• Polymer(Korea)
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• v.24 no.4
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• pp.477-487
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• 2000

A series of poly(L-lactic acid) (PLLA)/poly($\beta$-hydroxynonanoate) (PHN) blend were prepared to study the miscibility and the crystallization behaviors. The thermal behaviors and characterization of PLLA/PHN blends Were studied using differential scanning calorimetry (DSC), XRD and polarizing optical microscopy (POM). The PLLA and PHN are partially miscible in amorphous region. The crystallinity of PLLA increased as the content of PHN increased, and T$_{g}$, T$_{c}$, and T$_{m}$ of PLLA shift as the content of PHN increased. Moreover, the number of PLLA spherulite increased as the content of PHN increased in the POM experiment. Thus, PHN acted as a nucleating agent to PLLA.

• Polymer(Korea)
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• v.26 no.2
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• pp.174-178
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• 2002

PLLA-POE-PLLA block copolymers were prepared using PLLA and POE with different compositions. Copolymers were obtained in high yield and the polydispersity of the copolymers was very narrow. A dispersed solution of 0.1 g/mL of PLLA-POE-PLLA copolymer was mixed with a dispersed solution of 0.1 g/mL of PDLA-POE-PDLA copolymer. Gel formation was observed from the mixed product obtained at the human body temperature of $37^{\circ}C$. The mixed product comprising PDLA-POE-PDLA and PLLA-POE-PLLA was found to have higher cloud points than that of PLLA-POE-PLLA copolymer. The cloud points decreased with increasing the concentration of the mixed copolymer dispersed solution.

• Polymer(Korea)
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• v.24 no.5
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• pp.656-663
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• 2000

The Effects of thermal history during the melt spinning process on the mechanical properties and crystallinity of polylactic acid (PLLA) fibers have been studied. Thermal history applied on PLLA during the melt process caused the decrease of number-average molecular weights and this resulted in the lowering of orientation and crystallinity in PLLA fibers. As a result, the longer applied thermal history, the less tensile strength and modulus, and the higher elongation at break. It was also found that primary factor for controlling crystallinity of PLLA fiber was the stress induced crystallization while the thermal induced crystallization had a little effect on the crystallinity of PLLA fibers. However, the thermal induced crystallization turn out to be important in the crystallinity developed by annealing of PLLA fibers.

• Macromolecular Research
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• v.13 no.5
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• pp.446-452
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• 2005

The interactions between the surface of scaffolds and specific cells play an important role in tissue engineering applications. Some cell adhesive ligand peptides including Arg-Gly-Asp (RGD) have been grafted into polymeric scaffolds to improve specific cell attachment. In order to make cell adhesive scaffolds for tissue regeneration, biodegradable nonporous poly(L-lactic acid) (PLLA) films were prepared by using a solvent casting technique with chloroform. The hydrophobic PLLA films were surface-modified by Argon plasma treatment and in situ direct acrylic acid (AA) grafting to get hydrophilic PLLA-g-PAA. The obtained carboxylic groups of PLLA-g-PAA were coupled with the amine groups of Gly-Arg-Asp-Gly (GRDG, control) and GRGD as a ligand peptide to get PLLA-g-GRDG and PLLA-g-GRGD, respectively. The surface properties of the modified PLLA films were examined by various surface analyses. The surface structures of the PLLA films were confirmed by ATR-FTIR and ESCA, whereas the immobilized amounts of the ligand peptides were 138-145 pmol/$cm^2$. The PLLA surfaces were more hydrophilic after AA and/or RGD grafting but their surface morphologies showed still relatively smoothness. Fibroblast adhesion to the PLLA surfaces was improved in the order of PLLA control

• Korean Journal of Environmental Biology
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• v.25 no.3
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• pp.260-266
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• 2007

