Key Engineering Materials Vols. 342-343

Abstract: In bone tissue engineering, porous scaffolds served as the temporary matrix are often subjected to mechanical stress when implanted in the body. Based on this fact, the goal of this study was to examine the effects of mechanical loading on the in vitro degradation characteristics and kinetics of porous scaffolds in a custom-designed loading system. Porous Poly(L-lactic acid)/β-Tricalcium Phosphate (PLLA/β-TCP) composite scaffolds fabricated by using solution casting/compression molding/particulate leaching technique (SCP) were subjected to degradation in simulated body fluid (SBF) at 37°C for up to 6 weeks under the conditions: with and without static compressive loading, respectively. The results indicated that the increase of the porosity and decrease of the compressive strength under static compressive loading were slower than that of non-loading case, and so did the mass loss rate. It might be due to that the loading retarded the penetration, absorption and transfer of simulated body fluid. These data provide an important step towards understanding mechanical loading factors contributing to degradation.

Abstract: Biomaterials Center is composed of five groups and collaborate each other to examine interdisciplinary fields of biomaterials. In the ceramics-based biomaterials research, we have been developing three novel bone regeneration materials, i.e., high-porosity hydroxyapatite (HAp) ceramics with high-strength, guided bone regeneration (GBR) membranes and bone-like nanocomposite composed of HAp and collagen. The GBR membrane composed of β-tricalcium phosphate and biodegradable copolymer of lactide, glycolide and ε-caprolactone has thermoplastic, pH auto-adjustment and enough mechanical property to protect an invasion of surrounding tissues. With the membrane, bone defect up to 20 × 10 × 10 mm3 in length in mandibles and segmental bone defect up to 20 mm in length in tibiae of beagles are regenerated without any additional bone fillers or cell transplantations. The bone-like nanocomposite is synthesized by a co-precipitation of HAp and collagen via their self-organization. The dense composite has a half to quarter mechanical strength (40 MPa) to cortical bone and the porous one demonstrates sponge-like viscoelasticity. The composites implanted into bone are incorporated into bone remodeling metabolism like as autogenous bone graft, i.e., they are resorbed by osteolasts followed by osteogenesis by osteoblasts.

Abstract: In this study, muscle-derived stem cell (MDSC)/Pluronics/polycaprolactone (PCL) microparticle hybrid mixture was prepared as a potential injectable urethral bulking agent for the treatment of urinary incontinence. The MDSCs were isolated from the gastrocnemius muscles of SD rats by a modified preplate method and characterized through FACS analysis using various primary antibodies (CD34, Sca-1, CD45 and desmin). The hybrid mixture was prepared by the mixing of PCL microparticles (diameter, 100~200 μm) and MDSCs-containing thermo-sensitive Pluronic (F127/F68 mixture) solution (4.5/5.5, w/v). The hybrid mixture was easily injected through 18G needle into the body and stably remained in the applied site without initial volume decrease, owing to a well-packed structure of PCL particles exhibited in the hybrid mixture. It was observed that the MDSCs were stably grown in the hybrid mixture without severe inflammation and immune reaction. From the results, we recognized that the hybrid mixture can be a good candidate as an injectable bulking agent for the treatment of urinary incontinence, due to their good injectability, volume retention and biocompatibility.

Abstract: Chitosan cylindrical scaffolds with gradually increasing pore size along the longitudinal direction were fabricated by a novel centrifugation method to investigate pore size effect on cell interactions. The scaffold was fabricated by the centrifugation of a cylindrical mold containing fibril-like chitosans. The pore size ranges of the scaffold could be controlled by adjusting the centrifugal speed: the scaffold with gradually increasing pore size (from ~80 #m to ~400 #m) and porosity (from ~82 % to ~93 %) along the cylindrical axis was obtained by applying the centrifugal speed, 3,000 rpm. The scaffold sections were examined for their in vitro cell interactions using different kinds of cells (fibroblasts, chondrocytes, and osteoblasts) in terms of scaffold pore sizes. It was observed that different kinds of cells were shown to have different pore size ranges in the scaffold for effective cell growth. The chitosan scaffold section with ~400 #m pore size showed better cell growth for chondrocytes and osteoblasts, while the scaffold section with ~190 #m pore size was better for fibroblast growth. The pore size gradient scaffolds fabricated by the centrifugation method can be a good tool for the systematic studies of the interactions between cells or tissues and scaffolds with different pore size.

Abstract: Porous polydioxanone (PDO)/polyvinyl alcohol (PVA) scaffolds were fabricated by blending PDO with a small amount of PVA to improve the hydrophilicity and cell/tissue compatibility of the scaffolds for tissue engineering applications. PDO/PVA scaffolds with different PVA compositions up to 10 wt% were fabricated by a melt-molding particulate-leaching method (non-solvent method). The prepared scaffolds exhibited highly porous, uniform open-cellular pore structures. The PDO/PVA scaffolds with PVA compositions more than 5 % were easily wetted in cell culture medium. The hydrophilized PDO/PVA (5 wt%) scaffold showed better cell adhesion and growth than the control hydrophobic PDO scaffold. The PDO/PVA (5 wt%) scaffold also showed faster tissue infiltration into the scaffold than the PDO scaffold. It seems that 5 wt% addition of PVA to PDO to fabricate PDO/PVA scaffolds is enough for improving the hydrophilicity and cell/tissue compatibility of the scaffolds.

