| A photocrosslinkable azide hydroxypropyl chitosan(Az-HPCS) was prepared by introducing photoreactive azide groups (4-azidobenzoic acid, Az-) to the amino groups of hydroxypropyl Chitosan (HPCS), a water-soluble chitosan derivate, Its structure and Az- substitution degree was characterized by NMR, FT-IR, elemental analysis. Az-HPCS solution (25 mg/ml) was crosslinked to form hydrogel under UV irridiation (4w, 254nm, 90sec). We are interested in the potential of this hydrogel as wound dressing, tissue engineering scaffold, and multi-layer skin substitute.We characterized the in situ formed hydrogel membrane for evaluating its potentiality as a wound dressing. Generally, in situ formed hydrogel dressings create minimally invasive methods that offer advantages over the use of preformed dressings such as conformability in any wound bed, convenience of application, and improved patient compliance and comfort. The hydrogel membrane is stable, flexible, and transparent, with a bulk network structure of smoothness, integrity, and density. Fluid uptake ability, water vapor transmission rate, water retention and adherence strength of the resulted hydrogel membranes (0.1mm thick) were determined to range from 97.0~96.3%, 2934~2561g/m2/day, 36.69~22.94% (after 6 days), and 4.8~12.3N/cm2, respectively. These data indicates that the hydrogel membrane can maintain a long period of a moist environment over wound bed for enhancing re-epithelization. Specifically, these properties of the hydrogel membrane were controllable to some extent, by adjusting the substitution degree of the photoreactive azide groups. The hydrogel membrane also exhibited barrier function, as it was impermeable to bacteria but permeable to oxygen. In vitro experiments using two major skin cell types (dermal fibroblast and epidermal keratinocyte) revealed the hydrogel membrane does not have cytotoxicity or effects on cell proliferation. Taken together, the in situ photocrosslinked Az-HPCS hydrogel membrane has a great potential in the management of wound healing and skin burn.We also assess the possibility of applying Az-HPCS in skin tissue engineering. The crosslinked Az-HPCS hydrogel was pre-freeze at -80°C then lyophilized, obtaining the Az-HPCS scaffold. Scanning electron microscopy, measurement of pore size and porosity, mechanical test, swelling test, in vitro biodegradation determination, in vitro releasing of incorporated bovine serum albumin (BSA) were used to determined the properties of the scaffolds. When DS of Az- groups increased from 2.8% to 5.6%, We found that (i) the pore size of Az-HPCS scaffolds increased by about 2-fold and the porosity increased slightly, probably due to more N2 released from the crosslinking reaction with the increasing of DS; (ii) both the tensile stress and strain increased by about 3-fold, relating to the increasing of joint points, pore size and porosity at a relative high DS; (iii) the swelling ratio and degradation rate decreased with the increasing of Az- DS, due to the forming of a more compact network structure. Preliminary data of cell culture on Az-HPCS scaffold revealed that this hydrogel scaffold has good biocompatibilty. Taken together, it could be an poteintial tissue culture scaffold with controllable properties.We combined the advantages of Az-HPCS hydrogel membrane and Az-HPCS scaffold to develop a bilayer chitosan skin regeneration template. The bilayer material was composed by a dense Az-HPCS membrane upper layer and a sponge-like Az-HPCS scaffold sublayer. The sublayer has a great biocompatibility to the attachment and ingrowth of fibroblast. Thus the bilayer chitosan material can be applied to treat the full-thickness skin defect. |
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