Advances in Composite Materials and Structures

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Authors: Chan Wai Chan, Ling Qin, K.M. Lee, H.Y. Yeung, Yun Yu Hu, K.H.K. Wong, R.C.L. Yip, Jack C.Y. Cheng
Abstract: Grafting of autologous iliac crest and decortication approach in posterior spinal fusion surgery has been the “gold standard”. However, the limited source of autograft has prompted extensive research into bone substitute and biological enhancement of the fusion mass. In this study, the application of stem cell therapy by tissue engineering method was investigated to enhance posterior spinal fusion with -tricalcium phosphate ceramics in rabbit model. Rabbit bone marrow derived mesenchymal stem cells were aspirated from trochanter region of proximal femur. The mesenchymal stem cells were grown and directed to differentiate into osteogenic cells by osteogenic supplement (ascorbic acid, -glycerophosphate and dexamethasone) in basal medium (10% FBS in DMEM). The osteogenic cells were seeded on tricalcium phosphate ceramics for one day (MSC group, n=6). The cell-ceramics composite was implanted onto autologous L5 and L6 transverse processes with decortication approach in posterior spinal fusion. The cell free ceramics acts as control (Control group, n=6) and iliac crest autograft as positive control (Autograft group). The spinal segments were harvested at week 7 post-operation. Manual palpation was performed with spinal segments to assess any movement of L5-L6 vertebral joint. The stiffness of the joint was considered as solid fusion. The specimens then were fixed by formalin and transferred to 70% ethanol. The BMC and volume of fusion transverse processes of L5 and L6 was measured by peripheral quantitative computed tomography. In manual palpation, 50% solid fusion was found in MSC group, 60% in autograft group but none in control group. Moreover, the BMC of L5 and L6 transverse processes in MSC group was greater than autograft and control group (45%, 40% respectively, p<0.01). The volume of transverse processes in MSC group was greater than autograft by 45% (p<0.01) and control group by 26% (p<0.05). In conclusion, the mesenchymal stem cells derived osteogenic cells augmented spinal fusion and bone mineralization.
Authors: H.Y. Yeung, Ling Qin, K.M. Lee, K.S. Leung, Jack C.Y. Cheng
Abstract: Porous calcium phosphate ceramics have been widely investigated in orthopaedic surgery as bone extensor. Attention has been given to manufacturing of a porous bioceramic that mimics the trabecular bone structure for proper bone regeneration and integration. Although different methods have been applied to manufacture the porous structure, it was unable to visualize the pores and their interconnections within the ceramic and had objective measurement of the calcium phosphate ceramics. With the advance of biomedical imaging through micro-computed tomography (microCT), the study attempted to quantify the pore structure of different calcium phosphate ceramics. Three kinds of bioceramic blocks, namely BSC, ChronOS, and THA, were synthesized by three methods and tested in the study. Six blocks of each bioceramic were evaluated by conventional water immersion method and microCT. The pore size and connectivity of the pores were evaluated with standardized protocols. The three-dimensional analysis of the pores and their distribution by microCT was presented. The ChronOS had more functional pores (200-400μm in diameter) than the BSC and THA did (p<0.05). Providing objective information on the functional pores, the microCT evaluation serves as a good standard for specification of the bioceramic-related implants.
Authors: Ai Hua Yao, De Ping Wang, Wen Hai Huang
Abstract: PEG-modified ZnGd0.1Fe1.9O4 ferrite nanoparticles were synthesized by a coprecipitation process combined with a microemulsion technique. The effect of modification on the structure, magnetic properties of ZnGd0.1Fe1.9O4 nanoparticles was also investigated by XRD, FTIR, TEM and VSM. The results showed immobilizing PEG on the surfaces of magnetic nanoparticles effectively improved their dispersibility. Magnetic measurements indicated that the as-prepared PEG-modified nanoparticles exhibited relatively high magnetic properties, although a slight reduction in saturation and remanent magnetization were observed compared with unmodified samples. Therefore, with promising high magnetic behavior and potentially good biocompatibility, PEG-modified ZnGd0.1Fe1.9O4 ferrite nanoparticles would be feasible as thermoseeds for interstitial hyperthermia to tumor.
