Micro-architecture of calcium phosphate granules and fibrin glue composites for bone tissue engineering

Calcium phosphate ceramics are currently used as bone graft substitutes in various types of clinical applications. Fibrin glue is also used in surgery due to its haemostatic, chemotactic and mitogenic properties. By combining these two biomaterials, new composite scaffolds were prepared. In this study, we attempt to analyse whether thrombin concentration in the fibrin glue could influence the properties of the composite. The association between fibrin glue and calcium phosphate ceramic granules was characterized at the ultra structural level. Micro and macroporous biphasic calcium phosphate ceramic granules with a diameter of 1-2mm composed of hydroxyapatite and beta-tricalcium phosphate (60/40) were associated to fibrin glue. The composites were observed by scanning and transmission electron microscopy and microcomputed tomography. Fibre thickness, porosity and homogeneity of the fibrin clot were modified by increased the thrombin concentration. Mixing fibrin glue with calcium phosphate granules (1:2) did not modify the microstructure of the fibrin clot in the composite. Nevertheless, thrombin interacted with the bioceramic by inducing the nucleation of crystalline precipitate at the ceramic/fibrin glue interface. Combining fibrin sealant and calcium phosphate ceramics could lead to new scaffolds for bone tissue engineering with the synergy of the properties of the two biomaterials.

Calcium phosphate cement composites in revision hip arthroplasty

Loosening of the femoral component in a total hip arthroplasty with concomitant bone loss can pose a problem for revision surgery due to inadequate structure in the remaining femur. While impaction allografting has shown promise, it has also shown serious complications, especially with moderate to severe bone loss. It may be possible to stabilize the graft layer with a bioresorbable cement to improve clinical results. This study examines the mechanical properties of a potential morsellized bone-bioresorbable composite. Morsellized bone was mixed with a commercially available bioresorbable cement (alpha-BSM, Etex Corp.) in compositions of 0%, 25%, 50% and 75% bone. Unconfined compression and diametral tensile and confined compression tests were performed to determine the composite mechanical properties. The composition containing 50% bone tended to exhibit the highest uniaxial strengths, as well as the highest confined compression modulus. The uniaxial compressive strength and stiffness of this composition was in the range of cancellous bone. Uniaxial compressive modulus decreased with increasing bone fraction whereas elongation exhibited the opposite trend. Bone fraction had a significant effect on compressive strength (p < 0.0001), compressive modulus (p < 0.0001), elongation (p < 0.01), tensile strength (p < 0.0001) and confined compressive modulus (p = 0.04). The addition of a bioresorbable cement to the allograft layer may improve the properties of the layer, preventing early subsidence seen in some clinical studies of impaction allografting, and therefore improving the clinical results. Further testing is required to evaluate the in vitro mechanical performance, as well as in vivo remodelling characteristics.

Surface charge and the effect of excess calcium ions on the hydroxyapatite surface

This paper describes the use of surface titration as a more direct probe of the surface chemistry of hydroxyapatite (HA) than zeta-potential measurements. The variation in HA surface charge with pH for two different KCl electrolyte concentrations was determined titrimetrically and the point of zero charge (PZC) found to be at a pH of 7.3 +/- 0.1. The curves also demonstrated that HA accumulates positive charge more readily below the PZC than it accumulates negative charge above it. Extended titration data indicated that dissolution occurred more rapidly in increasingly acidic conditions, but was inhibited by increasing electrolyte strength. Similar experiments with 2.5 mM Ca(2+) in the electrolyte show that Ca(2+) adsorption balances loss of H(+) to give a near-neutral surface at any pH above 7 (subject to availability of calcium ions and adsorption sites). The mechanism for adsorption has been shown to be deprotonation of adjacent surface HPO(4)(2-) sites and subsequent adsorption of a calcium ion to the lattice surface site. Furthermore, inhibition of dissolution under alkaline conditions in the presence of Ca(2+) suggested that dissolution was driven by desorption of Ca(2+). Modelling of the adsorption/desorption processes demonstrated that in both pure water and under physiological conditions phosphate groups will predominate at the HA surface. Furthermore, the (200) plane was identified as the likely form of the HA surface. These methodologies and findings are particularly relevant to investigation of biological response with respect to modification of surface hydrophobicity and surface energy or charge.

