Antarctic krill (Euphausia
superba) is one of the important bioresources in Antarctic
waters, containing
many bioactives (e.g., astaxanthin), which have a highly potential
value for commercial exploitation. In this study, the effects of processing
methods on the content, structural isomers, and composition of astaxanthins
(free astaxanthin and astaxanthin esters) were studied. Three drying
methods, comprising freeze-drying, microwave drying, and hot-air drying,
were used. Free astaxanthin (Ast), astaxanthin monoesters (AM), and
astaxanthin diesters (AD) in boiled krill (control) and dried krill
were extracted and analyzed using high-resolution mass spectrometry
with ultraviolet detection. After the three processes, total astaxanthin
loss ranged from 8.6 to 64.9%, and the AM and AD contents ranged from
78.3 to 16.6 and 168.7 to 90.5 μg/g, respectively. Compared
to other kinds of astaxanthin esters, astaxanthin esters, which linked
to eicosapentaenoic acid and docosahexaenoic acid, as well as the
Ast, were more easily degraded, and AM was more susceptible to degradation
than AD. All-E-astaxanthin easily transformed to
the 13Z-astaxanthin than to the 9Z-astaxanthin during the drying process, but the proportions of optical
isomers changed due to drying by no more than 5%. The results suggested
that freeze-drying, low-power microwave drying (≤1 kW), and
low-temperature hot-air drying (≤60 °C) are optimal drying
methods for ensuring the quality of krill products.
Multifunctional
hydrogel-based wound dressings have been explored
for decades due to their huge potential in multifaceted medical intervention
to wound healing. However, it is usually not easy to fabricate a single
hydrogel with all of the desirable functions at one time. Herein,
a bilayer model with an outer layer for hydrogel wound dressing was
proposed. The inner layer (Hm-PNn) was a hybrid
hydrogel prepared by N-isopropylacrylamide and chitosan-N-2-hydroxypropyl trimethylammonium chloride (HACC), and
the outer layer (PVAo-PAmp) was prepared by
polyvinyl alcohols and acrylamide. The two hydrogel layers of the
bilayer model were covalently connected with excellent interfacial
strength by photoinduced electron/energy transfer-reversible addition-fragmentation
chain transfer (PET-RAFT) polymerization. The outer layer exposed
to the ambient environment exhibited good stretchability and toughness,
while the inner-layer hydrogel adhered to the skin exhibited excellent
softness, antibacterial activity, thermoresponsivity, and biocompatibility.
In particular, the inner layer of a hydrogel demonstrated excellent
antibacterial capability toward both Staphylococcus
aureus as Gram-positive bacteria and Escherichia coli as Gram-negative bacteria. Cell
cytotoxicity showed that the cell viability of all Hm-PNn layer hydrogels exceeds 80%, confirming that the hydrogels
bear excellent biocompatibility. In vivo experimental results indicated
that the Hm-PNn/PVAo-PAmp bilayer hydrogel has a significant effect on the acceleration of
wound healing, which was demonstrated in a full-thickness skin defect
model showing improved collagen disposition and granulation tissue
thickness. With these results, the established multifunctional bilayer
hydrogel exhibits potential as an excellent wound dressing for wound
healing applications, especially for open and infected traumas.
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