No abstract

The purpose of this work was to synthesize and characterize a pH- and temperature-sensitive block copolymer containing repeating sequences from silk (Gly-Ala-Gly-Ala-Gly-Ser) and elastin (Gly-Val-Gly-Val-Pro) protein. The monomer contained one repeat of silk and eight repeat units of elastin, with the first valine in one of the elastin repeats being replaced by glutamic acid. The copolymer was synthesized using genetic engineering techniques. The sensitivity of the copolymer to pH and temperature was examined at various polymer concentrations and ionic strengths. Turbidity measurements were carried out over a temperature range of 20 to 100 degrees C at various pH, concentration, and ionic strength values. The introduction of an ionizable residue (glutamic acid) rendered the copolymer sensitive to changes in pH. The transition termperature (T(t)), the temperature at which the polymer became insoluble upon increase in temperature, was modulated by changing the pH. In general, the T(t) value, was found: (1) to increase with an increase in pH, (2) to decrease with increasing ionic strength, and (3) to decrease with increasing concentration. Results of these studies suggest that by strategic placement of charged amino acids in genetically engineered silk-elastinlike protein block copolymers it is possible to precisely control sensitivity to stimuli such as pH and temperature.

Differentially charged analogues of block copolymers containing repeating sequences from silk (GAGAGS) and elastin (GVGVP) were synthesized using genetic engineering techniques by replacing a valine residue with glutamic acid. The sensitivity to pH and temperature was examined at various polymer concentrations, ionic strengths, and polymer lengths. The polymers transitioned from soluble to precipitate state over narrow temperature ranges. The transition temperature T(t) (the temperature at which half-maximal spectrophotometric absorption was observed) increased with increasing pH up to pH 7.0 and leveled off above this value for the Glu-containing polymer (17E)(11). T(t) was independent of pH for the Val-containing polymer (17V)(11). It decreased with increasing ionic strength, polymer concentration, and polymer length for both polymers. These results suggest that by substituting charged amino acids for neutral amino acids at strategic locations in the polymer backbone and by control of the length of silkelastin-like block copolymers using genetic engineering techniques, it is possible to precisely control sensitivity to pH, temperature, and ionic strength.