Ceramic bioactivity: progresses, challenges and perspectives

Potential role of calcium sulfate/β-tricalcium phosphate/graphene oxide nanocomposite for bone graft application_mechanical and biological analyses

BACKGROUND

Bone grafts are extensively used for repairing bone defects and voids in orthopedics and dentistry. Moldable bone grafts offer a promising solution for treating irregular bone defects, which are often difficult to fill with traditional rigid grafts. However, practical applications have been limited by insufficient mechanical strength and rapid degradation.

METHODS

This study developed a ceramic composite bone graft composed of calcium sulfate (CS), β-tricalcium phosphate (β-TCP) with/without graphene oxide (GO) nano-particles. The biomechanical properties, degradation rate, and in-vitro cellular responses were investigated. In addition, the graft was implanted in-vivo in a critical-sized calvarial defect model.

RESULTS

The results showed that the compressive strength significantly improved by 135% and the degradation rate slowed by 25.5% in comparison to the control model. The addition of GO nanoparticles also improved cell compatibility and promoted osteogenic differentiation in the in-vitro cell culture study and was found to be effective at promoting bone repair in the in-vivo animal model.

CONCLUSIONS

The mixed ceramic composites presented in this study can be considered as a promising alternative for bone graft applications.

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.

Influence of Strontium on the Biological Behavior of Bioactive Glasses for Bone Regeneration

Bioactive glasses (BGs) can potentially be applied in biomedicine, mainly for bone repair and replacement, given their unique ability to connect to natural bone tissue and stimulate bone regeneration. Since their discovery, several glass compositions have been developed to improve the properties and clinical abilities of traditional bioactive glass. Different inorganic ions, such as strontium (Sr2+), have been incorporated in BG due to their ability to perform therapeutic functions. Sr2+ has been gaining prominence due to its ability to stimulate osteogenesis, providing an appropriate environment to improve bone regeneration, in addition to its antibacterial potential. However, as there are still points in the literature that are not well consolidated, such as the influence of ionic concentrations and the BG production technique, this review aims to collect information on the state of the art of the biological behavior of BGs containing Sr2+. It also aims to gather data on different types of BGs doped with different concentrations of Sr2+, and to highlight the manufacturing techniques used in order to analyze the influence of the incorporation of this ion for bone regeneration purposes.

Bone screws of porous silicon carbide coated with tantalum improve osseointegration and osteogenesis in goat femoral neck fractures

Traditional metal materials, such as stainless steel and titanium (Ti) alloys, are still the gold standards for fracture fixation. However, the elastic moduli of these materials differ from that of human cortical bone, and the stress shielding effect affects fracture healing, leading to secondary fractures. Herein, a new porous Ta coated SiC (pTa-SiC) scaffold using in internal fixation devices with good mechanical and biological properties was prepared based on porous silicon carbide (SiC) scaffold and tantalum (Ta) metal. The osteogenic and osseointegration properties of the pTa-SiC scaffold were investigated by bothin vitroandin vivotests. The results showed that compared with porous titanium (pTi), the pTa-SiC promoted the proliferation, migration, and osteogenic differentiation of human bone marrow-derived mesenchymal stem cells. Moreover, the internal fixation tests were carried out in a goat load-bearing femoral neck fracture model. Histological results showed good osseointegration around the pTa-SiC screws. And the acid etching results showed that bone cells grew tightly on the pTa-SiC throughout bone canaliculi, and the growth mode was contact osteogenesis, which indicated good biological fixation effects. Therefore, it is reasonable to be expected that the new pTa-SiC scaffold with excellent mechanical and biological properties could be a promising candidate for bone implant field.

