In vitro degradation of a polyhydroxybutyrate/polyhydroxyvalerate copolymer

Injection-moulded PHB/7% PHV (molecular mass 580 000) samples were placed in buffered saline at varying pHs for long-termin vitro studies. Anomalies between sample mass loss and Young's modulus were found for the different pHs. The Young's modulus anomaly was explained by examination of the molecular mass distribution (MMD) changes with time. The molecular mass measurements also showed that the MMD moved to a lower molecular mass, and also showed an increase in peak height, irrespective of pH. From theMn data, curves for (Mn(O)/Mn(t) –1) were plotted and the linearity showed that the solution pH was a rate-controlling factor.     

声作用功率对炭/炭复合材料表面磷酸钙生物活性陶瓷涂层的影响

采用阴极声电沉积工艺在炭／炭复合材料表面制备了生物活性透钙磷石涂层，考察了超声场中不同声作用功率条件下的电流密度、端电压特征和声作用功率对涂层组成结构、形貌的影响及涂层与基体的结合力，SEM、EDAX、FTIR、XRD等结果分析表明：电流密度以及端电压具有更大的调节范围，且在沉积过程中两参数不随时间而改变，说明该工艺具有自优化特征；所制透钙磷石涂层形貌呈片状，由两种不同晶格参数单斜相组成；炭／炭复合材料中制备时残留的孔隙仍保留。在小于声作用功率临界条件下作用超声波，生物活性透钙磷石涂层不脱落。     

Release behaviors of drug loaded chitosan/calcium phosphate coatings on titanium

Implants with antibiotic drug loaded bioactive coatings have been increasingly applied in orthopedic operations. Here we report the drug release behavior of gentamycin loaded chitosan/calcium phosphate coatings on titanium. Chitosan/calcium phosphate coatings with different component ratios and surface topographies were prepared by electrochemical deposition method. Our results showed that the drug release from these coatings was controlled by their component ratio and surface topography, and the former ratio played a more significant role. The present coatings could provide an effective way to create both good bioactivity and antibacterial activity.     

Preparation and mechanical properties of calcium phosphate/copoly-L-lactide composites

New artificial bone materials were prepared using calcium phosphates, hydroxyapatite and -tricalicum phosphate, and copoly-L-lactide, CPLA. Calcium phosphate powder and CPLA were mixed at 453 K for 10 min with various mixing ratios. Scanning electron microscope observations indicated that the composites of -tricalicum phosphate and CPLA were homogeneously dispersed and highly adhesive. Youngs modulus of the composites was the same as bone, and bending strength was over half that of bone. The improvement of Youngs modulus compared to the original two materials was due to a composite effect. The composites are expected to be usable as artificial bone materials.     

Mechanical and in vitro degradation behavior of ultrafine calcium polyphosphate reinforced magnesium-alloy composites

Magnesium alloy (ZK60A) matrix composites reinforced with 2.5, 5, 7.5 and 10 wt.% calcium polyphosphate particles, which were sphere-like in shape with average size of about 750 nm, were fabricated by powder metallurgy. The microstructure, mechanical properties and degradation behavior in physiological saline of the composites were investigated. The obtained results show that ultrafine calcium polyphosphate particles uniformly distribute in the ZK60A matrices without voids for the composites containing 2.5 and 5 wt.% calcium polyphosphate. For the composites containing 7.5 and 10 wt.% calcium polyphosphate, however, calcium polyphosphate particles agglomerate in the ZK60A matrices, and some obvious voids appear. The ultimate tensile strengths, yield strengths and elastic moduli of the composites tend to increase when the calcium polyphosphate contents increase from 0 to 5 wt.%, however, appear to decrease with the further increase of calcium polyphosphate from 5 to 10 wt.%. The weight losses of the composites, pH values and Mg ion concentrations of the solutions immersing the composites gradually decrease with increase of calcium polyphosphate content, which indicates that the addition of more calcium polyphosphate into ZK60A alloy results in significant degradation slow-up of the composites. This can be attributed to the formation of dense corrosion product layers on the composites. The composites have good mechanical properties and controllable degradation rates and thereby have potential to be used as load-bearing bone implants.     