Sol–gel synthesis of a multifunctional, hierarchically porous silica/apatite composite

In this study, a degradable, hierarchically porous silica/apatite composite material is developed from a simple low-temperature synthesis. Mesoporosity is induced in the silica portion by the use of supramolecular templating. The template is further removed by calcination. Firstly, hydroxyapatite is synthesized through a sol-gel method at near room temperature conditions. After the mineralization process, the crystal surface is coated with a mesoporous silica matrix using the templates already present in the bulk solution. The material is characterized by XRD, N(2)-sorption, FT-IR, SEM/EDS, and TEM. The coating layer is distributed fairly homogeneously over the apatite surface and the coating thickness is easily adjustable and dependent on the amount of added silica precursor. The hybrid material is shown to efficiently induce calcium phosphate formation under in vitro conditions and simultaneously work as a carrier system for drugs.

Effectiveness of three extraction techniques in the development of a decellularized bone–anterior cruciate ligament–bone graft

In this study, porcine bone-anterior cruciate ligament-bone (B-ACL-B) grafts were decellularized using one of three protocols incorporating surfactants lauryl sulfate (SDS), Triton X-100, and/or an organic solvent (tributyl phosphate (TnBP)). The effectiveness of Triton-SDS, Triton-Triton or Triton-TnBP treatments in removing cellular materials was determined and possible changes in biochemical composition and mechanical properties due to each treatment were investigated. Treatment with Triton-SDS was most effective at removing cell nuclei and intracellular protein (vimentin) from the ACL but affected both the collagen and glycosaminoglycan (GAG) components of the extracellular matrix while increasing the tensile stiffness of the ligament. Triton-Triton was the least effective of the three treatments in terms of cellular extraction, but did not significantly change the mechanical and biochemical properties of the ACL. Triton-TnBP matched the level of decellularization achieved by Triton-SDS in terms of visible cell nuclei; however, the extraction of intracellular vimentin was less consistent. TnBP treatment also slightly decreased the collagen content of the ACL but did not alter its mechanical properties. Overall, all three decellularization treatments maintained adequate mechanical and biochemical properties of B-ACL-B grafts to justify the further investigation of all three decellularization protocols. The selection of a superior treatment will depend on future studies of the propensity of treated tissues for repopulation by host ACL fibroblasts and, ultimately, on any immunogenic and/or remodeling host response induced in vivo.

High strength, low stiffness, porous NiTi with superelastic properties

Near-stoichiometric NiTi with up to 18% closed porosity was produced by expansion at 1200 degrees C of argon-filled pores trapped by powder metallurgy within a NiTi billet. When optimally heat-treated, NiTi with 6-16% porosity exhibits superelasticity, with recoverable compressive strains up to 6% at a maximum compressive stress up to 1700 MPa. The apparent Young's modulus of NiTi with 16% porosity, measured during uniaxial compression, is in the range of 15-25 GPa (similar to human bone), but is much lower than measured ultrasonically (approximately 40 GPa), or predicted from continuum elastic mechanics. This effect is attributed to the reversible stress-induced transformation contributing to the linear elastic deformation of porous NiTi. The unique combination of low stiffness, high strength, high recoverable strains and large energy absorption of porous superelastic NiTi, together with the known biocompatibility of NiTi, makes this material attractive for bone-implant applications.

Nano-composite of poly(-lactide) and surface grafted hydroxyapatite: Mechanical properties and biocompatibility

In order to improve the bonding between hydroxyapatite (HAP) particles and poly(L-lactide) (PLLA), and hence to increase mechanical properties of the PLLA/HAP composite as potential bone substitute material, the HAP nano-particles were surface-grafted with PLLA and further blended with PLLA. The structure and properties of the composites were subsequently investigated by the mechanical property testing, the differential scanning calorimeter measurements (DSC), the scanning electron microscopy (SEM), the polarized optical microscopy (POM), and the cell culture. The PLLA molecules grafted on the HAP surfaces, as inter-tying molecules, played an important role in improving the adhesive strength between the particles and the polymer matrix. At a low content (approximately 4 wt%) of surface grafted-HAP (g-HAP), the PLLA/g-HAP nano-composites exhibited higher bending strength and impact energy than the pristine PLLA, and at a higher g-HAP content (e.g., 20 wt%), the modulus was remarkably increased. It implied that PLLA could be strengthened as well as toughened by g-HAP nano-particles. The results of biocompatibility test showed that the g-HAP existing in the PLLA composite facilitated both adhesion and proliferation of chondrocytes on the PLLA/g-HAP composite film.

