Photopolymerizable degradable polyanhydrides with osteocompatibility.

We have developed a new family of photopolymerizable, methacrylated anhydride monomers and oligomers that combine high strength, controlled degradation, and photoprocessibility in a singular system. Networks with degradation times ranging from 1 week to nearly 1 year and that retain up to 90% of their tensile modulus at 40% mass loss are attainable. In vivo studies in rats have shown that these networks possess excellent osteocompatibility. These combined properties could offer many advantages in medical applications ranging from dentistry to orthopedics.

Synthetic, implantable polymers for local delivery of IUdR to experimental human malignant glioma.

PURPOSE: Recently, polymeric controlled delivery of chemotherapy has been shown to improve survival of patients with malignant glioma. We evaluated whether we could similarly deliver halogenated pyrimidines to experimental intracranial human malignant glioma. To address this issue we studied the in vitro release from polymers and the in vivo drug delivery of IUdR to experimental human U251 glioblastoma xenografts. METHODS AND MATERIALS: In vitro: To measure release, increasing (10%, 30%, 50%) proportions of IUdR in synthetic [(poly(bis(p-carboxyphenoxy)-propane) (PCPP):sebacic acid (SA) polymer discs were serially incubated in buffered saline and the supernatant fractions were assayed. In vivo: To compare local versus systemic delivery, mice bearing flank xenografts had intratumoral or contralateral flank IUdR polymer (50% loading) treatments. Mice bearing intracranial (i.c.) xenografts had i.c. versus flank IUdR polymer treatments. Four or 8 days after implantation of polymers, mice were sacrificed and the percentage tumor cells that were labeled with IUdR was measured using quantitative microscopic immunohistochemistry. RESULTS: In vitro: Increasing percentage loadings of IUdR resulted in higher percentages of release: 43.7 + 0.1, 70.0 + 0.2, and 90.2 + 0.2 (p < 0.001 ANOVA) for the 10%, 30%, and 50% loadings, respectively. In vivo: For the flank tumors, both the ipsilateral and contralateral IUdR polymers resulted in similarly high percentages labeling of the tumors versus time. For the ipsilateral IUdR polymers, the percentage of tumor cellular labeling after 4 days versus 8 days was 45.8 +/- 7.0 versus 40.6 +/- 3.9 (p = NS). For the contralateral polymer implants, the percentage of tumor cellular labeling were 43.9 +/- 10.1 versus 35.9 +/- 5.2 (p = NS) measured 4 days versus 8 days after implantation. For the i.c. tumors treated with extracranial IUdR polymers, the percentage of tumor cellular labeling was low: 13.9 +/- 8.8 and 11.2 +/- 5.7 measured 4 and 8 days after implantation. For the i.c. tumors having the i.c. IUdR polymers, however, the percentage labeling was comparatively much higher: 34.3 +/- 4.9 and 35.3 +/- 4.0 on days 4 and 8, respectively. For the i.c. tumors, examination of the percentage cellular labeling versus distance from the implanted IUdR polymer showed that labeling was highest closest to the polymer disc. CONCLUSION: Synthetic, implantable biodegradable polymers provide the local, controlled release of IUdR and result in the high, local delivery of IUdR to experimental intracranial human malignant glioma. This technique holds promise for the local delivery of IUdR for radiosensitization of human brain tumors.

Stimulation of neurite outgrowth using an electrically conducting polymer.

Damage to peripheral nerves often cannot be repaired by the juxtaposition of the severed nerve ends. Surgeons have typically used autologous nerve grafts, which have several drawbacks including the need for multiple surgical procedures and loss of function at the donor site. As an alternative, the use of nerve guidance channels to bridge the gap between severed nerve ends is being explored. In this paper, the electrically conductive polymer--oxidized polypyrrole (PP)--has been evaluated for use as a substrate to enhance nerve cell interactions in culture as a first step toward potentially using such polymers to stimulate in vivo nerve regeneration. Image analysis demonstrates that PC-12 cells and primary chicken sciatic nerve explants attached and extended neurites equally well on both PP films and tissue culture polystyrene in the absence of electrical stimulation. In contrast, PC-12 cells interacted poorly with indium tin oxide (ITO), poly(L-lactic acid) (PLA), and poly(lactic acid-co-glycolic acid) surfaces. However, PC-12 cells cultured on PP films and subjected to an electrical stimulus through the film showed a significant increase in neurite lengths compared with ones that were not subjected to electrical stimulation through the film and tissue culture polystyrene controls. The median neurite length for PC-12 cells grown on PP and subjected to an electrical stimulus was 18.14 micron (n = 5643) compared with 9.5 micron (n = 4440) for controls. Furthermore, animal implantation studies reveal that PP invokes little adverse tissue response compared with poly(lactic acid-co-glycolic acid).

