Core-Shell Polymer Capsule Shells for pH-Triggered Intestinal Release
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Solution Overview
Problem
Existing hard shell capsules made from gelatin or HPMC disintegrate in stomach acid and require additional enteric coatings, which are difficult to apply and can cause unstable dimensions, while enteric polymers applied thickly do not disintegrate in the intestine due to thickness, and (meth)acrylate copolymers have failed as capsule materials.
Innovation Solution
A capsule shell comprising 40-99% core-shell polymer with specific ethyl acrylate and methacrylic acid ratios, and 1-60% cellulose, allowing for a wide range of disintegration profiles by controlling the ratio of core-shell polymer to cellulose.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If capsule shells are made from gelatin or HPMC, then they are easy to manufacture, but they disintegrate in stomach acid requiring additional enteric coatings
Solution Approach 1:
The capsule shell uses a composite material system consisting of (meth)acrylate copolymer particles suspended in a gelatin or HPMC matrix. The (meth)acrylate copolymer provides enteric resistance while the gelatin/HPMC provides structural integrity and ease of manufacturing. This composite approach combines the advantages of both material systems.
Solution Approach 2:
The enteric properties are localized to specific regions within the capsule shell structure. The (meth)acrylate copolymer particles are distributed throughout the matrix to provide enteric resistance at the points where they are present, while the surrounding gelatin/HPMC matrix maintains the overall shell structure and provides gastric solubility.
2Strength
If enteric polymers are applied as thick coatings to ensure dimension stability, then capsule wall strength is improved, but disintegration in intestine is delayed for many hours
Solution Approach 1:
The enteric resistance is localized to discrete particles distributed throughout the shell wall rather than being uniformly distributed. This allows the capsule shell to maintain sufficient enteric resistance through the presence of these particles, while the gelatin/HPMC matrix provides structural support, enabling thinner overall wall thickness and faster disintegration.
Solution Approach 2:
The composite structure allows the enteric polymer particles to provide chemical resistance properties while the gelatin/HPMC continuous phase provides mechanical strength. This division of functional roles enables optimized wall thickness that is sufficient for both strength and timely disintegration.
3Reliability
If enteric coatings are applied to filled capsules, then enteric protection is achieved, but additional bandings are required to ensure tightness
Solution Approach 1:
The enteric protection function and the capsule shell structural function are merged into a single integrated shell structure. The (meth)acrylate copolymer particles embedded in the gelatin/HPMC matrix simultaneously provide enteric resistance and structural integrity, eliminating the need for separate enteric coating and banding steps.
Solution Approach 2:
The enteric properties are built into the capsule shell during the shell formation process itself, before the capsule is filled. The (meth)acrylate copolymer is incorporated into the shell matrix during manufacturing, so the shell is pre-equipped with enteric resistance, eliminating the need for post-filling coating operations.
4Reliability
If precoating of capsule shells with enteric polymers is performed, then enteric protection is achieved, but capsule shell dimension stability becomes unstable
Solution Approach 1:
The gelatin or HPMC matrix provides a stable, dimensionally robust continuous phase that maintains capsule shell geometry. The embedded (meth)acrylate copolymer particles provide enteric resistance without compromising the dimensional stability provided by the continuous gelatin/HPMC phase, unlike precoating methods where the enteric polymer forms the primary structural layer.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The solution provides capsules that resist stomach acid and disintegrate at intestinal pH, with controlled release profiles from slightly delayed to strongly delayed, overcoming the limitations of existing materials and manufacturing methods.
Implementation Method 1
capsules that are resistant against acidic conditions of the stomach but disintegrate at the higher pH conditions in the intestine
Data Source
AI summary
The invention is concerned with a capsule shell comprising 40 to 99 % by weight of a core-shell polymer, comprising 50 to 90 % by weight of a core, comprising polymerized units of 65 to 75 % by weight of ethyl acrylate and 25 to 35 % by weight of methyl methacrylate, and 10 to 50 % by weight of a shell, comprising polymerized units of 45 to 55 % by weight of ethyl acrylate and 45 to 55 % by weight of methacrylic acid, and 1 to 60 % by weight of a cellulose.