• Journal of the Korean Society of Manufacturing Process Engineers
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• v.13 no.3
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• pp.35-41
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• 2014

Poly(g-glutamic acid) (g-PGA) is a very promising biodegradable polymer that is produced by microorganism of Bacillus subtilis. Because g-PGA is water-soluble, anionic, biodegradable, and even edible, its potential applications have been studied from an industrial standpoint. In this study, we fabricated porous g-PGA foams by means of a freeze-solvent extraction method for tissue-engineering applications. Porous g-PGA foams were chemically cross-linked using a hexamethylene diisocyanate solution. An aqueous basic solution was used to neutralize g-PGA foam for cell culturing. During an in vitro cell culture study, it was observed that primary rabbit ear chondrocytes were well at tached and spread over the surface oft hree-dimensional cross-linkedg-PGA foam. From these results, it is concluded that cross-linkedg-PGA foam is aprom is in gmaterial for tissue-engineering applications, especially those pertaining to the regeneration of human cartilage.

• Bulletin of the Korean Chemical Society
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• v.33 no.12
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• pp.3950-3956
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• 2012

In order to improve the bioactivity and mechanical properties of hydroxyapatite (HAp), chitosan (Chi) was in situ combined into HAp to fabricate a composite scaffold by a sublimation-assisted compression method. A highly porous film with sufficient mechanical strength was prepared and the bioactivity was investigated by examining the apatite formed on the scaffolds incubated in simulated body fluid. In addition, the cytotoxicity of the HAp/Chi composite was studied by evaluating the viability of murine fibroblasts (L-929 cells) exposed to diluted extracts of the composite films. The apatite layer was assessed using scanning electronic microscopy, inductively coupled plasma-optical emission spectrometry and weight measurement. Composite analysis showed that a layer of micro-sized, needle-like crystals was formed on the surface of the composite film. Additionally, the WST-8 assay after L-929 cells were exposed to diluted extracts of the composite indicated that the HAp/Chi scaffold has good in vitro cytocompatibility. The results indicated that HAp/Chi composites with porous structure are promising scaffolding materials for bone-patch engineering because their porous morphology can provide an environment conductive to attachment and growth of osteoblasts and osteogenic cells.

• 한국신재생에너지학회:학술대회논문집
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• 2011.11a
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• pp.85.2-85.2
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• 2011

현재 중온의 고체산화물 연료전지를 위해 다양한 전해질에 대한 연구되었으며 1994년 Ishihara et al.에서 1074K의 온도에서 높은 이온전도도를 갖는 페록스카이 구조를 갖는 LSGM 물질을 발표하였다. Sr과 Mg을 도핑한 Lanthanum gallate는 이온전도도가 1073K에서 0.14S/cm로 YSZ의 5배로 높은 이온전도도를 갖고 있으며 산화환경에서부터 환원환경에서 화학적으로 안정한 특성을 갖고 있다. 또한 LSGM 전해질은 넓은 산소 농도범위에서 안정적인 특성을 갖는 장점을 갖고 있다. 그러나 LSGM은 가장 널리 사용되는 연료극의 Ni 촉매와 고온 소결시 상호확산현상에 의한 2차상을 생성시켜 성능 저감의 원인으로 그 해결방안이 요원한 실정이다. 이에 본 논문에서는 LSGM 전해질에 LSGM scaffold를 형성하고 형성된 scaffold에 연료극 촉매 solution을 infiltration 시켜 저온에서 anode를 형성하여 그 성능을 연구하였다.

• Proceedings of the Materials Research Society of Korea Conference
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• 2010.05a
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• pp.42.2-42.2
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• 2010

Recently, highly porous bone substitutes, which have interconnected open pore structure, have been focused on improving their mechanical properties and modifying their functions. Especially, it is highly required to develop functional gradient structured bone substitute which is available for controlling their material properties such as bioresorption rate and elastic modulus. Porous $ZrO_2$ scaffold was fabricated by the sponge replica method using PU sponge. After 3 times of dip coating and the subsequent oven drying, burning out and microwave sintering were carried out. Various $ZrO_2$-BCP powder mixtures were prepared depending on the ratio and coated on the $ZrO_2$ scaffold by dip coating process. X-ray diffraction analysis was performed to characterize the phase identification of the scaffolds. Microstructures of the bone substitutes were observed using scanning electron microscopy.

• International Journal of Industrial Entomology and Biomaterials
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• v.25 no.1
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• pp.75-79
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• 2012

Low-melting-temperature agarose gel solution, as a novel porogen was combined with a silk fibroin solution to generate interconnected porous networks. The porosity of the resultant silk fibroin-agarose scaffolds was greater than that of the scaffolds generated with agarose and deionized water. The porosities of silk fibroin scaffolds containing agarose gel at 0.5%, 1.0%, 1.5%, 2.0% [w/v] were 110.9%, 111.7%, 120.9%, and 123.0%, respectively. Lastly, the internal space generated in scaffolds after dissolution of the agarose gel provides a good environment for cell growth and movement within the scaffold.

