Journal of Biomimetics, Biomaterials and Tissue Engineering Vol. 14

Abstract: Osteogenic differentiation of mesenchymal stem cells (MSC) is important in the field of bone tissue engineering. The identification of biological factors that influence osteogenesis is vital for developing a broader understanding of how complex microenvironments play a role in differentiation. The aim of this study was to demonstrate that adipose-derived stem cell (ADSC) osteogenesis is enhanced through interaction with extracellular matrices (ECM) secreted by ADSC undergoing osteogenesis. ADSC were obtained from human patients following elective abdominoplasty. Cells were selected for plastic adherence, characterized, and induced to differentiate using osteogenic supplements (OS; dexamethasone, ascorbic acid, and beta-glycerol phosphate). Cells were removed at several time points during osteogenesis and the secreted ECM was isolated. Undifferentiated cells were re-seeded onto the cell secreted ECMs and induced to differentiate with OS. At several time points, cells cultured on ECMs or tissue culture plastic controls (i.e. uncoated surface) were collected and RNA isolated. QPCR and gene array analysis revealed enrichment of osteogenic markers and more rapid progression through osteogenic maturational phases in cells seeded onto ECM secreted at the midpoint in differentiation (ca. 15 days). Our results demonstrate that the cumulative deposition of ECM reaches a critical point at approximately 15 days, before which there appear to be no definitive osteogenic cues from the matrix, and after which, strong drivers of osteogenesis are present. The creation of microenvironments that contain essential morphogenic matrix signals is an important step towards methods of growing and differentiating MSC in a rapid effective manner, particularly for bone-related clinical applications.

Abstract: Tissue engineering of airway tissues poses many complex challenges. As tissue form is determined by function and vice versa, it is necessary to consider mechanical and physiological constraints in conjunction with standard biologic and biochemical factors when culturing tissues in vitro. This study involved the development and validation of a novel 3-dimensional (3-D) construct with the capacity to periodically expose a cell scaffold to air and medium at application of physiologic strain rates. The ultimate objective was to mimic respiratory conditions experienced by airway tissues during breathing whilst ensuring compatibility with proven cell culture techniques. The Biaxx design consists of an elastomeric porous synthetic scaffold integrated with a unique biopolymer coupling unit which engages with an IAXSYS bioreactor actuator. Uniform biaxial strain was imparted by the coupling unit whilst simultaneously creating a periodic air-liquid interface. Biaxx scaffolds with and without a coating of particulate 45S5 bioglass were employed in an assay to assess cell attachment and proliferation whilst subject to periodic strain. Physiologic lung tissue strain of 5-15% was achieved for over 200,000 cycles at 0.2Hz. Preliminary biological studies with H460 human lung carcinoma cells confirmed cell attachment, growth and proliferation on this promising construct.

Abstract: Severe damage is produced in tissues by freezing and thawing. Until now, a great majority of the studies are performed qualitatively, lacking any quantitative approach. An important step is to choose the best option among different freezing methods. To approach the complex problem of damage produced in tissues by freezing, in this paper we present the classical mechanics approach and a quantitative study making use of a fractal methodology (evaluation of fractal dimension by box-counting method). A comparative fractal analysis between two different steps of freezing the human thoracic diaphragm muscle has been performed to quantify the voids and cracks produced by freezing (samples were placed in a cryostat chamber). Moreover, a standard Euclidean morphometry was performed to determine area and shape of the muscle nuclei after the two steps of freezing. Fractal dimension of the ice-tissue interface structures increased with decreasing temperature (p<0.0001), percentage of cell muscle decreased (p<0.01), while standard morphometry of the nuclei didnt show any modifications. Our results show the ability of the fractal approach to accurately quantify the damage produced by freezing and reveals that the lowest temperature produces the most damage.

