Journal of Biomimetics, Biomaterials and Tissue Engineering Vol. 1

Abstract: The paper reports about different kind of sutures, their suitability and performance. An ideal suture should possess many characteristics such as - easy to handle, bio-compatibility, minimal tissue reaction, resistance to bacterial growth, adequate tensile strength and elasticity, knot security, strength loss versus healing rate of tissues. Selection of suture is often very complex for satisfying host of physical, mechanical and biological properties, and fulfilling contradictory requirements in varied applications. The paper develops an understanding about the selection of suture depending on the varied requirement. Past research work pertaining to the development of suture as reported in this paper, provides insight about the suitability of different surgical sutures and possible direction of future research.

Abstract: In this work, two systems of mesoporous bioactive glasses (MBGs) with a series of different SiO2:CaO:P2O5 ratios were derived via a sol-gel method involving the usage of block copolymers Pluronic F127 and P123 as templates, respectively. A two-dimensional hexagonal (P6mm) mesoporous structure was obtained in the two systems with a SiO2:CaO:P2O5 ratio of 80:16:4. With the decrease of the SiO2 content, the porous structure of MBGs became less regular, and the BET surface area and the pore volume were also decreased. Mesoporous bioactive glasses from the template F127 displayed a higher degree of bioactivity than those from the template P123, as a result of the existence of more defects on the walls of the mesopores.

Abstract: A general model of transport of gases in an artificial epidermal layer (membrane) was established. The model was developed based on Dusty Gas Model (DGM), solution diffusion and surface diffusion. As a result, solutions of the model for different transport conditions were derived. In this investigation, parameters of oxygen and carbon dioxide gases through an artificial “epidermal” membrane of varying porosity were used to calculate semi-empirical solutions of the general model. In other words, the solutions of the general model were analytically obtained for different transport conditions, using experimentally obtained parameters of oxygen and carbon dioxide gases through the artificial “epidermal” membrane of varying porosity. The obtained solutions of the general model were for the oxygen and carbon dioxide gases through the artificial “epidermal” membrane of the varying porosity.

Abstract: Hydroxyapatite-zirconia composites have received much attention during the last decade due to their combination of the desirable mechanical properties of zirconia and the excellent bioactivity of hydroxyapatite (HA). However, thermal decomposition of the hydroxyapatite phase and reaction between the zirconia phase and the hydroxyapatite phase remain a major problem in the hydroxyapatite-zirconia composites. In this study, thermally stable and fluorine-substituted hydroxyapatite (Ca10(PO4)6(OH)0.8F1.2; coded as HA06F) was prepared by a sol-gel method to replace the hydroxyapatite. Yttria-stabilized zirconia (YTZP) was also prepared by a sol-gel method in order to produce HA06F-YTZP composites with 5, 10, 15, 20, 40, and 60 wt% YTZP by simple and cost-effective pressureless sintering. Thermogravimetric analysis (TGA) and x-ray diffraction (XRD) of the HA06F-YTZP composites showed that the thermal stability of the HA06F matrices could be maintained when the YTZP content did not exceed 20 wt% and for sintering temperatures less than 1400 oC. Dilatometric analysis and microstructural observation revealed that the YTZP phase in the HA06F-YTZP composites retarded the densification of the composites if the zirconia content was over 20 wt%. Electron scanning microscopy (SEM) and high resolution transmission electron microscopy (HR-TEM) of the HA06F-YTZP composites showed that the YTZP second phase had a size in the nanometer scale and the reaction between the HA06F phase and the zirconia phase was suppressed. Mechanical properties including the Knoop hardness, the Young’s modulus, and the fracture toughness of the HA06F-YTZP composites increased with the YTZP content until the optimal content of 20 wt%; higher YTZP contents led to low mechanical properties due to poor densification of the composites and the severe thermal decomposition of the HA06F phase. The optimal HA06F-20YTZP composite also showed desirable attachment and proliferation of osteoblast cells. Nevertheless, the study of the composite system indicated the limitations of the pressureless sintering technique. To achieve the full potential of the composites for medium or low load bearing applications, a pressure-assisted sintering technique would still be necessary.