IUdR polymers for combined continuous low-dose rate and high-dose rate sensitization of experimental human malignant gliomas.

Local polymeric delivery enhances IUdR radiosensitization of human malignant gliomas (MG). The combined low-dose rate (LDR) (0.03 Gy/h) and fractionated high-dose rate (HDR) treatments result in cures of experimental MGs. To enhance efficacy, we combined polymeric IUdR delivery, LDR, and HDR for treatments of both subcutaneous and intracranial MGs. In vitro: Cells (U251 MG) were trypsinized and replated in triplicate 1 day prior to LDR irradiation in media either without (control) or with 10 microM IUdR. After 72 hr, LDR irradiation cells were acutely irradiated (1.1 Gy/min) with increasing (0, 1.25, 2.5, 5.0, or 10 Gy) single doses. Implantable IUdR polymers [(poly(bis(p-carboxyphenoxy)-propane) (PCPP): sebaic acid (PCPP:SA), 20:80] (50% loading; 10 mg) were synthesized. In vivo: For flank vs. intracranial tumors, mice had 6 x 10(6) subcutaneous vs. 2 x 10(5) intracranial cells. For intracranial or subcutaneous MGs, mice had intratumoral blank (empty) vs. IUdR polymer treatments. One day after implantation, mice had immediate external LDR (3 cGy/h x 3 days total body irradiation) or HDR (2 Gy BID x 4 days to tumor site) or concurrent treatments. For the in vitro IUdR treatments, LDR resulted in a striking increase in cell-killing when combined with HDR. For the in vivo LDR treatments of flank tumors, the growth delay was greater for the IUdR vs. blank polymer treatments. For the combined LDR and HDR, the IUdR treatments resulted in a dramatic decrease in tumor volumes. On day 60 the log V/V0 were -1.7 +/- 0.22 for combined LDR + HDR + IUdR polymer (P < 0.05 vs. combined LDR + HDR + blank polymer). Survival for the intracranial controls was 22.9 +/- 1.2 days. For the blank polymer + LDR vs. blank polymer + LDR + HDR treatments, survival was 25.3 +/- 1.7 (P = NS) vs. 48.1 +/- 3.5 days (P < 0.05). For IUdR polymer + LDR treatment survival was 27.3 +/- 2.3 days (P = NS). The most striking improvement in survival followed the IUdR polymer + LDR + HDR treatment: 66.0 + 6.4 days (P < 0.05 vs. blank polymer + LDR + HDR). The polymeric IUdR delivery plus combined continuous LDR and HDR treatments results in growth delay and improved survival in animals bearing the MG xenografts. This treatment may hold promise for the treatment of human MGs.

Preliminary in vivo report on the osteocompatibility of poly(anhydride-co-imides) evaluated in a tibial model.

A novel class of polymers with mechanical properties similar to cancellous bone are being investigated for their ability to be used in weight-bearing areas for orthopedic applications. The poly(anhydride-co-imide) polymers based on poly[trimellitylimidoglycine-co-1,6-bis(carboxyphenoxy)hexan e] (TMA-Gly:CPH) and poly[pyromellitylimidoalanine-co-1,6-bis(carboxyphenoxy)hexa ne] (PMA-Ala:CPH) in molar ratios of 30:70 were investigated for osteocompatibility, with effects on the healing of unicortical 3-mm defects in rat tibias examined over a 30-day period. Defects were made with surgical drill bits (3-mm diameter) and sites were filled with poly(anhydride-co-imide) matrices and compared to the control poly(lactic acid-glycolic acid) (PLAGA) (50:50), a well-characterized matrix frequently used in bone regeneration studies, and defects without polymeric implants. At predetermined time intervals (3, 6, 9, 12, 20, and 30 days), animals were sacrificed and tissue histology was examined for bone formation, polymer-tissue interaction, and local tissue response by light microscopy. The studies revealed that matrices of TMA-Gly:CPH and PMA-Ala:CPH produced responses similar to the control PLAGA with tissue compatibility characterized by a mild response involving neutrophils, macrophages, and giant cells throughout the experiment for all matrices studied. Matrices of PLAGA were nearly completely degraded by 21 days in contrast to matrices of TMA-Gly:CPH and PMA-Ala:CPH that displayed slow erosion characteristics and maintenance of shape. Defects in control rats without polymer healed by day 12, defects containing PLAGA healed after 20 days, and defects containing poly(anhydride-co-imide) matrices produced endosteal bone growth as early as day 3 and formed bridges of cortical bone around matrices by 30 days. In addition, there was marrow reconstitution at the defect site for all matrices studied along with matured bone-forming cells. This study suggests that novel poly(anhydride-co-imides) are promising polymers that may be suitable for use as implants in bone surgery, especially in weight-bearing areas.