Abstract
Hydrogels based on poly(caprolactone)–b-poly(ethylene glycol)–b-poly(caprolactone) (PCL–PEG–PCL) have been evaluated extensively as potential injectable fillers or depots for controlled release of drugs. Common drawbacks of these copolymer systems include instability of aqueous solutions and low mechanical strength of gels, issues which are commonly overcome by adding pendant groups to the end of the copolymer chains. Here, a systematic study of the effects of increasing polymer molecular weight (MW) is presented, utilizing PEG blocks of MW 2, 4 or 8 kDa. Triblock copolymers were prepared by the ring-opening polymerization of Ɛ-caprolactone by PEG. Copolymers prepared with PEG MW 2 kDa did not form hydrogels at any copolymer molecular weight. Copolymers prepared with PEG MW 4 kDa formed gels at MW between 11 and 13.5 kDa, and copolymers prepared with PEG MW 8 kDa formed gels at MW between 16 and 18 kDa. Copolymers with PEG block 8 kDa formed hydrogels with high viscosity (17,000 Pa·s) and mechanical strength (G′ = 14,000 Pa). The increased gel strength afforded by increased molecular weight represents a simple modification of the reactants used in the reaction feed without added synthetic or purification steps. Shear-thinning of PCL-PEG-PCL triblock copolymer hydrogels allowed for injection through a standard 23G syringe, allowing for potential use as dermal fillers or drug delivery depots.
Highlights
Biocompatible and biodegradable polymers are ubiquitous across modern medicine [1], finding their most common use as implants [2,3] or as drug delivery systems [4,5]
PCL–poly(ethylene glycol) (PEG)–PCL triblock copolymers were synthesized by ring-opening polymerization (ROP) of
Gelling behavior and viscoelastic properties of poly(caprolactone)–b-poly(ethylene glycol)–b-poly(caprolactone) (PCL–PEG–PCL) hydrogels are influenced by the molecular weight (MW) of each polymer block [23]
Summary
Biocompatible and biodegradable polymers are ubiquitous across modern medicine [1], finding their most common use as implants [2,3] or as drug delivery systems [4,5]. Decades of research have produced polymers that may be fine-tuned to match nearly any desired application [6]. Some polymers may form hydrogels, three-dimensional systems which are able to retain large quantities of water due to either chemical or physical crosslinking, rendering these polymers attractive platforms for dermal fillers or for the delivery of hydrophilic drugs [7,8]. Triblock copolymers of poly(ethylene glycol) (PEG) and poly(caprolactone) (PCL) have been studied extensively as injectable depot-forming hydrogels [11].
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