Materials that are capable of changing their properties upon exposure to an external stimulus are attracting widespread attention, notably for applications in the biomedical field. Mechanically adaptive materials mimicking the mechanical switching behaviour of the sea cucumber’s skin have been demonstrated to allow for the design of implantable cortical devices, which are initially stiff, and can readily be inserted, but once inserted in the body, the materials soften to better match the mechanical properties of the biological tissue. The capability to use photolithography to process such materials is important to fabricate complex, miniaturized devices.<br/><br/>We here report an initially stiff photopatternable polymer that softens when placed in an aqueous environment. For this purpose, photo-cross-linkable films were casted from a solution containing a photoacid generator and a terpolymer based on 2-hydroxyethyl methacrylate (HEMA), 2-hydroxyethyl acrylate and 2-ethylhexyl methacrylate in methanol. Cross-linking can be achieved through an acid-catalyzed transesterification reaction involving the HEMA repeating unit. The suitability of the system for photolithography was demonstrated, and the relation between photo-exposure as well as post-exposure baking conditions and the materials properties was investigated. A spatial gradient of the cross-linking density and thus of the softening behaviour can be achieved by changing the irradiation and post-exposure bake conditions, while leaving the initial composition of the material unaltered. Such functionally graded materials exhibiting a softening gradient could be used as mechanical buffer between a stiff device and the soft tissues.<br/><br/>The mechanical properties of the polymer networks were studied by dynamic mechanical analysis, in the dry state and upon exposure to water. A dry storage modulus of ~1.9 GPa at 25°C was observed for all irradiation and baking conditions tested. Upon exposure to simulated physiological conditions, the storage modulus decreased to 210-0.60 MPa upon moderate swelling (10-25% w/w), depending on the irradiation and baking conditions.

Mechanically adaptive, photopatternable polymers for biomedical applications

Macromolecular Chemistry: The Second Century

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ACS Spring 2020 National Meeting & Expo

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.