Designing Interfacial Reactions for Nanometer-Scale Surface Patterning of PDMS with Controlled Elastic Modulus.

Control over the surface chemistry of elastomers such as polydimethylsiloxane (PDMS) is important for many applications. However, achieving nanostructured chemical control on amorphous material interfaces below the length scale of substrate heterogeneity is not straightforward, and can be particularly difficult to decouple from changes in network structure that are required for certain applications (e.g., variation of elastic modulus for cell culture). We have recently reported a new method for precisely structured surface functionalization of PDMS and other soft materials, which displays high densities of ligands directly on the material surface, maximizing steric accessibility. Here, we systematically examine structural factors in the PDMS components (e.g., base and cross-linker structures) that impact efficiency of the interfacial reaction that leads to surface functionalization. Applying this understanding, we demonstrate routes for generating equivalent nanometer-scale functional patterns on PDMS with elastic moduli from 0.013 to 1.4 MPa, establishing a foundation for use in applications such as cell culture.

Nanostructured Surface Functionalization of Polyacrylamide Hydrogels Below the Length Scale of Hydrogel Heterogeneity.

Hydrogels are broadly used in applications where polymer materials must interface with biology. The hydrogel network is amorphous, with substantial heterogeneity on length scales up to hundreds of nanometers, in some cases raising challenges for applications that would benefit from highly structured interactions with biomolecules. Here, we show that it is possible to generate ordered patterns of functional groups on polyacrylamide hydrogel surfaces. We demonstrate that, when linear patterns of amines are transferred to polyacrylamide, they pattern interactions with DNA at the interface, a capability of potential importance for preconcentration in chromatographic applications, as well as for the development of nanostructured hybrid materials and supports for cell culture.

Nanometer-Scale Precision Polymer Patterning of PDMS: Multiscale Insights into Patterning Efficiency Using Alkyldiynamines.

Most high-resolution interfacial patterning approaches are restricted to crystalline inorganic interfaces. Recently, we have shown that it is possible to generate 1 nm resolution functional patterns on soft materials, such as polydimethylsiloxane (PDMS), by creating highly structured striped patterns of functional alkyldiacetylenes on a hard crystalline surface, photopolymerizing to set the molecular pattern as a striped-phase polydiacetylene (sPDA), and then covalently transferring the sPDAs to PDMS. Transfer depends on the diacetylene polymerization, making it important to understand design principles for efficient sPDA polymerization and cross-linking to PDMS. Here, we combine single-molecule and fluorescence-based metrics for sPDA polymerization and transfer, first to characterize sPDA polymerization of amine striped phases, and then to develop a probabilistic model that describes the transfer process in terms of sPDA-PDMS cross-linking reaction efficiency and number of reactions required for transfer. We illustrate that transferred patterns of alkylamines can be used to direct both adsorption of CdSe nanocrystals with alkyl ligand shells and covalent reactions with fluorescent dyes, highlighting the utility of functional patterning of the PDMS surface.