Photochemically Stable, Non-Leaching, Bridged Polysilsesquioxane Based Sunscreens

This technology is a non-toxic, long-lasting sun protection based on nanoparticles of bridged polysilsesquioxanes.

Background: 
UV radiation (100 – 400 nm) represents ~10% of electromagnetic radiation (sunlight) that reaches the Earth's surface, and can be separated into three main types: UVC (100 – 290 nm), which has the shortest wavelength and highest energy; UVB (290 – 320 nm); and UVA (320 – 400 nm), which has the longest wavelength and lowest energy. UVB has traditionally been thought to be the most harmful radiation to skin, and the prevalence of UVB absorbing active ingredients in commercial sunscreens has reflected this belief. Recent studies, however, have detailed the harmful effects of UVA exposure as well, for sufficient doses of UVA, particularly UVA-II, can in fact induce sunburn. While the sunburn potential of UVA is less than that of UVB, exposure to lower energy UVA over a prolonged period will result in the same degree of sunburn as exposure to higher energy UVB for a shorter period of time.

Interestingly, due to the deeper penetration depth of UVA in skin, increased absorption of UVA in persons protected with sunscreens that only filter UVB, and in turn extended hours in the sun without the warning of sunburn, UVA has been found to be the major contributor of accelerated skin aging. For this reason, commercial sunscreen formulations are increasingly including active ingredients to attenuate UVA radiation. To mitigate UV exposure, the use of sunscreens, which contain active ingredients that block UV, is recommended.

Applications:

• According to embodiments of the present inventions, the sunscreens based on nanoparticles of bridged polysilsesquioxanes were prepared and found to have superior photochemical stability to ultraviolet light compared to hollow silica particles containing liquid organic sunscreens or sunscreens with pendant polysilsesquioxanes.
• The present invention features a method of protecting a skin of a mammal from harmful photo-biological effects of UV radiation. The method may comprise topically applying to the skin of the mammal an effective coating of a sunscreen formulation comprising any of the sunscreen composition.
• The present invention features a method for preventing leaching of a UV absorbing compound from the sunscreen particle. Moreover, the sunscreen particle can be resistant to photo-degradation.
• In some embodiments, the sunscreen formulation is in a form suitable for topical application. Examples include, but are not limited to, creams, ointment, suspensions, powders, lotions, gels, solids, foams, emulsions, liquid dispersions, sprays and aerosols.

Advantages:

• Minimized leaching and decreased levels of photo-degradation were achieved with covalent incorporation, with bridged incorporation necessary to ensure isolation of the sunscreen and any photo-products from skin.
• SPF values of were found to be comparable to existing commercial sunscreens. Furthermore the bridged polysilsesquioxane based sunscreens can be classified as broad-spectrum, and rate from moderate to superior in terms of UVA protective ability.
• Enhanced UV stability can be afforded with these bridged compounds since the increased immobilization ensures minimal excited state interactions.
• The sunscreen composition may be prepared by sol gel polymerization, microemulsion polymerization, or modified Stöber polymerization.
• The sunscreen formulation may further comprise an anti-oxidant to aid in preventing or reducing erythema and boost SPF.

Status: issued U.S. patent #11,389,386

Related Publications: 

ACS Appl. Mater. Interfaces, 2016, 8 (5), pp 3160–3174 

http://pubs.acs.org/doi/pdf/10.1021/acsami.5b10472