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Plastic particle pollution has been shown to be almost completely ubiquitous within our surrounding environment. This ubiquity in combination with a variety of unique properties (e.g. density, hydrophobicity, surface functionalization, particle shape and size, transition temperatures, and mechanical properties) and the ever-increasing levels of plastic production and use has begun to garner heightened levels of interest within the scientific community. However, as a result of these properties, plastic particles are often reported to be challenging to study in complex (i.e. real) environments. Therefore, this review aims to summarize research generated on multiple facets of the micro- and nanoplastics field; ranging from size and shape definitions to detection and characterization techniques to generating reference particles; in order to provide a more complete understanding of the current strategies for the analysis of plastic particles. This information is then used to provide generalized recommendations for researchers to consider as they attempt to study plastics in analytically complex environments; including method validation using reference particles obtained via the presented creation methods, encouraging efforts towards method standardization through the reporting of all technical details utilized in a study, and providing analytical pathway recommendations depending upon the exact knowledge desired and samples being studied.

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Purified collagen possesses weak mechanical properties, hindering its broad application in tissue engineering. Strategies based on manipulating the hydrogel to induce fiber formation or incorporate nanomaterials have been proposed to overcome this issue. Herein, we use a microfluidic device to fabricate, for the first time, collagen hydrogels with aligned and oriented fibers doped with gold nanoparticles and carbon nanotubes. Results based on rheology, atomic force microscopy, and scanning electron microscopy reveal the formation of aligned and oriented collagen fibers possessing greater rigidity and stiffness on the doped hydrogels in comparison with native collagen. The mechanical properties of the hydrogels increased with the nanomaterial loading percentage and the stiffest formulations were those prepared in the presence of carbon nanotubes. We further evaluate the in vitro response of NIH-3T3 fibroblasts to the change in stiffness. The cells were found to be viable on all substrates with directional cell growth observed for the carbon nanotube-doped collagen fibers. No significant differences in the cell area, aspect ratio, and intensification of focal adhesions driven by the increase in stiffness were noted. Nonetheless, fibroblast proliferation and secretion of TGF-ß1 were greater on the hydrogels doped with carbon nanotubes. This nanomaterial-collagen composite provides unique features for cell and tissue substrate applications.

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We have demonstrated colorimetric and fluorescence detection of a peptide, melittin, based on polydiacetylene (PDA) made of 1,2-bis(10,12-tricosadiynoyl)-sn-glycero-3-phosphocholine (DC(8,9)PC). The PDA used in this work has a phosphocholine headgroup, which mimics peptide-cell membrane interactions better than the conventional PDAs with carboxyl headgroups. The dose curve (colorimetric response vs. melittin concentration) showed a half maximum response at the melittin concentration of 0.1 mg ml-1, which is similar to that reported in traditional PDA assays. It suggests that the replacement of the headgroup was achieved without sacrificing the sensitivity. From the dose curve, the Hill coefficient was extracted as αHill = 2.1. The value is in agreement with the results from previous melittin studies with phospholipids, which reflects the benefit of having a biologically relevant headgroup. In addition, we found an unexpectedly slow spectral change when DC(8,9)PC-PDA was incubated with melittin. The origin of the time-dependent signal was studied by combining UV/VIS spectroscopy, fluorescence spectroscopy and dynamic light scattering.

RESUMEN

Polydiacetylene (PDA) is a conductive polymer that has mechanochromism. When the polymer is exposed to mechanical stresses, change in temperature (thermochromism), pH (ionochromism), and so forth, the structural perturbation can be seen by the change in its color. Although it presents interesting electrical and optical properties, the relationship between these signals has rarely been investigated. We studied the correlation between the electrical conductivity and the absorption spectra of PDA. Upon UV irradiation, PDA absorption spectra presented a blue shift, which coincided with the decrease in the electrical conductivity.