Abstract: Electrospinning is a fabrication process that can produce highly porous nano-scale fiber-based matrices using an electrostatically driven jet of polymer solution. This method represents an attractive approach for polymeric biomaterial processing which provides the membrane structure that may retain mechanical strengths, flexibility, and high surface area. In this study, we prepared a guided bone regeneration (GBR) membrane with selective permeability, hydrophilicity, good mechanical strength and adhesiveness with bone using polycaprolactone (PCL) and Tween 80 by the electrospinning method. The prepared PCL and PCL/Tween 80 electrospun sheets were characterized via morphology observation, mechanical property, water absorbability, and model nutrient permeability. It was observed that the PCL/Tween 80 (3 wt%) electrospun sheet have an effective permeation of nutrients as well as the good mechanical strength to maintain a secluded space for the bone regeneration. From the results, the hydrophilized PCL/Tween 80 (3 wt%) electrospun sheet seem to be a good candidate as a GBR membrane.

Abstract: Biodegradable porous poly(L-lactic acid) (PLLA) scaffolds were prepared using gas foaming method. The PLLA scaffolds with a hydrophobic surface were subjected to Ar plasma treatment and in situ acrylic acid (AA) grafting to obtain hydrophilic PLLA scaffold (PLLA-PAA). Cell-adhesive RGD peptide was then immobilized onto the AA-grafted PLLA (PLLA-PAA-RGD). Once rabbit bone marrow-derived mesenchymal stem cells (BM-MSC) were isolated, MSCs were seeded into PLLA control, PLLA-PAA, and PLLA-PAA-RGD scaffold and cultured for up to 4 weeks in chondrogenic medium with the addition of 10 ng/ml transforming growth factor (TGF)-β1. Surface analysis of AA-grafted PLLA identified significant alterations of surface characteristics, including reduced contact angle and different atomic compositions. From WST-1 assay at 4 weeks, cells were found more proliferative in PLLA-PAA than the others. Upon the histological analysis of Safranin O staining, chondrogenic differentiation of MSCs appeared to be progressed more actively in PLLA-PAA. The effect of RGD immobilization on MSC differentiation was barely notable.

Abstract: Pluronic F127 has received increasing attention over many years as drug delivery systems, biomaterials, and hydrogels for tissue engineering. In this study, we synthesized temperature-sensitive and cell-adhesive triblock F127 copolymers, in which Arg-Gly-Asp (RGD) peptide ligand was grafted to Pluronic F127-4-methacryloxyethyl trimellitic anhydride (4-META) to obtain F127-META-RGD. The chemical structures of the F127-META-RGD block copolymers were confirmed by FTIR, 1H and 13C NMR, and GPC. The resultant F127-META-RGD showed very similar thermosensitive behaviors to F127 and F127-META. The critical micelle temperature (CMT) of the F127 copolymers decreased in the order of F127 < F127-META < F127-META-RGD, whereas the particle size followed an opposite trend. Interactions between the F127 copolymers and adipose-derived stem cells (ASC) were evaluated in terms of cell adhesion and proliferation on the hydrogel. These thermosensitive RGD-grafted Pluronic hydrogels that display the enhanced cell adhesiveness, are expected to be useful as a functional injectable scaffold for tissue engineering.

Abstract: In prior work we have shown that titanium oxide (Ti-O) thin films have good blood compatibility. However, as well as being hemocompatible, biomaterials used in contact with blood should be cell compatible also. In the work described here, Ti-O films were synthesized using unbalanced magnetron sputtering (UBMS) and were modified by immobilizing laminin on the film surface for improving human umbilical vein endothelial cell (HUVEC) adhesion and growth. Scanning electron microscopy (SEM), Fourier Transform Infrared spectroscopy (FTIR) and contact-angle measurements were used to investigate the surface characteristics of the Ti-O films and the modified Ti-O films. The results suggest that Laminin can be biochemically immobilized on the Ti-O film surface. The modified layer of Laminin can improve the hydrophilicity and wettability of Ti-O films. In vitro HUVEC investigations reveal that Laminin immobilized on the film surface greatly enhances cell adhesion and growth on Ti-O films.

Abstract: Macrophages play a critical role in inflammatory response to implanted biomaterials and formation of restenosis. Macrophage adhesion may lead to macrophage activation and smooth muscle cell proliferation. Titanium oxide films on stainless steel are potential biomaterials for application to vascular stents. They have different influences on smooth muscle cell proliferation in in vivo tests, which could be the main reason for restenosis, but the mechanism is not clear. In this study we show that titanium oxide films can reduce inflammatory reaction with macrophages. Unstimulated macrophages release small amounts of chemical substance such as NO and give slight effect on smooth muscle cell proliferation.