Key Engineering Materials Vols. 493-494

Abstract: Chitosan-GPTMS (γ-Glycidoxypropyltrimethoxysilane) hybrid hydrogels were synthesized with β-glycerophosphate (β-GP) as the additive agent. Chitosan-GPTMS sols were fluid at room temperature and transformed to hydrogel at 36.5°C in several min. The gelation time of the hydrogels was shortened by the addition of GPTMS. From NMR experiments, this gelation behavior depended on some factors, namely, electrostatic interaction between the phosphate groups of β-GP and the amino groups of chitosan chains, crosslinking between the epoxy groups of GPTMS and the amino groups of chitosan, and polycondensation of the methoxy groups of GPTMS. The Si(IV) released from the hydrogels promoted the cell adhesion and ALP activity of osteoblastic cells MG63.

Abstract: The failure of organs and tissues caused by trauma and other injuries is one of the most costly of human health problems. It is estimated that 1.6 million people experience work limitations caused by osteoarthritis and related disorders, representing 8.3% of all main conditions. Joint injuries frequently lead to progressive joint degeneration and post-traumatic osteoarthritis. Articular cartilage has only a limited capacity for self-healing, mainly due to the fact that it is avascular; and once seriously damaged, articular cartilage lesions will not regenerate. There is strong evidence that cartilage lesions may lead to osteoarthritis when left untreated. Numerous animal experiments and clinical studies have shown that early biological reconstruction of circumscribed cartilage defects in the knee is superior to conservative or delayed surgical treatment. Tissue engineering has shown promising therapeutic strategies for repair or regeneration of damaged tissues. Currently, ceramic based and polymeric scaffolds have been developed to bring about the restoration of tissue functions. The bioceramics associated with water-soluble polymers have been developed as substitutes for various orthopedic applications. The objectives of this work are the processing and characterization of a composite of carboxymethylcellulose (CMC) and biphasic calcium phosphate (Biphasic Calcium Phosphate - BCP) in the form of a hydrogel, and a study of its cytotoxicity (in vitro), aimed at its application as an injectable biomaterial in order to repair the extracellular matrix of articular cartilage. The CMC and BCP were characterized by Fourier Transform Infrared Spectrometry (FTIR) and X-Ray Diffraction (XRD), X-ray fluorescence (XRF), respectively, and scanning electron microscopy (SEM) of powders and the composite. To evaluate the biological effect of the composite hydrogel, tests of cytotoxicity (MTT) and rheological tests under real conditions of use were performed. The composite of carboxymethylcellulose (CMC) and bioceramics (biphasic calcium phosphate-BCP) in the form of hydrogel showed an adequate injectability in the conditions studied, and a non-toxic response, presenting potential for use as fillers or to stimulate the healing of cartilage defects in the extracellular matrix of articular cartilage.

Abstract: Due to the lack of macroporosity in current available Calcium Phosphate cement used in osteoarticular surgery, Micro and Macroporous Biphasic CaP Cement (MCPC™) was developed. The MCPC™ concept was the association of a settable and a fast resorbable matrix and a sieved fraction of microporous biphasic calcium phosphate (BCP) granules, recognized for the high osteoconductive and osteogenic properties. During the resorption of the matrix, a porous structure is created and the osteoconductive effect of the granules promotes the bone ingrowth. A goat preclinical study was realized to evaluate the efficacy of MCPC™ for C3 and C4 vertebral body filling defects during 6 months. Bone remodelling was evidenced demonstrating bone ingrowth at the expense of the cement and surrounding the residual BCP granules. Bone trabeculae were observed coming from the spongious bone to the implant site. Human vertebral body filling cases demonstrated the biocompatibility and the safety of MCPC™ for bone reconstruction. Results of this study demonstrated the importance of special combination of calcium phosphate granules in the MCPC™ to provide macroporosity and scaffolding for newly formed bone.