Authors: Yun Chen, Arthur F.T. Mak, Min Wang
Abstract: Bonelike apatite coating was formed on poly(L-lactic acid) (PLLA) scaffolds and poly(glycolic acid) (PGA) scaffolds in 24 hours through an accelerated biomimetic process. The ion concentrations in the simulated body fluid (SBF) were nearly 5 times of those in human blood plasma. The apatite formed in 5SBF was similar in morphology and composition to that formed in the classical biomimetic process employing SBF or 1.5SBF, and similar to that of natural bone. To facilitate coating into scaffolds, the flowing condition was introduced into the accelerated biomimetic process. It was found that the accelerated biomimetic process performed in the flowing condition yielded more uniform spatial distribution of apatite particles than that in the regular shaking condition.
Authors: Ya Liu, Min Wang
Abstract: Two series of bioactive and biodegradable composite materials consisting of particulate β-tricalcium phosphate (β-TCP) and polyhydroxybutyrate (PHB) and its copolymer polyhydroxybutyrate-co-hydroxyvalerate (PHBV) were produced and investigated for bone tissue repair. A manufacturing route employing injection moulding was established for producing the biomedical composites. In the process, plates of composites containing 10%, 20%, 30% or 40% by volume of micro-sized TCP particles were successfully injection moulded for both TCP/PHB and TCP/PHBV composites. Thermal properties of as-produced TCP/PHB and TCP/PHBV composites were systematically evaluated using differential scanning calorimetry (DSC). The mechanical performance of TCP/PHB and TCP/PHBV composites was assessed using dynamic mechanical analysis (DMA).
Authors: Wen You Zhou, Min Wang, W.L. Cheung
Abstract: Nano-sized carbonated hydroxyapatite (CHAp) particles were firstly synthesized using a nanoemulsion method. TEM analyses revealed that as-synthesized nanoparticles were calcium-deficient and spherical in shape (diameter: 16.8±2.6nm). Biocomposite microspheres comprising CHAp nanoparticles and poly(L-lactide) (PLLA) were fabricated using the single emulsion solvent evaporation technique. SEM images showed that composite microspheres were mainly 5-30 μm in size despite the change of CHAp nanoparticle content. When the CHAp nanoparticle content in composite microspheres was below 10 wt%, all nanoparticles were encapsulated within the microspheres which possessed a nanocomposite structure. DSC results showed that the crystallinity of the PLLA matrix of microspheres increased from 38 to 42% when the CHAp nanoparticle content was increased from 0 to 20 wt%. The biocomposite microspheres should be a suitable material for constructing bone tissue engineering scaffolds.
Authors: Wen You Zhou, S.H. Lee, Min Wang, W.L. Cheung
Abstract: This paper reports a study on the modification of a commercial selective laser sintering (SLS) machine for the fabrication of tissue engineering scaffolds from small quantities of poly(L-lactide) (PLLA) microspheres. A miniature build platform was designed, fabricated and installed in the build cylinder of a Sinterstation 2000 system. Porous scaffolds in the form of rectangular prism, 12.7×12.7×25.4 mm3, with interconnected square and round channels were designed using SolidWorks. For initial trials, DuraFormTM polyamide powder was used to build scaffolds with a designed porosity of ~70%. The actual porosity was found to be ~83%, which indicated that the sintered regions were not fully dense. PLLA microspheres in the size range of 5-30 μm were made using an oil-in-water emulsion solvent evaporation procedure and they were suitable for the SLS process. A porous scaffold was sintered from the PLLA microspheres with a laser power of 15W and a part bed temperature of 60oC. SEM examination showed that the PLLA microspheres were partially melted to form the scaffold. This study has demonstrated that it is feasible to build tissue engineering scaffolds from small amounts of biomaterials using a commercial SLS machine with suitable modifications.
Authors: Naznin Sultana, Min Wang
Abstract: This paper reports the fabrication and characterization of three-dimensional, highly porous polyhydroxybutyrate (PHB), polyhydroxybutyrate-co-valerate (PHBV) and composite scaffolds made by the emulsion freezing / freezing-drying technique. Freeze-drying of the polymer/solvent/ water phase emulsions produced hard and tough scaffolds with interconnected pores. The effects of the fabrication parameters such as polymer concentration in emulsions and emulsion stabilizer were examined and optimized. The density of polymer scaffolds was found to increase with an increasing polymer concentration. Structural analyses of selected samples using scanning electron microscopy indicated that the scaffolds had pore sizes ranging from several microns to a few hundred microns. The porosity of scaffolds of up to 85% was achieved and it increased with a decreasing polymer concentration. It was found that mechanical properties of composite scaffolds increased with the increasing amount of hydroxyapatite (HA) incorporated in the scaffolds.

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