Cellular investigations on electrochemically deposited calcium phosphate composites

Electrochemically deposited calcium phosphate (CaP) coatings are fast resorbable and existent only during the first period of osseointegration. In the present study, composite coatings with varying solubility (hydroxyapatite (HA), brushite with less HA and monetite (M) with less HA) were prepared and the influence of the degradation and the reprecipitation of CaP on osteoblastic cells were investigated. On the brushite composite coating a new precipitated, finely structured CaP phase was observed during immersion in cell culture medium with or without osteoblastic cells. The surface morphology of monetite and HA coatings were entirely unmodified under the same conditions. So it could be assumed that electrochemically deposited brushite with less HA acts as a precursor for new precipitated CaP. On this surface osteoblastic cells revealed a well-spread morphology with pronounced actin cytoskeleton and demonstrated good proliferation behaviour. Thus we suggest that brushite seems to be especially suitable for coating of implants as a matrix for nucleation and growth of new bone.     

Evaluation of the effect of three calcium phosphate powders on osteoblast cells

The aim of the present study was to assess the effect of three calcium phosphate powders entering in the composition of bone substitute materials on osteoblast-cells activity. These powders were hydroxyapatite (HA) widely used as a biomaterial, nanocrystalline carbonate apatite (C A) very close to bone mineral crystals, and an experimental one: calcium phosphate cement-1 (CPC-1) composed of an amorphous Ca-P phase and brushite. The powders were physico-chemically characterized. The very reactive CPC-1 powder became transformed in cell culture medium: recrystallization of amorphous precursors and hydrolysis of brushite into poorly crystalline apatite occurred. Osteoblast-cells activity was evaluated: for low level of calcium phosphates (>100 g/ml) CPC-1 enhanced proliferation and, to a lesser degree, differentiation on alkaline phosphatase activity. For 100 g/ml of powders we observed a great alteration of biological activity of the osteoblasts: evaluation of proliferation indicated an inhibition for all samples, and a decrease of two differentiation markers: alkaline phosphatase activity and osteocalcin release were noticed, suggesting a down regulation due to the presence of large amount of mineral powder. © 2001 Kluwer Academic Publishers     

Cell growth and function on calcium phosphate reinforced chitosan scaffolds

Macroporous chitosan scaffolds reinforced by calcium phosphate powders such as hydroxyapatite (HA) or calcium phosphate invert glass were fabricated using a thermally induced phase separation technique. Human osteoblast-like MG63 cells were cultured on the composite scaffolds for up to 11 days, and the cell growth and function were analyzed. The cell growth is much faster on the chitosan/HA scaffolds incorporated with the glass (CHG) than on the chitosan/HA scaffold without the glass (CH). The total protein content of cells were quantified and increased over time on both composites (CH, CHG) but was significantly higher on CHG after 7 days of culture. The cells on CHG also expressed significantly higher amount of alkaline phosphatase at days 7 and 11 and osteocalcin at day 7 than those on CH. The results suggested that the addition of glass in chitosan/hydroxyapatite composite scaffolds might enhance the proliferation and osteoblastic phenotype expression of MG63 cells. However, the chitosan-matrix scaffolds did not show higher phenotype expression of MG63 cells, in comparison with the TCPS plate, probably due to the degradation of chitosan and release of acidic byproducts. Larger amount of soluble calcium phosphate invert glasses should be added into the scaffolds to prevent chitosan from fast degradation that may affect the differentiation of osteoblast cells.     

Microwave assisted-in situ synthesis of porous titanium/calcium phosphate composites and their in vitro apatite-forming capability

Microwave irradiation has been proven to be an effective heating source in synthetic chemistry, and can accelerate the reaction rate, provide more uniform heating and help in developing better synthetic routes for the fabrication of bone-grafting implant materials. In this study, a new technique, which comprises microwave heating and powder metallurgy for in situ synthesis of Ti/CaP composites by using Ti powders, calcium carbonate (CaCO₃) powders and dicalcium phosphate dihydrate (CaHPO₄·2H₂O) powders, has been developed. Three different compositions of Ti:CaCO₃:CaHPO₄·2H₂O powdered mixture were employed to investigate the effect of the starting atomic ratio of the CaCO₃ to CaHPO₄·2H₂O on the phase, microstructural formation and compressive properties of the microwave synthesized composites. When the starting atomic ratio reaches 1.67, composites containing mainly alpha-titanium (α-Ti), hydroxyapatite (HA), beta-tricalcium phosphate (β-TCP) and calcium titanate (CaTiO₃) with porosity of 26%, pore size up to 152 μm, compressive strength of 212 MPa and compressive modulus of 12 GPa were formed. The in vitro apatite-forming capability of the composite was evaluated by immersing the composite into a simulated body fluid (SBF) for up to 14 days. The results showed that biodissolution occurred, followed by apatite precipitation after immersion in the SBF, suggesting that the composites are suitable for bone implant applications as apatite is an essential intermediate layer for bone cells attachment. The quantity and size of the apatite globules increased over the immersion time. After 14 days of immersion, the composite surface was fully covered by an apatite layer with a Ca/P atomic ratio approximately of 1.68, which is similar to the bone-like apatite appearing in human hard tissue. The results suggested that the microwave assisted-in situ synthesis technique can be used as an alternative to traditional powder metallurgy for the fabrication of Ti/CaP biocomposites.     

