Problem 3. You want to make a drug delivery implant for controlled release of a small molecule anticancer drug to the brain. The implant is a long rectangular rod with a thickness of 1 cm (See Fig 1) and the clinician you are collaborating with recommends that the implant erode by bulk degradation. You are trying to choose between two materials: 1) a poly(ester) and 2) a poly(anhydride). These materials have the same molecular weight per repeat unit (Mw,repeat 100 g/mol). Other data for the two materials is shown below. Units g/cm Variable PEster PAnhydride DH20, Ester DH20, Anhydride Description Mass density of ester Mass density of anhydride Diffusivity of H2O in ester Diffusivity of H2O in anhydride g/cm Value 1.04 1.04 5.00E-08 5.00E-08 cm?/sec cm/sec a. Using data in the statement and data from class, calculate the respective erosion numbers of the potential materials to be evaluated in this study. b. What are the corresponding degradation mechanisms of the poly(ester) and poly(anhydride)? c. You want to use the poly(anhydride) because of FDA recommendations, but first you must change the geometry of the implant to achieve bulk degradation (Fig 2). You decide to modify the implant with fins to reduce the effective thickness of the device. What should the thickness of the fins be in the modified device be to meet the requirements? Initial Device Thickness = 1 cm Modified Device Thickness = ??? cm Saline (water) source Fig 1. Saline (water) source Fig 2. Problem 3. You want to make a drug delivery implant for controlled release of a small molecule anticancer drug to the brain. The implant is a long rectangular rod with a thickness of 1 cm (See Fig 1) and the clinician you are collaborating with recommends that the implant erode by bulk degradation. You are trying to choose between two materials: 1) a poly(ester) and 2) a poly(anhydride). These materials have the same molecular weight per repeat unit (Mw,repeat 100 g/mol). Other data for the two materials is shown below. Units g/cm Variable PEster PAnhydride DH20, Ester DH20, Anhydride Description Mass density of ester Mass density of anhydride Diffusivity of H2O in ester Diffusivity of H2O in anhydride g/cm Value 1.04 1.04 5.00E-08 5.00E-08 cm?/sec cm/sec a. Using data in the statement and data from class, calculate the respective erosion numbers of the potential materials to be evaluated in this study. b. What are the corresponding degradation mechanisms of the poly(ester) and poly(anhydride)? c. You want to use the poly(anhydride) because of FDA recommendations, but first you must change the geometry of the implant to achieve bulk degradation (Fig 2). You decide to modify the implant with fins to reduce the effective thickness of the device. What should the thickness of the fins be in the modified device be to meet the requirements? Initial Device Thickness = 1 cm Modified Device Thickness = ??? cm Saline (water) source Fig 1. Saline (water) source Fig 2
