biodegradible polymers are provided which may contain a biologically active substance , e . g . a drug such as insulin , which is released over a period of time as the polymer erodes when in contact with a body fluid . the polymer contains an amine functionality whereby it erodes faster at low acid ph &# 39 ; s than at higher acid ph &# 39 ; s . as an example , the polymer may contain insulin and may contain or may have an encapsulating hydrogel containing glucose oxidase . as the blood sugar level of a diabetic person rises , e . g ., afte a meal , glucose diffuses into the polymer or hydrogel and is converted to gluconic acid which lowers the ph , and accelerates erosion and the release of insulin .