Pharmaceutical electrospinning and 3D printing scaffold design for bone regeneration

Bone regenerative engineering provides a great platform for bone tissue regeneration covering cells, growth factors and other dynamic forces for fabricating scaffolds. Diversified biomaterials and their fabrication methods have emerged for fabricating patient specific bioactive scaffolds with controlled microstructures for bridging complex bone defects. The goal of this review is to summarize the points of scaffold design as well as applications for bone regeneration based on both electrospinning and 3D bioprinting. It first briefly introduces biological characteristics of bone regeneration and summarizes the applications of different types of material and the considerations for bone regeneration including polymers, ceramics, metals and composites. We then discuss electrospinning nanofibrous scaffold applied for the bone regenerative engineering with various properties, components and structures. Meanwhile, diverse design in the 3D bioprinting scaffolds for osteogenesis especially in the role of drug and bioactive factors delivery are assembled. Finally, we discuss challenges and future prospects in the development of electrospinning and 3D bioprinting for osteogenesis and prominent strategies and directions in future.

Reconstruction of Large Skeletal Defects: Current Clinical Therapeutic Strategies and Future Directions Using 3D Printing

The healing of bone fractures is a well-orchestrated physiological process involving multiple cell types and signaling molecules interacting at the fracture site to replace and repair bone tissue without scar formation. However, when the lesion is too large, normal healing is compromised. These so-called non-union bone fractures, mostly arising due to trauma, tumor resection or disease, represent a major therapeutic challenge for orthopedic and reconstructive surgeons. In this review, we firstly present the current commonly employed surgical strategies comprising auto-, allo-, and xenograft transplantations, as well as synthetic biomaterials. Further to this, we discuss the multiple factors influencing the effectiveness of the reconstructive therapy. One essential parameter is adequate vascularization that ensures the vitality of the bone grafts thereby supporting the regeneration process, however deficient vascularization presents a frequently encountered problem in current management strategies. To address this challenge, vascularized bone grafts, including free or pedicled fibula flaps, or in situ approaches using the Masquelet induced membrane, or the patient’s body as a bioreactor, comprise feasible alternatives. Finally, we highlight future directions and novel strategies such as 3D printing and bioprinting which could overcome some of the current challenges in the field of bone defect reconstruction, with the benefit of fabricating personalized and vascularized scaffolds.

Osteoblast Cell Response to Naturally Derived Calcium Phosphate-Based Materials

The demand of calcium phosphate bioceramics for biomedical applications is constantly increasing. Efficient and cost-effective production can be achieved using naturally derived materials. In this work, calcium phosphate powders, obtained from dolomitic marble and Mytilus galloprovincialis seashells by a previously reported and improved Rathje method were used to fabricate microporous pellets through cold isostatic pressing followed by sintering at 1200 °C. The interaction of the developed materials with MC3T3-E1 pre-osteoblasts was explored in terms of cell adhesion, morphology, viability, proliferation, and differentiation to evaluate their potential for bone regeneration. Results showed appropriate cell adhesion and high viability without distinguishable differences in the morphological features. Likewise, the pre-osteoblast proliferation overtime on both naturally derived calcium phosphate materials showed a statistically significant increase comparable to that of commercial hydroxyapatite, used as reference material. Furthermore, evaluation of the intracellular alkaline phosphatase activity and collagen synthesis and deposition, used as markers of the osteogenic ability of these bioceramics, revealed that all samples promoted pre-osteoblast differentiation. However, a seashell-derived ceramic demonstrated a higher efficacy in inducing cell differentiation, almost equivalent to that of the commercial hydroxyapatite. Therefore, data obtained demonstrate that this naturally sourced calcium-phosphate material holds promise for applications in bone tissue regeneration.

Calcium phosphate fibers coated with collagen: In vivo evaluation of the effects on bone repair

