# Control of Cytocompatible Metallic and Polymeric Wrinkle Morphologies Using Programming via Printing (PvP)

## TL;DR

This paper introduces a 3D printing method to create controllable wrinkle patterns on shape-memory materials, which are compatible with cells for biological studies.

## Contribution

A novel, accessible 3D printing-based strategy (PvP) for generating cytocompatible wrinkle morphologies on shape-memory substrates.

## Key findings

- PvP enables uniaxial or biaxial contraction in shape-memory substrates, controlling wrinkle formation.
- AFM imaging revealed that orthogonal layers induce transitions from aligned to complex 2D wrinkle patterns.
- C3H10T1/2 cells showed high viability on all wrinkle morphologies, indicating cytocompatibility.

## Abstract

Mechanical instability-driven
wrinkling of a thin rigid film on
a compliant substrate, such as a shape-memory polymer (SMP), offers
spatiotemporal control of surface topography and morphology. Current
strategies for creating wrinkles on SMPs often rely on mechanical
actuation achieved via costly or complicated uniaxial or multiaxial
loading rigs. There is a need for an accessible and easily democratizable
strategy that can produce both simple aligned wrinkles and complex
two-dimensional (2D) postbuckling patterns. Using a hobbyist three-dimensional
(3D) printer, here we employed a recently developed single-step SMP
fabrication approach, programming via printing (PvP), to prepare preprogrammed
shape-memory substrates capable of uniaxial or biaxial contraction
of varying magnitudes, with the strain controlled by the nozzle temperature
and number of orthogonal layers within the substrate. Samples without
an orthogonal layer (all filaments are parallel) produced a maximum
uniaxial contraction along the same axis as the extruded filament
(up to 40%) and underwent Poisson expansion along the perpendicular
direction (up to 15%). The substrates were coated with either gold
or polystyrene, and shape-memory-driven change was triggered to cause
mechanical instability-driven wrinkling of the thin film. To characterize
the relationship between orthogonal layers and wrinkle morphology,
wrinkles were imaged at the microscopic level using atomic force microscopy
(AFM). The transition from unidirectional to bidirectional contractile
strain generated by the orthogonal layers was observed to induce a
transition from simple aligned wrinkles to complex 2D postbuckling
patterns. C3H10T1/2 cells showed high viability (>90%) irrespective
of wrinkle morphology 24 h post seeding. Collectively, the results
demonstrate a convenient fabrication strategy for producing both simple
aligned wrinkles and complex 2D postbuckling patterns, including cytocompatible
wrinkles suitable for cell studies.