Key Engineering Materials Vols. 284-286

Abstract: This study explores how a) the resin grafting potential for amorphous calcium phosphate (ACP) and b) particle size of ACP affects physicochemical properties of composites. Copolymers and composites were evaluated for biaxial flexure strength (BFS), degree of vinyl conversion (DC), mineral ion release and water sorption (WS). Milled ACP composites were superior to unmilled ACP composites and exhibited 62 % and 77 % higher BFS values (dry and wet state, respectively). The average DC of copolymers 24 h after curing was 80 %. DC of composites decreased 10.3 % for unmilled Zr-ACP and 4.6 % for milled Zr-ACP when compared to the corresponding copolymers. The WS increased as follows: copolymers < milled Zr-ACP composites < unmilled Zr-ACP composites. The levels of Ca and PO4 released from both types of composites increased with the increasing EBPADMA/TEGDMA ratio in the matrix. They were significantly above the minimum necessary for the redeposition of HAP to occur. No significant consumption of released calcium by the carboxylic groups of methacryloxyethyl phtahalate (MEP) occurred at a mass fraction of 2.6 % of MEP in the resin. Improvements in ACP composite’s physicochemical properties are achieved by fine tuning of the resin and improved ACP’s dispersion within the polymer matrix after ball-milling.

Abstract: A two component, capsule mixed dental restorative system based on a biomineral has been developed. After mixing the two components the material is to be regarded as a chemically bonded ceramic (CBC). In this work some basic mechanical properties has been evaluated and compared to high strength glass ionomer cement (GIC) and an amalgam. In addition the microstructure and fractured surfaces of the material has been investigated. The strength measurements show that the CBC material have comparable initial strength to an amalgam as measured by DTS. The flexural and the compressive strength of the fully hardened CBC material are comparable with a high strength GIC. The setting time showed to be easily adjustable and a final setting under 6 minutes can be reached. The microstructure of the CBC material shows that all components have been fully dispersed resulting in a homogenous microstructure. When looking at the fracture surface of tested DTS samples of the CBC material a “pull-out” effect was revealed originating from the fibres added to the composition to increase the strength.

Abstract: In the present work, a novel biocomposite has been developed based on lignin (Lig) and HA/b-TCP bioceramic materials. The Lig/HA and Lig/b-TCP systems were investigated by Scanning Electron Microscopy coupled to EDX microprobe (SEM/EDX). Lignin is a lignosulfonate natural polymer with complex random coupling and the exact chemical structure is yet unknown. FTIR spectroscopy is an important tool for lignin characterization based on several major vibration bands associated with generally found chemical groups. Consequently, FTIR spectroscopy was used to evaluate the chemical functionalities and major components present in the material. SEM photomicrographs of biocomposites Lig/HA and Lig/b-TCP have shown uniform dispersion of the natural polymer binder in the bioceramic matrix. Also, chemical composition obtained by EDX spectra have indicated lignin evenly distributed in the HA and b-TCP compounds. Novel biocomposites based on lignin/HA and lignin/b-TCP were developed with porosity ranging from 50 to 100 µm. These results have confirmed the high potential application of lignin as a non-toxic natural polymer binder to be used as 3D scaffold template for biomedical applications.

Abstract: The purpose of this study was to evaluate the physical properties of the composite membrane before and after soaking in simulated body fluid (SBF) and discuss both degradation and maintenance of their properties. Before and after soaking in SBF, some deposits were found on the preexisted apatite crystals, and Ca and P were mainly detected by energy dispersive X-ray analyzer (EDX). Our results suggest that the composite membrane consisting of apatite and the biodegradable PLGA copolymer would have excellent biocompatibility and maintain adequate physical properties for in vivo use.

Abstract: A ceramic-polymer nano-hybrid, in which the bioactive silicate surface is nano-hybridized with flexible silicone bulk, was synthesized in the tetraethoxysilane (TEOS)-polydimethylsiloxane (PDMS) sol-gel system. Different solutions for surface silicate and bulk silicone, whose component ratio of SiO2: PDMS were respectively 100: 0 and 50: 50, were subjected to lamination and delayed polymerization and condensation process, producing a large transparent crack-free monolithic bulk. Characterizations at near-surface cross-section of the hybrid bulk revealed typical bioactive silicate structure with no distinct interface with the interior, indicating possibility of a novel bioactive nano-composite with enhanced physical and biological functions.