A construction of novel iron-foam-based calcium phosphate/chitosan coating biodegradable scaffold material

Slow corrosion rate and poor bioactivity restrict iron-based implants in biomedical application. In this study, we design a new iron-foam-based calcium phosphate/chitosan coating biodegradable composites offering a priority mechanical and bioactive property for bone tissue engineering through electrophoretic deposition (EPD) followed by a conversion process into a phosphate buffer solution (PBS). Tensile test results showed that the mechanical property of iron foam could be regulated through altering the construction of polyurethane foam. The priority coatings were deposited from 40% nano hydroxyapatite (nHA)/ethanol suspension mixed with 60% nHA/chitosan-acetic acid aqueous solution. In vitro immersion test showed that oxidation-iron foam as the matrix decreased the amount of iron implanted and had not influence on the bioactivity of this implant, obviously. So, this method could also be a promising method for the preparation of a new calcium phosphate/chitosan coating on foam construction.     

Preparation, characterization, and in vitro evaluation of nanostructured chitosan/apatite and chitosan/Si-doped apatite composites

Chitosan/apatite (CHI/Ap) composites are attracting great attention as biomaterials for bone repair and regeneration procedures. The reason is their unique set of properties: bioactivity and osteoconductivity provided by Ap and resorbability supplied by CHI among others. Thus, in this study, CHI/Ap and CHI/Si-doped Ap composites were prepared and characterized. Particle size, surface area, in vitro physiological stability, enzymatic biodegradation, and bioactivity were evaluated. Unimodal particle size distribution was obtained for composites with high CHI/Ap ratios while bimodal distribution was present in composites with low CHI/Ap ratio. Physiological stability decreased with Si doping and with the CHI content. Acetylation degree and molecular weight of CHI did not affect in vitro stability. Rate of enzymatic degradation increased with the CHI content in composites. Si-doped Ap composites also showed increased degradation with respect to non-doped ones. The bioactivity of the composites was evidenced by the deposition on their surface of a calcium phosphate layer with Ap morphology after immersion in simulated body fluid. Both, biodegradation and bioactivity were dependent on the molecular weight of the polymeric CHI matrix. These results suggest that the CHI/Ap composites obtained are promising materials for bone regeneration applications.     

Micromorphological effect of calcium phosphate coating on compatibility of magnesium alloy with osteoblast

Abstract

Octacalcium phosphate (OCP) and hydroxyapatite (HAp) coatings were developed to control the degradation speed and to improve the biocompatibility of biodegradable magnesium alloys. Osteoblast MG-63 was cultured directly on OCP- and HAp-coated Mg-3Al-1Zn (wt%, AZ31) alloy (OCP- and HAp-AZ31) to evaluate cell compatibility. Cell proliferation was remarkably improved with OCP and HAp coatings which reduced the corrosion and prevented the H₂O₂ generation on Mg alloy substrate. OCP-AZ31 showed sparse distribution of living cell colonies and dead cells. HAp-AZ31 showed dense and homogeneous distribution of living cells, with dead cells localized over and around corrosion pits, some of which were formed underneath the coating. These results demonstrated that cells were dead due to changes in the local environment, and it is necessary to evaluate the local biocompatibility of magnesium alloys. Cell density on HAp-AZ31 was higher than that on OCP-AZ31 although there was not a significant difference in the amount of Mg ions released in medium between OCP- and HAp-AZ31. The outer layer of OCP and HAp coatings consisted of plate-like crystal with a thickness of around 0.1 μm and rod-like crystals with a diameter of around 0.1 μm, respectively, which grew from a continuous inner layer. Osteoblasts formed focal contacts on the tips of plate-like OCP and rod-like HAp crystals, with heights of 2–5 μm. The spacing between OCP tips of 0.8–1.1 μm was wider than that between HAp tips of 0.2–0.3 μm. These results demonstrated that cell proliferation depended on the micromorphology of the coatings which governed spacing of focal contacts. Consequently, HAp coating is suitable for improving cell compatibility and bone-forming ability of the Mg alloy.     

