Papers by Author: Soo Hyun Kim

Abstract: Mechano-active scaffolds were fabricated from very elastic poly(lactide-co-carprolactone) by a gel-pressing method. The scaffolds were seeded with bone marrow stromal cells and the continuous compressive deformation was applied to cell-polymer constructs in the chondrogenic media. Then, they were implanted in nude mice subcutaneously to evaluate for the effect of dynamic compression for regeneration of cartilage. From the biochemical analyses, chondrogenic differentiation was sustained and enhanced significantly and chondral extracellular matrix was increased through mechanical stimulation. Histological analyses showed that implants stimulated mechanically formed mature and well-developed cartilaginous tissue, as evidenced by bone marrow derived chondrocytes within lacunae. Consequently, the periodic application of dynamic compression can encourage bone marrow stromal cells to differentiation to chondrogenic lineage and to maintain their phenotypes.

Abstract: Mechano-active scaffolds were fabricated from very elastic poly(L-lactide-co-ε-carprolactone). The scaffolds with 80 % porosity and 300~500 μm pore size were prepared by a gel-pressing method. As a control group for elastic properties of polymer scaffolds, rigid poly L-lactide scaffolds were fabricated. The scaffolds were seeded with chondrocytes and cultured to evaluate the effect of elastic properties of polymer scaffolds for the differentiation and the ECM secretion of chondrocytes. Also, the chondrocytes-seeded constructs were implanted in nude mice subcutaneously to investigate their biocompatibility and cartilage formation. From the biochemical analyses, chondrogenic differentiation was sustained and enhanced significantly and chondral extracellular matrix was increased through mechanical stimulation of dynamic environment in the dynamic body systems. Histological analysis showed that implants of PLCL constructs formed mature and well-developed cartilaginous tissue, as evidenced by chondrocytes within lacunae. Consequently, the elastic PLCL scaffolds could be used to engineer cartilage in mechanically dynamic environments

Abstract: In cartilage tissue engineering, as a cell source, adult stem cells are very attractive for clinical applications. Recent studies suggest that human adipose tissue-derived stromal cells (ASCs) have multilineage potential similar to bone marrow-derived stromal cells (BMSCs). ASCs are obtained from adipose tissue easily isolated by suction-assisted lipectomy in various body parts. Also, as one of major factors of cartilage tissue engineering, scaffolds have an important role in cartilage formation. Poly(L-lactide-co-ε-carprolactone) scaffolds have physiological activity, biodegradability, high cell affinity, and mechano-activity. The object of this study is cartilaginous tissue formation using highly elastic PLCL scaffolds and ASCs in vitro and in vivo. Poly(L-lactide-co-ε-carprolactone) copolymers were synthesized from lactide and ε-carprolactone in the presence of stannous octoate as catalyst. The scaffolds with 85% porosity and 300-500μm pore size were fabricated by gel-pressing method. ASCs were seeded on scaffolds and cultured for 21days in vitro. Cell/polymer constructs were characterized by reverse transcriptase-polymerase chain reaction for confirming differentiation to chondrocytes onto PLCL scaffolds. Also, for examining cartilaginous tissue formation in vivo, ASCs seeded scaffolds which were induced chondrogenesis for 2 weeks were implanted in nude mice subcutaneously for up to 8weeks. Histological studies showed that implants partially developed cartilaginous tissue within lacunae. And there was an accumulation of sulfated glycoaminoglycans. Immunohistochemical analysis revealed that implants were positively stained for specific extracellular matrix. These results indicate that ASCs and PLCL scaffols could be used to cartilage tissue engineering.

Abstract: Porosity and pore size are needed for successful cell seeding and proliferation into porous scaffolds. This study was focused on a hydrogel-seeding method to improve cell adhesion and proliferation in tubular porous scaffolds for vascular grafts application. Tubular scaffolds were fabricated from a biodegradable elastic polymer, poly(L-lactide-co-ε-caprolactone) (PLCL) (50:50, Mn 1.58×105), by an extrusion-particulate leaching method. Vascular smooth muscle cells (VSMCs) were dispersed in collagen hydrogel and then seeded into the tubular PLCL scaffolds having various pore sizes, 50-100 μm, 100-200 μm, and 300-500 μm, respectively. As a result, the efficiency of cell adhesion and proliferation was dependent on the pore size of the scaffolds. Especially, the cell proliferation efficiency was improved by using the hydrogel-seeding method as compared with by using a previously established method. In summary, this study demonstrates that the efficiency of cell adhesion and proliferation was dependent on the pore size of the scaffolds in the hydrogel-seeding method.

