Protein and Peptide Release from in Situ Gelling Polymer

Stable polyanhydride synthesized from sebacic acid and ricinoleic acid

Poly(anhydride) are unstable and prone to hydrolytic degradation and depolymerisation via anhydride interchange. They are stored at -20°C, packed under inert atmosphere until use. We synthesized a new poly(anhydride) from ricinoleic (RA) and sebacic (SA) acid with alternating ester-anhydride structure that is stable at 25°C for over 18months. The copolymer is also stable in chloroform solution and under γ-irradiation. The polymer hydrolyses through anhydride cleavage lasting ~7days to form oligoesters, which are stable for >30days. The release of gentamycin from the synthesized alternate polymer matrix is sustained compared to the random copolymer.

Poly(ester-anhydride) for controlled delivery of hydrophilic drugs

Injectable pasty polyester-anhydride based on sebacic acid and ricinoleic acid at a 30:70 w/w ratio, poly(sebacic-co-ricinoleic-ester-anhydride) 3:7, was synthesized from the esterification of ricinoleic acid on poly(sebacic acid) followed by polyanhydride condensation. The effect of castor oil, citric acid, and glycerol added at 1% w/w as branching agents was determined. Castor oil and citric acid increased the viscosity, while glycerol decreased the viscosity of the polymer. Constant release of gentamicin and thyrotropin-releasing hormone incorporated in the polymer paste was monitored during 28 days.

Trehalose limits BSA aggregation in spray-dried formulations at high temperatures: implications in preparing polymer implants for long-term protein delivery

Polymer implants are promising systems for sustained release applications but their utility for protein delivery has been hindered because of concerns over drug stability at elevated temperatures required for processing. Using bovine serum albumin (BSA) as a model, we have assessed whether proteins can be formulated for processing at elevated temperatures. Specifically, the effect of trehalose and histidine-HCl buffer on BSA stability in a spray-dried formulation has been investigated at temperatures ranging from 80°C to 110°C. When both the sugar and buffer are present, aggregation is suppressed even when exposed to 100°C, the extrusion temperature of poly(lactide-co-glycolide) (PLGA), a bioresorbable polymer. Estimation of aggregation rate constants (k) indicate that though both trehalose and histidine-HCl buffer contribute to BSA stability, the effect because of trehalose alone is more pronounced. BSA-loaded PLGA implants were prepared using hot-melt extrusion process and in vitro release was conducted in phosphate buffered saline at 37°C. Comparison of drug released from implants prepared using four different formulations confirmed that maximal release was achieved from the formulation in which BSA was least aggregated. These studies demonstrate that when trehalose and histidine-HCl buffer are included in spray-dried formulations, BSA stability is maintained both during processing at 100°C and long-term residence within implants.

Pasty injectable biodegradable polymers derived from natural acids

Pasty biodegradable polymers that can be mixed with drugs at room temperature and injected to tissue as neat composition are advantageous as they allow simple preparation and delivery of drugs, particularly for heat sensitive drugs. A series of biodegradable pasty poly (ester-anhydride)s were prepared from alkanedicarboxylic acids and ricinoleic acid and its oligomers by transesterification-repolymerization method. The polymers were characterized by common spectroscopic, chromatography, and thermal methods. Polymers containing 70% ricinoleic acid and 30% linear dicarboxylic acids with 4-10 methylene groups were synthesized. The melting point of these poly (ester-anhydride)s increased as the number of methylenes in the alkanedicarboxylic acid increased. Use of short oligomers of ricinoleic acid instead of ricinoleic acid itself increased the melting point and decreased the softness of the resulting polymers. The polymers released model drugs for a few weeks while being degraded to their fatty acid counterparts. Copolymerization of alkanedicarboxylic acids with ricinoleic acid resulted in pasty biodegradable polymers useful as injectable carriers for drugs.