A poly(lactic acid)/calcium metaphosphate composite for bone tissue engineering

A new method to prepare PLA/CMP (poly-L-lactide/calcium metaphosphate) composite scaffolds was developed for effective bone tissue engineering. This novel sintering method is composed of pressing the mixture of PLA, CMP, and salt particles at 150 MPa for 3 min followed by heat treatment at 210 degrees C for 30 min. The scaffolds had a homogeneously interconnected porous structure without a skin layer, and they exhibited a narrower pore size distribution and higher mechanical strength in comparison with scaffolds made by a solvent casting method. The scaffolds were seeded by osteoblasts and cultured in vitro or implanted into nude mice subcutaneously for up to 5 weeks. The number of cells attached to and proliferated on the scaffolds at both in vitro and in vivo was in the order of; PLA by novel sintering < PLA/CMP by solvent casting < PLA/CMP by novel sintering. In addition, the alkaline phosphatase activity of and calcium deposition in the scaffolds explanted from mice were enhanced significantly for the scaffolds by novel sintering compared to them by solvent casting. The in vitro results agreed well with the in vivo data. Such a superior characteristic of the novel sintering method should have resulted from the fact that the CMP particles could contact directly with cells/tissues to stimulate the cell proliferation and osteogenic differentiation, while the CMP particles would be coated by polymers and hindered to interact with cells/tissues in the case of a solvent casting method. As the novel sintering method does not use any solvents it offers another advantage to avoid problems associated with solvent residue.

Synthesis and characterization of porous β-tricalcium phosphate blocks

Porous beta-tricalcium phosphate (beta-TCP) blocks with four different macropore sizes (pore larger than 50 microm were synthesized using "calcium phosphate emulsions", and characterized by optical, geometrical, gravimetric, and radiological methods. The reproducibility of the synthesis method was excellent. Moreover, the macropore size could be easily controlled without modifying the microporosity (pore smaller than 50 microm) or the total porosity (microporosity+macroporosity). Based on the initial composition of the blocks and their final apparent density, the microporosity, macroporosity, and the total block porosity were calculated to be close to 21%, 54%, and 75%, respectively. These values were confirmed by microcomputed tomography (microCT). The mean macropore diameters were close to 150, 260, 510 and 1220 microm, as measured optically. Consistently lower values (25% lower) were obtained by microCT, but the linear correlation between microCT and optical method was high (r(2)>0.97). The macropore size distribution calculated from microCT scans appears to be narrow and normally distributed. The very good correlation between the results of the various methods and the possibility to determine the pore size distribution suggest that microCT is an ideal tool to non-destructively characterize macroporous calcium phosphate bone substitutes.

Compositional effects on the formation of a calcium phosphate layer and the response of osteoblast-like cells on polymer-bioactive glass composites

Biodegradable polymer-ceramic composites are attractive systems for bone tissue engineering applications. These composites have the combined advantages of the component phases, as well as the inherent ease in optimization where desired material properties can be tailored in a well-controlled manner. This study focuses on the optimization of a polylactide-co-glycolide (PLAGA) and 45S5 bioactive glass (BG) composite for bone tissue engineering. The first objective is to examine the effects of composition or overall BG content on the formation of a Ca-P layer on the PLAGA-BG composite. It is expected that with increasing BG content (0%, 10%, 25%, 50% by weight), the required incubation time in a simulated body fluid (SBF) for the composite to form a detectable surface Ca-P layer will decrease. Both the kinetics and the chemistry will be determined using SEM+EDAX, FTIR, and mu-CT methods. Solution phosphorous and calcium concentrations will also be measured. The second objective of the study is to determine the effects of BG content on the maturation of osteoblast-like cells on the PLAGA-BG composite. It is hypothesized that mineralization will increase with increasing BG content, and the composite will support the proliferation and differentiation of osteoblasts. Specifically, cell proliferation, alkaline phosphatase activity and mineralization will be monitored as a function of BG content (0%, 10%, 50% by weight) and culturing time. It was found that the kinetics of Ca-P layer formation and the resulting Ca-P chemistry were dependent on BG content. The response of human osteoblast-like cells to the PLAGA-BG composite was also a function of BG content. The 10% and 25% BG composite supported greater osteoblast growth and differentiation compared to the 50% BG group. The results of this study suggest that there is a threshold BG content which is optimal for osteoblast growth, and the interactions between PLAGA and BG may modulate the kinetics of Ca-P formation and the overall cellular response.

