# Polycaprolactone/Polyethylene Glycol/Hydroxypropylmethylcellulose Blends: Tailoring Thermomechanical and Rheological Properties for Injection-Molded Capsules for Colon-Targeted Delivery Applications

## TL;DR

This paper develops a polymer blend for colon-targeted drug delivery, showing controlled release under colonic pH conditions.

## Contribution

The study introduces HPMC into PCL/PEG blends for colon-targeted capsules, demonstrating pH-sensitive release behavior.

## Key findings

- Blends with 34% HPMC showed 38% release in 12 h and 73% in 24 h under colonic pH.
- Release was minimal in gastric and intestinal pH environments.
- A two-stage release model based on pH and HPMC content was proposed and validated.

## Abstract

Colon-targeted delivery systems offer a promising approach
for
local drug administration. In this study, we developed a customized
polymeric blend for this purpose, combining polyethylene glycol (PEG),
polycaprolactone (PCL), and hydroxypropyl methylcellulose (HPMC).
Although PEG and PCL have been extensively studied, the inclusion
of HPMC in such blends remains underexplored; however, its use in
this context shows significant potential due to its pH sensitivity.
To achieve this, various formulations were tested to optimize the
thermomechanical and release characteristics of capsules produced
through injection molding. Three blends containing 22, 24, and 34
wt% HPMC were processed and analyzed using rheological methods, ATR-FTIR,
TGA, DSC, SEM, and in vitro release tests with methylene blue as a
model compound. Simulated pH-release tests (pH 2.5, 5, and 6.8) showed
minimal release in gastric and intestinal environments, with controlled
and sustained release under colonic pH conditions. It was also observed
that the initial HPMC content affects the release rate of the model
compound. Specifically, when the blend contains 34% HPMC, approximately
38% of the compound is released within 12 h and 73% within 24 h. These
results highlight the potential of pH-sensitive polymer blends as
effective platforms for colon-targeted drug delivery. A model illustrating
how the release rate depends on pH value and HPMC amount was also
proposed and validated. The process was considered to happen in two
stages: initially, the release medium penetrates the capsule and solubilizes
the model compound; then, the model compound is released into the
surrounding environment.