Low molecular weight poly(5-ethylene ketal ε-caprolactone-co-d,l-lactide) (PEKCDLLA) is being consideredas a viscous liquid, injectable depot for localized drug delivery.This polymer degrades in vitro via surface erosion, which is potentiallyadvantageous for the proposed application. However, the in vivo degradationrate and mechanism, and tissue response, to polymers based on 5-ethyleneketal ε-caprolactone have not yet been reported. The purposeof this study was to measure the in vivo weight loss and change inpolymer properties and assess the tissue response to PEKCDLLA aftersubcutaneous injection in rats. The tissue response was assessed histologicallyusing Massonâs trichrome staining and immunohistochemicallyby staining for CD68 positive cells. The polymer lost weight withtime in a nearly linear fashion but did not exhibit significant changesin number average molecular weight, polydispersity index, and glasstransition temperature or monomer ratio, consistent with a surfaceerosion process. The tissue response to the polymer was moderate andcomparable to that reported in the literature for other degradablepolymers used in clinical applications. These findings indicate thatPEKCDLLA is a promising candidate for injectable drug delivery. [ABSTRACT FROM AUTHOR]