Micro- and Nanopatterned Silk Substrates for Antifouling Applications.

A major problem of current biomedical implants is the bacterial colonization and subsequent biofilm formation, which seriously affects their functioning and can lead to serious post-surgical complications. Intensive efforts have been directed toward the development of novel technologies that can prevent bacterial colonization while requiring minimal antibiotics doses. To this end, biocompatible materials with intrinsic antifouling capabilities are in high demand. Silk fibroin, widely employed in biotechnology, represents an interesting candidate. Here, we employ a soft-lithography approach to realize micro- and nanostructured silk fibroin substrates, with different geometries. We show that patterned silk film substrates support mammal cells (HEK-293) adhesion and proliferation, and at the same time, they intrinsically display remarkable antifouling properties. We employ Escherichia coli as representative Gram-negative bacteria, and we observe an up to 66% decrease in the number of bacteria that adhere to patterned silk surfaces as compared to control, flat silk samples. The mechanism leading to the inhibition of biofilm formation critically depends on the microstructure geometry, involving both a steric and a hydrophobic effect. We also couple silk fibroin patterned films to a biocompatible, optically responsive organic semiconductor, and we verify that the antifouling properties are very well preserved. The technology described here is of interest for the next generation of biomedical implants, involving the use of materials with enhanced antibacterial capability, easy processability, high biocompatibility, and prompt availability for coupling with photoimaging and photodetection techniques.

Conjugated polymers optically regulate the fate of endothelial colony-forming cells.

The control of stem and progenitor cell fate is emerging as a compelling urgency for regenerative medicine. Here, we propose a innovative strategy to gain optical control of endothelial colony-forming cell fate, which represents the only known truly endothelial precursor showing robust in vitro proliferation and overwhelming vessel formation in vivo. We combine conjugated polymers, used as photo-actuators, with the advantages offered by optical stimulation over current electromechanical and chemical stimulation approaches. Light modulation provides unprecedented spatial and temporal resolution, permitting at the same time lower invasiveness and higher selectivity. We demonstrate that polymer-mediated optical excitation induces a robust enhancement of proliferation and lumen formation in vitro. We identify the underlying biophysical pathway as due to light-induced activation of TRPV1 channel. Altogether, our results represent an effective way to induce angiogenesis in vitro, which represents the proof of principle to improve the outcome of autologous cell-based therapy in vivo.

Conjugated polymers mediate effective activation of the Mammalian Ion Channel Transient Receptor Potential Vanilloid 1.

Selective and rapid regulation of ionic channels is pivotal to the understanding of physiological processes and has a crucial impact in developing novel therapeutic strategies. Transient Receptor Potential (TRP) channels are emerging as essential cellular switches that allow animals to respond to their environment. In particular, the Vanilloid Receptor 1 (TRPV1), besides being involved in the body temperature regulation and in the response to pain, has important roles in several neuronal functions, as cytoskeleton dynamics, injured neurons regeneration, synaptic plasticity. Currently available tools to modulate TRPV1 activity suffer from limited spatial selectivity, do not allow for temporally precise control, and are usually not reversible, thus limiting their application potential. The use of optical excitation would allow for overcoming all these limitations. Here, we propose a novel strategy, based on the use of light-sensitive, conjugated polymers. We demonstrate that illumination of a polymer thin film leads to reliable, robust and temporally precise control of TRPV1 channels. Interestingly, the activation of the channel is due to the combination of two different, locally confined effects, namely the release of thermal energy from the polymer surface and the variation of the local ionic concentration at the cell/polymer interface, both mediated by the polymer photoexcitation.