Helical rosette nanotubes: a biomimetic coating for orthopedics?

Helical rosette nanotubes (HRN) are obtained through an entropically driven self-assembly process of low-molecular-weight synthetic modules under physiological conditions. Counter-intuitively, these materials undergo extensive self-assembly under the effect of temperature, resulting in networks of very long nanotubes. We have previously shown, using an in vitro model, that titanium (Ti) coated with HRN containing a lysine side chain (HRN-K1) displayed enhanced osteoblast (OB) adhesion when compared to uncoated Ti (p < 0.01). Because it has been widely known that proteins play a critical role in OB adhesion on nanophase materials, here we examine OB adhesion on heated (+T) and unheated (-T) HRN-K1-coated Ti under serum (+S, presence of proteins) and serum-free (-S, absence of proteins) conditions. The results demonstrated that (a) while proteins enhanced OB adhesion on +T HRN-K1-coated Ti, they had no effect on -T HRN-K1-coated Ti, suggesting an active role played by the rosette nanotubes in promoting OB adhesion, and (b) under -S conditions, +T HRN-K1 induced the same level of OB adhesion as uncoated Ti under +S conditions, suggesting that +T HRN-K1 acts as a protein substitute. Finally, transmission electron microscopy and atomic force microscopy studies of +T and -T HRN-K1-coated Ti revealed a significant change in surface coverage, density and hierarchical organization of the nanotubes upon heating, which was correlated with their ability to promote cell adhesion.

Computer-Aided Tissue Engineering of a Human Vertebral Body

Tissue engineering is developing into a less speculative science involving the careful interplay of numerous design parameters and multidisciplinary professionals. Problem solving abilities and state of the art research tools are required to develop solutions for a wide variety of clinical issues. One area of particular interest is orthopedic biomechanics, a field that is responsible for the treatment of over 700,000 vertebral fractures in the United States alone last year. Engineers are currently lacking the technology and knowledge required to govern the subsistence of cells in vivo, let alone the knowledge to create a functional tissue replacement for a whole organ. Despite this, advances in computer-aided tissue engineering are continually growing. Using a combinatory approach to scaffold design, patient-specific implants may be constructed. Computer-aided design, optimization of geometry using voxel finite element models or other optimization routines, creation of a library of architectures with specific material properties, rapid prototyping, and determination of a defect site using imaging modalities highlight the current availability of design resources. This study proposes a novel methodology from start to finish which could, in the future, be used to design a tissue-engineered construct for the replacement of an entire vertebral body.

Preparation and characterization of porous beta-tricalcium phosphate/collagen composites with an integrated structure

Porous beta-tricalcium phosphate (TCP)/collagen composites with different beta-TCP/collagen weight ratio were prepared. The influences of the preparation conditions on the microstructure of porous composite and the joint status of beta-TCP particles with collagen fibrils were characterized by X-ray diffractometer, scanning electron microscopy and transmission electron microscopy. The results showed: (1) an acid treatment could effectively disassemble collagen fibrils; (2) in the resulting porous composites, beta-TCP particles homogenously existed on the skeleton of the collagen fibril network and bonded tightly to both the fibrils and themselves. The tight bonding formation could be due to the reaction between Ca ions in the particles and carboxyl groups in collagen polypeptide chains and due to the reprecipitation of partially dissolved beta-TCP during synthesis. The tight bonding between beta-TCP particles and collagen fibrils in the composites demonstrated an integrated structure, which was reproducible when beta-TCP/collagen ratio ranged from 2 to 4. Such integrated structure would make significant contributions in reliably tailoring properties of the porous composites by varying beta-TCP content. In addition, the porous composites had large porosity (approximately 95%) and appropriate pore size (approximately 100 microm), showed no negative impact in cytotoxicity assay and complete bone tissue regeneration after 12 weeks in animal test.

