Phenolic Acid-based Poly(anhydride-esters) as Antioxidant Biomaterials.

Poly(anhydride-esters) comprised of naturally occurring, non-toxic phenolic acids, namely syringic and vanillic acid, with antioxidant properties were prepared via solution polymerization methods. Polymer and polymer precursor physiochemical properties were characterized, including polymer molecular weight and thermal properties. In vitro release studies illustrated that polymer hydrolytic degradation was influenced by relative hydrophobicity and degree of methoxy substitution of the phenolic acids. Further, the released phenolic acids were found to maintain antioxidant potency relative to free phenolic acid controls as determined by a 2,2-diphenyl-1-picrylhydrazyl assay. Polymer cytotoxicity was assessed with L929 fibroblasts in polymer-containing media; appropriate cell morphology and high fibroblast proliferation were obtained for the polymers at the lower concentrations. These polymers deliver non-cytotoxic levels of naturally occurring antioxidants, which could be efficacious in topical delivery of antioxidant therapies.

A novel approach for incorporation of mono-functional bioactive phenols into polyanhydrides.

Antiseptics based on phenol and phenolic derivatives were chemically incorporated into polyanhydrides as pendant groups via ester linkages. Polyanhydrides with antiseptic loadings of 46-58 wt.-% were obtained with molecular weights ranging from 9 400-23 000. In general, polymers with the bulkier antiseptics were more difficult to polymerize and yielded lower molecular weights. All polyanhydrides were amorphous with glass transition temperatures ranging from 27-58 °C. Polymers were deemed noncytotoxic after culturing L929 mouse fibroblast cells in media containing the polymers at two concentrations (0.10 and 0.01 mg · mL(-1) ) over three days. In summary, mono-functional bioactives can be chemically incorporated into noncytotoxic polyanhydrides.

Non-steroidal anti-inflammatory drug (NSAID)-derived poly(anhydride-esters) in bone and periodontal regeneration.

Bioresorbable polymers offer the potential to deliver biologically active agents that selectively modulate wound healing in bone and periodontal regeneration. This preliminary study characterizes early wound healing in calvarial defects grafted with demineralized bone matrix (DBM) overlaid with membranes made from a novel class of non-steroidal anti-inflammatory drug (NSAID)-derived poly(anhydride-esters). These polymers chemically incorporate either salicylic acid (SA) or 5-(2',4'-difluorophenyl)salicylic acid (diflunisal) into the polymeric backbone and release the NSAIDs upon hydrolysis. Inflammatory cell infiltrate in response to the novel NSAID-derived polymers was compared to defects grafted with DBM alone at 10 days and to defects grafted with DBM and overlaid with poly(lactic acid) (PLA; Atrisorb) at 21 days in 8 Wistar rats (350-450 g). Histological analysis of the calvarial sites at 10 days revealed that the NSAID-derived polymers were associated with moderate levels of inflammation similar to defects grafted without polymer (2.3 +/- 0.96 versus 2.0 +/- 0.82, respectively), consistent with the therapeutic activity of salicylic acid and diflunisal. Defects grafted with DBM and overlaid with NSAID-derived polymers at 21 days exhibited mild inflammation; whereas, defects treated with PLA were consistently associated with moderate to severe inflammatory cell infiltrate (1.8 +/- 0.50 versus 2.7 +/- 0.58, respectively). Histopathological findings, such as foreign body giant cells or fibrous encapsulation, were not observed in any defects with NSAID-derived polymers. Cellular features consistent with bone formation were found in all grafted defects. This novel class of non-steroidal anti-inflammatory drug-derived poly(anhydride-esters) were well tolerated and elicited no demonstrable increase in inflammation, as shown with PLA, during osseous wound healing in a regenerative application.

Characterization and in vitro degradation of salicylate-derived poly(anhydride-ester microspheres).

