• Advanced Composite Materials
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• v.16 no.4
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• pp.335-347
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• 2007

Green composites composed of long maize fibers and poly $\varepsilon$-caprolactone (PCL) biodegradable polyester matrix were manufactured by the thermo-mechanical processing termed as 'Sequential Molding and Forming Process' that was developed previously by the authors' research group. A variety of processing parameters such as fiber area fraction, molding temperature and forming pressure were systematically controlled and their influence on the tensile properties was investigated. It was revealed that both tensile strength and elastic modulus of the composites increase steadily depending on the increase in fiber area fraction, suggesting a general conformity to the rule of mixtures (ROM), particularly up to 55% fiber area fraction. The improvement in tensile properties was found to be closely related to the good interfacial adhesion between the fiber and polymer matrix, and was observed to be more pronounced under the optimum processing condition of $130^{\circ}C$ molding temperature and 10 MPa forming pressure. However, processing out of the optimum condition results in a deterioration in properties, mostly fiber and/or matrix degradation together with their interfacial defect as a consequence of the thermal or mechanical damages. On the basis of microstructural observation, the cause of strength degradation and its countermeasure to provide a feasible composite design are discussed in relation to the optimized process conditions.

• Macromolecular Research
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• v.15 no.7
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• pp.646-655
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• 2007

To achieve targeted drug delivery for chemotherapy, a ligand-mediated nanoparticulate drug carrier was designed, which could identity a specific receptor on the surfaces of tumor cells. Biodegradable poly(ethylene oxide)/poly$({\varepsilon}-caprolactone)$ (PEG/PCL) amphiphilic block copolymers coupled to biotin ligands were synthesized with a variety of PEG/PCL compositions. Block copolymeric nanoparticles harboring the anticancer drug paclitaxel were prepared via micelle formation in aqueous solution. The size of the biotin-conjugated PEG/PCL nanoparticles was determined by light scattering measurements to be 88-118 nm, depending on the molecular weight of the block copolymer, and remained less than 120 nm even after paclitaxel loading. From an in vitro release study, biotin-conjugated PEG/PCL nanoparticles containing paclitaxel evidenced sustained release profiles of the drug with no initial burst effect. The biotin-conjugated PEG/PCL block copolymer itself evidenced no significant adverse effects on cell viability at $0.005-1.0{\mu}g/mL$ of nanoparticle suspension regardless of cell type (normal human fibroblasts and HeLa cells). However, biotin-conjugated PEG/PCL harboring paclitaxel evidenced a much higher cytotoxicity for cancer cells than was observed in the PEG/PCL nanoparticles without the biotin group. These results showed that the biotin-conjugated nanoparticles could improve the selective delivery of paclitaxel into cancer cells via interactions with over-expressed biotin receptors on the surfaces of cancer cells.

• Proceedings of the Polymer Society of Korea Conference
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• 2006.10a
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• pp.263-263
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• 2006

Poly (ethylene glycol)(PEG) - Poly (${\varepsilon}-caprolactone(CL)$) - Poly (D,L lactide(LA) (PCLA-PEG-PCLA) was synthesized by ring-opening polymerization to form temperature sensitive hydrogel triblock copolymer. The triblock copolymer was acrylated by acryloyl chloride. ${\beta}-amino$ ester was used as a pH sensitive moiety, in this study ${\beta}$- amino ester obtained from 1,4-butandiol diacrylate, and 4, 4' trimethylene dipiperidine, it have pKb around 6.6. pH/temperature sensitive penta-block copolymer (PAE-PCL-PEG-PCL-PAE) was synthesized by addition polymerization from acrylated triblock copolymer, 1,4-butandiol diacrylate, and 4, 4' trimethylene dipiperidine. Their physicochemical properties of triblock and penta-block copolymers were characterized by $^1H-NMR$ spectroscopy and gel permeation spectroscopy. Sol-gel phase transition behavior of PAE-PCL-PEG-PCL-PAE block copolymers were investigated by remains stable method. Aqueous media of the penta-block copolymer (at 20 wt%) changed from a sol phase at pH 6.4 and $10^{\circ}C$ to a gel phase at pH 7.4 and $37^{\circ}C$. The sol-gel transition properties of these block copolymers are influenced by the hydrophobic/hydrophilic balance of the copolymers, block length, hydrophobicity, stereo-regularity of the hydrophobic of the block copolymer, and the ionization of the pH function groups in the copolymer depended on the changing of environmental pH, respectively. The degradation and the stabilization at pH 7.4 and $37^{\circ}C$, and the stabilization at pH 6.4 and $10^{\circ}C,\;5^{\circ}C,\;0^{\circ}C$, of the gel were determined. The results of toxicity experiment show that the penta block copolymer can be used for injection drug delivery system. The sol?gel transition of this block copolymer also study by in vitro test ($200{\mu}l$ aqueous solution at 20wt% polymer was injected to mouse). Insulin loading and releasing by in vitro test was investigated, the results showed that insulin can loading easily into polymer matrix and release time is around 14-16days. The PAE-PCL-PEG-PCL-PAE can be used as biomaterial for drug, protein, gene loading and delivery.