Nucleation and growth of calcium phosphate on amine-, carboxyl- and hydroxyl-silane self-assembled monolayers

Upon implantation, calcium phosphate (Ca-P) surfaces form on materials that are bone bioactive. In this study, the evolving surface characteristics associated with calcium phosphate precipitation are modeled using self-assembled monolayers (SAMs), in a one-step nucleation process. SAMs were used to create amine (-NH2), carboxyl (-COOH) and hydroxyl (-OH) functionalized surfaces by grafting 3-aminopropyltriethoxysilane, 3-triethoxysilylpropyl succinic anhydride and glycidoxypropyl tri-methoxysilane, respectively, onto oxidized silicon wafers. The SAM surfaces were characterized using ellipsometry to establish the presence of grafted molecules. On the surfaces incubated in simulated physiological fluids for 7 days, the thickness of Ca-P layer grew slowly over the first few hours, increasing strongly between 1 and 5 days and then slowed down again. FTIR showed the dependence of calcium phosphate morphology on the type of surface groups, with stronger P-O bands seen on the OH-terminated surface. SEM analysis showed dispersed Ca-P precipitates on the -COOH and -OH terminated surfaces after 1 day immersion. After 7 days, all SAM surfaces were covered with uniformly dispersed and denser Ca-P precipitates. The underlying Ca-P layer showed cracks on the -NH2-terminated surface. Rutherford backscattering spectrometry (RBS) data analysis confirmed that Ca/P ratio is in excellent agreement with the theoretical value of 1.67 for hydroxyapatite. X-ray diffraction (XRD) analysis also showed evidence of apatite formation on all the surfaces, with stronger evidence on the -OH-terminated surface. Highly porous Ca-P precipitates were observed on the SAM surfaces portrayed by the AFM scans with nanoscale RMS roughness. Thus, using highly controlled surface chemistry, under physiological conditions, in vitro, this study demonstrates that a hydroxylated surface enhances Ca-P nucleation and growth relative to other surfaces, thereby supporting the concept of its beneficial effect on bone tissue formation and growth.

The complete process of bioresorption and bone replacement using devices made of forged composites of raw hydroxyapatite particles/poly l-lactide (F-u-HA/PLLA)

Here we document the complete process of bioresorption and bone replacement of rods made of forged composites of unsintered hydroxyapatite particles/poly l-lactide (F-u-HA/PLLA) implanted in the femoral medullary cavities of rabbits. Bioresorption, osteoconductive bioactivity and bone replacement were compared in three implantation sites. In the first site, the end of the rod was located near the endosteum in the proximal medullary cavity. In the second, the rod was located at the centre of the bone marrow space without contacting the endosteum. In the third, the rod was in direct contact with cancellous bone within the distal femoral condyle. Micro-computerised tomography, scanning electron microscopy and photomicrographs of stained sections were used to document the complete process of bioresorption and bone replacement. At the first implantation site, the rod was completely resorbed and unbound u-HA particles were detected in and around the endosteum 5-6 years after implantation. At the second site, the rod showed significant shrinkage 4-5 years after implantation due to the release of almost all the PLLA, although a contracted cylindrical structure containing a few u-HA persisted even after approximately 6 years. At the third site, u-HA particles were almost completely replaced with bone after 5-6 years. Conversely, PLLA-only rods showed little bone conduction, and small amounts of degraded PLLA debris and intervening some tissue persisted even after long periods. Namely, the u-HA/PLLA composites were replaced with bone in the distal femoral condyle, where they were in direct contact with the bone and new bone formation was anatomically necessary. By contrast, composite rods were resorbed without replacement in the proximal medullary cavity, in which new bone growth was not required. We therefore conclude that the F-u-HA30/40 composites containing 30 wt%/40 wt% u-HA particles are clinically effective for use in high-strength bioactive, bioresorbable bone-fixation devices with the capacity for total bone replacement.