Abstract: A tubular and fibrous scaffold was fabricated from an elastic polymer, poly (L-lactideco- ε-caprolactone) (PLCL; Mn 193,813, Mw 538,623) 50:50 by using a novel gel spinning apparatus. To characterize the gel-spun scaffold, we investigated morphology, tensile property, tissue in-growth rate and degradation rate. From SEM images, fibrous structure in the scaffold wasn’t fabricated well in the condition of 4% gel concentration. In general, the thickness level of microfibers increased as the gel concentration increased. In addition, the gel-spun scaffolds showed stronger tensile properties in the circumferential direction than the longitudinal direction. 5%, 7.5%, 10% and 12.5% scaffolds were analyzed in both directions: circumferential direction and longitudinal direction. On the other hand, the gel-spun scaffolds have been implanted in mouse to examine the degradation rate in vivo and tissue in-growth aspects, compared to extruded scaffolds. Both shows very similar degradation rates, but the aspect in tissue in-growth was different. In conclusion, gel-spun PLCL scaffolds have good characteristics as a plausible scaffold for cardiovascular tissue engineering.

Abstract: We have developed a direct conjugation method of RGD (Arg-Gly-Asp) into polylactide (PLA) using co-solvent system, which showed high reaction yield compared to one solvent system presumably due to good solubility of reactants. First, hydroxyl groups at the end of PLA were changed into carboxyl acid by ring opening reaction of succinic anhydride. For a coupling reaction with high solubility, RGD was dissolved in water and then PLA in dioxane was added into RGD solution in the presence of 1-(3-dimenthylaminopropyl)3-ethylcarbodiimide hydrochloride (EDC). The conjugation of RGD was confirmed by 1H-NMR, GPC and elementary analysis. The RGD conjugated PLA (RGD-PLA) on poly(lactide-co-glycolide) (PLGA) film significantly increased the number of attached cells compared to PLGA without RGD-PLA, while it did not change static contact angle of PLGA. This result demonstrated this conjugation method would be a useful tool to increase cell affinity of biomaterials without change in hydrophilic/hydrophobic property for tissue engineering applications.

Abstract: Poly-L-lactic acid (PLLA) is a desirable and very attractive polymer for fabricating porous scaffolds. As of now, a solvent casting method with organic solvents has been used in scaffold fabrication process. However, residual organic solvents in the scaffolds have the problems of decreasing the effect of osteogenic induction due to the hindrance of bioceramic by polymer solution and it’s harmfulness in vivo. To avoid these disadvantages of scaffolds by organic solvent casting method, we developed a new method fabricating polymer (PLLA)/ceramic (β -TCP) composite scaffolds by baking method without using solvent, and then we tested properties of scaffolds on animals. As the result, non-toxicity has been proved through animal experiment and newly fabricated polymer/ceramic composites by a novel sintering method were induced rapid bone regeneration through enhancing the interaction of cells and a bone induction factor without any host immune response.

Abstract: To engineer cartilaginous constructs with a mechano-active scaffold and dynamic compression was performed for effective cartilage tissue engineering. Mechano-active scaffolds were fabricated from very elastic poly(L-lactide-co-ε-carprolactone)(5:5). The scaffolds with 85 % porosity and 300~500 μm pore size were prepared by a gel-pressing method. The scaffolds were seeded with chondrocytes and the continuous compressive deformation of 5% strain was applied to cell-polymer constructs with 0.1Hz to evaluate for the effect of dynamic compression for regeneration of cartilage. Also, the chondrocytes-seeded constructs stimulated by the continuous compressive deformation of 5% strain with 0.1Hz for 10 days and 24 days respectively were implanted in nude mice subcutaneously to investigate their biocompatibility and cartilage formation. From biochemical analyses, chondrogenic differentiation was sustained and enhanced significantly and chondrial extracellular matrix was increased through mechanical stimulation. Histological analysis showed that implants stimulated mechanically formed mature and well-developed cartilaginous tissue, as evidenced by chondrocytes within lacunae. Masson’s trichrome and Safranin O staining indicated an abundant accumulation of collagens and GAGs. Also, ECM in constructs was strongly immuno-stained with anti-rabbit collagen type II antibody. Consequently, the periodic application of dynamic compression can improve the quality of cartilaginous tissue formed in vitro and in vivo.

Abstract: A novel process was developed to fabricate polymer/ceramic composites for bone tissue engineering. The mixture of polylactic acid (PLA), calcium metaphosphate (CMP), and NaCl were compressed and subsequently heated. After dissolving the NaCl salts, porous biodegradable polymer/ceramic composite scaffolds were formed. The characteristics of the scaffolds were compared to those of scaffolds fabricated using a conventional solvent casting method, in terms of pore structure, pore size distribution, and mechanical properties. The scaffolds were seeded by osteoblasts and cultured in vitro or implanted into nude mice subcutaneously for up to 5 weeks. Cells were better grown to form tissue-like structures on CMP/PLA composites fabricated by the Press-and-Baking method. In addition, the alkaline phosphatase activity of and calcium deposition in the scaffolds explanted from mice were enhanced significantly for the scaffolds by Press-and-Baking compared to them by solvent casting. Taken together, these results suggest that CMP promote cell differentiation and proliferation via direct interaction with cells in the CMP/PLA composites. This novel PLA/CMP composite will be applicable for bone tissue engineering to support and cell differentiation and growth.