Emergent Soft Lithographic Tools for the Fabrication of Functional Polymeric Microstructures

Abstract

Polymeric microstructures (PMs) are useful to a broad range of technologies applicable to, for example, sensing, energy storage, and soft robotics. Due to the diverse application space of PMs, many techniques (e. g., photolithography, 3D printing, micromilling, etc.) have been developed to fabricate these structures. Stemming from their generality and unique capabilities, the tools encompassed by soft lithography (e. g., replica molding, microcontact printing, etc.), which use soft elastomeric materials as masters in the fabrication of PMs, are particularly relevant. By taking advantage of the characteristics of elastomeric masters, particularly their mechanical and chemical properties, soft lithography has enabled the use of non‐planar substrates and relatively inexpensive equipment in the generation of many types of PMs, redefining existing communities and creating new ones. Traditionally, these elastomeric masters have been produced from relief patterns fabricated using photolithography; however, recent efforts have led to the emergence of new methods that make use of masters that are self‐forming, dynamic in their geometric and chemical properties, 3D in architecture, and/or sacrificial (i. e., easily removed/released using phase changes). These “next generation” soft lithographic masters include self‐assembled liquid droplets, microscale balloons, templates derived from natural materials, and hierarchically microstructured surfaces. The new methods of fabrication supported by these unique masters enable access to numerous varieties of PMs (e. g., those with hierarchical microstructures, overhanging features, and 3D architectures) that would not be possible following established methods of soft lithography. This review explores these emergent soft lithographic methods, addressing their operational principles and the application space they can impact.

Microlenses arrays: Fabrication, materials, and applications

“…Soft lithography has been widely used in the fabrication of microstructures in recent years (Rogers & Nuzzo, 2005; Rose et al, 2019; Whitesides et al, 2003). This technology mainly uses soft elastic materials for fabrication.…”

3D Patterning within Hydrogels for the Recreation of Functional Biological Environments

“…[ 69 ] Soft‐lithographic techniques, developed by Whitesides and colleagues more than two decades ago, have had an enormous impact in the fields of cell biology, biochemistry, biotechnology, and bioengineering. [ 70,71 ] Inspired by this work, techniques such as dip pen nanolithography, [ 72 ] nanoimprint lithography, [ 73 ] and molecular assembly patterning [ 74 ] have enabled well‐defined patterns of biomolecules on 2D surfaces, which have facilitated studies of cell adhesion, [ 75 ] proliferation, [ 76 ] differentiation, [ 77 ] and communication [ 78 ] amongst others. Furthermore, topographical patterns (also referred to as 2.5D patterns) have also been explored and used to guide cells and biological processes through physical features at the nano, [ 79 ] micro, [ 80 ] and nano/micro scales, [ 81 ] within 3D structures, [ 82–84 ] or in combination with chemical signals.…”

Photothermally Reconfigurable Shape Memory Magnetic Cilia

“…[1,2] In some instances, soft composite microstructures can be fabricated through simple self-assembly approaches instead of requiring top-down patterning that is typically employed for pneumatically or electrically driven systems. [3][4][5] Scaling to small sizes can also facilitate mechanical flexibility. [6] Cilia are tiny hair-like structures that line the lungs of humans and many animals and cover the surfaces of cells.…”