In vitro degradation of a biodegradable polyurethane foam, based on 1,4-butanediisocyanate: a three-year study at physiological and elevated temperature.

Biodegradable polyesterurethanes (PUs) may be used as scaffold materials for tissue regeneration applications, because of their excellent mechanical properties. In this study, the degradation of highly porous PU foams was evaluated in vitro. The PU had amorphous soft segments of DL-lactide/epsilon-caprolactone and uniform hard segments, synthesized from 1,4-butanediisocyanate and butanediol. The foams were degraded for 3 years in a Sörensen buffer solution (pH 7.4) at 37 and 60 degrees C. Dimensions of the foams, intrinsic viscosity, mass loss, thermal properties, and composition of the remaining material were evaluated. Copolyester (CP) foams of DL-lactide/epsilon-caprolactone served as controls. The PU foams kept their dimensions for 20 weeks at 37 degrees C, whereas CP foams collapsed after 3 weeks. PU mass loss reached a maximum of 80% at both 37 and 60 degrees C. CP mass loss reached 99.9% at 60 degrees , and 92% at 37 degrees C after 3 years. The degradation processes at 37 and 60 degrees C are initially the same, but eventually degradation products with different thermal properties are being formed. (1)H NMR studies showed that the hard urethane segments of the PU do not degrade in vitro at pH 7.4. It was concluded that the PU material has favorable characteristics for a scaffold material. Compared to long-term in vivo results of the same PU these in vitro results are not representative for the in vivo situation and therefore total resorption has to be investigated in long-term in vivo studies.

An animal model for oroantral communications: a pilot study with Göttingen minipigs.

A pilot study was performed to investigate whether the Göttingen minipig is a suitable animal model for creating and closing oroantral communications (OACs) and to test whether these defects can be closed with a biodegradable polyurethane (PU) foam. In three adult minipigs, an OAC was created on both sides of the maxilla. The left side was closed by a standard surgical buccal flap procedure, the right side by applying a PU foam. The pigs were killed after two weeks, one month and three months, respectively. Postmortem and histological examination showed that an OAC was created in only one of six cases. In the remaining cases, the infraorbital canal was perforated instead of the floor of the maxillary sinus. It was concluded that the Göttingen minipig is not a suitable animal model for OAC investigations. As a result, the closure of OACs with a biodegradable PU could not be evaluated.

Short-term in vitro and in vivo biocompatibility of a biodegradable polyurethane foam based on 1,4-butanediisocyanate.

In this study short-term in vitro and in vivo biocompatibility apects of a biodegradable polyurethane (PU) foam were evaluated. The PU consists of hard urethane segments and amorphous soft segments based on a copolyester of dl-lactide and epsilon-caprolactone. The urethane segments are of uniform length and synthesized with 1,4-butanediisocyanate. The foam has good mechanical properties and will be used for tissue regeneration applications. Degradation tests were carried out in a buffer solution for twelve weeks. Cytotoxicity was determined using extract and direct contact test methods with incubation periods varying form 24 to 72 h. The foam was implanted subcutaneously for one, four and twelve weeks and the tissue response to the material was histologically evaluated. In vitro, the mass loss was 3.4% after twelve weeks. In the cytotoxicity tests the PU caused no abnormal growth behaviour, nor morphological changes or inhibition in metabolic activity. The in vivo studies showed no toxic tissue response to the PU. Connective tissue ingrowth, accompanied by vascular ingrowth was complete at twelve weeks. In vivo degradation had started within four to twelve weeks. In conclusion, the PU shows a good in vitro and in vivo biocompatibility in these short-term experiments.