• Proceedings of the Materials Research Society of Korea Conference
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• 2007.11a
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• pp.146.2-146.2
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• 2007

• Proceedings of the Materials Research Society of Korea Conference
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• 2007.11a
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• pp.147.1-147.1
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• 2007

• Proceedings of the Polymer Society of Korea Conference
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• 2006.10a
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• pp.268-268
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• 2006

Due to their multipotency, stem cells can differentiate into a variety of specialized cell types, such as chondrocytes, osteoblasts, myoblasts, and nerve cells. As an alternative to mature tissue cells, stem cells are of importance in tissue engineering and regenerative medicine. Since interactions between scaffold and cells play an important role in the tissue development in vitro, synthetic oligopeptides have been immobilized onto polymeric scaffolds to improve specific cell attachment and even to stimulate cell differentiation. In this study, chondrogenic differentiation of stem cells was evaluated using surface-modified PLLA scaffolds, i.e., either hydrophilic acrylic acid (AA)-grafted PLLA or RGD-immobilized one. Porous PLLA scaffolds were prepared using a gas foaming method, followed by plasma treatment and subsequent grafting of AA to introduce a hydrophilicity (PLLA-PAA). This was further processed to fix RGD peptide to make an RGD-immobilized scaffold (PLLA-PAA-RGD). Stem cells were seeded at $1{\times}10^{6}$ cells per scaffold and the cell-PLLA constructs were cultured for up to 4 weeks in the chondrogenic medium. Using these surface-modified scaffolds, adhesion, proliferation, and chondrogenic differentiation of stem cells were evaluated. The surface of PLLA scaffolds turned hydrophilic (water contact angle, 45 degrees) with both plasma treatment and AA grafting. The hydrophilicity of RGD-immobilized surface was not significantly altered. Cell proliferation rate on the either PLLA-PAA or PLLA-PAA-RGD surface was obviously improved, especially with the RGD-immobilized one as compared to the control PLLA one. Chondrogenic differentiation was clearly identified with Safranin O staining of GAG in the AA- or RGD-grafted PLLA substrates. This study demonstrated that modified polymer surfaces may provide better environment for chondrogenesis of stem cells.

• Korean Journal of Materials Research
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• v.24 no.6
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• pp.310-318
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• 2014

In this experiment, a highly porous scaffold of biphasic calcium phosphate (BCP) was prepared using the spongereplica method. The BCP scaffold was coated with 58S bioactive glass (BG) and sintered for a second time. The resulting scaffold was coated with gelatin (Gel) and cross-linked with [3-(3-dimethyl aminopropyl) carbodiimide] and N-Hydroxysuccinamide (EDC-NHS). The initial average pore size of the scaffold ranged from 300 to $700{\mu}m$, with more than 85 % porosity. The coating of BG and Gel had a significant effect on the scaffold-pore size, decreasing scaffold porosity while increasing mechanical strength. The material and surface properties were evaluated by means of several experiments involving scanning electron microscopy (SEM), energy-dispersive X-ray (EDX) and X-ray diffraction (XRD). Cytotoxicity was evaluated using MTT assay and confocal imaging of MC3T3-E1 pre-osteoblast cells cultured in vitro. Three types of scaffold (BCP, BCP-BG and BCP-BG-Gel) were implanted in a rat skull for in vivo evaluation. After 8 weeks of implantation, bone regeneration occurred in all three types of sample. Interestingly, regeneration was found to be greater (geometrically and physiologically) for neat BCP scaffolds than for two other kinds of composite scaffolds. However, the other two types of scaffolds were still better than the control (i.e., defect without treatment).

• Korean Journal of Materials Research
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• v.20 no.8
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• pp.418-422
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• 2010

As a starting material, BCP (biphasic calcium phosphate) nano powder was synthesized by a hydrothermal microwave-assisted process. A highly porous BCP scaffold was fabricated by the sponge replica method using 60 ppi (pore per inch) of polyurethane sponge. The BCP scaffold had interconnected pores ranging from $100\;{\mu}m$ to $1000\;{\mu}m$, which were similar to natural cancellous bone. To realize the antibacterial property, a microwave-assisted nano Ag spot coating process was used. The morphology and distribution of nano Ag particles were different depending on the coating conditions, such as concentration of the $AgNO_3$ solution, microwave irradiation times, etc. With an increased microwave irradiation time, the amount of coated nano Ag particles increased. The surface of the BCP scaffold was totally covered with nano Ag particles homogeneously at 20 seconds of microwave irradiation time when 0.6 g of $AgNO_3$ was used. With an increased amount of $AgNO_3$ and irradiation time, the size of the coated particles increased. Antibacterial activities of the solution extracted from the Ag-coated BCP scaffold were examined against gram-negative (Escherichia coli) and gram-positive bacteria (Staphylococcus aureus). When 0.6 g of $AgNO_3$ was used for coating the Ag-coated scaffold, it showed higher antibacterial activities than that of the Ag-coated scaffold using 0.8 g of $AgNO_3$.