Carbonate-containing hydroxyapatite derived from calcium tripolyphosphate gel with urea

Carbonate containing hydroxyapatite (CO3HAp) is one of the candidate materials as a bioresorbable bone substitute. In the present work, CO3HAp was efficiently prepared by a hydrothermal treatment of calcium tripolyphosphate gel with urea at 140 degrees C for 24 h. Chemical potential plots of the CO3HAp for estimation of its dissolution behavior suggested that the CO3HAp is more soluble than hydroxyapatite (HAp) and is as soluble as octacalcium phosphate (OCP) and/or beta -tricalcium phosphate (TCP). This material is expected to be applied to bioresorbable materials such as bone fillers.

Macroporous calcium phosphate glass-ceramic prepared by two-step pressing technique and using sucrose as a pore former

Macroporous calcium phosphate glass-ceramic with an initial glass composition of 60CaO.30P2O5.3TiO2.7Na2O in mol% was successfully prepared by sintering the mixture compact consisting of calcium phosphate glass and sucrose powders, which was formed using a two-step pressing technique. After burning off the sucrose phase, a 3D interconnected macroporous structure was formed in the sintered body, in which the skeleton consisting of the calcium phosphate glass-ceramic (including beta-calcium pyrophosphate and beta-tricalcium phosphate as the crystalline phases) was transformed from the initial glass during the sintering. The macropores with several hundred microns in diameter and the large interconnection size (approximately 100 microm), which result from the controllably large-sized sucrose particles and the hot-pressing at a little higher temperature than the sucrose's melting point, are believed to meet the requirements for cell adhesion and bone tissue regeneration well. Moreover, in vitro dissolution behavior study indicates that the calcium phosphate glass-ceramic is soluble to an acetic acid solution of pH 5-7. These, together with the simplicity and feasibility of the innovative fabrication method itself, show that the formed porous glass-ceramic has a promising potential for application to a scaffold for bone tissue engineering.

Processing of an apatite-mullite glass-ceramic and an hydroxyapatite/phosphate glass composite by selective laser sintering

The work presented details the results of an investigation into the feasibility of using Selective Laser Sintering (SLS) to directly produce customised bioceramic implants. The materials used were bioactive in nature and included a glass-ceramic and a combination of hydroxyapatite and phosphate glass. The glass-ceramic was selected from the range of apatite-mullite materials in the SiO2.Al2O3.CaO.CaF2.P2O5 series, due to their potentially suitable biological and mechanical properties. The hydroxyapatite and phosphate glass combination was chosen to allow an alternative production approach to be investigated. The viability of using both these materials with the SLS process was assessed and the process route and resulting material properties characterised using a variety of techniques including Differential Thermal Analysis (DTA), X-ray Diffraction (XRD) and Scanning Electron Microscopy (SEM). The results obtained indicate that it was possible to produce multiple layer components from both materials using the SLS process. The glass-ceramic materials could only be processed at very low scan speeds and powers, yielding relatively brittle components. It was though possible to produce parts from the hydroxyapatite and phosphate glass combination across a much wider range of parameters, producing parts which had a greater potential for possible implant production.

Synthesis of bioactive PMMA bone cement via modification with methacryloxypropyltri-methoxysilane and calcium acetate