Optimization of the mechanical properties of calcium phosphate/multi-walled carbon nanotubes/bovine serum albumin composites using response surface methodology

Response surface methodology (RSM) coupled with the central composite design (CCD) was used to optimize the mechanical properties of calcium phosphate cement/multi-walled carbon nanotubes/bovine serum albumin (CPC/MWCNTs/BSA) composites. In this study, CPC composites were reinforced by multi-walled carbon nanotubes (MWCNTs) and bovine serum albumin (BSA) in order to induce high mechanical properties in the CPC/MWCNTs/BSA system. The effect of various process parameters on the compressive strength of CPC/MWCNTs/BSA composites was studied using design of experiments (DOE). The process parameters studied were: wt.% of MWCNTs (0.2–0.5 wt.%), wt.% of BSA (5–15 wt.%) and type of MWCNTs (e.g. as-pristine MWCNT (MWCNT-AP), hydroxyl group functionalized MWCNT (MWCNT-OH) and carboxyl group functionalized MWCNT (MWCNT-COOH)). Based on the CCD, a quadratic model was obtained to correlate the process parameters to the compressive strength of CPC/MWCNTs/BSA composites. From the analysis of variance (ANOVA), the most significant factor affected on the experimental design response was identified. The predicted compressive strength after process optimization was found to agree well with the experimental value. The results revealed that at 0.5 wt.% of MWCNT-OH and 15 wt.% of BSA, the highest compressive strength of 14 MPa was obtained.     

In-situ mineralization of chitosan/calcium phosphate composite and the effect of solvent on the structure

Solvent played an important role in the formation of calcium phosphate phase of the chitosan/calcium phosphate composites. In this investigation, ethanol-acetic acid mixtures were employed as solvents, and various calcium phosphate phases, such as brushite, amorphous calcium phosphate, and hydroxyapatite, were introduced into the chitosan/calcium phosphate composites by using in-situ preparation process. The results showed that the structures of composite were influenced remarkably by the morphology and the distribution of calcium phosphate phase. In addition, the bioactivity of composites was governed mainly by the characters of calcium phosphate phases in composites, since calcium phosphate phases could induce the growth of hydroxyapatite coating on the surfaces of composites. On the surface of chitosan/brushite composite, the formed hydroxyapatite coating consisted of oriented plate crystallites, which self-assembled into spherical-like crystals. When other calcium phosphate phase was introduced into composites, the polymorphs of hydroxyapatite layer would change greatly. The oriented plate crystallites became bigger, and meanwhile, the self-assembled aggregates became less and smaller. In addition, with the shift of the prior nucleating point, the growth orientation of plate crystallites was transformed.     

Increased osteoblast density in the presence of novel calcium phosphate coated magnetic nanoparticles

Bone diseases (including osteoporosis, osteoarthritis and bone cancer) are of great concern to the medical world. Drugs are available to treat such diseases, but often these drugs are not specifically targeted to the site of the disease and, thus, lack an immediate directed therapeutic effect. The optimal drug delivery system should enhance healthy bone growth with high specificity to the site of bone disease. It has been previously shown that magnetic nanoparticles can be directed in the presence of a magnetic field to any part of the body, allowing for site-specific drug delivery and possibly an immediate increase in bone density. The objective of the present study was to build off of this evidence and determine the density of osteoblasts (bone forming cells) in the presence of various uncoated and coated magnetic nanoparticles that could eventually be used in drug delivery applications. Results showed that some magnetic nanoparticles (specifically, γ-Fe(2)O(3)) significantly promoted osteoblast density (that is, cells per well) after 5 and 8 days of culture compared to controls (no particles). These magnetic nanoparticles were further coated with calcium phosphate (CaP; the main inorganic component of bone) to tailor them for treating various bone diseases. The coatings were conducted in the presence of either bovine serum albumin (BSA) or citric acid (CA) to reduce magnetic nanoparticle agglomeration, a common problem resulting from the use of nanoparticles which decreases their effectiveness. Results with these coatings showed that magnetic nanoparticles, specifically (γ-Fe(2)O(3)), coated in the presence of BSA significantly increased osteoblast density compared to controls after 1 day. In this manner, this study provided unexpected evidence that CaP-coated γ-Fe(2)O(3) magnetic nanoparticles increased osteoblast density (compared to no particles) and, thus, should be further studied to treat numerous bone diseases.     