Abstract: The possibility of enhancing mechanical properties by incorporation of polymeric components to sol-gel derived materials is extremely attractive to prepare macroporous scaffolds, leading to materials with potential applications in both hard and soft tissue regeneration. In this work bioactive glass-polyvinyl alcohol hybrids were developed and their mechanical behavior was evaluated. Hybrids were synthesized by adding polyvinyl alcohol to a sol-gel precursor solution, which was then foamed with the addition of a surfactant and vigorous agitation. The foams were cast, aged and dried at 40°C. A cleaning step to decrease the acidic character of the obtained hybrids was undertaken by immersion in a NH4OH solution. The mechanical behavior of the hybrids was evaluated in compression using both stress and strain control tests. Hybrid foams had a high porosity varying from 60-90% and the macropore diameter ranged from 10 to 600 µm. The modal macropore diameter varied with the inorganic phase composition and with the polymer content in the hybrid. The strain at fracture of the as prepared hybrid foams was substantially greater than pure gel-glass foams. The cleaned hybrids presented a slightly higher strength and lower deformation than the as prepared foams.

Abstract: In the present work we describe the synthesis of starch-based/BG 45S5 particles and their in vitro bioactivity behaviour by means of immersion in a simulated body fluid. The composite particles have shown to form a layer of Ca-P at their surface, whose nature was confirmed by chemical and morphological analysis. In order to evaluate the ability of these particles to be used as carriers for cell culture, undifferentiated rat cells were selected and parameters like cell adhesion, proliferation and expression of osteoblastic markers, were evaluated. The starch-based micro-particles have shown to support cellular activity, allowing cells to attach, proliferate and express specific markers while cultured in the particles surface. The final goal is to be able to use these particles as carriers for cells and simultaneously as in-situ forming constructs for tissue engineering and regenerative medicine applications.

Abstract: A bioactive chitosan-siloxane nano-hybrid material was newly developed and evaluated for the potential application as a bone graft material. The chitosan which can be dissolved in organic solvent was synthesized by the reaction with phtalic anhydride (Ph-Chitosan) and it was then reacted with 3-isocyanatopropyl triethoxysilane (Si-Chitosan) in dimethylformamide. Following this, the Si-Chitosan was hydrolyzed and condensed to yield a hybrid sol-gel material (Si-O-Chitosan). The gelation was carried out for 1 week at ambient condition in a covered Teflon mold with a few pinholes and then dried under vacuum at room temperature for 48 h. The bioactivity of the chitosan nano-hybrid material was evaluated by examining the apatite forming ability in the simulated body fluid (SBF). The surface microstructure and functional groups of the specimen was analyzed by field emission scanning electron microscopy and Fourier transformed infrared spectroscopy, respectively. The crystal phases of the specimen before and after the bioactivity testing were analyzed by thin film X-ray diffractometry. Newly developed chitosan nano-hybrid material showed apatite-forming ability in the SBF within 1 week soaking and this ability was believed to come from the silanol group formed on the surface of Si-O-Chitosan and calcium salt which increased the ionic activity product of apatite in the SBF.

Abstract: We investigated the biocompatibility, osteoconductivity, and biodegradability of porous composite of Hydroxyapatite (HA) and Poly D/L-lactide (PDLLA). At 6weeks afterimplantation to rabbit femoral condyle, HA/PDLLA was covered with bone and contacted with bone directly. The amounts of newly formed bone in the pores had increased during the examined period. By 26weeks, bone remodeling of formed bone in the pores was seen and bone marrow tissue formation was seen in the pores of HA/PDLLA. Porous HA/PDLLA was resorbed much faster than porous HA as a control. Porous HA/PDLLA was resorbed constantly through the bone formation and bone remodeling but porous HA was hardly resorbed during the period. It might be one of the desirable materials for bone substitute. To evaluate for a scaffold, disc shaped blocks loaded with rat bone marrow cell were implanted in the subcutaneous pouch of the back of syngeneic rat. At 3weeks afterimplantation, newly bone formation in the pores was observed at ectopic site. It also suggested the availability of this material as cell scaffolds.

Abstract: Ethylene-vinyl alcohol copolymer (EVOH), poly(ethylene terephthalate) (PET) and polyethylene (PE) were modified with calcium silicate on their surfaces by a sol-gel method, before or after glow discharge treatment in O2 gas, soaked in a simulated body fluid (SBF) and implanted into knee bone of a rabbit. EVOH and PET formed nano-sized bonelike apatite uniformly on their surfaces in SBF, without being subjected to the glow discharge, and bonded to the living bone of the rabbit, whereas PE formed the apatite only sparsely even when being subjected to the glow discharge. Three dimensional fabrics with open spaces in various sizes of the former fibers modified with the calcium silicate might be useful as bone substitutes.