Bone cement consisting of polymethylmethacrylate (PMMA) powder and methylmethacrylate (MMA) liquid is clinically used for fixation of implants such as artificial hip joints. However, it does not show bone-bonding ability, i.e., bioactivity. The lack of bioactivity would be one of factors which cause loosening between the cement and the implant. The present authors recently showed the potential of bioactive PMMA-based bone cement through modification with gamma-methacryloxypropyltrimethoxysilane (MPS) and calcium acetate. In this study, the effects of the kinds of PMMA powder on setting time, apatite formation and compressive strength were investigated in a simulated body fluid (Kokubo solution). The cement modified with calcium acetate calcined at 220 degrees C could set within 15 min when the PMMA powder had an average molecular weight of 100,000 or less. The addition of calcium acetate calcined at 120 degrees C in the PMMA powder required a much longer period for setting. The modified cements formed an apatite layer after soaking in the Kokubo solution within 1 day for cement starting from PMMA powder with a molecular weight of 100,000 or less. Compressive strengths of the modified cements were more than 70 MPa for cements starting from 100,000 and 56,000 in molecular weight. After soaking in Kokubo solution for 7 days, the modified cement consisting of PMMA powder of 100,000 in molecular weight showed a smaller decrease in compressive strength than that consisting of 56,000 in molecular weight. These results indicate that bioactive PMMA cement can be produced with appropriate setting time and mechanical strength when PMMA powders with a suitable molecular weight are used. Such a type of design of bioactive PMMA bone cement leads to a novel development of bioactive material for bone substitutes.

The crystallization of Hydroxyapatite in the presence of sodium alginate

The effect of sodium alginate on the crystal growth of hydroxyapatite (HAP) was investigated at sustained supersaturation by the constant composition technique. Sodium alginate was found to inhibit HAP crystal growth at low concentrations and reduced the crystal growth rates by 42-86% for inhibitor concentrations of 2.1x10(-7)-12.6x10(-7) mol/l. The inhibition effect on the crystal growth rate may be explained possibly through adsorption onto the active growth sites. A detailed kinetics analysis suggested a Langmuir-type adsorption of the alginate on HAP surface and a value of 1.63x10(7) l/mol was obtained for the affinity constant of sodium alginate for the surface of HAP. The apparent order for the crystallization reaction was determined to be approximately 2, thus suggesting a surface diffusion controlled spiral growth mechanism.

Effect of fiber diameter on spreading, proliferation, and differentiation of osteoblastic cells on electrospun poly(lactic acid) substrates

Electrospinning is a promising method to construct fused-fiber biomaterial scaffolds for tissue engineering applications, but the efficacy of this approach depends on how substrate topography affects cell function. Previously, it has been shown that linear, parallel raised features with length scales of 0.5-2 microm direct cell orientation through the phenomenon of contact guidance, and enhance phenotypic markers of osteoblastic differentiation. To determine how the linear, random raised features produced by electrospinning affect proliferation and differentiation of osteoprogenitor cells, poly(lactic acid) and poly(ethylene glycol)-poly(lactic acid) diblock copolymers were electrospun with mean fiber diameters of 0.14-2.1 microm onto rigid supports. MC3T3-E1 osteoprogenitor cells cultured on fiber surfaces in the absence of osteogenic factors exhibited a lower cell density after 7 and 14 days of culture than cells cultured on spin-coated surfaces, but cell density increased with fiber diameter. However, in the presence of osteogenic factors (2 mM beta-glycerophosphate, 0.13 mM L-ascorbate-2-phosphate), cell density after 7 and 14 days of culture on fiber surfaces was comparable to or exceeded spin-coated controls, and alkaline phosphatase activity after 14 days was comparable. Examination of cell morphology revealed that cells grown on fibers had smaller projected areas than those on planar surfaces. However, cells attached to electrospun substrates of 2.1 microm diameter fibers exhibited a higher cell aspect ratio than cells on smooth surfaces. These studies show that topographical factors designed into biomaterial scaffolds can regulate spreading, orientation, and proliferation of osteoblastic cells.

Process and kinetics of bonelike apatite formation on sintered hydroxyapatite in a simulated body fluid

