Parameterization of the optical constants of polydopamine films for spectroscopic ellipsometry studies

Dopamine-Assisted Layer-by-Layer Deposition Providing Coatings with Controlled Thickness, Roughness, and Functional Properties

In this study, dopamine-assisted deposition combined with layer-by-layer assembly was investigated as an efficient method for preparing coatings with tunable thickness, roughness, and functional properties. By this method, one can first benefit from the versatile chemistry of dopamine allowing the co-deposition of various functional materials, for example, polymers, ions, and nanoparticles, within the coating. Moreover, the layer-by-layer approach allows tuning the coating thickness and surface roughness, as well as varying the chemical composition of the coating in the vertical direction. Herein, we demonstrated the benefits of using this method in fabricating both single- and multi-component coatings.

Optical Epidermal Mimicry from Ultraviolet to Infrared Wavelengths

Optical tissue phantoms present substantial value for medical imaging and therapeutic applications. We have developed an epidermal tissue phantom to mimic the optical properties of human skin from the ultraviolet to the infrared region, exceeding the breadth of existing studies. An epoxy matrix is combined with melanin-mimicking polydopamine via a cost-effective fabrication strategy. Reflectance and transmittance measurements enable calculation of the wavelength-dependent complex refractive index and absorption coefficient. Results are compared with literature data to establish agreement with a real human epidermis. By analyzing emissive power at a typical skin temperature, the epidermal tissue phantom is shown to accurately mimic the radiative properties of human skin. This simple, multifunctional material represents a promising substitute for human tissue for a variety of medical and bioengineering applications.

Fast Light-Driven Motion of Polydopamine Nanomembranes

The actuation of micro- and nanostructures controlled by external stimuli remains one of the exciting challenges in nanotechnology due to the wealth of fundamental questions and potential applications in energy harvesting, robotics, sensing, biomedicine, and tunable metamaterials. Photoactuation utilizes the conversion of light into motion through reversible chemical and physical processes and enables remote and spatiotemporal control of the actuation. Here, we report a fast light-to-motion conversion in few-nanometer thick bare polydopamine (PDA) membranes stimulated by visible light. Light-induced heating of PDA leads to desorption of water molecules and contraction of membranes in less than 140 μs. Switching off the light leads to a spontaneous expansion in less than 20 ms due to heat dissipation and water adsorption. Our findings demonstrate that pristine PDA membranes are multiresponsive materials that can be harnessed as robust building blocks for soft, micro-, and nanoscale actuators stimulated by light, temperature, and moisture level.