Thermo- and pH-responsive semi-IPN polyampholyte hydrogels were prepared by using carboxymethyl chitosan and P(2-(dimethylamino)
ethyl methacrylate) with NN'-Methylenebisacrylamide (BIS) as crosslinking agent. It was found that the semi-IPN hydrogel shrunk most at the isoelectric
point (IEP) and swelled when pH deviated from the IEP. Its swelling ratio dramatically decreased between 30 and 50 °C at pH 6.8
buffer solution. It also showed good reversibility. The UV results showed that when the pH values of drug release medium were
3.7, 6.8, and 9 at 25 °C, the cumulative release rates reached 83.1, 51.5, and 72.2%, respectively. The release rate of coenzyme
A (CoA) was higher at 50 °C than 37 and 25 °C at pH 6.8 solution. The release rate decreased with increasing the content of
carboxymethyl chitosan at 25 °C in pH 6.8 solution. The results showed that semi-IPN hydrogel seems to be of great promise
in pH/temperature drug delivery systems. 相似文献
Summary: Biodegradable thermosensitive triblock copolymers based on poly(ethylene glycol) and poly(lactic-co-glycolic acid) (PLGA-PEG-PLGA) prepared via ring opening polymerization were modified by itaconic anhydride (ITA), which gives copolymer both reactive double bonds and functional carboxylic acid groups essential for the reaction with biological active material. Functionalization conditions comprising ITA purification, temperature, time and presence of solvent were optimized with the respect to amount of end-capped ITA. Maximum of 76.6 mol. % of bonded ITA were reached via “one pot” reaction in a bulk at 110 °C after 1.5 h. ITA functionalization thermally stabilized the original copolymer by increasing the initial degradation temperature Td from 284 °C to 294 °C and changing the negative glass transition temperature (Tg = -1.8 °C) to positive one up to 2.4 °C. The novel functionalized macromonomer can be cross-linked either chemically or physically in order to produce new functionalized hydrogel network applicable as biomedical material in tissue engineering. 相似文献
Bioresorbable polymers composed of Poly(lactide), Poly(glycolide) and their related copolymers have become increasingly popular for the preparation of bone substitute constructs. In vitro tests assessing the degradative changes in physicochemical, mechanical, and biological properties of bioresorbable polymers are generally carried out at 37 °C, in pH 7.4 phosphate-buffered saline (PBS). However, long degradation times, varying from months to years make it difficult to assess these polymers at their late stages of degradation. An increased temperature accelerated degradation methodology, that simulates the long-term degradation of Poly(d,l-lactide-co-glycolide) and Poly(l-lactide-co-glycolide), has been validated in this study. Samples were degraded in PBS, under sterile conditions. Degradation temperatures of 47 °C, 57 °C and 70 °C were selected and compared to physiological temperature, 37 °C. At predetermined time intervals, samples were retrieved and evaluated for changes in mass, swelling, molecular weight, crystallinity, and thermal properties. The results from this study suggest that the degradation mechanism at elevated temperatures is similar to that observed at 37 °C. It is recommended that 47 °C is adopted by the research community to accelerate the degradation of these polymers. It is hoped the application of this methodology could be used as a valuable tool, prior to the assessment of the long-term biocompatibility of these polymers. 相似文献
Summary: After synthesizing both hard poly(organophosphazenes), which acted as strong hydrogels at a temperature below 37 °C, and soft poly(organophosphazenes), which displayed the opposite properties, we blended the polymers. When these polymers were blended at an appropriate ratio, the blended aqueous solution changed into a transparent hydrogel with improved mechanical properties at a temperature of 37 °C. According to DSC and IR measurements, the two polymers blended homogeneously and exhibited a behavior characteristic of a completely different copolymer.
