Yong Woo Cho

Porous chitosan scaffold containing microspheres loaded with transforming growth factor-β1: Implications for cartilage tissue engineering

Damaged articular cartilage, caused by traumatic injury or degenerative diseases, has a limited regenerative capacity and frequently leads to the onset of osteoarthritis. As a promising strategy for the successful regeneration of long-lasting hyaline cartilage, tissue engineering has received increasing recognition. In this study, we attempted to design a novel type of porous chitosan scaffold, containing transforming growth factor-beta1 (TGF-beta1), to enhance chondrogenesis. First, to achieve a sustained release of TGF-beta1, chitosan microspheres loaded with TGF-beta1 (MS-TGFs) were prepared by the emulsion method, in the presence of tripolyphosphate; with an identical manner, microspheres loaded with BSA, a model protein, were also prepared. Both microspheres containing TGF-beta1 and BSA had spherical shapes with a size ranging from 0.2 to 1.5 microm. From the release experiments, it was found that both proteins were slowly released from the microspheres over 5 days in a PBS solution (pH 7.4), in which the release rate of TGF-beta1 was much lower than that of BSA. Second, MS-TGFs were seeded onto the porous chitosan scaffold, prepared by the freeze-drying method, to observe the effect on the proliferation and differentiation of chondrocytes. It was obviously demonstrated from in vitro tests that, compared to the scaffold without MS-TGF, the scaffold containing MS-TGF significantly augments the cell proliferation and production of extracellular matrix, indicating the role of TGF-beta1 released from the microspheres. These results suggest that the chitosan scaffold containing MS-TGF possesses a promising potential as an implant to treat cartilage defects.

Biodistribution and anti-tumor efficacy of doxorubicin loaded glycol-chitosan nanoaggregates by EPR effect

An in vivo tumor targeting test of glycol-chitosan nanoaggregates was carried out with FITC-conjugated glycol-chitosan nanoaggregates (FTC-GC) and the doxorubicin conjugated glycol-chitosan (GC-DOX). To investigate its biodistribution in tumor-bearing rats, glycol-chitosan was labeled with fluorescein isothiocyanate (FITC), which formed nanoaggregates with a diameter of about 250 nm in aqueous media. GC-DOX nanoaggregates containing acid-sensitive spacers were prepared. The GC-DOX formed micelle-like nanoaggregates spontaneously in aqueous media. GC-DOX nanoaggregates had a narrow and unimodal size distribution, and its hydrodynamic diameter measured by dynamic light scattering ranged from 250 to 300 nm. A loading content of doxorubicin into GC-DOX nanoaggregates as high as 38%, with 97% loading efficiency, could be obtained using a physical entrapment method. A tumor-bearing animal model was developed by inoculating tumor cells into the back of a rat. The FTC-GC nanoaggregates were injected into the tail vein of tumor-bearing rats and their tissue distribution was examined. The FTC-GC nanoaggregates were distributed mainly in kidney, tumor and the liver and were scarcely observed in other tissues. They were maintained at a high level for 8 days and their distribution in tumor tissues increased gradually. This suggests that chitosan nanoaggregates accumulate passively in the tumor tissue due to the enhanced permeability and retention (EPR) effect. Doxorubicin loaded GC-DOX nanoaggregates (DOX/GC-DOX) were injected into the tail vein of tumor-bearing rats and their anti-tumor effect was examined. Tumor growth was suppressed over 10 days.

Assessment of PEO/PTMO multiblock copolymer/segmented polyurethane blends as coating materials for urinary catheters: in vitro bacterial adhesion and encrustation behavior.

The effective long-term use of indwelling urinary catheters has often been hindered by catheter-associated infection and encrustation. In this study, the suitability of poly(ethylene oxide) (PEO)-based multiblock copolymer/segmented polyurethane (SPU) blends as coating materials for the commercial urinary catheters was assessed by measuring swellability, bacterial adhesion, and encrustation behavior. When exposed to PBS (pH 7.4), the blends absorbed a significant amount of water, which was proportional to the copolymer content. It was demonstrated from bacterial adhesion tests that compared to bare SPU, the blend surfaces could significantly reduce the adhesion of E. coli, P. mirabilis, and S. epidermidis; the number of adherent bacteria correlated with the amount of copolymer additive. indicating that the swellability of the blends affected bacterial adhesion. Of the bacteria studied, the greatest effect of the copolymer additive was observed in S. epidermidis adhesion, in which there was an 85% decrease compared to bare SPU with a small amount of copolymer additive as low as 5% based on a dried blend. By using an artificial bladder model, allowing the catheter to be blocked by encrustation, it was revealed that the blend surfaces could effectively resist encrustation. The duration of patency was extended up to 20 +/- 3.1 h on the blend surface containing 10% of the copolymer additive, whereas the silicone-coated catheter, a control, required the least time for blockage, 7.8 +/- 3.1 h. The superior characteristics of the blends compared to other surfaces might be attributed to their PEO-rich surfaces, produced by the migration of PEO phase in the copolymer chain of the blends in an aqueous environment, and provide promising potential as a coating material on the urinary catheter for long-term catheterization.