The aim of this study was to assess the characteristics of the CaP/Col composites, in powder and fiber form, via scanning electron microscopy (SEM), pH and calcium release evaluation after immersion in SBF and to evaluate the performance of these materials on the bone repair process in a tibial bone defect model. For this, four different formulations (CaP powder - CaPp, CaP powder with collagen - CaPp/Col, CaP fibers - CaPf and CaP fibers with collagen - CaPf/Col) were developed. SEM images indicated that both material forms were successfully coated with collagen and that CaPp and CaPf presented HCA precursor crystals on their surface. Although presenting different forms, FTIR analysis indicated that CaPp and CaPf maintained the characteristic peaks for this class of material. Additionally, the calcium assay study demonstrated a higher Ca uptake for CaPp compared to CaPf for up to 5 days. Furthermore, pH measurements revealed that the collagen coating prevented the acidification of the medium, leading to higher pH values for CaPp/Col and CaPf/Col. The histological analysis showed that CaPf/Col demonstrated a higher amount of newly formed bone in the region of the defect and a reduced presence of material. In summary, the results indicated that the fibrous CaP enriched with the organic part (collagen) glassy scaffold presented good degradability and bone-forming properties and also supported Runx2 and RANKL expression. These results show that the present CaP/Col fibrous composite may be used as a bone graft for inducing bone repair.

Biomineralization and biocompatibility studies of bone conductive scaffolds containing poly(3,4-ethylenedioxythiophene):poly(4-styrene sulfonate) (PEDOT:PSS)

Considering the well-known phenomenon of enhancing bone healing by applying electromagnetic stimulation, manufacturing conductive bone scaffolds is on demand to facilitate the delivery of electromagnetic stimulation to the injured region, which in turn significantly expedites the healing procedure in tissue engineering methods. For this purpose, hybrid conductive scaffolds composed of poly(3,4-ethylenedioxythiophene), poly(4-styrene sulfonate) (

PEDOT

PSS), gelatin (Gel), and bioactive glass (BaG) were produced employing freeze drying technique. Concentration of

PEDOT

PSS were optimized to design the most appropriate conductive scaffold in terms of biocompatibility and cell proliferation. More specifically, scaffolds with four different compositions of 0, 0.1, 0.3 and 0.6% (w/w)

PEDOT

PSS in the mixture of 10% (w/v) Gel and 30% (w/v) BaG were synthesized. Immersing the scaffolds in simulated body fluid (SBF), we evaluated the bioactivity of samples, and the biomineralization were studied in details using scanning electron microscopy, energy dispersive spectroscopy, X-ray diffraction analysis and Fourier transform infrared spectroscopy. By performing cytocompatibility analyses for 21 days using adult human mesenchymal stem cells, we concluded that the scaffolds with 0.3% (w/w)

PEDOT

PSS and conductivity of 170 μS/m has the optimized composition and further increasing the

PEDOT

PSS content has inverse effect on cell proliferation. Based on our finding, addition of this optimized amount of

PEDOT

PSS to our composition can increase the cell viability more than 4 times compared to a nonconductive composition.

Bone regeneration strategy inspired by the study of calcification behavior in deer antler

Bone regeneration has attracted much attention from various researchers and inspired numerous strategies for bone formation. In this study, rapid calcification of deer antlers was studied to unravel bone biology by investigating mineral composition, morphology and microstructure. Calcification model was hypothesized and preliminarily established by in vitro experiments. In our model, mineral deposition and phase conversions in the gel matrix were mimicked. Results revealed that mineral metabolism including deposition and phase conversion plays key roles in calcification in vivo, which inspired the bone regeneration strategy with three main components, i.e. enhanced mineral nucleation, mineral ions sources and crystals habits. Rapid mineral metabolism of implant apatite biomaterials was supposed as the critical aspect of bone regeneration. This study will provide a relatively ideal model for peer bone regeneration studies.

Influence of ceramic disk material, surface hemispheres, and SBF volume on in vitro mineralization

Calcium phosphate ceramics are the main mineral constituents of bone and teeth and have therefore been extensively investigated for bone regenerative applications. In the current study, the effect of disk material, surface geometry, and SBF volume on mineralization capacity was investigated. Hemispherical concavities were created on the surfaces of disks made of different materials (i.e., hydroxyapatite (HA), β-tricalcium phosphate (β-TCP), biphasic calcium phosphate (BCP) and titanium (Ti)) which were sintered at 1200 °C. Mineralization of CaP was assessed on disk surfaces after immersion of the samples in different volumes of simulated body fluid (SBF) up to 14 days by means of calcium assay and scanning electron microscopy (SEM). This study showed that different SBF volumes have different effects on mineralization, with an optimum material/liquid ratio of 5 mL of SBF per cm(2) . Additionally, at this volume, apparent differences based on disk material became obvious. Evidently, surface hemispherical concavities acted as initiator areas for nucleation and crystal growth.

