Background: This study explored the most suitable materials for incorporating cyano-phycocyanin (C-PC) into hydrogels, focusing on maintaining the C-PC’s long-term structural integrity and stabilityNext, the release of C-PC from the hydrogels and its skin penetration were investigated. Methods: A series of 1% (w/w) C-PC hydrogels was prepared using various gelling agents and preservatives. Spectrophotometric measurements compared the amount of C-PC in the hydrogels to the initially added amount. After selecting the most suitable gelling agent and preservative, two C-PC hydrogels, with and without propylene glycol (PG) (Sigma-Aldrich, St. Louis, MO, USA), were produced for further testing. In vitro release studies utilized modified Franz-type diffusion cells, while ex vivo skin-permeation studies employed Bronaugh-type cells and human skin. Confocal laser scanning microscopy analyzed C-PC accumulation in the skin. Results: The findings demonstrated that sodium alginate (Sigma-Aldrich, St. Louis, MO, USA), hydroxyethyl cellulose (HEC) (Sigma-Aldrich, St. Louis, MO, USA), and Soligel^TM (Givaudan, Vernier, Switzerland) are effective biopolymers for formulating hydrogels while maintaining C-PC stability. After 6 h, C-PC release from the hydrogel containing PG was approximately 10% or 728.07 (±19.35) μg/cm², significantly higher than the nearly 7% or 531.44 (±26.81) μg/cm² release from the hydrogel without PG (p < 0.05). The ex vivo qualitative skin-permeation study indicated that PG enhances C-PC penetration into the outermost skin layer. Conclusion: PG’s ability to enhance the release of C-PC from the hydrogel, coupled with its capacity to modify the skin barrier ex vivo, facilitates the penetration of C-PC into the stratum corneum.

This study aimed to develop and evaluate cyano-phycocyanin (C-PC)-loaded enriched transfersomes for topical application, improved skin delivery, and antioxidant protection. The main objective was to overcome the limitations associated with C-PC's instability and poor skin permeability due to its high molecular weight and hydrophilicity. Six formulations were prepared using an organic solvent-free two-step method: glycerol-enriched transfersomes (Gly-transfersomes),glycerol and cholesterol-enriched transfersomes (Gly-chol-transfersomes),hyaluronate-enriched transfersomes (Hyal-transfersomes),hyaluronate and cholesterol-enriched transfersomes (Hyal-chol-transfersomes),glycerol and hyaluronate-enriched transfersomes (Hyal-gly-transfersomes), anda combination of all three (Hyal-gly-chol-transfersomes). Empty vesicles were prepared via direct sonication, then C-PC was gently loaded using mild sonication in a temperature-controlled ultrasonic bath. All formulations demonstrated properties suitable for skin delivery, with mean diameters <115 nm, polydispersity indexes <0.2, and zeta potential below -30 mV. Cryo- transmission electron microscopy confirmed spherical, unilamellar or oligolamellar morphology. Gly- and Gly-chol-transfersomes exhibited the highest encapsulation efficiency (∼52 %) and remained stable for up to 8 months at 4 °C. Antioxidant activity of C-PC (∼23-27 μmol TE/g of dry C-PC) was confirmed via DPPH assay. Biological tests on HaCaT cells exposed to H₂O₂-induced oxidative stress showed ∼80 % cell viability after treatment with C-PC formulations, compared to ∼60 % in untreated cells, indicating cytoprotective activity. Ex vivo skin penetration studies revealed significantly higher C-PC accumulation in the epidermis especially for Gly- and Gly-chol-transfersomes versus aqueous C-PC. These findings confirm the potential of enriched transfersomes as effective carriers to improve the skin delivery and bioactivity of C-PC in antioxidant skin care formulations.