Abstract: Following a polyelectrolytical complex reaction, the poly-L-ornithine (PLO)-alginate microcapsules were prepared by coating PLO on calcium alginate beads which were produced by a high-voltage electrostatic droplet generator. The biocompatibility of the microcapsules at the molecular level was evaluated through investigating the mRNA expression of pro-inflammatory cytokines; that is, the effect of the PLO coating of alginate beads on the mRNA expression of TNF-α, IL-1β, and IL-6 were measured using the RT-PCR method. The resulting PLO-coated alginate microcapsules have a smooth surface with a mean diameter of 309µm. The molecular biocompatibility studies show that coating microcapsules with PLO has no significant effect on the biocompatibility of alginate microcapsules (p>0.05), and both alginate microcapsules and PLO-coated microcapsules are significantly different from the positive control (p<0.05); however, both are also capable of causing an inflammatory response at a molecular level since both are significantly different from the blank control (p<0.05). Furthermore, with the increase in concentration of microcapsules or co-cultured time, part of the mRNA expression of cytokines is significantly increased. The results also demonstrate that the method used in this study, co-incubating the microcapsules with macrophages and measuring the mRNA expression of cytokines by RT-PCR, may be a useful method for evaluating the biocompatibility of coating materials of microcapsules.

Abstract: In the present work, samples were prepared allowing yeast to grow simply on YPDA-agar medium at a particular incubation temperature using streaking procedure. Doped specimens of yeast were prepared using YPDA-agar medium in presence of ZnO and TiO₂ nanoparticles in a nutrient medium for yeast. ZnO and TiO₂ nanoparticles for delivery over yeast cell were prepared with Gum Arabica and Ethanol (CH₃CH₂OH) respectively as capping agent. Specimens were also developed by laser irradiation on the ZnO doped nanoclusters and pure yeast. FTIR spectroscopy was employed to investigate the effects of nanoclusters and laser irradiation over yeast cell under different conditions. Application of laser irradiation exhibits some positive effect on pure yeast. Effect of ZnO and TiO₂ nanocluster doping on yeast are found to be toxic over Yeast Amide in general. Laser irradiation on nanocluster doped yeast cell enhanced the toxicity of nanoclusters. The later part of this study confirms the destruction of Amides in yeast. This preliminary work is an in-vivo application of drug delivery principle using ZnO nanocluster in Gum Arabica background.

Abstract: Wollastonite coatings on titanium alloys substrates were prepared by sol-gel with different heat treatment temperatures. Microstructures of the specimens were analyzed by XRD. SEM was used to observe surface morphologies of wollastonite coatings. The results show that with the heat treatment temperature increasing, the amorphous coating transforms to a crystalline coating. There are many pores in coatings prepared by sol-gel when heat treatment temperature higher than 900°C with the PH value to 2.5. There are no cracks in coating under such conditions.

Abstract: In this study, dense, fine-grained biphasic calcium phosphate bioceramics were designed via sintering method. nanosize hydroxyapatite / β-tricalcium (HA/β-TCP) phosphate powders with average grain size of 80 nm were prepared by the wet chemical precipitation method with calcium nitrate and di-ammonium hydrogen phosphate as calcium and phosphorus precursors, respectively. The precipitation process employed was also found to be suitable for the production of sub-micrometre HA/β-TCP powder in situ. The sinterability of the nanosize powders, and the microstructure, mechanical strength of the prepared HA/β-TCP bioceramics were investigated. Bioceramic sample characterization was achieved by powder X-ray diffraction (XRD), scanning electron microscopy (SEM), fourier transform infrared spectroscopy (FTIR), and density measurements. Powders compacted and sintered at 800, 900, 1000 and 1100°C showed an increase in relative density from 57% to 93%. The results revealed that the maximum hardness of 229 H_V was obtained for HA/β-TCP sintered at 1100°C.

Abstract: PSZ (ZrO₂ Fiber)-reinforced HAp was sintered using conventional and microwave hybrid heating. Microwave heating cycles were ~50 times faster than conventional sintering cycles and enabled the use of reduced densification temperatures and soak times by as much as ~100°C and 55 min, respectively. However, although there was a significant improvement in densification levels attainable before decomposition, the improvements were insufficient to produce near-fully or fully dense samples. However, the promising gains made suggest that microwave hot pressing would be a suitable area for future work. Keywords: Hydroxyapatite, microwave sintering, fibre-reinforced ceramics, bioceramics, zirconia fibre