The aim of the present study was to test whether or not the application of an in situ formed synthetic hydrogel made of polyethylene glycol (PEG) used as a biodegradable membrane for guided bone regeneration will result in the same amount of bone regeneration as with the use of an expanded polytetrafluoro-ethylene (ePTFE) membrane. In eight New Zealand White rabbits, four evenly distributed 6 mm diameter defects were drilled into the calvarial bone. Three treatment modalities were evenly distributed among the 32 defects: hydroxyapatite (HA)/tricalciumphosphate (TCP) granules covered at the outer and inner surface with a PEG membrane (test), HA/TCP granules covered at the outer and inner surface with an ePTFE membrane (positive control) and HA/TCP granules alone without membranes (negative control). After 4 weeks, the animals were sacrificed and the calvarial bones were removed. The area fraction of newly formed bone was determined by histomorphometrical analysis of the vertical sections from the middle of the defect and by micro-computed tomography of the entire defect. Multiple regression analysis (SAS GLM) was used to model the amount of new bone formation. The quantitative histomorphometric analysis clearly revealed higher values of newly formed bone for the two membrane groups compared with the negative control group. The average area fractions of newly formed bone measured within the former defect amounted to 20.3+/-9.5% for the PEG membrane, 18.9+/-9.9% for the ePTFE membrane, and 7.3+/-5.3% for the sites with no membrane. The micro-computed tomography also showed higher values of new bone formation for the PEG and for the ePTFE groups compared with the negative control group. The GLM revealed a highly significant effect of the treatment on the amount of bone formation (P=0.0048). The values for the negative control group were significantly lower than the ones found in the PEG membrane group (P=0.0017), whereas the ePTFE membrane group showed no significant difference from the PEG membrane group. It is concluded that the PEG membrane can be used successfully as a biodegradable barrier membrane in the treatment of non-critical-size defects in the rabbit skull, and leads to similar amounts of bone regeneration as an ePTFE membrane.

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The use of guided bone regeneration (GBR) techniques requires new materials meeting the needs of clinical application. Design criteria for GBR devices are biocompatibility, tissue occlusion, space provision, and clinical manageability. This study evaluates a novel biodegradable poly (ethylene glycol) (PEG) based material as tissue occlusive membrane. A subcutaneous implant model in rats was developed to test the barrier function of the PEG hydrogels over time. Fourteen rats received three membrane implants and two positive controls each. Explants were collected over a period of 7 months. Histological analysis revealed that for at least 4 months cellular infiltration in the membrane explants was lower than 1% of that of the positive controls. Therefore, the PEG based hydrogel can be regarded as tissue occlusive during this period of time. A barrier function seems to be maintained for up to 6 months. In vitro degradation studies performed with the same PEG constructs confirm the in vivo result. In conclusion, our results indicate that this novel PEG‐based material has potential for use as a GBR barrier membrane. © 2007 Wiley Periodicals, Inc. J Biomed Mater Res, 2008

The polyiminophosphazene bases Et‐P2 and t‐Bu‐P4 were used as a promoter for ethylene oxide and siloxane polymerizations. Initiation by an alcohol in combination with t‐Bu‐P4 lead to an extremely rapid polymerization reaction of octamethylcyclotetrasiloxane. In the case of ethylene oxide, well‐defined polymers were obtained, however the rate of polymerization decreased during the polymerization reaction due to decomposition of the counterion. In combination with organolithium compounds, the phosphazene bases lead to well‐defined polymers in the case of cyclotrisiloxanes as well as in the case of ethylene oxide.

Methanol, in combination with a non-ionic phosphazene base, was used to initiate the polymerization of octamethylcyclotetrasiloxane. In bulk, an instantaneous and large increase in viscosity was observed upon addition of the initiator. In toluene solution, the equilibrium state was reached in approximately 1 min. In addition to its high polymerization rate, another advantage of this system, as compared with e. g. alkali metal hydroxides, is that it is homogeneous.