The surfaces of two hydroxyapatites (HA), which have been sintered at different temperatures of 800 and 1200 degrees C, was investigated as a function of soaking time in simulated body fluid (SBF) using transmission electron microscopy (TEM) attached with energy-dispersive spectrometry (EDX) and laser electrophoresis spectroscopy. The TEM-EDX indicated that after soaking in SBF, both the HAs form bonelike apatite by undergoing the same surface structural change, i.e., formations of a Ca-rich amorphous or nano-crystalline calcium phosphate (ACP) and a Ca-poor ACP, which eventually crystallized into bonelike apatite. Zeta potential characterized by the electrophoresis indicated that during exposure to SBF, the HA surfaces reveal negative surface charge, thereby interacting with the positive calcium ions in the fluid to form the Ca-rich ACP, which gains positive surface charge. The Ca-rich ACP on the HAs then interacts with the negative phosphate ions in the fluid to form the Ca-poor ACP, which stabilizes by being crystallized into bonelike apatite with a low solubility in the SBF. The exposure times for formations of these phases of the Ca-rich ACP, the Ca-poor ACP as well as the apatite were, however, all late on HA sintered at 1200 degrees C, compared with the HA sintered at 800 degrees C. This phenomenon was attributed to a lower initial negative surface charge of the HA sintered at 800 degrees C than of that one sintered at 1200 degrees C, owing to poverty in surface hydroxyl and phosphate groups which are responsible for the surface negativity of the HA. These indicate that sintered temperature of HA might influence not in terms of the process but in terms of the rate of formation of biologically active bonelike apatite on its surface, through which the HA integrates with living bone.

Microstructures and bond strengths of plasma-sprayed hydroxyapatite coatings on porous titanium substrates

Hydroxyapatite (HA) coating was carried out by plasma spraying on bulk Ti substrates and porous Ti substrates having a Young's modulus similar to that of human bone. The microstructures and bond strengths of HA coatings were investigated in this study. The HA coatings with thickness of 200-250 microm were free from cracks at interfaces between the coating and Ti substrates. XRD analysis revealed that the HA powder used for plasma spraying had a highly crystallized apatite structure, while the HA coating contained several phases other than HA. The bond strength between the HA coating and the Ti substrates evaluated by standard bonding test (ASTM C633-01) were strongly affected by the failure behavior of the HA coating. A mechanism to explain the failure is discussed in terms of surface roughness of the plasma-sprayed HA coatings on the bulk and porous Ti substrates.

The effect of processing on the structural characteristics of vancomycin-loaded amorphous calcium phosphate matrices

Calcium polyphosphate antibiotic delivery matrices were prepared using a unique processing technique involving the exposure of calcium polyphosphate pastes to high humidity for 0, 5, 24 or 48 h to induce gelling. Subsequently, samples were dried for a minimum of 24 h. The mild conditions associated with matrix fabrication readily allowed for vancomycin incorporation within an environment that did not disrupt antibiotic activity. While reproducible from a processing standpoint, the gelling and drying process did contribute to a decrease in matrix tensile strength and the formation of significant pores near the surface of the matrices. Generally, the core of the gelled matrices appeared to be denser than their non-gelled counterparts. The degree of phosphate chain lysis during the gelling and drying stages was quantified using solution 31P nuclear magnetic resonance (NMR) spectroscopy. Both NMR and Raman spectroscopy indicated that the presence of vancomycin did not appreciably alter the matrix formation process. The ability to incorporate clinically relevant levels of antibiotic within this degradable bone substitute matrix suggests the potential of this approach for creating a localized antibiotic delivery system to treat osteomyelitis infections.

Composite formation from hydroxyapatite with sodium and potassium salts of polyphosphazene

The low temperature synthesis of composites potentially suitable as bone substitutes which form in vivo, was investigated. The composites were comprised of stoichiometric hydroxyapatite (SHAp) and water-soluble poly phosphazenes. These constituents were selected because of their biocompatibility, and were mixed as powders with a phosphate buffer solution (PBS) to form the composites. The effects of poly[bis(sodium carboxylatophenoxy)phosphazene] (Na-PCPP) or poly[bis(potassium carboxylatophenoxy) phosphazene] (K-PCPP) on stoichiometric hydroxyapatite (SHAp) formation from tetracalcium phosphate and anhydrous dicalcium phosphate were assessed. The kinetics and reaction chemistries of composite formation were followed by isothermal calorimetry, X-ray diffraction, infrared spectroscopy and scanning electron microscopy. In the presence of 1% by weight of polyphosphazenes, composites comprised of SHAp and calcium cross-linked polymer salts were formed. Thus a mechanism for binding between polymer chains was established. Elevated proportions (5 and 10% by weight) of polyphosphazene, however, resulted in the inhibition of SHAp formation. This is attributed to the formation of viscous polymer solution coatings on the calcium phosphate precursors, retarding their reaction, and consequently inhibiting SHAp formation.