Four Usnea longissima polysaccharides
(ULPs; ULP15, ULP30, ULP50, and ULP70) were obtained from the lichen U. longissima via water extraction and graded ethanol
precipitation. The obtained ULPs were all heteropolysaccharides with
a few proteins, with which glucose was the major monosaccharide composition.
With the increase in the precipitated ethanol concentrations, the
content of galactose, xylose, and mannose increased, whereas that
of glucose decreased. Moreover, the antioxidant activity test demonstrated
that ULP15 exhibited better reducing power and stronger scavenging
ability on 2,2-diphenyl-1-picrylhydrazyl (DPPH) and hydroxyl free
radicals. Importantly, ULP15 also had a better proliferative effect
on human HaCaT keratinocytes and dermal fibroblasts. Meanwhile, ULP15
protected HaCaT keratinocytes from UVB-induced proliferation inhibition
and exhibited tyrosinase inhibition activity. Therefore, this work
provides interesting insight into the preparation of cosmetic ingredients
using the polysaccharide ULP15.
Composite
films with comprehensive high tensile strength, great
electrical conductivity, and excellent degradable property meet the
requirement to serve as flexible and transient electronics; however,
integrating these properties together remains to be achieved. In this
work, poly(vinyl alcohol) (PVA)–carbon dot (CCD)–EGaIn
composite films combining these admirable properties were prepared
using nontoxic raw materials and facile cast-dropping methods. In
the obtained PVA–CCD–EGaIn composite films, CCD acted
as a physical cross-linker to improve the mechanical properties due
to the H-bond interactions between PVA and CCD, contributing to an
improved tensile strength of 65.0 MPa (relative variation of 22.2%)
and a high tensile modulus of 2.24 GPa (relative variation of 96.5%).
EGaIn acted as a conductive additive to endow the composite film with
a high electrical conductivity (5.35 S/m). The resultant PVA–CCD–EGaIn
composite films also demonstrated preferable thermal stability and
advantageous photothermal conversion behavior. Moreover, the electrical
conductivity of composite films was stable under repeated bending–unbending
tests, allowing for the real-time detection of human activities. Interestingly,
the composite films were also degradable in a HCl solution (pH = 5),
which was an attractive feature for the emerging transient electronics.
This work provides a workable guideline for the fabrication of green
and economical multifunctional composite materials.
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