Won Ho Park

Blood compatibility and biodegradability of partially N-acylated chitosan derivatives

Chitosan was selectively N-acylated with various carboxylic anhydrides, e.g., acetic, propionic, n-butyric, n-valeric and n-hexanoic anhydrides, in the presence of methanol. The degree of N-acylation of about 20-50% was obtainable without occurrence of gelation by using carboxylic anhydrides of 0.3-1.2 mol per glucosamine residue. In vitro blood compatibility tests of N-acyl chitosans were performed by rheological measurement, blood clotting test and scanning electron microscopic observation for human blood and plasma protein. The rheological measurement of coagulation of plasma protein, considering the shear flow effect of blood, gave precise and quantitative results compared with other methods. N-Acyl chitosans showed more blood compatible properties than N-acetyl chitosan and, in particular, N-hexanoyl chitosan was the most compatible. Enzymatic degradation was also investigated by adding a lysozyme solution to the N-acyl chitosan solution and film, incubating at 37 degrees C. N-Acyl chitosans had as high a susceptibility to lysozyme as N-acetyl chitosans. It was considered that the amount of derivatized groups and the physical form of N-acyl chitosans contributed to biodegradability. The molecular weight (Mw) of the material liberated from the N-acyl chitosan film by the action of lysozyme was 2 x 10(4) - 10 x 10(4).

Electrospinning of polysaccharides for regenerative medicine.

Electrospinning techniques enable the production of continuous fibers with dimensions on the scale of nanometers from a wide range of natural and synthetic polymers. The number of recent studies regarding electrospun polysaccharides and their derivatives, which are potentially useful for regenerative medicine, is increasing dramatically. However, difficulties regarding the processibility of the polysaccharides (e.g., poor solubility and high surface tension) have limited their application. In this review, we summarize the characteristics of various polysaccharides such as alginate, cellulose, chitin, chitosan, hyaluronic acid, starch, dextran, and heparin, which are either currently being used or have potential to be used for electrospinning. The recent progress of nanofiber matrices electrospun from polysaccharides and their biomedical applications in tissue engineering, wound dressings, drug delivery, and enzyme immobilization are discussed.

Collagen-based biomimetic nanofibrous scaffolds: preparation and characterization of collagen/silk fibroin bicomponent nanofibrous structures.

Electrospinning of collagen (COL)/silk fibroin (SF) blend solutions in 1,1,1,3,3,3-hexafluoro-2-propanol was investigated for fabrication of a biocompatible and biomimetic nanostructured scaffold for tissue engineering. The morphology of the electrospun COL/SF blend nanofibers was observed by scanning electron microscopy. The average diameters of COL/SF blend fibers ranged from 320 to 360 nm, irrespective of SF content in the blends. Both COL and SF components in the as-spun COL/SF blend matrices were stabilized by glutaraldehyde and water vapor, respectively, under the saturated glutaraldehyde aqueous solution at 25 degrees C. The glutaraldehyde vapor chemically stabilized the COL component via cross-linking, whereas the water vapor physically stabilized the SF component via crystallization to the beta-sheet structure. These structural changes of after-treated COL/SF blend matrices were examined using ATR-IR and CP/MAS (13)C NMR spectroscopy. To assay the cytocompatibility and cellular behavior of the COL/SF blend nanofibrous scaffolds, cell attachment and the spreading of normal human epidermal keratinocytes (NHEK) and fibroblasts (NHEF) seeded on the scaffolds were studied. In addition, both morphological changes and cellular responses of COL/SF blend nanofibrous matrices were also compared with COL/SF hybrid nanofibrous matrices. Generally similar levels of cell attachment and spreading of NHEF were shown in the COL/SF blend nanofibrous matrix compared with those of the pure COL and pure SF matrices; the cellular responses of NHEK were, however, markedly decreased in the COL/SF blend nanofibrous matrix as compared to the pure matrices. In contrast, cell attachment and spreading of NHEK on the COL/SF hybrid nanofibrous matrix were significantly higher than that of the COL/SF blend nanofibrous matrix. Our results indicate that a COL/SF hybrid nanofibrous matrix may be a better candidate than a COL/SF blend nanofibrous matrix for biomedical applications such as wound dressing and scaffolds for tissue engineering.

