledge regarding the eventual structural organisation of the bone-implant interface is reviewed, with a focus on solid devices intended for permanent anchorage in bone, and certain biomaterials that undergo surface and bulk degradation. The bone-implant interface is a heterogeneous zone consisting of mineralised, partially mineralised, and unmineralised areas. Within the meso-micro-nano-continuum, mineralised collagen fibrils form the structural basis of the bone-implant interface, in addition to accumulation of non-collagenous macromolecules such as osteopontin, bone sialoprotein, and osteocalcin.

Synergistic effect of Si-hydroxyapatite coating and VEGF adsorption on Ti6Al4V-ELI scaffolds for bone regeneration in an osteoporotic bone environment

The osteogenic and angiogenic responses to metal macroporous scaffolds coated with silicon substituted hydroxyapatite (SiHA) and decorated with vascular endothelial growth factor (VEGF) have been evaluated in vitro and in vivo. Ti6Al4V-ELI scaffolds were prepared by electron beam melting and subsequently coated with Ca₁₀(PO₄)_5.6(SiO₄)_0.4(OH)_1.6 following a dip coating method. In vitro studies demonstrated that SiHA stimulates the proliferation of MC3T3-E1 pre-osteoblastic cells, whereas the adsorption of VEGF stimulates the proliferation of EC₂ mature endothelial cells. In vivo studies were carried out in an osteoporotic sheep model, evidencing that only the simultaneous presence of both components led to a significant increase of new tissue formation in osteoporotic bone. STATEMENT OF SIGNIFICANCE: Reconstruction of bones after severe trauma or tumors extirpation is one of the most challenging tasks in the field of orthopedic surgery. This scenario is even more complicated in the case of osteoporotic patients, since their bone regeneration capability is decreased. In this work we present a porous implant that promotes bone regeneration even in osteoporotic bone. By coating the implant with osteogenic bioceramics such as silicon substituted hydroxyapatite and subsequent adsorption of vascular endothelial growth factor, these implants stimulate the bone ingrowth when they are implanted in osteoporotic sheep.

Characterization and biological properties of a novel synthesized silicon-substituted hydroxyapatite derived from eggshell

In the present study, the effect of adding different concentrations of silicon on physical, mechanical and biological properties of a synthesized aqueous precipitated eggshell-derived hydroxyapatite (e-HA) was evaluated. No secondary phases were detected by X-ray diffraction for the specimens e-HA and e-HA containing silicon (Si-e-HAs) before and after heating at 1200°C. A reduction in the crystallite size and a-axis as well as an increase in c-axis was occurred when silicon replacement was happened in the structure of e-HA. The presence of Si-O vibrations and carbonate modes for Si-e-HAs was confirmed by Fourier transform infrared spectroscopy analysis. The range of porosity and density was varied from 25% and 2.4 g cm^-3 to 7% and 2.8 g cm^-3 for e-HA and Si-e-HAs. The values of Young's modulus ( E) and compressive strength were varied for e-HA and Si-e-HAs. The porous structure of the samples was reduced when they were heated as e-HA kept the porous microstructure containing some dense areas and Si-e-HAs possessed a rough surface including slight levels of microporosity. The acellular in vitro bioactivity represented different apatite morphologies for e-HA and Si-e-HAs. The G-292 osteoblastic cells were stretched well on the surface with polygon-shaped morphology for 0.8Si-e-HA after 7 days of culture. According to MTT assay and alkaline phosphatase test, the maximum cell activity was related to 0.8Si-e-HA. The minimum inhibitory concentration for 0.8Si-e-HA and e-HA was estimated to be about 3.2 and 4.4 mg/mL, respectively. In overall, the sample 0.8Si-e-HA exhibited a higher bacteriostatic effect than e-HA against gram-negative bacterial strain Escherichia coli.

Water Adsorption on the β-Dicalcium Silicate Surface from DFT Simulations

β-dicalcium silicate (β-Ca2SiO4 or β-C2S in cement chemistry notation) is one of the most important minerals in cement. An improvement of its hydration rate would be the key point for developing environmentally-friendly cements with lower energy consumption and CO2 emissions. However, there is a lack of fundamental understanding on the water/β-C2S surface interactions. In this work, we aim to evaluate the water adsorption on three β-C2S surfaces at the atomic scale using density functional theory (DFT) calculations. Our results indicate that thermodynamically favorable water adsorption takes place in several surface sites with a broad range of adsorption energies (−0.78 to −1.48 eV) depending on the particular mineral surface and adsorption site. To clarify the key factor governing the adsorption of the electronic properties of water at the surface were analyzed. The partial density of states (DOS), charge analysis, and electron density difference analyses suggest a dual interaction of water with a β-C2S (100) surface including a nucleophilic interaction of the water oxygen lone pair with surface calcium atoms and an electrophilic interaction (hydrogen bond) of one water hydrogen with surface oxygen atoms. Despite the elucidation of the adsorption mechanism, no correlation was found between the electronic structure and the adsorption energies.

Preparation and properties of biodegradable polymer/nano-hydroxyapatite bioceramic scaffold for spongy bone regeneration

Biodegradable polymer/bioceramic composite scaffolds can overcome the limitations of conventional ceramic bone substitutes, such as brittleness and difficulty in shaping. To better mimic the mineral components and microstructure of natural bone, a novel nano-hydroxyapatite (nHAp)–chitosan composite scaffold including gelatin and polymer (poly(lactic acid)) with high porosity was developed using a sol-gel method and subsequently lyophilized for efficient bone tissue engineering. The nanocrystalline structure of hydroxyapatite was observed using X-ray diffraction analysis and the composite showed crystallinity due to the presence of nHAp. The pore diameter of the composite containing 5% nHAp was found to be 125 μm, while the composites with 10%, 15%, and 20% nHAp revealed a smaller pore size in the range of 15–28 μm. The highest compressive strength of 5.5 MPa was observed for the 10% nHAp-containing scaffold, whereas thermogravimetric analysis showed 90%–94% degradation at a temperature of 600°C, which demonstrated its excellent thermal stability. Antibacterial and cytotoxicity test results revealed that the composite is resistant toward microbial attack and has low sensitivity in cytotoxicity. The compressive strength data suggests that the composite does not have enough strength as that of human compact bone; however, the highly porous structure as observed in scanning electron microscopy makes it possible for use as an excellent substrate in the spongy bone of humans.

Silicocarnotite Synthesis and Bioactivity in Artificial Saliva Medium

The aim of this study is the synthesis and investigation of bioactive response of acrystalline silicophosphate.A monophasic silicocarnotite was elaborated by solid state reaction from a mixture of beta-tricaliciumphosphate and dicalcium silicate based on mussel shells according to the diagram of system Ca3(PO4)2–Ca2SiO4, at 65 % and 35% respectively , these starting materials are heated up to 1450 °C to obtain a monophasic silicocaronitite. The obtained result probed that the main crystalline phase which was detected and recognized in the heated sample at 1400 and 1450 °C was a well-crystallized silicocarnotite. The test of bioactivity of silicocarnotite in artificial saliva causes the appearance of a reaction layer on the materials surface after 4 hours soaking and growth up during 30 days.This layer is constituted of a biphasic mixture of Si–Ca–P–H material, silicated hydroxyapatite and hydroxyapatite phase are the mainly developing ones with increasing soaking time.The analysis and characterization of the precipitated appearing on the material surface has confirmed experimentally the in vitro bioactivity of silicocarnotite monophasic material.