Molded porous poly (L-lactide) membranes for guided bone regeneration with enhanced effects by controlled growth factor release

Processing and properties of porous poly(L-lactide)/bioactive glass composites

Porous poly(L-lactide)/bioactive glass (PLLA/BG) composites were prepared by phase separation of polymer solutions containing bioactive glass particles (average particle size: 1.5 microm). The composite microstructures consist of a porous PLLA matrix with glass particles distributed homogeneously throughout. Large pores (>100 microm) are present in a network of smaller (<10 microm) interconnected pores. The porous microstructure of the composites was not significantly influenced by glass content (9 or 29 vol%), but silane pretreatment of the glass resulted in better glass incorporation in the matrix. Mechanical tests showed that an increase in glass content increased the elastic modulus of the composites, but decreased their tensile strength and break strain. Silane pretreatment enhanced the increase in modulus and prevented the decrease in tensile strength with increasing glass content. Composites soaked in simulated body fluid (SBF) at body temperature formed bone-like apatite inside and on their surfaces. The silane pretreatment of glass particles delayed the in vitro apatite formation. This bone-like apatite formation demonstrates the composites' potential for integration with bone.

A photo-crosslinked poly(vinyl alcohol) hydrogel growth factor release vehicle for wound healing applications

The objective of this study was to develop and evaluate a hydrogel vehicle for sustained release of growth factors for wound healing applications. Hydrogels were fabricated using ultraviolet photo-crosslinking of acrylamide-functionalized nondegradable poly(vinyl alcohol) (PVA). Protein permeability was initially assessed using trypsin inhibitor (TI), a 21 000 MW model protein drug. TI permeability was altered by changing the solids content of the gel and by adding hydrophilic PVA fillers. As the PVA content increased from 10% to 20%, protein flux decreased, with no TI permeating through 20% PVA hydrogels. Further increase in model drug release was achieved by incorporating hydrophilic PVA fillers into the hydrogel. As filler molecular weight increased, TI flux increased. The mechanism for this is most likely an alteration in protein/gel interactions and transient variations in water content. The percent protein released was also altered by varying protein loading concentration. Release studies conducted using growth factor in vehicles with hydrophilic filler showed sustained release of platelet-derived growth factor (PDGF-beta,beta) for up to 3 days compared with less than 24 hours in the controls. In vitro bioactivity was demonstrated by doubling of normal human dermal fibroblast numbers when exposed to growth factor-loaded vehicle compared to control. The release vehicle developed in this study uses a rapid and simple fabrication method, and protein release can be tailored by modifying solid content, incorporating biocompatible hydrophilic fillers, and varying protein loading concentration.

Enhanced bone augmentation by controlled release of recombinant human bone morphogenetic protein-2 from bioabsorbable membranes

BACKGROUND

The present study was undertaken to determine the effect of recombinant human bone morphogenetic protein-2 (rhBMP-2)-loaded biodegradable membranes on bone augmentation in a rabbit calvarial model.

METHODS

Five microg of rhBMP-2 was loaded into a stiff hemispherical dome membrane made of poly(L-lactide) and tricalcium phosphate (PLLA/TCP). The release kinetics of rhBMP-2 from the membrane were determined in vitro using a human BMP-2 immunoassay. Twelve rhBMP-2-loaded dome membranes (test group) and 12 control dome membranes (control group) were placed on the partial-thickness calvarial defects of 24 rabbits. The animals were sacrificed at 4 and 8 weeks, and undecalcified ground sections were prepared. Newly formed bone area and height were measured histomorphometrically and calculated by percentage ratio to the total submembranous space area and height below the dome.

RESULTS

In vitro release results demonstrated that rhBMP-2 was released consistently over a 4-week period following a high initial burst release on the first day. At both 4 and 8 weeks, histomorphometric analysis revealed that the test group showed significantly higher newly formed bone heights and areas than the control group (P < 0.01). In the control group, new bone height was 36.3% of the dome height and the new bone area reached 8.2% of the submembranous space area at 8 weeks, while the test group reached 87.3% and 35.4%, respectively.

CONCLUSION

These results suggest that the use of rhBMP-2-loaded PLLA/TCP membranes can result in additional bone augmentation, which is due to the osteoinductive properties of rhBMP-2 released from the membrane during healing.

Compartmentalized bone regeneration of cranial defects with biodegradable barriers--effects of calcium sodium phosphate surface coatings on LactoSorb

In bony defects of the cranium, bone healing may be complicated by prolapse of surrounding tissue into the defect. This tissue acts as a potential obstruction to the migration of osteogenic cells, resulting in impaired bone formation. It has been shown in previous studies that when a membrane composed of resorbable polymers (LactoSorb) is placed over a cranial bone defect, it inhibits connective tissue from entering the wound and improves the rate and quality of the bony regenerate. This study is an extension of this work and specifically evaluated the effects of differing calcium-based surface coatings on membrane-covered cranial defects in the rabbit model. In non-critical size, full-thickness defects of the mature rabbit calvarium, four differently treated LactoSorb membranes were evaluated in each animal model over a 1-year postoperative period. The surface coatings (three treated, one untreated) consisted of a base-powdered material of calcium sodium phosphate (Osteostim, EBI, NJ), which were applied by different methods (pressed, brushed, one-sided versus two-sided). Evaluation consisted of cross-sectional histologic assessment of the cranial detects determining the quantitative bony fill and the presence of residual polymer material and calcium sodium phosphate. This study produced the following findings: (1) cranial defect regeneration occurs faster with calcium-coated membranes and is complete by 3 months; (2) no difference could be seen between the different methods of calcium sodium phosphate coating; (3) the calcium sodium phosphate coatings did not inhibit resorption of the biodegradable membranes for those systems that had coatings on one side; however, systems completely covered showed delayed resorption; and (4) the calcium sodium phosphate coatings did not produce any inflammatory reactions. These findings suggest that, in addition to inhibiting connective tissue from entering the wound site, the calcium coatings on resorbable devices may have beneficial effects in selected clinical conditions, especially in conditions where faster bone regeneration is necessary.