Polyelectrolyte Complexes of Sodium Alginate with Chitosan or Its Derivatives for Microcapsules

Chitosan, a cationic polysaccharide, was heterogeneously deacetylated with a 47% sodium hydroxide solution and followed by a homogeneous reacetylation with acetic anhydrides to control the N-acetyl content of the chitosan having a similar molecular weight. The chitosans having different degrees of N-acetylation were complexed with sodium alginate, an anionic polysaccharide, and the formation behavior of polyelectrolyte complexes (PECs) was examined by the viscometry in various pH ranges. The maximum mixing ratio (Rmax) increased with a decrease in the degree of N-acetylation of the chitosan at the same pH, and with a decrease in pH at the same degree of N-acetylation. Similarly, N-acylated chitosans were also prepared. The N-acyl chitosans scarcely affected the formation behavior of PECs with sodium alginates. For the application of the PECs produced, the microencapsulation of a drug was performed and the release property of drug was tested. The microcapsules were prepared in one step by the extrusion of a solution of guaifenesin and sodium alginate into a solution containing calcium chloride and chitosan through interpolymeric ionic interactions. The drug release during the drug-loaded microcapsules storage in saline was found to depend on the pH where the microcapsules were formed and the kind of N-acyl groups introduced to the chitosan.

Synthesis of chitooligosaccharide derivative with quaternary ammonium group and its antimicrobial activity against Streptococcus mutans

A derivative of chitooligosaccharide (COS) with quaternary ammonium functionality was synthesized and characterized by means of FT-IR and NMR spectroscopy. Its amtimicrobial activity was evaluated against Streptococcus mutans, which is a principal etiological agent of dental caries in humans. Introduction of quaternary ammonium group to COS has been easily accomplished by coupling of glycidyl trimethylammonium chloride (GTMAC) to COS in aqueous solution without an additional catalyst. The degree of substitution (%), as determined by (1)H NMR, of GTMAC to the COS increased up to 116% at 70 degrees C for 24h. The resulting COS-GTMAC exhibited the growth inhibition of above 80% against S. mutans after 5h, whereas the COS showed the growth inhibition of about 10%. It was found that antimicrobial activity of the COS could be considerably enhanced by the introduction of quaternary ammonium functionality.

Superhydrophobicity of PHBV fibrous surface with bead-on-string structure

A poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) fibrous surface with various bead-on-string structures was fabricated by electrospinning. PHBV was electrospun at various concentrations and then CF4 plasma treatment was employed to further improve the hydrophobicity of the PHBV fiber surfaces. The surface morphology of the electrospun PHBV mats was observed by scanning electron microscopy (SEM). The surface properties were characterized by water contact angle (WCA) measurements and X-ray photoelectron spectroscopy (XPS). The surface morphology of the electrospun PHBV fibrous mats with the bead-son-string structure varied with the solution concentration. The WCA of all of the electrospun PHBV mats was higher than that of the PHBV film. In particular, a very rough fiber surface including porous beads was observed when PHBV was electrospun from the solution with a concentration of 26 wt%. Also, its WCA further increased from 141 degrees to 158 degrees after CF(4) plasma treatment for 150 s. PHBV can be rendered superhydrophobic by controlling the surface morphology and surface energy, which can be achieved by adjusting the electrospinning and plasma treatment conditions.

Plasma-Treated Poly(Lactic-co-glycolic acid) Nanofibers for Tissue Engineering

Nanofibers were prepared by electrospinning a solution of poly(lactic-co-glycolic acid) (PLGA) and their mean diameter was 340 nm. The PLGA nanofibers were treated with a plasma in the presence of either oxygen or ammonia gas to change their surface characteristics. The hydrophilicity of the electrospun PLGA nanofibers was significantly increased by the gas plasma treatment, as confirmed by contact angle measurements. XPS analysis demonstrated that the chemical composition of the PLGA nanofiber surface was influenced by the plasma treatment, resulting in an increase in the number of polar groups, which contributed to the enhanced surface hydrophilicity. The degradation behavior of the PLGA nanofibers was accelerated by the plasma treatment, and the adhesion and proliferation of mouse fibroblasts on the plasma-treated nanofibers were significantly enhanced. This approach to controlling the surface characteristics of nanofibers prepared from biocompatible polymers could be useful in the development of novel polymeric scaffolds for tissue engineering.

