Silk fibroin hydrogels for potential applications in photodynamic therapy

Advances and perspectives in use of semisolid formulations for photodynamic methods

Although nearly 30 years have passed since the introduction of the first clinically approved photosensitizer for photodynamic therapy, progress in developing new pharmaceutical formulations remains unsatisfactory. This review highlights that despite years of research, many recurring challenges and issues remain unresolved. The paper includes an analysis of selected essential studies involving aminolevulinic acid and its derivatives, as well as other photosensitizers with potential for development as medical products. Among various possible vehicles, special attention is given to gelatin, alginates, poly(ethylene oxide), polyacrylic acid, and chitosan. The focus is particularly on infectious and cancerous diseases. Key aspects of developing new semi-solid drug forms should prioritize the creation of easily manufacturable and biocompatible preparations for clinical use. At the same time, new formulations should preserve the primary function of photosensitizers, which is the generation of reactive oxygen species capable of destroying pathogenic cells or tumors. Additionally, the use of adjuvant properties of carriers, which can enhance the effectiveness of macrocycles, is emphasized, especially in chitosan-based antibacterial formulations. Current research indicates that many promising dyes and macrocyclic compounds with high potential as photosensitizers in photodynamic therapy remain unexplored in formulation and development work. This review outlines potential new and previously explored pathways for advancing photosensitizers as active pharmaceutical ingredients (APIs).

Optimizing protein delivery rate from silk fibroin hydrogel using silk fibroin-mimetic peptides conjugation

Controlled release of proteins, such as growth factors, from biocompatible silk fibroin (SF) hydrogel is valuable for its use in tissue engineering, drug delivery, and other biological systems. To achieve this, we introduced silk fibroin-mimetic peptides (SFMPs) with the repeating unit (GAGAGS)n. Using green fluorescent protein (GFP) as a model protein, our results showed that SFMPs did not affect the GFP function when conjugated to it. The SFMP-GFP conjugates incorporated into SF hydrogel did not change the gelation time and allowed for controlled release of the GFP. By varying the length of SFMPs, we were able to modulate the release rate, with longer SFMPs resulting in a slower release, both in water at room temperature and PBS at 37 °C. Furthermore, the SF hydrogel with the SFMPs showed greater strength and stiffness. The increased β-sheet fraction of the SF hydrogel, as revealed by FTIR analysis, explained the gel properties and protein release behavior. Our results suggest that the SFMPs effectively control protein release from SF hydrogel, with the potential to enhance its mechanical stability. The ability to modulate release rates by varying the SFMP length will benefit personalized and controlled protein delivery in various systems.

Silk Fibroin/Poly(vinyl Alcohol) Microneedles as Carriers for the Delivery of Singlet Oxygen Photosensitizers

Photodynamic therapy (PDT) is a medical treatment in which a combination of a photosensitizing drug and visible light produces highly cytotoxic reactive oxygen species (ROS) that leads to cell death. One of the main drawbacks of PDT for topical treatments is the limited skin penetration of some photosensitizers commonly used in this therapy. In this study, we propose the use of polymeric microneedles (MNs) prepared from silk fibroin and poly(vinyl alcohol) (PVA) to increase the penetration efficiency of porphyrin as possible applications in photodynamic therapy. The microneedle arrays were fabricated from mixtures in different proportions (1:0, 7:3, 1:1, 3:7, and 0:1) of silk fibroin and PVA solutions (7%); the polymer solutions were cast in polydimethylsiloxane (PDMS) molds and dried overnight. Patches containing grids of 10 × 10 microneedles with a square-based pyramidal shape were successfully produced through this approach. The polymer microneedle arrays showed good mechanical strength under compression force and sufficient insertion depth in both Parafilm M and excised porcine skin at different application forces (5, 20, 30, and 40 N) using a commercial applicator. We observe an increase in the cumulative permeation of 5-[4-(2-carboxyethanoyl) aminophenyl]-10,15,20-tris-(4-sulphonatophenyl) porphyrin trisodium through porcine skin treated with the polymer microneedles after 24 h. MNs may be a promising carrier for the transdermal delivery of photosensitizers for PDT, improving the permeation of photosensitizer molecules through the skin, thus improving the efficiency of this therapy for topical applications.

