Processing and properties of two different poly (ortho esters)

Processing and properties of two structurally different poly (ortho esters) (POE) and their in vitro behavior have been compared. One POE was a copoly mer of diketene acetal 3,9-diethylidene-2,4,8,10-tetraoxaspiro[5.5]undecane , trans-cyclohexanedimethanol and polyacetal. The other POE was a copolymer of diketene acetal 3,9-diethylidene-2,4,8,10-tetraoxaspiro[5.5]undecane, t rans-cyclohexanedimethanol and trans-cyclohexanedimethanol-dilactide. The p olyacetal POE was also used as a matrix incorporating two different model d rugs, caffeine and furosemide. Both polymers were ultrasonically molded int o slabs. The lactide modified POE was also melt-extruded into rods and self -reinforced using a solid state die-drawing technique. The initial strength values of both ultrasonically molded and extruded samples were close to th ose of non-oriented poly lactic acids. Self-reinforcing increased the shear strength, bending strength and modulus of the rods from 41.7 +/- 1.7MPa to 66.7 +/- 2.3MPa, from 78.5 +/- 22.8MPa to 183 +/- 23MPa and from 2.5 +/- 0 .3GPa to 4.4 +/- 0.3GPa, respectively. In vitro hydrolysis of samples was s tudied either in phosphate buffer saline (PBS) or in simulated body fluid ( SBF) at 37 degrees C. Samples degraded faster in unchanged PBS than in PBS changed weekly. The total in vitro strength retention time was relatively s hort varying from 14 days to 42 days depending on the processing method and polymer type. Samples retained their wet weight at initial level for a lon ger time but dry weight started to decrease already after the first in vitr o week. Polymers or degradation products crystallized in SBF but remained a morphous when hydrolyzed in PBS. Some of the devices showed evidence of sur face erosion, and the processing method affected the erosion. The storage t ime of these polymers was found to be limited. However, both polymers were found to be of interest in bone fixation and tissue engineering. (C) 2000 K luwer Academic Publishers.