Enhancing the corrosion resistance and surface bioactivity of a calcium-phosphate coating on a biodegradable AZ60 magnesium alloy via a simple fluorine post-treatment method

A simple fluorine post-treatment was attempted on a calcium-phosphate coating on an AZ60 alloy. Optimum fluorine post-treatment parameters were obtained. The fluorine post-treated coating showed improved corrosion protectiveness and surface bioactivity.

Significance of calcium phosphate coatings for the enhancement of new bone osteogenesis--a review

A systematic analysis of results available from in vitro, in vivo and clinical trials on the effects of biocompatible calcium phosphate (CaP) coatings is presented. An overview of the most frequently used methods to prepare CaP-based coatings was conducted. Dense, homogeneous, highly adherent and biocompatible CaP or hybrid organic/inorganic CaP coatings with tailored properties can be deposited. It has been demonstrated that CaP coatings have a significant effect on the bone regeneration process. In vitro experiments using different cells (e.g. SaOS-2, human mesenchymal stem cells and osteoblast-like cells) have revealed that CaP coatings enhance cellular adhesion, proliferation and differentiation to promote bone regeneration. However, in vivo, the exact mechanism of osteogenesis in response to CaP coatings is unclear; indeed, there are conflicting reports of the effectiveness of CaP coatings, with results ranging from highly effective to no significant or even negative effects. This review therefore highlights progress in CaP coatings for orthopaedic implants and discusses the future research and use of these devices. Currently, an exciting area of research is in bioactive hybrid composite CaP-based coatings containing both inorganic (CaP coating) and organic (collagen, bone morphogenetic proteins, arginylglycylaspartic acid etc.) components with the aim of promoting tissue ingrowth and vascularization. Further investigations are necessary to reveal the relative influences of implant design, surgical procedure, and coating characteristics (thickness, structure, topography, porosity, wettability etc.) on the long-term clinical effects of hybrid CaP coatings. In addition to commercially available plasma spraying, other effective routes for the fabrication of hybrid CaP coatings for clinical use still need to be determined and current progress is discussed.

Calcium phosphate ceramics in bone tissue engineering: a review of properties and their influence on cell behavior

Calcium phosphate ceramics (CPCs) have been widely used as biomaterials for the regeneration of bone tissue because of their ability to induce osteoblastic differentiation in progenitor cells. Despite the progress made towards fabricating CPCs possessing a range of surface features and chemistries, the influence of material properties in orchestrating cellular events such as adhesion and differentiation is still poorly understood. Specifically, questions such as why certain CPCs may be more osteoinductive than others, and how material properties contribute to osteoinductivity/osteoconductivity remain unanswered. Therefore, this review article systematically discusses the effects of the physical (e.g. surface roughness) and chemical properties (e.g. solubility) of CPCs on protein adsorption, cell adhesion and osteoblastic differentiation in vitro. The review also provides a summary of possible signaling pathways involved in osteoblastic differentiation in the presence of CPCs. In summary, these insights on the contribution of material properties towards osteoinductivity and the role of signaling molecules involved in osteoblastic differentiation can potentially aid the design of CPC-based biomaterials that support bone regeneration without the need for additional biochemical supplements.