An aqueous poly(organophosphazene) solution at room temperature (left) is reversibly and rapidly transformed into a transparent hydrogel at body temperature (right) when a hard poly(organophosphazene) is blended with a soft one at an appropriate ratio. 相似文献
Polyester/cotton fabric swith blend ratios of 0/100, 11/89, 20/80, 30/70, 50/50, and 65/35 were investigated via thermogravimetric analysis in both nitrogen and air atmospheres. The samples were heated from ambient to 750°C at a heating rate of 5°C min?1. The same fabrics were analyzed after treatment with tetrakis (hydroxymethyl) phosphonium chloride-urea-poly(vinyl bromide) (Thpc-urea-PVBr) flame retardant.Weight losses observed during pyrolysis were assigned to the cotton and polyester portions of the blends. Both cotton and polyester thermally decompose to yield gases and solid char byproducts. In nitrogen the 100% cotton fabric undergoes one major weight loss between 270 and 370°C, with the maximum rate of weight loss, 0.15 mg/min-mg occurring at 346°C. Thermal decomposition of the 100% polyester occurs over a range of 335–470°C, with the peak rate of weight loss, 0.11 mg/min-mg, measured at 416°C. In an air atmosphere, both volatile gases and solid char by- products of pyrolysis undergo combustion. The combustion reactions are associated with measured weight losses. The maximum rate of weight loss for the cotton portion increases to 0.25 mg/min-mg and occurs at 317°C. The maximum rate of polyester decomposition remains the same in both air and nitrogen, but the temperature decreases to 405°C. 相似文献
Attempts are being made to develop an ideal wound dressing with excellent biomechanical and biological properties. Here, a thermos-responsive hydrogel is fabricated using chitosan (CTS) with various concentrations (1%, 2.5%, and 5% w/v) of solubilized placental extracellular matrix (ECM) and 20% β-glycerophosphate to optimize a smart wound dressing hydrogel with improved biological behavior. The thermo-responsive CTS (TCTS) alone or loaded with ECMs (ECM-TCTS) demonstrate uniform morphology using SEM. TCTS and ECM1%-TCTS and ECM2.5%-TCTS show a gelation time of 5 min at 37 °C, while no gel formation is observed at 4 and 25 °C. ECM5%-TCTS forms gel at both 25 and 37 °C. The degradation and swelling ratios increase as the ECM content of the hydrogel increase. All the constructs show excellent biocompatibility in vitro and in vivo, however, the hydrogels with a higher concentration of ECM demonstrate better cell adhesion for fibroblast cells and induce expression of angiogenic factors (VEGF and VEGFR) from HUVEC. Only the ECM5%-TCTS has antibacterial activity against Acinetobacter baumannii ATCC 19606. The data obtained from the current study suggest the ECM2.5%-TCTS as an optimized smart biomimetic wound dressing with improved angiogenic properties now promises to proceed with pre-clinical and clinical investigations. 相似文献
Sebacyl bisketene was generated in solution at ?78°C. Copolymerization in solution at 0°C with the secondary diamines, piperazine and N,N′dimethyl-1,6-hexamethylenediamine, yielded the polyamides poly(1,4-piperazylsebacyl) and poly[(methylimino)hexamethylene(methylimino)sebacyl], respectively. The polyamides were obtained in yields of 50–90%. The former had a glass transition temperature (Tg) at 30°C and a melting temperature at 165°C, whereas the latter had only a Tg at ?15°C. The polymers were insoluble in the usual polyamide solvents. Copolymerization with the diol bisphenol A yielded poly(oxy-1,4-phenyleneisopropylidene-1,4-phenyleneoxysebacyl). The polyester was obtained in yields up to 99%. Gel permeation chromatography (GPC) determinations showed molecular weights up to 50,000 when acetone was the reaction solvent but only 12,000 when tetrahydrofuran (THF) was the reaction solvent; the Tg for the polyester varied with the molecular weight with a maximum at 15°C. Tensile properties were obtained for the polyesters with molecular weights greater than 35,000. 相似文献