Modification of Stimuli-responsive Polymers by Self-assembling for Application in Biomimetic Materials

• Main Authors: Hsiu-wen Yang, 楊琇雯
• Other Authors: Jem-kun Chen
• Format: Others
• Language: zh-TW
• Published: 2014
• Online Access: http://ndltd.ncl.edu.tw/handle/12979914043306789927

博士 === 國立臺灣科技大學 === 材料科學與工程系 === 102 === (1) Association of poly(N-isopropylacrylamide) containing nucleobase multiple hydrogen bonding of adenine for DNA recognition: In this study we used the poly(N-isopropylacrylamide) (PNIPAAm) as a medium to generate PNIPAAm–adenine supramolecular complexes. A nucleobase-like hydrogen bonding (NLHB) between PNIPAAm and adenine was found that changed the morphology, crystalline structure, and temperature responsiveness of PNIPAAm microgels relatively to the adenine concentrations. With increasing the adenine concentration, the PNIPAAm–adenine supramolecular complexes gradually altered their morphologies from microgel particles to thin film structures and suppressed the thermodynamical coilto-globule transition of PNIPAAm because of the NLHB existed between the PNIPAAm amide and ester groups and the adenine amide groups (C=O‧‧‧H-N and N-H‧‧‧N-R), verified by FTIR spectral analysis. NLHB was also diverse and extensive upon increasing the temperature; therefore, the thermoresponsive behavior of the complexes was altered with the NLBH intensity, evaluated by the inter-association equilibrium constant (Ka) above and below their LCST. Therefore, PNIPAAm can be as a medium to recognize adenine in various concentrations, which could potentially be applied in DNA recognition. (2) Thermo-responsive Hydrogel Semiconductor of Poly(N-isopropylacrylamide)-Nucleobase Supramolecular Complexes via Bio-multiple Hydrogen Bonding Poly(N-isopropylacrylamide) (PNIPAAm) is exploited as a matrix to hybridize with five kinds of nucleobase units including adenine, thymine, uracil, guanine and cytosine generating PNIPAAm-nucleobase supramolecular complexes (PNSC) via bio-multiple hydrogen bonding (BMHB). These nucleobase units interact with PNIPAAm by various strength BMHB leading to a competition between BMHB and intramlecular HB interaction of PNIPAAm. Various changes in morphology, crystalline structure, and thermo-responsive behavior of PNIPAAm are relative to the strength of BMHB interaction between PNIPAAm and nucleobase units. The species of nucleobase units that generate BMHB interaction from high to low strength is following : guanine > adenine > thymine > cytosine > uracil, verified by FTIR, lower critical solution temperature (LCST), and inter-association equilibrium constant (Ka). The PNSCs also exhibit remarkable improvement in conductivity due to formation of rich proton transport of BMHB. Neat PNIPAAm film, regarded as a insulator, could be turned to a semiconductor after hybridizing with nucleobase units. Especially for PNIPAAm-guanine supramolecular complexes, the resistivity is reduced to 1.35 × 105 (ohm-cm). The resistivity of PNIPAAm-cytosine supramolecular complexes exhibits significant change from 5.83 × 106 to 3 × 108 when temperature increases from 40 to 50?aC, which could be applied in thermo-sensing. The results showed that conductivity of hydrogels can be improved significantly via BMHB using a simple approach, which may provide hydrogels a novel sight in application of bioelectronics. (3) Degradable coronas comprising polyelectrolyte complexes of PDMAEMA and gelatin for pH-triggered antibiotic release Carboxyl-modified polystyrene (PS) nanospheres were used as sacrificial cores upon which cross-linked gelatin (CGA) was assembled through successive immobilization with poly(N,N-dimethylaminoethyl methacrylate) (PDMAEMA), forming polyelectrolyte complexes (PECs) stabilized through electrostatic interactions and hydrogen bonding. The PEC coronas, possessing hollow structure, of the PEC CGA@PDMAEMA after removing the PS cores were obtained. At pH 2.2, the protonated PDMAEMA swelled the PEC coronas completely, leading to the disappearance of the inner cavities, which reappeared after increasing the pH to 5.5. Further increasing the pH to 8.1 caused the deprotonated PDMAEMA to collapse completely to cover the CGA surface, generating a solid shell. This pH-responsive structural change of the PEC coronas suggested that they could be used as drug capsules. Accordingly, amoxicillin (AMX) was loaded into the coronas as a medium to inhibit the bacterial viability of Escherichia coli and Staphylococcus aureus. Both of bacterial growth rates of E. coli and S. aureus in solution at pH 8.1 in the presence of the AMX-loaded PEC coronas did not change significantly within 8 h comparing with that in a blank experiment, indicating that the PEC coronas confined the AMX units within the hollow structure. With decrease of the pH to 5.5, the bacterial growth rates were inhibited obviously within 2 h relative to that in a blank experiment, confirming that the AMX units could be released from the PEC coronas by tuning pH value.