Fabrication of Controlled Release Biodegradable Foams by Phase Separation

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Abstract
Highly porous biodegradable foams with controlled release function were fabricated by a phase separation technique. This technique involved inducing phase changes in a homogeneous solution of polymers with naphthalene or phenol used as solvents. A variety of foams with pore sizes ranging from 20 to 500 µm were made of poly(L-lactic acid) (PLLA), poly(bisphenol A-phenylphosphonate (BPA/PP), and its copolymer with poly[bis(2-ethoxy)- hydrophosphonic terephthalate] (PP/PPET). Controlled delivery capability was demonstrated by studying the release of sulforhodamine B and alkaline phosphatase (AP) from these highly porous structures. After an initial burst, AP was released from BPA/PP and PLLA foams at a near steady rate of 0.32 ± 0.04 and 0.49 ± 0.13 mg/day/g foam, respectively. These foams were intended for use as cell transplantation devices and tissue grafts such as synthetic bone grafts. Hydroxyapatite (HA) was added into the foams in an attempt to enhance interaction of these foams with bone. This composite was analyzed by energy dispersive spectroscopy, differential scanning calorimetry, and thermomechanical analysis. Since phosphates are known to have good affinity to calcium, poly(phosphoester) foams were treated with 1M calcium chloride solution in an attempt to study the possible interaction of the degrading poly(phosphoester) with calcium. After three weeks in 1 M calcium chloride solution, the complex modulus of the poly(phosphoester) foams changed from 40 to 1948 kPa, with a concurrent decrease in loss tangent from 0.349 to 0.170.

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