A thermophilic bacterium capable of poly (L-lactide)(PLLA) degradation was isolated from cultivating soil in Korea. The isolate was Gram positive rod-shaped bacterium, and was identified as Geobacillus caldoxylosilyticus based on the 16S rDNA sequence analysis. The strain proved to be a new PLLA degrading bacterium which has not been reported in the open literatures yet. The degradation activity of the strain was assessed in a sterilized compost inoculated with the strain under controlled compost condition at $58^{\circ}C$ for 40 days. The strain mineralized 66%, 57%, 41% and 40% of PLLA5000, PLLA11000, PLLA34000 and PLLA256000 whose weight average molecular weights were 5000, 11000, 34000 and 256000, respectively. Incorporation of 0.1% each of gelatin, yeast extract and ammonium sulfate in the compost containing PLLA256000 as a nutritional supplement raised the biodegradation activity by 27%, 13% and 10%, respectively. Increase of the inoculum size from $10^9cfu\;g^{-1}\;to\;10^{10}cfu\;g^{-1}\;and\;10^{11}cfu\;g^{-1}$ also enhanced the biodegradation activity by 14% and 20%, respectively.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.31 no.7 s.262
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• pp.732-738
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• 2007

Effects of melt-mixing conditions on fracture properties of hydroxyapatite filled bioabsorbable poly(L-lactic acid)(HA/PLLA) composites was investigated by measuring the firacture toughness value of HA/PLLA composites prepared under different mixing time and rotor speed. The fracture surface morphology was also examined by profile measurement and scanning electron microscopies. It was found that the fracture toughness of HA/PLLA composites decreases due to decrease of ductile deformation of PLLA matrix and debonding of interfaces with increase of the rotor speed and mixing time. Effect of mixing process on neat PLLA was also assessed, and it was found that the fracture toughness of PLLA decreases due to disappearance of multiple craze formation and increase of defects. Such thermal and shear-stress degradation were found to be the primary mechanisms of the degradation of HA/PLLA composites during melt-mixing process.

• KSBB Journal
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• v.29 no.6
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• pp.405-413
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• 2014

In this study, gemcitabine (Gem)-Poly(L-lactic acid) (PLLA) conjugates were synthesized through an amide linkage reaction. Then, the microparticles of Gem-PLLA/PLLA blends containing gemcitabine were prepared using a supercritical fluid process, called aerosol solvent extraction system (ASES). Gemcitabine-loaded Gem-PLLA/PLLA microparticles obtained from the ASES process showed a spherical shape. The amount of gemcitabine released after 30 day incubation in a phosphate buffer solution of pH 7.4 was about 90% of the total amount of gemcitabine present in the product.

• Journal of the Korean Applied Science and Technology
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• v.20 no.4
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• pp.324-331
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• 2003

Particulate leaching method for the preparation of porous PLLA scaffolds was carried out and especially, the effect of PLLA/$CHCl_3$ solution concentration on the salt leaching rate and the pore structure of PLLA scaffolds were considered. It was found that maintaining lower PLLA/$CHCl_3$ concentration and higher $CHCl_3$ evaporation temperature in the preparation of PLLA/NaCl mixtures resulted in the enhancement of salt leaching rat e and higher porosity. This is understood that those conditions could minimize the formation of dense PLLA layer on the surface of PLLA/NaCl mixture as well as introducing better porosity on the surface. Higher salt leaching temperature accelerated the salt leaching rate but it seems that there is no influence on the porosity of PLLA scaffolds.

• Applied Chemistry for Engineering
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• v.26 no.3
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• pp.251-258
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• 2015

In the study, PLLA with 12,000 g/mol ($M_n$) and 14,000 g/mol ($M_w$) was synthesized from L-lactide, and used to synthesize PLLA-Br intermediate. PLLA-block-PMMA with 84,000 g/mol ($M_n$) and 126,000 g/mol ($M_w$) was finally synthesized from PLLA-Br intermediate. The glass transition temperature ($T_g$) and initial pyrolysis temperature of PLLA-block-PMMA are $95.5^{\circ}C$ and $289^{\circ}C$, respectively. The PLA film of $50{\pm}3{\mu}m$ thickness was prepared by blending PLA with 9 phr PLLA-block-PMMA followed by stretching biaxially at 3 times under $95^{\circ}C$, and annealing at $120^{\circ}C$ for 2 min. The light transmittance at 550 nm and tensile strength of the film are 88.5% and 44.5 MPa, respectively. To enhance the tensile strength of PLA film, it was required to keep the film more than 2 min at $120^{\circ}C$ during the annealing step after a biaxially orientation.

• 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.