Problem Set 1 BE.462J/3.962J Biodegradable Solid Polymers Spring 2003 Issued: Day 1 Due: Day 3 1. The chemical structure of a new degradable polymer, poly(ethylene glycol)-b-polylysine-b poly(D,L-lactide), is shown below. a. Based on chemical structure alone, discuss your prediction of whether this material will degrade more quickly or more slowly than poly(L-lactide) in vivo. b. Cite 2 physical data you would want to know to make a better prediction in part (a), and explain why these would aid in this estimate. c. What will the end-point degradation products of this polymer be if it is degraded by incubation in vitro in phosphate buffered saline, pH 7.4 at 37°C? Would these products be different if the material were degraded in vivo? 2. The generation of acidic or basic degradation products is a serious issue complicating the design of devices for in vivo application, even for well-established materials like poly(lactide co-glycolide). Propose an approach to limit or eliminate the generation of a low pH within and near a PLGA device implant. Be creative! (limit ~1/2 page explanation). BE.462J/3.962J PS 1 1 of 1 3. Propose a route to synthesize the hydrolyzable polymer shown below. Show the structure of the monomers you would use and any initiators/catalysts. CH 3 O O H CH 3 -C-O-C-CH 2 -CH 2 -O-(C-CH-O-C-CH-N) n -H CH 3 O CH 3 (CH 2 ) 4 NH 2 4. In order to carry out studies of polymer hydrolysis on reasonable experimental timescales, a number of researchers have used elevated temperature to speed up degradation. Using the data given below, determine the degradation mechanism (surface or bulk erosion) for a sample of polycaprolactone (ρ = 1.146 g/cm 3 ) 0.02m thick degraded in water at 37°C and whether the mechanism is changed by degrading the sample at 85°. (Hint: assume both the hydrolysis rate constant and the diffusivity of water in the polymer have an Arrhenius form.) At 37°C: k = 9.7x10 -8 s -1 D H2O = 10 -8 cm 2 s -1 At 50°C: k = 5.4x10 -7 s -1 D H2O = 3.5x10 -8 cm 2 s -1 k = rate constant of PCL bond hydrolysis D H2O = diffusivity of water in PCL BE.462J/3.962J PS 1 2 of 2