Light-to-Heat Converting ECM-Mimetic Nanofiber Scaffolds for Neuronal Differentiation and Neurite Outgrowth Guidance

Abstract

The topological cues of fibrous scaffolds (in particular extracellular matrix (ECM)-mimetic nanofibers) have already proven to be a powerful tool for influencing neuronal morphology and behavior. Remote photothermal optical treatment provides additional opportunities for neuronal activity regulation. A combination of these approaches can provide “smart” 3D scaffolds for efficient axon guidance and neurite growth. In this study we propose two alternative approaches for obtaining biocompatible photothermal scaffolds: surface coating of nylon nanofibers with light-to-heat converting nanoparticles and nanoparticle incorporation inside the fibers. We have determined photoconversion efficiency of fibrous nanomaterials under near infrared (NIR) irradiation, as well as biocompatible photothermal treatment parameters. We also measured photo-induced intracellular heating upon contact of cells with a plasmonic surface. In the absence of NIR stimulation, our fibrous scaffolds with a fiber diameter of 100 nm induced an increase in the proportion of β3-tubulin positive cells, while thermal stimulation of neuroblastoma cells on nanoparticles-decorated scaffolds enhanced neurite outgrowth and promoted neuronal maturation. We demonstrate that contact guidance decorated fibers can stimulate directional growth of processes of differentiated neural cells. We studied the impact of nanoparticles on the surface of ECM-mimetic scaffolds on neurite elongation and axonal branching of rat hippocampal neurons, both as topographic cues and as local heat sources. We show that decorating the surface of nanofibers with nanoparticles does not affect the orientation of neurites, but leads to strong branching, an increase in the number of neurites per cell, and neurite elongation, which is independent of NIR stimulation. The effect of photothermal stimulation is most pronounced when cultivating neurons on nanofibers with incorporated nanoparticles, as compared to nanoparticle-coated fibers. The resulting light-to-heat converting 3D materials can be used as tools for controlled photothermal neuromodulation and as “smart” materials for reconstructive neurosurgery.

Biological Applications of Thermoplasmonics

“…The local heat produced by laser-irradiated nanoparticles can activate cell sensing and has been employed to study temperature-induced changes in transmembrane potentials in neurons with consequent induction of action potentials, 2 activation of heat shock proteins (HSPs), 3 and modulation of cell differentiation. 4 These effects illustrate the potential of manipulating biological functions. In addition, thermoplasmonics allows for precise ablation at the subcellular or cellular level, which has been used for photothermal therapy in cancer 5 and investigation of cellular membrane repair to nanoscopic injuries induced by local heating in living cells.…”

“…Thermoplasmonics can be applied for different purposes in biological systems. The local heat produced by laser-irradiated nanoparticles can activate cell sensing and has been employed to study temperature-induced changes in transmembrane potentials in neurons with consequent induction of action potentials, activation of heat shock proteins (HSPs), and modulation of cell differentiation . These effects illustrate the potential of manipulating biological functions.…”

“…70 Copper ions have traditionally been used to trigger this differentiation, but by using laser irradiation of copper nanoparticles, it was possible to thermally induce the mesenchymal differentiation and simultaneously weaken the side effects of having free copper ions in the blood. Remote modulation of myotube 71 and neuronal 4,72 cell differentiation was also achieved using plasmonic heating (Figure 6B), and while the mechanism behind the observed biological effects remains poorly understood, it has been shown that several proteins are regulated through thermally altered gene expression, including HSP and other stress sensitive proteins. 50,71 We envisage that plasmonic heating will provide a useful tool in research on stem cell-based therapeutics and tissue engineering by remote heating and wireless stimulation of muscle cells.…”

Implication of thermal signaling in neuronal differentiation revealed by manipulation and measurement of intracellular temperature

“…Physical signals such as mechanical force 14,15 , electric field 16,17 , light [18][19][20][21] , and temperature [22][23][24][25][26][27][28][29] , have also been reported to influence neuronal differentiation. In particular, spontaneous temperature fluctuations, which are larger than the changes in deep body temperature (<1 °C) due to biological rhythms (e.g., circadian rhythm 30 or menstrual cycle 31 ), occur in the brain 32,33 .…”

“…These fluctuations suggest a profound relationship between temperature and brain functions. Recently, the relationship between neurite outgrowth and temperature has been investigated, showing that thermal stimuli (e.g., heat shock) induce neurite outgrowth [23][24][25]28 . Additionally, the direction of neurite outgrowth (i.e., axon guidance) is influenced by extracellular heating 26,27 .…”