(177ae) Simple Fabrication of Block Copolymer Gels with Stiffness Gradients

Gels with chemical and/or physical property gradients can provide opportunities for improved material performance. One common example of this is the use of gradient polyacrylamide hydrogels for more efficient protein purification (e.g., gel filtration chromatography). The polyacrylamide concentration gradient in these gels translates to a decreasing internal void volume across the film and, as a result, better separation of protein mixtures compared to a homogenous hydrogel of the same polymer. Naturally, polymer gels with concentration gradients also exhibit stiffness gradients due to the intimate connection between polymer concentration and mechanical response. The ease in fabrication of these materials can vary considerably due to the range of methods used to synthesize the polymer concentration gradient. We propose that organogel materials composed of styrenic triblock copolymer (i.e., thermoplastic elastomer) and aliphatic mineral oil offer an easy and scalable platform for preparing bulk gels with tunable stiffness gradients. The present work explores the efficacy of a simple ‘plug-and-play’ approach for creating gradients. More specifically, our approach consists of carefully arranging gels of different copolymer concentration within a mold in a pattern that mimics the targeted gradient and subsequently melt pressing that gel-containing mold to form a contiguous sample. Chemical and physical gradients in the resultant material are assessed using visual, chemical, and mechanical characterization techniques.