• Journal of Environmental Science International
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• v.21 no.4
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• pp.507-515
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• 2012

To improve the mechanical properties of hydroxyapatite (HA)/waterborne polyurethane (WBPU) composites, the hydroxyl group of HA was modified by urethane reactions: the hydroxyl groups of HA were reacted with aliphatic or cyclic diisocyanate, and then the modified HAs were extended by adding polyol and/or ${\varepsilon}$-caprolactone. Composites were prepared by the prepolymer process method: the modified HA was directly pured into the urethane reaction of isocyanate and polyol. The properties of modified HA/WBPU composites were investigated by thermogravimetric analysis, tensile strength, and water resistance. The results showed that the reactivity of aliphatic diisocyanate to the hydroxy group of HA was faster than that of cyclic one. Comparing to those of pure HA/WBPU composite films, the thermal stability, water resistance, and mechanical properties of the modified composite films increased with a degree of modification of HA.

• Proceedings of the Korean Institute of Surface Engineering Conference
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• 2018.06a
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• pp.24-24
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• 2018

One of the challenges in tissue engineering is the design of optimal biomedical scaffolds, which can be governed by topographical surface characteristics, such as size, shape, and direction. Of these properties, we focus on the effects of nano - to micro - sized hierarchical surface. To fabricate the hierarchical surface structure on poly(${\varepsilon}$-caprolactone) (PCL) film, we employed a nano/micro-casting technique (NCT) and modified plasma process. The micro size topography of PCL film was controlled by sizes of the micro structures on lotus leaf. Also, the nano-size topography and hydrophilicity of PCL film were controlled by modified plasma process. After the plasma treatment, the hydrophobic property of the PCL film was significantly changed into hydrophilic property, and the nano-sized structure was well developed, as increasing the plasma exposure time and applied power. The surface properties of the modified PCL film were investigated in terms of initial cell morphology, attachment, and proliferation using osteoblast-like-cells (MG63). In particular, initial cell attachment, proliferation and osteogenic differentiation in the hierarchical structure were enhanced dramatically compared to those of the smooth surface.

• Proceedings of the Materials Research Society of Korea Conference
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• 2009.05a
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• pp.46.2-46.2
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• 2009

In vitro 상에서 골조직을 원활하게 재생하기 위해서는 3차원 지지체를 이용한 세포 배양과 세포 배양 시 세포의 형태와 기능을 유지/향상시키기 위한 인체 내 미세 환경 재현은 필수적이다. 따라서 본 연구에서는 뼈 성분과 유사한 생체 활성 물질인 hydroxyapatite (HA)와 생분해성 고분자인 poly $\varepsilon$-caprolactone (PCL)를 복합재료로 이용하여 내부 연결성이 우수한 골조직 재생용 3차원 지지체를 제작하였으며, 골 재생 능력 향상을 위하여 인체내 골조직의 기계적 미세 환경을 체외에서 구현한 새로운 형태의 perfusion bioreactor system을 개발/적용하였다. 또한 본 연구에서 개발된 perfusion bioreactor system의 생물학적 평가를 위해 MG63 (osteoblast like cell, 한국 세포주 은행)과 New Zealand White Rabbit에서 분리한 중간엽 줄기세포를 골조직 재생용 3차원 지지체에 파종하였다. 48시간 동안 안정화 후 perfusion bioreactor system을 이용하여 기계적 자극을 파종된 세포에 인가하였으며, 배양 기간 동안 세포의 증식 확인 및 형태학적 관찰을 실시하였다. 본 연구 결과, perfusion bioreactor system을 이용하여 기계적 자극을 인가한 실험군에서 세포의 증식 및 활성도가 대조군에 비해 우수함을 확인 할 수 있었다. 따라서, perfusion bioreactor를 이용한 세포 배양은 세포의 활성 향상 및 골조직 재생에 도움이 될 것으로 사료된다. 차후 perfusion bioreactor를 이용한 다양한 패턴의 자극이 골재생 능력 및 중간엽 줄기세포의 골 분화능에 미치는 영향에 대한 연구가 필요할 것으로 사료된다.

