Corelease of bioactive VEGF and HGF from viscous liquid poly(5-ethylene ketal ε-caprolactone-co-D,L-lactide).

The potential of a viscous liquid injectable delivery system composed of poly(5-ethylene ketal ε-caprolactone-co-D,L-lactide) (PEKCDLLA) to release bioactive vascular endothelial growth factor (VEGF) and hepatocyte growth factor (HGF) using an osmotic pressure release mechanism for the purpose of treating critical limb ischemia was investigated. VEGF and HGF were lyophilized separately with trehalose and bovine serum albumin (BSA) and incorporated into the polymer by simple mixing. VEGF and HGF were released by convective flow through superhydrated regions formed within the polymer as a result of the osmotic activity generated upon dissolution of the particles, along with the contributions of polymer degradation at later time points. A sustained release of highly bioactive VEGF and HGF for over 40 days with minimal burst was achieved under conditions of multidirectional delivery. The solubility of the growth factors in the concentrated trehalose solution formed upon dissolution of the particle within the polymer was determined to be a key parameter governing the rate and extent of growth factor release. This formulation approach, of using a low viscosity polymer delivery vehicle, is potentially useful for localized delivery of acid and temperature sensitive proteins, such as VEGF and HGF. This system may also serve as a platform for controlled and predictable delivery patterns for other therapeutic proteins in other clinical settings.

Osmotic pressure driven protein release from viscous liquid, hydrophobic polymers based on 5-ethylene ketal ε-caprolactone: potential and mechanism.

In this study, the potential of low molecular weight, viscous liquid polymers based on 5-ethylene ketal ε-caprolactone for localized delivery of proteins via an osmotic pressure release mechanism was investigated. Furthermore, the osmotic release mechanism from viscous liquid polymers was elucidated. 5-Ethylene ketal ε-caprolactone was homopolymerized or copolymerized with D,L-lactide (DLLA) by ring-opening polymerization. Polymer hydrophobicity was adjusted by choice of initiator; hydrophobic polymers were prepared by initiating with octan-1-ol, while more hydrophilic polymers were prepared by initiating with 350 g/mol methoxy poly(ethylene glycol) (PEG). Particles consisting of bovine serum albumin (BSA) as a model protein drug were co-lyophilized with trehalose at 50:50 and 10:90 (w/w) ratios and were mixed into the polymers at 1% and/or 5% (w/w) particle loading. The release and mechanism of release of BSA from the polymers were assessed in vitro. BSA was released in a sustained manner, with a near zero-order release profile and with minimal burst effect for 5-80 days depending on the polymer's hydrophilicity; the release was faster from the PEG initiated polymers than from the octan-1-ol initiated polymers. Increasing the particle loading from 1% to 5% (w/w) resulted in a more noticeable burst effect, but did not significantly increase the mass fraction release rate. This release behavior was determined to proceed as follows. Release from the polymer was triggered by the water activity gradient between the surrounding aqueous medium and the saturated solution, which forms when water is absorbed from the surrounding medium to dissolve a given particle. The generated pressure initiates swelling around the particle/polymer interface and creates a superhydrated polymer region through which the solute is transported by convection, at a rate determined by the osmotic pressure generated.

In vivo degradation and tissue response to poly(5-ethylene ketal ε-caprolactone-co-D,L-lactide).

Low molecular weight poly(5-ethylene ketal ε-caprolactone-co-D,L-lactide) (PEKCDLLA) is being considered as a viscous liquid, injectable depot for localized drug delivery. This polymer degrades in vitro via surface erosion, which is potentially advantageous for the proposed application. However, the in vivo degradation rate and mechanism, and tissue response, to polymers based on 5-ethylene ketal ε-caprolactone have not yet been reported. The purpose of this study was to measure the in vivo weight loss and change in polymer properties and assess the tissue response to PEKCDLLA after subcutaneous injection in rats. The tissue response was assessed histologically using Masson's trichrome staining and immunohistochemically by staining for CD68 positive cells. The polymer lost weight with time in a nearly linear fashion but did not exhibit significant changes in number average molecular weight, polydispersity index, and glass transition temperature or monomer ratio, consistent with a surface erosion process. The tissue response to the polymer was moderate and comparable to that reported in the literature for other degradable polymers used in clinical applications. These findings indicate that PEKCDLLA is a promising candidate for injectable drug delivery.