Oxidative
stress represents a common issue in most neurological
diseases, causing severe impairments of neuronal cell physiological
activity that ultimately lead to neuron loss of function and cellular
death. In this work, lipid-coated polydopamine nanoparticles (L-PDNPs)
are proposed both as antioxidant and neuroprotective agents, and as
a photothermal conversion platform able to stimulate neuronal activity.
L-PDNPs showed the ability to counteract reactive oxygen species (ROS)
accumulation in differentiated SH-SY5Y, prevented mitochondrial ROS-induced
dysfunctions and stimulated neurite outgrowth. Moreover, for the first
time in the literature, the photothermal conversion capacity of L-PDNPs
was used to increase the intracellular temperature of neuron-like
cells through near-infrared (NIR) laser stimulation, and this phenomenon
was thoroughly investigated using a fluorescent temperature-sensitive
dye and modeled from a mathematical point of view. It was also demonstrated
that the increment in temperature caused by the NIR stimulation of
L-PDNPs was able to produce a Ca
2+
influx in differentiated
SH-SY5Y, being, to the best of our knowledge, the first example of
organic nanostructures used in such an approach. This work could pave
the way to new and exciting applications of polydopamine-based and
of other NIR-responsive antioxidant nanomaterials in neuronal research.
Polydopamine (PDA) is a polymer that derives from the self-polymerization of the biomolecule dopamine. It can be easily synthesized to obtain spherical nanoparticles (PDNPs), tunable in terms of size, loaded cargo, and surface functionalization. PDNPs have been increasingly attracting the attention of the research community due to their elevated versatility in the biomedicine field, for their excellent ability to encapsulate drugs, to convert near-infrared (NIR) radiation into heat, and to act as an antioxidant agent. Size is an important aspect to be considered, especially concerning the specific intended field of application. This work aims at investigating how changes in the size of PDNPs affect the nanoparticle properties relevant for biomedical applications, especially focusing on cancer nanomedicine. A library of differently sized PDNPs (from 145 to 957 nm) has been obtained by varying the ammonia/dopamine molar ratio during the synthesis procedure, and detailed characterization in terms of biocompatibility, cell internalization, antioxidant capacity, and photothermal conversion has been carried out. Experiments showed that nanoparticles with a larger diameter display higher NIR absorbance, superior resistance to degradation, and higher photothermal conversion capacity (the latter confirmed by a mathematical model). On the other hand, a reduction in diameter size induces both improved antioxidant properties and enhanced cellular uptake. Herein, we provide a useful tool, allowing one to choose the proper size of PDNPs tailored for specific biomedical applications.
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