Chitosan-coated poly(vinyl alcohol) nanofibers for wound dressings

A PVA nanofibrous matrix was prepared by electrospinning an aqueous 10 wt % PVA solution. The mean diameter of the PVA nanofibers electrospun from the PVA aqueous solution was 240 nm. The water resistance of the as-spun PVA nanofibrous matrix was improved by physically crosslinking the PVA nanofibers by heat treatment at 150 degrees C for 10 min, which were found to be the optimal heat treatment conditions determined from chemical and morphological considerations. In addition, the heat-treated PVA (H-PVA) nanofibrous matrix was coated with a chitosan solution to construct biomimetic nanofibrous wound dressings. The chitosan-coated PVA (C-PVA) nanofibrous matrix showed less hydrophilic and better tensile properties than the H-PVA nanofibrous matrix. The effect of the chitosan coating on open wound healing in a mouse was examined. The C-PVA and H-PVA nanofibrous matrices showed faster wound healing than the control. The histological examination and mechanical stability revealed the C-PVA nanofibrous matrix to be more effective as a wound-healing accelerator in the early stages of wound healing than the H-PVA nanofibrous matrix.

Plasma-treated silk fibroin nanofibers for skin regeneration

Silk fibroin (SF) nanofibers were prepared by electrospinning and treated with plasma in the presence of oxygen or methane gas to modify their surface characteristics. The surface characteristics of the SF nanofibers after plasma treatment were examined using contact angle measurements and XPS analysis. The hydrophilicity of the electrospun SF nanofibers decreased slightly by the CH(4) plasma treatment. On the other hand, the hydrophilicity of the SF nanofibers increased greatly by an O(2) plasma treatment. The O(2)-treated SF nanofibers showed higher cellular activities for both normal human epidermal keratinocytes (NHEK) and fibroblasts (NHEF) than the untreated ones.

Novel three-dimensional scaffolds of poly(L-lactic acid) microfibers using electrospinning and mechanical expansion: Fabrication and bone regeneration

Poly(L-lactic acid) (PLLA) microfibrous scaffolds with three-dimensional (3D) structures were fabricated using an electrospinning technique with a subsequent mechanical expansion process. To achieve a 3D fibrous structure, the fusion at the contact points of the as-spun PLLA microfibers was avoided using an appropriate binary solvent system of methylene chloride and acetone. The solvent composition was optimized based on the solvent power, volatility, and viscosity (methylene chloride:acetone = 9:1 volume ratio). The final 3D structure of the electrospun scaffolds was obtained after mechanical expansion of the electrospun microfibrous mats. The pore sizes of the scaffolds were controlled by varying the degree of expansion of the nonbonded microfibrous mats, and they were in the range of several microns up to 400 μm. The 3D scaffolds were examined for their morphological properties and their potential use for the proliferation of osteoblasts. Generally recognized electrospun 2D nanofibrous membranes were also tested in order to compare the cell behaviors using different scaffold geometries. The 3D scaffolds demonstrated a high level of osteoblast proliferation (1.8-fold higher than nanofibrous membranes in a week). The osteoblasts actively penetrated the inside of the 3D scaffold and showed a spatial cell distribution, as confirmed by SEM and H&E staining, while a monolayer formed in the case of the 2D nanofibrous membranes with limited cell infiltration. In vivo results further showed that 3D electrospun microfibrous matrices were a favorable substrate for cell infiltration and bone formation after 2 and 4 weeks, using a rabbit calvarial defect model. In this study, the 3D microfibrous PLLA scaffolds fabricated using electrospinning techniques might be an innovative addition to tissue engineering applications.