The impact of heat treatment on interactions of contact-poled biphasic calcium phosphates with proteins and cells

A number of studies have reported improved bone integration for calcium phosphate based materials electrically "poled" by an external electric field prior to implantation. In our study we investigated the effects of electrical polarization of a biphasic ceramic composed of 80% hydroxyapatite and 20% β-tricalcium phosphate. As contact poling involves elevated temperatures as a prerequisite for inducing charge, we used two reference types: samples without any heat treatment and poling, and samples with no poling but heat treatment identical to that of the poled samples. All heat-treated samples (poled or unpoled) showed an improved wettability, which was attributed to a reduced hydrocarbon contamination. Heat treatment alone provoked an accelerated spreading of osteoblast-like cells, whereas on poled samples a retarded cell spreading was observed. While proliferation and several differentiation markers were not influenced by either heat treatment or poling, the release of proinflammatory cytokines interleukin-6 and -8 was significantly reduced for all heat-treated samples, irrespective of additional electrical poling. The study demonstrated that the behaviour of cells in contact with poled biphasic ceramics was influenced by two parameters: heating and charge. Our data revealed that heating of the calcium phosphate ceramics had a much more pronounced effect on cell behaviour than charge.

Evaluation of the Bioactivity Behavior of a 48 Wt %SiO2 Bioglass through Experiments in Simulated Body Fluid

Among bioceramics materials, bioglasses which exhibits either a bioactive or resorbable behavior has been studied for many applications, such as bone substitutive and regeneration. When in contact with body fluid, the bioglasses can induce the formation of a hydroxyapatite surface layer. In this paper, we studied the bioactivity of a bioglass containing 48 wt %SiO2, 27 wt% Na2O, 19 wt % CaO and 6 wt %P2O5. After fusion and annealing, the samples were immersed in SBF for different periods, up to 14 days. The samples were characterized through XRD, DRIFT and SEM before and after bioactivity experiments. The overall results suggest the formation of a surface layer of consisting of hydroxyapatite, which was crystallized within seven days after in vitro experiments, leading to a suitable bioactivity. Moreover, the samples showed a glass network with high cohesion due to calcium addition, leading to materials with high corrosion resistance.

Titanium-containing bioactive phosphate glasses

The use of biomaterials has revolutionized the biomedical field and has received substantial attention in the last two decades. Among the various types of biomaterials, phosphate glasses have generated great interest on account of their remarkable bioactivity and favourable physical properties for various biomedical applications relating to both hard and soft tissue regeneration. This review paper focuses mainly on the development of titanium-containing phosphate-based glasses and presents an overview of the structural and physical properties. The effect of titanium incorporation on the glassy network is to introduce favourable properties. The biocompatibility of these glasses is described along with recent developments in processing methodologies, and the potential of Ti-containing phosphate-based glasses as a bone substitute material is explored.

Fabrication and characterization of poly(lactic-co-glycolic acid) microsphere/amorphous calcium phosphate scaffolds

Although hydroxyapatite (HAP) and β-tricalcium phosphate have been used extensively as osteoconductive minerals in biomaterial scaffolds for bone regeneration, they lack the capacity to stimulate osteoblastic differentiation of progenitor cells. In contrast, amorphous calcium phosphates (ACPs), which convert to HAP under aqueous conditions, have the potential to facilitate osteoblastic differentiation through the transient local release of calcium and phosphate ions. Therefore, in this study ACPs were synthesized using zinc and zirconia divalent cations as stabilizers (denoted ZnACP and ZrACP, respectively) and compared to HAP. Analysis of ion release into serum-containing cell culture medium revealed transiently elevated levels of calcium and phosphorous, consistent with the enhanced solubility of ZrACP and ZnACP relative to HAP. In addition, X-ray diffraction analysis revealed partial conversion of ZrACP to HAP but no conversion of ZnACP after 96 h. Next, scaffolds were fabricated by sintering mixtures of 300-500 µm poly(D,L-lactic-co-glycolic acid) (PLGA) microspheres and 0.5 wt% calcium phosphate mineral (HAP, ZrACP or ZnACP) at 70 °C for 24 h. Scanning electron microscopy revealed a porous microsphere matrix with calcium phosphate particulates clinging to the microsphere surfaces both prior to and after 14 days in culture medium. Finally, the incorporation of calcium phosphate resulted in a lower compressive modulus in the range 127 to 74-89 MPa. Taken together, these results indicate that ZrACP, ZnACP and HAP minerals exhibit very different properties, and therefore may elicit different osteoblastic responses in vitro.