Nano-hydroxyapatite reinforced polyhydroxybutyrate composites: A comprehensive study on the structural and in vitro biological properties

Nanocomposites based on polyhydroxybutyrate (PHB) and hydroxyapatite (HAp) have recently been proposed for application in bone repair and regeneration, but very limited studies have investigated the effect of HAp on the rheological and thermal behavior of PHB. More important, the efficiency of a biomaterial depends greatly on its ability to interact with cells, but little is known about this interaction for this kind of nanocomposite. Hence, this paper dealt with some of the characteristics of solution-casted PHB/HAp nanocomposite films, and tried to explore the effect of HAp nanoparticles on cellular responses. The results showed that both rheological and thermal properties can be tailored by incorporating appropriate amounts of nanoparticles. In vitro studies showed a significant increase in proliferation and differentiation of MC3T3-E1 on nanocomposites compared to the neat polymer. Surface examination indicated that topography and chemistry of surface are important factors influencing cellular processes; while no cell differentiation was found on the neat polymer, nanocomposite with 15 wt.% filler content exhibited a pronounced differentiation resulting from high surface roughness and large amount of exposed HAp. These results suggest that HAp particles play a much more important role in determining the biological performance of PHB than has previously been supposed.     

Effect of hydrolysis on mechanical properties of tricalcium phosphate/poly-l-lactide composites

In order to investigate hydrolysis behavior and associated variation in mechanical properties of bioresorbable plastic composites, beta-tricalcium phosphate (beta-TCP)/poly(L: -lactide) (PLLA), the immersion tests into phosphate buffered solution (PBS) with different pH were conducted. After the immersion tests, tensile, bending and compressive tests were conducted on the specimen. The significant decrease in the mechanical properties of the specimens with 5.0 wt% beta-TCP contents were not observed in the pH = 7.4 immersion tests, whereas significant decrease were observed for the specimen with 9.5 and 14.0 wt% contents after 24 weeks. In the pH = 6.4 immersion tests, the degradation was accelerated. From the fracture surface observation, debondings between beta-TCP and PLLA grew into the void shape in the ductile fracture surface before immersion tests, whereas the voids were observed in the brittle fracture surface after immersion tests. This is due to the bioresorption of beta-TCP particles and/or beta-TCP/PLLA interface. In order to discuss the degradation of mechanical properties, tensile modulus degradation was analyzed based on the micromechanics supposing the damaged particles as voids. Degradation tendency predicted was in good agreement with experimental results. These results suggested that the degradation in modulus was attributed to lower load capacity of beta-TCP particles and lower load transfer to beta-TCP particles due to the hydrolysis of the beta-TCP particles and the interface between beta-TCP and PLLA.     

Amorphous calcium phosphate/urethane methacrylate resin composites. I. Physicochemical characterization

Urethane dimethacrylate (UDMA), an oligomeric poly(ethylene glycol) extended UDMA (PEG-U) and a blend of UDMA/PEG-U were chosen as model systems for introducing both hydrophobic and hydrophilic segments and a range of compliances in their derived polymers. Experimental composites based on these three resins with amorphous calcium phosphate (ACP) as the filler phase were polymerized and evaluated for mechanical strength and ion release profiles in different aqueous media. Strength of all composites decreased upon immersion in saline (pH = 7.4). Both polymer matrix composition and the pH of the liquid environment strongly affected the ion release kinetics. In saline, the UDMA/PEG-U composite showed a sustained release for at least 350 h. The initially high ion release of the PEG-U composites decreased after 72 h, seemingly due to the mineral re-deposition at the composite surface. Internal conversion from ACP to poorly crystallized apatite could be observed by X-ray diffraction. In various lactic acid (LA) environments (initial pH = 5.1) ion release kinetics was much more complex. In LA medium without thymol and/or carboxymethylcellulose, as a result of unfavorable changes in the internal calcium/phosphate ion stoichiometry, the ion release rate greatly increased but without observable conversion of ACP to apatite. Official contribution of the National Institute of Standards and Technology; not subject to copyright in the United States.