The aim of this study was to investigate how glass transition temperature (Tg) influenced polymer microsphere formation and degradation of three chemically, similar novel salicylatebased poly(anhydride-esters): poly[1,6-bis(o-carboxyphenoxy)hexanoate] (CPH), Tg = 59 degrees C; poly[1,8-bis(o-carboxyphenoxy)octanoate] (CPO), Tg = 30 degrees C; and poly[1,10-bis(ocarboxyphenoxy) decanoate] (CPD), Tg = 27 degrees C. Microspheres of these polymers were prepared using a modified oil-in-water solvent evaporation method and processed by either resuspension or washed by centrifugation. The morphology of the microspheres determined by scanning electron microscopy (SEM) revealed that an extra washing step appears to increase aggregation as the Tg decreases; whereas only limited aggregation occurred in the polymer with the lowest Tg, CPD, in those not washed by centrifugation. Residual polyvinyl alcohol apparently affected the drug release rates from the microspheres by a stabilization process that produced an 8 h lag time and a 5% decrease in the amount of drug released over a 7 day period compared to microspheres washed free of PVA. These results demonstrate that salicylate-based poly(anhydride-esters) with sufficiently high Tgs, can be processed into microspheres that release salicylate over a time period amenable for drug delivery applications.

Biodegradation of poly(anhydride-esters) into non-steroidal anti-inflammatory drugs and their effect on Pseudomonas aeruginosa biofilms in vitro and on the foreign-body response in vivo.

The ability of poly(anhydride-esters) composed of non-steroidal anti-inflammatory drugs that biodegrade to salicylic acid (SA) and adipic acid to prevent colonization by Pseudomonas aeruginosa and their effects on the foreign-body response were studied in vitro and in vivo, respectively. Soluble SA in bacterial medium at concentrations up to 300 mg/L did not affect the growth rate or viability of P. aeruginosa, indicating that SA does not exhibit a direct toxicity effect on the bacterium. Batch degradation rates of the salicylate-based polymer in the presence of an actively growing bacterial culture only marginally (14%) increased relative to polymer degradation rates in sterile medium. Short-term (3h) bacterial adhesion studies in agitated batch systems indicated a 47% reduction in the rate of P. aeruginosa adhesion relative to a control polymer that does not release SA upon biodegradation. Long-term (3-day) biofilm accumulation studies indicated a dramatic reduction in biofilm formation on salicylate-based polymer versus controls. A recombinant P. aeruginosa pMHLAS, containing a fluorescent reporter gene prior to the las regulon, was employed to determine whether salicylate-based polymer prevents biofilm formation by the released SA inhibiting quorum sensing pathways. Long-term biofilm accumulation studies with P. aeruginosa pMHLAS insinuate that salicylate-based polymer prevents biofilm accumulation by inhibiting the las quorum sensing system. Furthermore, unlike control polymer, salicylate-based polymer implanted subcutaneously for a period of 4 weeks-resisted cell-mediated degradation and remained intact. Histological and immunohistochemical analysis indicated a reduction in overall encapsulation and paucity of macrophages in the area of the salicylate-based polymer implant.

Effect of Linker Structure on Salicylic Acid-Derived Poly(anhydride-esters).

A series of salicylic acid-derived poly(anhydride-esters) were synthesized by melt polym erization methods, in which the structures of the molecule ("linker") linking together the two salicylic acids were varied. To determine the relationship between the linker and the physical properties of the corresponding poly(anhydride-ester), several linkers were evaluated including linear aliphatic, aromatic, and aliphatic branched structures. For the linear aliphatic linkers, higher molecular weights were obtained with longer linear alkyl chains. The most sterically hindered linkers yielded lower molecular weight polymers. The thermal decomposition temperature increased with the alkyl chain length, but the glass transition temperature decreased, due to the enhanced flexibility of the polymer. The highest glass transition temperatures were obtained by using aromatic linkers as a result of increased π-π interactions. Water contact angles determined the relative hydrophobicity of the polymers, which correlated to hydrolytic degradation rates; i.e., the highest contact angle values yielded the slowest degrading polymers.