Efficacy of silicate-substituted calcium phosphate ceramic in posterolateral instrumented lumbar fusion

STUDY DESIGN/SETTING

Retrospective review of a consecutive, nonrandomized series operated on by 2 surgeons.

OBJECTIVE

To evaluate the clinical and radiographic effectiveness of a silicated hydroxyapatite ceramic as a bone graft substitute in a series of patients undergoing posterolateral instrumented lumbar fusion.

SUMMARY OF BACKGROUND DATA

Newer-generation synthetic ceramics have been refined to maximize their host-graft interaction and stimulation of new tissue formation, including silicate-substitution.

METHODS

An independent radiologist interpreted the computed tomography images at 6, 12, and 24 months after surgery. Forty-two patients with 1- or 2-level lumbar degenerative disorders underwent posterior laminectomy (when indicated) and posterolateral fusion with instrumentation. Surgical levels included 15 patients who underwent 2-level and 27 single-level fusion procedures (57 levels operated on in total).

RESULTS

The average back pain scores improved from 5.6 ± 2.5 preoperative to 2.1 ± 2.5 at follow-up (P < 0.05). Similar results were seen with leg pain improvement from 5.8 ± 2.5 to 1.4 ± 1.9 (P < 0.05). At 6 months, 35% of levels revealed fusion, which increased to 76.2% and 76.5% at 12 and 24 months, respectively. No evidence of ectopic bone formation or osteolysis was noted.

CONCLUSION

In this study, a silicated calcium phosphate-based ceramic has been shown to be effective as a graft substitute and eliminate the need for autogenous iliac crest bone graft. The results confirm radiographic healing in posterolateral instrumented lumbar fusion at 24-months follow-up. The clinical outcomes also substantiate significant pain improvement consistent with published data in the literature compared with other bone graft alternatives.

Imaging resin-cast osteocyte lacuno-canalicular system at bone-bioactive glass interface by scanning electron microscopy

The morphology of the osteocyte lacuno-canalicular system at the bone-biomaterial implant-interface has not been fully investigated. In this study, the resin-cast scanning electron microscopy technique was used, for the first time, to image the lacuno-canalicular network within neoformed bone around bioactive glass (BG) particles implanted in rat tibia bone marrow. The most salient finding was that the osteocyte canaliculi pass through the calcium-phosphorus layer formed at the bone-BG interface and reach the silica-rich layer of the reacted BG.

Control of alpha-alumina surface charge with carboxylic acids

In this work, we studied the surface charge of alpha-alumina treated with carboxylic acids with different carbon chain length. The results show the possibility of controlling surface charges of alumina by using different concentrations of carboxylic acids or changing the size of the carbon chain of the acids. We also report that part of the acid found on the surface is strongly bound, therefore making it possible to obtain pH-resistant samples of alpha-alumina with an isoelectric point (IEP) of 5.5. It is found, that IEP values obtained for modified samples have a linear correlation with the number of carbon atoms of dicarboxylic acids for up to five carbon atoms. From a practical perspective, the method presented in this work has many advantages. First, it maintains the same hydrophilicity of the alumina surface. Second, the modification of the surface is stable in a long-range of pH. Finally, the presented method is easy-to-use and cheap, as the modification consists of only two simple steps carried out at low temperatures with inexpensive and nontoxic reagents.

Organic / inorganic bioactive materials Part I: Synthesis, structure and in vitro assessment of collagen/silicocarnotite biocoatings

The silicocarnotite, as an inorganic part of the coatings, has been synthesized using a polystep sol-gel method. The chemical composition of the prepared silicocarnotite sol is described as 58.12 CaO, 29.42 P2O5, 12.45 SiO2 (wt%), where Ca/P+Si = 1,67. The acid soluble type I collagen, as an organic part of the obtained coatings, was mixed with silicocarnotite powder in a weight ratio of 25:75 and 75:25 weight ratio without cross-linkage. The acidity of the obtained mixture was readjust with 25% NH4OH to pH = 9.0. The mixture was then dried at 37°C for 12 h.