• Macromolecular Research
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• v.13 no.4
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• pp.344-351
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• 2005

pH-sensitive block copolymers were synthesized by coupling reaction of sulfamethazine and amphiphilic diblock copolymer, and their micellization-demicellization behavior was investigated. Sulfamethazine (SM), a derivative of sulfonamide, was introduced as a pH responsive moiety while methoxy poly(ethylene glycol)poly(D,L-lactide) (MPEG-PDLLA) and methoxy poly(ethylene glycol)-poly($D,L-lactide-co-{\varepsilon}-caprolactone$) (MPEG-PCLA) were used as biodegradable amphiphilic diblock copolymers. After the sulfamethazine was carboxylated by the reaction with succinic anhydride, the diblock copolymer was conjugated with sulfamethazine by coupling reaction in the presence of DCC. The critical micelle concentration (CMC) and mean diameter of the micelles were examined at various pH conditions through fluorescence spectroscopy, dynamic light scattering and transmission electron microscopy. For MPEG-PDLLA-SM and MPEG-PCLA-SM solutions, the pH-dependent micellization-demicellization was achieved within a narrow pH band, which was not observed in the MPEG-PDLLA and MPEG-PCLA solutions. The micelle showed a spherical morphology and had a very narrow size distribution. This pH-sensitive block copolymer shows potential as a site-targeted drug carrier.

• Journal of Microbiology and Biotechnology
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• v.16 no.4
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• pp.511-518
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• 2006

A gene cluster for cyclohexanone oxidation was cloned from Rhodococcus sp. TK6, which is capable of growth on cyclohexanone as the sole carbon source. The 9,185-bp DNA sequence analysis revealed seven potential open reading frames (ORFs), designated as ssd-chnR-chnD-chnC-chnB-chnE-partial pcd. The chnBCDE genes encode enzymes for the four-step conversion of cyclohexanone to adipic acid, catalyzed by cyclohexanone monooxygenase (ChnB), $\varepsilon-caprolactone$ hydrolase (ChnC), 6-hydroxyhexanoate dehydrogenase (ChnD), and 6-oxohexanoate dehydrogenase (ChnE). Furthermore, the presence of a regulatory element in the downstream region of the chnD gene supports the notion that chnR is a putative regulatory gene. Among them, the activity of ChnB was confirmed and characterized, following their expression and purification in Escherichia coli harboring the modified chnB gene (chnB gene with 6 successive codons for His at the 3' terminus).

• Korean Journal of Metals and Materials
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• v.50 no.10
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• pp.763-768
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• 2012

The uniform and highly smooth nanofibers of biocompatible poly(${\varepsilon}$-caprolactone) (PCL) composited with different contents of multiwalled carbon nanotubes (MWCNTs) were successfully prepared by electrospinning. Experimental parameters were MWCNTs addition to a PCL solution and applied voltages. The topographical features of the composite nanofibers were characterized by scanning electron microscopy and its electrical properties were measured by a four-point probe method. The surface resistance gradually decreased with an increasing content of MWCNTs in PCL fibers because of the excellent electrical conductivity of MWCNTs. The nanofiber diameter could be regulated by varying the solution viscosity and voltages. Our results establish that this kind of electrospinning PCL/MWCNTs nanofibers with the control of fiber diameter and electrical conductivity may be a promising candidate for the application of scaffolds in tissue engineering.

• Bulletin of the Korean Chemical Society
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• v.34 no.6
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• pp.1800-1808
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• 2013

Dual-responsive amphiphilic block copolymers were synthesized by combining enzymatic ring-opening polymerization (eROP) of ${\varepsilon}$-caprolactone (CL) and ATRP of N,N-dimethylamino-2-ethyl methacrylate (DMAEMA). The obtained block copolymers were characterized by gel permeation chromatography (GPC), $^1H$ NMR and FTIR-IR. The critical micelle concentration (CMC) of copolymer was determined by fluorescence spectra, it can be found that with hydrophilic block (PDMAEMA) increasing, CMC value of the polymer sample increased accordingly, and the CMC value was 0.012 mg/mL, 0.025 mg/mL and 0.037 mg/mL for $PCL_{50}$-b-$PDMAEMA_{68}$, $PCL_{50}$-b-$PDMAEMA_{89}$, $PCL_{50}$-b-$PDMAEMA_{112}$, $PCL_{50}$-b-$PDMAEMA_{89}$ was chosen as drug carrier to study in vitro release profile of anti-cancer drug (taxol). The temperature and pH dependence of the values of hydrodynamic diameter (Dh) of micelles, and self-assembly of the resulting block copolymers in water were evaluated by dynamic light scattering (DLS). The result showed that with the temperature increasing and pH decreasing, the Dh decreased. Drug-loaded nanoparticles were fabricated using paclitaxel as model. Transmission electron microscopy (TEM) and atomic force microscopy (AFM) had been explored to study the morphology of the hollow micelles and the nanoparticles, revealing well-dispersed spheres with the average diameters both around 80 nm. In vitro release kinetics of paclitaxel from the nanoparticles was also investigated in different conditions (pH and temperature, etc.), revealing that the drug release was triggered by temperature changes upon the lower critical solution temperature (LCST) at pH 7.4, and at $37^{\circ}C$ by an increase of pH.