POLY(GAMMA-GLUTAMIC ACID) HYDROGEL PREPARED FROM MICROBIAL POLY(GAMMA-GLUTAMIC ACID) AND ALKANEDIAMINE WITH WATER-SOLUBLE CARBODIIMIDE

Poly(gamma-glutamic acid) (PGA) hydrogels have been prepared from micr obial PGA produced by Bacillus subtilis F-02-1, water-soluble carbodii mide (WSC), and alkanediamines such as 1,3-propanediamine (1,3-PD), 1, 4-butanediamine (1,4-BD), and 1,6-hexanediamine (1,6-HD) in aqueous me dium. The carboxyl groups of PGA were activated by the addition of WSC in deionized water, and the PGA-WSC adduct was produced. PGA hydrogel s could be produced after the mixing of PGA-WSC and alkanediamine in d eionized water. This alkanediamine to which both amino groups reacted with the carboxyl groups of PGA plays the role of a crosslinking point . When the amount of PGA was 100 mg, WSC was 50 mg or more, and 1,3-PD was 25 mu L or more in 2 mt of deionized water, PGA hydrogels could b e produced. Specific water contents (weight of absorbed water/weight o f dry gel) ranged from 300 to 1,993 g/g in the case of 1,3-PD. If the PGA-WSC adduct was freeze-dried, the yield of the PGA hydrogel became higher than that when PGA-WSC was not freeze-dried. The highest yield of the PGA. hydrogel from 100 mg of PGA, 100 mg of WSC, and 100 mu L o f 1,3-PD in 2 mt of deionized water using the freeze-dry method was 39 .9 mg of dry PGA hydrogel with a 650 g/g specific water content. The o rder of yield was 1,6-HD > 1,4-BD > 1,3-PD from 100 mg of PGA-100 mg o f WSC in 2 mt of deionized water. The order of the specific water cont ent was 1,3-PD (462 g/g) > 1,4-BD (234 g/g) > 1,6-HD (199 g/g). This o rder may be due to the higher reaction probability between the activat ed carboxyl groups in the PGA-WSC and both amino groups in the alkaned iamine with longer methylene chains, indicating that the crosslinking density of the PGA hydrogel is higher and the specific water content i s lower. (C) 1997 John Wiley & Sons, Inc.