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Title: A study of thermosensitive poly(N-isopropylacrylamide)/ polyurethane hydrogel modified nonwoven fabrics
Authors: Liu, Baohua
Degree: Ph.D.
Issue Date: 2007
Abstract: The purpose of the investigation is to study a novel smart textile which has the great merits of nutrient controlled release and antibacterial activities. Such a smart textile is suitable for facial and medical use. To achieve the research aims, the textile was modified by temperature sensitive poly(N-isopropylacrylamide)/polyurethane (PNIPAAm/PU) hydrogels and chitosan. Although stimuli sensitive hydrogels have been widely applied, reports on its application to textitles are still limited. The nonwoven fabric modified by the PNIPAAm/PU hydrogels has temperature and pH sensitivity. Then the hydrogel modified fabric was modified by chitosan, which enhances the fabic antibacterical activities. The antibacterial activities and nutrient controlled release behaviour of these composite fabrics have been studied systematically. The percentage of grafted hydrogels is greatly dependent on the monomer concentration. Thus the higher monomer concentration will result in more hydrogel grafting onto the nonwoven fabrics. A visual inspection found that thick layers of hydrogels were coated on the surface of the nonwoven fabrics. Two modifying mechanisms may exist during the process of modification. One is the free radical graft copolymerization of NIPAAm and PU with polysaccharide initiated by APS. Another mechanism involved might be physical entrapment and anchoring. The DSC results suggested that the phase transition temperature of the smart fabrics obtained is between 32 oC and 35 oC, which is very close to the lower critical solution temperature (LCST) of the pure PNIPAAm hydrogel. This result indicates that the incorporation of PU suppressed the heavy syneresis of pure PNIPAAm hydrogel without an effect on its thermal transition. With the support of nonwoven fabrics, the PNIPAAm/PU hydrogel has a good mechanical performance. After chitosan modification, the thermosensitive hydrogel modified nonwoven has antibacterial activity to S. aureus and E. coli. FTIR and XPS testing results confirmed that the chitosan was bound onto the surface of the samples. And the antibacterial efficiency is near 80% as determined by using shaking flask method. Moreover, the sample is still temperature-sensitive after chitosan modification and the higher the monomer concentration, the better antibacterial activity the sample has. The higher NIPAAm/PU feeding ratio led to higher antibacterial activity, because more chitosan was incorporaed onto the hydrogel surface. The antibacterial efficiency has almost no fluctuation for hydrogels with different crosslinking densities. The absorption mode and DNA/RNA interfering pattern might be the two main antibacterial mechanisms of the modified fabrics. To study the controlled release of the smart fabrics modified by thermosensitive hydrogels/ and chitosan, Vitamin C (Vc) was used as model nutrient. All the releasing manners are biphasic processes. The first stage is short but the releasing speed is fast. The second stage is a stable release process. The release behaviours of Vc from the PNIPAAm/PU hydrogels modified fabrics can be controlled by temperature. Moreover, after chitosan modification, the releasing mode has no significant changes. A diffusion-controlled mechanism and squeezing out controlled release mechanism may coexist in the release system because the PNIPAAm/PU copolymer hydrogel can swell below 32oC and deswell above 32oC. When the temperature is below the phase transition temperature of the hydrogel, the dominant mechanism is diffusion-controlled system, and the releasing rate is lower. When temperature increases above the LCST, the releasing process was controlled by diffusion and squeezing-off mechanisms together. These two mechanisms can enhance the release amount and speed. As a result, the release amount and speed at higher temperature is faster and higher, respectively, than those at lower temperature. Except for the network structure and swelling ratio of the hydrogel, the entrapping effect caused by the shrinkage of the PNIPAAm hydrogel will alter the releasing mode also. At 37oC, the fast shrinkage of the surface layer of the hydrogel will increase the entrapping effect. With a good temperature controlled release property and antibacterial activity, the novel smart fabric has great potential application in the medical and skin care cosmetic fields.
Subjects: Hong Kong Polytechnic University -- Dissertations.
Biomedical materials.
Nonwoven fabrics.
Colloids in medicine.
Polymers in medicine.
Pages: xxvi, 219 leaves : ill. ; 30 cm.
Appears in Collections:Thesis

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