Abstract: A new biphasic calcium phosphate ceramic material Hydros™ has been developed. The main attractive feature of BCP ceramic is their ability to form a strong direct bond with the host bone resulting in a strong interface. Currently, granules are more and more used in moldable, injectable bone substitutes. However, the biological behaviour of the particles can be influenced not only by chemical composition and crystallinity, but also by several parameters as microporosity and nano-micro sized particles. The aim of the study was to assess, in animal experiment, the role played by an Hydrated Putty Bioceramics (Hydros™), based on specific combination of hydrophilic micro and macrosized BCP particles, to obtain high osteogenic Injectable Bone Substitute. No sign of clinical rejection was noticed. In muscular area, no fibrous encapsulation was observed, degradation of the smaller particles is observed by macrophages and giant cells. At 12 weeks, more of 75% of BCP was resorbed. The biocompatibility and safety in human orthopaedic applications (tibial plateau fracture) has been demonstrated.

Abstract: A novel merwinite/ Poly(lactic-co-glycolic) nanocomposite was synthesized by a solvent casting/salt leaching technique with varying merwinite contents from 10 to 30% (w/w). Poly(lactic-co-glycolic) /merwinite foams with a co-continuous structure of interconnected pores were formed. The microstructure of the pores and the walls was controlled by varying the merwinite content. The pore structure becomes more and more irregular with increasing merwinite content. Pore sizes ranging from several microns to a few hundred microns were obtained. The degradation assessment of the scaffolds is performed in phosphate-buffered saline (PBS) solution at 37°C. Weight loss during storage at 37°C in PBS (pH 7.4) was determined for the scaffolds. Weight loss increased from pure to high content during incubation time. The prepared merwinite/ (Polylactic-co-glycolic) nanocomposite with uniform microstructure may be used in bone tissue engineering applications.

Abstract: Nano crystalline Hydroxyapatite (HAp) spheroids of uniform size distribution of diameter ~200 nm have been prepared by co-precipitation method at room temperature. The anionic surfactant SDS has been used as the template material. The calcinated samples were subjected to FTIR and XRD characterizations to confirm the phase of HAp. The Ca/P ratio that has been measured from the EDS spectrum 1.69 has good agreement with the theoretical value. The SEM and TEM images reveal the nano spherical nature and narrow size distribution of the HAp particles, which were good candidates for drug delivery applications.

Abstract: The encapsulation and immobilization of biomolecules on/in mesoporous silica materials (MPS) have been studied by using transmission electron microscopy (TEM). The mixture of tetraethyl orthosilicate (TEOS) and the triblock copolymer as a template was stirred, hydrothermally treated to form the mesoporous SBA-15 structure, and heat-treated at 550 °C. SEM observation indicated that long and narrow particles were linked together in the long axis direction to form secondary particles of SBA-15. UV-spectrometry was performed to determine the amount of bovine serum albumin (BSA), cytochrome C, myoglobin or -lactoglobulin encapsulated on/in SBA-15. The time profiles for adsorption of proteins can be well described by intraparticle diffusion model. The TEM observations of proteins on/in mesoporous SBA-15 revealed that proteins were embedded on/in mesoporous SBA-15 and the protein behaviors given by TEM observations may correspond to the intraparticle diffusion model.

Abstract: Various bone graft substitutes were used in clinical practise in the treatment of bone defects after trauma or osteoporosis. Many synthetic biomaterials were developed in recent years primarily based on hydroxyapatite (HA). NanoBone^® is a nanocrystalline hydroxyapatite (HA) embedded in a porous matrix of silica (SiO₂). The ratio of HA:SiO₂ varied between 76:24 (wt%; NanoBone^®) and 61:39 (wt%; Nanobone^® S). The two bone substitutes NB and NB S and a natural bovine bone substitute Bio-Oss^® (BO) were evaluated by means of implantation in the tibia of the rat. The aim of this study was to analyze the remodelling process and to measure new bone formation and degradation after implantation of these biomaterials. A tibia defect model was used for all investigations with testing periods of 12, 21 and 84 days. (n=5 for each time point). The results showed, that all bone grafts were well accepted by the host tissue without inflammatory reactions. In comparison to the biomaterial BO, NanoBone^® and NanoBone^® S were quickly degraded, whereas autologous proteins were incorporated into nanopores. New bone formation was statistically higher in NanoBone^® S compared to Bio-Oss^® in defect area after 84 days implantation. The presence of osteoclasts in tissue sections were demonstrated by TRAP- and ED1-immunohistology.