The growth of B-type carbonate containing hydroxyapatite (B-type CO3HA) in which CO3 2+→PO4 3− on the surface of collagen/silicocarnotite coatings soaked in 1.5 simulated body fluid (1.5 SBF) was observed. The nucleation of B-type CO3HA was estimated on the obtained coatings after 3 days immersion in 1.5 SBF. The negatively charged carboxylate groups from the collagen surface may be responsible for the HA deposition. This was confirmed by the “red shift” of carboxylate groups of collagen molecules in the FTIR spectra. After soaking in 1.5 SBF, the morphology of prepared coatings and HA formation was observed by SEM.

Bioactive silica-collagen composite xerogels modified by calcium phosphate phases with adjustable mechanical properties for bone replacement

The development of composites has been recognized as a promising strategy to fulfil the complex requirements of biomaterials. The present study reports on the modification of a novel silica-collagen composite material by varying the inorganic/organic mass ratio and introducing calcium phosphate cement (CPC) as a third component. The sol-gel technique is used for processing, followed by xerogel formation under specific temperature and relative humidity conditions. Cylindrical monolithic samples up to 400mm(3) were obtained without any sintering processes. Various hierarchical phases of the organic component were applied, ranging from tropocollagen and collagen fibrils up to collagen fibers, each characterized by atomic force microscopy. Focusing on the application of fibrils, various inorganic/organic mass ratios were used: 100/0, 85/15 and 70/30; their influence on the structure of the composite material was demonstrated by scanning electron microscopy. The composition was extended by the addition of 25wt.% CPC which led to increased bioactivity by accelerating the formation of bone apatite layers in simulated body fluid. Synchrotron microcomputed tomography demonstrated the homogeneous distribution of the cement particles in the silica-collagen matrix. Compressive strength tests showed that the mechanical properties of the brittle pure silica gel are changed significantly due to collagen addition. The highest ultimate strength of about 115MPa at about 18% total strain was registered for the 70/30 silica-collagen composite xerogels. Incorporation of CPC lowered the gel's strength. By demonstrating differentiation of human monocytes into osteoclast-like cells, an important feature of the composite material regarding successful bone remodeling is fulfilled.

Electrical characterization of hydroxyapatite-based bioceramics

This paper studies the AC conductivity and permittivity of hydroxyapatite (HA)-based ceramics from 0.1 Hz-1 MHz at temperatures from room temperature to 1000 degrees C. HA-based ceramics were prepared either as dense ceramics or in porous form with interconnected porosity and were sintered in either air or water vapour. Samples were thermally cycled to examine the influence of water desorption on AC conductivity and permittivity. Surface-bound water was thought to contribute to conductivity for both dense and porous materials at temperatures below 200 degrees C. At temperatures below 700 degrees C the permittivity and AC conductivity of HA was also influenced by the degree of dehydration and thermal history. At higher temperatures (700-1000 degrees C), bulk ionic conduction was dominant and activation energies were of the order of approximately 2 eV, indicating that hydroxyl ions are responsible for conductivity.

Coating of bone-like apatite for development of bioactive materials for bone reconstruction

Materials with bioactivity, i.e. bone-bonding ability, form a bone-like apatite layer on their surfaces in the body and bond to living bone through this bone-like apatite layer. Bone-like apatite is carbonated hydroxyapatite with small crystallites and low crystallinity. The coating of the bone-like apatite layer on the substrates is expected to be a useful technique to induce bioactivity on the substrates. The bone-like apatite layer can be formed on the surface of substrates in a solution mimicking body fluid when some functional groups are introduced to the substrates. This process is called a biomimetic process. Coating of bone-like apatite layers through this biomimetic process has received much attention in the fabrication of novel composites with bioactivity. An overview of the coating of bone-like apatite is described.