Topical
sunscreens are widely used to prevent sunburns and long-term
skin damage including cancer. Recently, conventional chemical UV absorbers
have been criticized and in some cases banned for adverse human and
environmental health impacts. In this investigation, we evaluated
naturally derived UV absorbers including vitamins, polyphenols, carotenoids,
and amino acids to determine safety and efficacy profiles. Human and
ecological hazards were evaluated, as well as the in vitro sun protection factor and critical wavelength. These attributes
were compared to commercial UV absorbers such as octinoxate and oxybenzone
to determine viability in personal care products. We found that resveratrol,
ferulic acid, and ethyl ferulate demonstrate significant UV-absorbing
capacity and lower hazard levels compared to current-use sunscreen
active ingredients.
Alginates gel rapidly under ambient conditions and have widely documented potential to form protective matrices for sensitive bioactive cargo. Most commonly, alginate gelation occurs via calcium mediated electrostatic crosslinks between the linear polyuronic acid polymers. A recent breakthrough to form crosslinked alginate microcapsules (CLAMs) by in situ gelation during spray drying (“CLAMs process”) has demonstrated applications in protection and controlled delivery of bioactives in food, cosmetics, and agriculture. The extent of crosslinking of alginates in CLAMs impacts the effectiveness of its barrier properties. For example, higher crosslinking extents can improve oxidative stability and limit diffusion of the encapsulated cargo. Crosslinking in CLAMs can be controlled by varying the calcium to alginate ratio; however, the choice of alginates used in the process also influences the ultimate extent of crosslinking. To understand how to select alginates to target crosslinking in CLAMs, we examined the roles of alginate molecular properties. A surprise finding was the formation of alginic acid gelling in the CLAMs that is a consequence of simultaneous and rapid pH reduction and moisture removal that occurs during spray drying. Thus, spray dried CLAMs gelation is due to calcium crosslinking and alginic acid formation, and unlike external gelation methods, is insensitive to the molecular composition of the alginates. The ‘extent of gelation’ of spray dried CLAMs is influenced by the molecular weights of the alginates at saturating calcium concentrations. Alginate viscosity correlates with molecular weight; thus, viscosity is a convenient criterion for selecting commercial alginates to target gelation extent in CLAMs.
A recently patented
one-step
in situ
cross-linked
alginate microencapsulation (CLAM) by spray-drying (i.e., the UC Davis
CLAMs technology) can overcome the high cost of scale-up that limits
commercial applications. While increasing calcium loading in the CLAMs
process can increase the extent of cross-linking and improve retention
and protection of the encapsulated cargo, the potential for residual
undissolved calcium salt crystals in the final product can be a concern
for some applications. Here, we demonstrate an alternate one-step
spray-dry CLAMs process using pH-responsive chelation of calcium.
The “Chelate CLAMs” process is an improvement over the
patented process that controls ion availability based on pH-responsive
solubility of the calcium salt. Hyaluronic acid was encapsulated in
CLAMs to minimize swelling and release in aqueous formulations. CLAMs
with 61% (d.b.) hyaluronic acid (HA-CLAMs) demonstrated restricted
plumping, limited water absorption capacity, and reduced leaching,
retaining up to 49% hyaluronic acid after 2 h in water. Alternatively,
“Chelate HA-CLAMs” formed by the improved process exhibited
nearly full retention of hyaluronic acid over 2 h in water and remained
visibly insoluble after 1 year of storage in water at 4 °C. Successful
hyaluronic acid retention in CLAMs is likely due in part to its ability
to cross-link with calcium.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.