Abstract: The present work aims to examine the effect of silicon substitution on thermal and in-vitro dissolution properties of carbonated hydroxyapatite. Hydroxyapatite [Ca₁₀(PO₄)₆(OH)₂, HA], carbonate substituted hydroxyapatite [Ca₁₀(PO₄)_6-x(CO₃)_x(OH)₂, x=1, 1CHA] and carbonate, silicate co-substituted hydroxyapatite [Ca₁₀(PO₄)_6-x-y(CO₃)_x(SiO₄)_y(OH)₂, x=1,y=1, 1C1SiHA] nanoparticles were prepared by microwave synthesis method under identical processing conditions. The XRD results of HA, 1CHA and 1C1SiHA correspond to the standard hexagonal HA (JCPDS 9-432). The crystallite size and lattice strain of the synthesized powder particles were estimated by Williamson-Hall isotropic strain model (W-H ISM) from powder X-ray diffraction data. The dislocation density was calculated by Williamson-Smallman formula. The functional groups present in the as-synthesized powder particles were analyzed by Fourier transform infrared (FT-IR) spectroscopy method. The size and the morphology were examined using a transmission electron microscope (TEM). The in-vitro dissolution behaviour of the synthesized powder particles was studied by ethylenediamine tetra-acetic acid (EDTA) titrimetric method. The W-H ISM results confirm that the prepared powder particles of HA, 1CHA and 1C1SiHA are nanocrystalline with an average crystallite size of 40 nm, 36 nm and 32 nm, respectively. Thus the crystallite size of hydroxyapatite was observed to be decreased gradually with increase in substitutions as indicated by the least size for the 1C1SiHA. In addition, the XRD results of powders annealed at 900 °C for 2 h show the improved thermal stability of 1C1SiHA compared to 1CHA. The TEM results show rod-like shaped morphology for HA, near rod-like with modified edge morphology and increased agglomeration for 1CHA and needle-like shaped morphology for 1C1SiHA powder particles. The in-vitro dissolution study results show a gradual increase in the solubility of HA with carbonate and carbonate-silicate co-substitutions. The calculated microstructural parameters, namely, crystallite size, root mean squared strain and dislocation density were correlated with in-vitro dissolution behaviour of hydroxyapatites.

Abstract: In this study, magnetite (Fe₃O₄) nanoparticles were synthesized at room temperature using FeCl₃.6H₂O (1.28 M), FeCl₂.4H₂O (0.64 M) and HCl (0.4 M) for preparing a solution as the iron source and NaOH (0.9-1.5 M) for to prepare a solution as the alkali source by the aqueous phase co-precipitation method under vigorous mechanical stirring (450 and 750 rpm) together with N₂ gas flowing through the reaction medium during synthesis operation in closed system. The powder samples were characterized by the commonly used techniques of scanning electron microscope (SEM), transmission electron microscope (TEM), Fourier transform infra-red (FTIR), X-ray diffraction (XRD), vibrating sample magnetometry (VSM) and BET analyses. SEM was used to observe the morphology and agglomeration state of the powder. Size and morphology of the precipitated crystallites were examined with TEM. The prevalence of functional groups in the synthesized powders was ascertained by FTIR spectroscopy. The pure magnetite and other phases according to processing parameters were observed by XRD analysis. The magnetic properties of magnetite (Fe₃O₄) nanoparticles were examined using VSM. Finally, the specific surface area of nanoparticles was measured by BET technique. The results indicate that smaller particles can be synthesized by increasing stirring rate and decreasing the NaOH concentration, which in this case corresponded to 35 nm using 0.9 M NaOH at 750 rpm. The VSM analysis showed a saturation magnetization range of (82-96 emu/g) and coercivity of (83-119 Oe) for particles between (35-96 nm) respectively. Also, the highest specific surface area of 40 m²/g was obtained at 0.9 M NaOH at 750 rpm and the smallest value of 15 m²/g at 1.5 M of NaOH at 450 rpm using BET analysis.