Three-dimensional porous collagen/chitosan complex sponge for tissue engineering

A three-dimensional, porous collagen/chitosan complex sponge was prepared to closely simulate basic extracellular matrix (ECM) constitutes, collagen and glycosaminoglycan. The complex sponge was prepared by a lyophilization method and had the regular network with highly porous structure, suitable for cell adhesion and growth. The pores were well interconnected, and their distribution was fairly homogeneous. The complex sponge was crosslinked using 1-ethyl-3-(3-dimethyl aminopropyl) carbodiimide (EDC) and N-hydroxysuccinimide (NHS) to increase its biological stability and enhance its mechanical properties. The crosslinking medium had a great effect on the inner structure of the sponge. The homogeneous, porous structure of the sponge was remarkably collapsed in an aqueous crosslinking medium. However, the morphology of the sponge remained almost intact in a water/ethanol mixture crosslinking milieu. Mechanical properties of the collagen/chitosan sponge were significantly enhanced by EDC-mediated crosslinking. The potential of the sponge as a scaffold for tissue engineering was investigated using a Chinese hamster ovary cell (CHO-K1) line.

Norfloxacin-releasing urethral catheter for long-term catheterization

Norfloxacin-releasing urethral catheters were prepared for the purpose of preventing urinary tract infections during long-term catheterization. The outer and inner surfaces of the catheters were coated with poly(ethylene-co-vinyl acetate) (EVA) and an amphiphilic multiblock co-polymer (PEO2kPDMS), composed of poly(ethylene oxide) and poly(dimethyl siloxane). Norfloxacin, a fluoroquinolone synthetic antibiotic, was impregnated into a coating layer. The in vitro drug release behavior was monitored for 30 days, the surface topography was investigated using scanning electron microscopy (SEM) and the antibacterial activity against different bacteria implicated in urinary tract infection was evaluated by the in vitro inhibition zone test. All the coated catheters showed continuous delivery of norfloxacin for up to 30 days owing to hydrophobic natures of norfloxacin and EVA. PEO2kPDMS incorporated in a coating layer produced a smooth and uniform surface. The coated catheters created considerable inhibition zones for 10 days against Escherichia coli, Klebsiella pneumoniae and Proteus vulgaris, indicating the continuous release of norfloxacin. Overall, it was evident that the catheters coated with EVA/PEO2kPDMS blends containing norfloxacin have a promising potential for the clinical use in patients undergoing long-term catheterization.

Gentamicin-releasing urethral catheter for short-term catheterization

Urethral catheters, widely used for the drainage of the bladder, are associated with most urinary tract infections (UTIs) that account for 40% of all episodes occurring in acute-care hospitals. This study aimed to develop a gentamicin-releasing catheter that effectively prevents UTIs for short-term catheterization. For physical loading of gentamicin, the urethral catheters were coated by the simple dipping method with poly(ethylene-co-vinyl acetate) (EVA) and EVA/poly(ethylene oxide) (PEO) blends containing gentamicin. By varying the molecular weight (MW) and contents of PEO in the blends, various catheter surfaces were produced. In vitro drug release studies demonstrated that all the coated catheters exhibited sustained release up to 7 days; however, the release pattern was significantly dependant on the coating layers. Of the coated catheters, EVA/PEO (MW = 100k)-coated catheters were utilized to evaluate the antibacterial activity using an inhibition zone test, since they showed a promising drug release behavior and had PEO-rich biocompatible surfaces. In accordance with drug release behavior, EVA/PEO-coated catheters exhibited antibacterial activities for 7 days against Proteus vulgaris, Staphylococcus aureus and Staphylococcus epidermidis. These results imply that the catheters coated with EVA/PEO have a potential for short-term catheterization.