Ganoderma Lucidum Polysaccharides Enhance the Abscopal Effect of Photothermal Therapy in Hepatoma-Bearing Mice Through Immunomodulatory, Anti-Proliferative, Pro-Apoptotic and Anti-Angiogenic

Hepatocellular carcinoma is a malignant tumor with high morbidity and mortality, a highly effective treatment with low side effects and tolerance is needed. Photothermal immunotherapy is a promising treatment combining photothermal therapy (PTT) and immunotherapy. PTT induces the release of tumor-associated antigens by ablating tumor and Ganoderma lucidum polysaccharides (GLP) enhance the antitumor immunity. Results showed that Indocyanine Green (ICG) was successfully encapsulated into SF-Gel. ICG could convert light to heat and SF-Gel accelerates the photothermal effect in vitro and in vivo. PTT based on ICG/ICG-SF-Gel inhibited the growth of primary and distal tumors, GLP enhanced the inhibitory efficacy. ICG/ICG-SF-Gel-based PTT and GLP immunotherapy improved the survival time. ICG/ICG-SF-Gel-based PTT induces tumor necrosis and GLP enhanced the photothermal efficacy. ICG/ICG-SF-Gel-based PTT inhibited cell proliferation and angiogenesis, induced cell apoptosis, enhanced cellular immunity, and GLP enhanced these effects. In conclusion, GLP could enhance the abscopal effect of PTT in Hepatoma-bearing mice.

Physically Cross-Linked Silk Fibroin-Based Tough Hydrogel Electrolyte with Exceptional Water Retention and Freezing Tolerance

Flexible ionic conductive hydrogel is attracting significant interest as it could be one of the crucial components for multifunctional ionotronic devices. However, their features of inevitably drying out without package and freezing at subzero temperatures may greatly limit the applications of conventional hydrogels in specific situations. Here, we present an ionic conductive hydrogel with water retention and freezing tolerance that consists of silk fibroin, ionic liquid, water, and inorganic salt. It is discovered that the ionic liquid serves multiple purposes to prevent water evaporation, decrease the freezing point, provide the essential conductivity of the hydrogel, etc. As a binary mixed solvent, the ionic liquid/water mixture enhances both water retention and freezing tolerance of the hydrogel electrolyte. Based on the silk fibroin (SF)/1-ethyl-3-methylimidazolium acetate (EMImAc)/H₂O/KCl hydrogel electrolyte, the flexible fiberlike supercapacitor could still function well at a temperature as low as -50 °C and after being stored in the open air for a long time. It is anticipated that this hydrogel will prove useful in developing new applications operating under harsh environments.

The Role of Amylogenic Fiber Aggregation on the Elasticity of a Lipid Membrane

This work presents a systematic study of the swelling behavior of a lecithin lamellar phase incorporating different amounts of the short peptide sequence diphenylalanine (FF). Small- and wide-angle X-ray scattering assays provide relevant information about the structure and elasticity of the lamellar stacking. These data show that important changes occur at the interface of the lipid membrane dependent not only on the peptide content but also on the hydration of the lamellar structure. Multilamellar-to-unilamellar transitions, previously observed for an increasing number of peptides, are now observed to be dependent on the hydration of the lamellar phase. Wide-angle X-ray scattering and electron microscopy observations (TEM) provide experimental evidence of peptide aggregation into long amylogenic fibers. We argue that aggregates that partition in water may become large enough to destabilize the lamellar structure. It is also shown that, for a given peptide concentration, the lamellar structure can be rendered more flexible or more rigid, by tuning the hydration.