Abstract: Palmitic acid was added into drug-loaded poly(L-lactide) (PLLA) to modify the drug release profiles of the polymer. The acid was added in different concentrations and gradients across the thickness of the polymer. Drug release was monitored using a UV spectrometer over a period of 90 days. Degradation was studied using gel permeation chromatography and differential scanning calorimetry (DSC) to follow the change in the molecular weight and glass transition temperature respectively. Addition of palmitic acid was found to accelerate the degradation of PLLA and resulted in an accelerated release of the drug as expected. Modification of release profiles by designing the acid gradient was also attempted. It was found that the total acid concentration is still the dominant factor over the gradient design in affecting the degradation and subsequently the release profiles. Different drug concentrations also played a role in the different release profiles exhibited. Surprisingly the sample with lower drug concentration (2wt%) showed a much higher initial burst than the 5wt% loaded samples. This was due to the induced nucleation of the polymer by the drug at low concentration resulting in higher crystallinity of the polymer and consequently overall lower solubility of the drug.

Abstract: The aim of this study was to investigate the feasibility of utilizing selective laser sintering (SLS) to build 3D porous tissue engineering scaffolds from small quantities of poly(L-lactide) (PLLA). PLLA microspheres with suitable particle sizes for the SLS process were produced by the oil-in-water emulsion solvent evaporation technique. A miniature build platform was designed, fabricated and incorporated in an existing Sinterstation® 2000 system to enable small quantities of polymer powder to be used for the production of 3D porous scaffolds. Trial runs were first performed using the DuraForm™ polyamide powder and interfacing problems between the miniature build platform and the existing machine were solved. Then 3D porous scaffolds were successfully built from the PLLA microspheres using the modified SLS machine. This study paved the way for further comprehensive studies on selective laser sintering of tissue engineering scaffolds using expensive biopolymers and their composites.

Abstract: NiTi shape memory alloys are a group of materials which have a lot of applications especially in aerospace industries and medical equipments because of their excellent properties. Shape memory effect (SME), pseudo-elasticity (PE), high corrosion resistance and biocompatibility is special properties of these alloys which lead to their extensive applications. The superior behavior of NiTi alloy is due to thermoelastic martensitic phase transformation. In the present paper, two NiTi shape memory alloys were prepared by non-consumable vacuum arc melting technique in copper water cooled crucible. One of them had commercial elements and the other had high purity elements. Metallographic investigation, chemical analysis, XRD and DSC were carried out on two alloys. Metallographic observation and XRD shows that structure at ambient temperature consists of austenite phase besides Ti2Ni, Ni3Ti intermetallic compounds and martensite phase. Transformation investigation determines that the impurity such as iron in commercial alloy causes two stage phase transformation B2→R→B19′.

Abstract: The limitations of autogenic, allogenic and xenogenic grafting methods have led to the development of synthetic grafts as an alternative. The aim of this study was to manufacture highly porous and well interconnected hydroxyapatite scaffolds and modify them with a poly(lactic-co-glycolic acid) (PLGA)-bioactive glass composite coating to achieve mechanical properties close to those of natural cancellous bones. In this study, hydroxyapatite scaffolds were prepared from a calcium phosphate cement (CPC) powder and cell culture using fibroblast cells was done to examine the cytotoxicity of the materials used for the scaffolds. The average pore size of the scaffolds was found to be 650μm and the total porosity was about 80%. The hydroxyapatite scaffolds without the coating had a mean compressive strength and a mean compressive modulus of 0.74 MPa and 20.46 MPa, respectively, which were in contrast to those of the scaffolds coated with the PLGA-bioacitve glass composite material (1.36 MPa and 24.58 MPa, respectively). The fibroblast cells were observed to proliferate well on the PLGA-bioactive glass coated scaffolds. The cells had also penetrated into the scaffold to a depth of approximately 2mm. Thus the scaffolds fabricated in this study exhibited a favourable porous structure and good cell response which are desirable for bone tissue engineering.