The modulation of fibroin solubility in aqueous environments through controlled regeneration processes allows the formation of stable solutions with variable concentrations between 1-8% weight/volume, a fundamental characteristic for gastroprotective applications that requires the formulation of uniform coatings adherent to mucosal surfaces. The control of crystallinity degree through temperature and pH variations during regeneration enables obtaining materials with mechanical and degradation properties specifically optimized for the gastric environment.
Adhesion mechanisms
The interaction of fibroin with gastrointestinal mucosa occurs through rather complex physicochemical mechanisms involving electrostatic forces, hydrogen bonds and hydrophobic interactions. The presence of functional groups such as amino, carboxyl and hydroxyl groups along the protein chain facilitates adhesion to mucosal glycoproteins, particularly to mucins MUC1, MUC5AC and MUC6 that constitute the protective mucous gel of the stomach.
The mucoadhesive capacity of fibroin is further enhanced by its ability to form thermoreversible gels at physiological temperature. Rheological studies have demonstrated that 2-4% fibroin solutions develop optimal viscoelastic properties for mucosal adhesion, with detachment force values ranging between 0.8-1.2 N/cm², superior to many synthetic polymers used in gastroprotective formulations. The residence time on the gastric surface is prolonged, with elimination half-lives varying from 4 to 8 hours depending on the concentration and degree of material crosslinking.
Biocompatibility and biodegradability
Silk fibroin presents excellent biocompatibility characteristics, demonstrated through numerous in vitro and in vivo studies. The absence of significant immunogenic reactions is attributable to the native protein structure that does not contain epitopes recognized as foreign by the human immune system. Cytotoxicity tests conducted on gastric epithelial cell lines (AGS, MKN-45) have shown IC50 values exceeding 1000 μg/ml, indicating a high safety profile for clinical applications.
The biodegradation of this silk protein in the gastric environment occurs mainly through the action of endogenous proteases, particularly pepsin, trypsin and chymotrypsin. The degradation kinetics can be modulated by controlling the degree of material crystallinity. Fibroins with higher β-sheet structure content have been shown to display more prolonged degradation times, compatible with mucosal lesion healing times. FTIR spectroscopic analyses have confirmed that degradation products consist mainly of biocompatible low molecular weight peptides that are easily absorbed or eliminated through normal physiological processes.
Applications in peptic ulcers
Peptic ulcers represent an ideal therapeutic target for gastroprotective fibroin application, given the need to protect mucosal lesions from the erosive action of gastric acid and pepsin. Experimental models in rats with ethanol- and indomethacin-induced ulcers have demonstrated that topically applied fibroin coatings significantly reduce ulcerated area by 65-80% compared to untreated controls.
The gastroprotective mechanism is based on the formation of a physical barrier that isolates the lesion from the acidic gastric environment, maintaining a neutral-basic pH microenvironment favorable to re-epithelialization. Simultaneously, fibroin facilitates adhesion and proliferation of gastric epithelial cells through the presentation of bioactive peptide sequences, particularly RGD motifs (arginine-glycine-aspartic acid) that interact with cellular integrins α5β1 and αvβ3.
Histological studies have shown that fibroin treatment accelerates tissue repair, promoting the formation of new epithelial tissue characterized by increased density of gastric pits and increment in growth factor expression such as EGF (epidermal growth factor) and VEGF (vascular endothelial growth factor). The optimal pharmacokinetic profile is achieved with repeated applications every 12 hours for a duration of 7-10 days, corresponding to the physiological healing times of superficial ulcers.
Efficacy in inflammatory bowel diseases
In chronic inflammatory bowel diseases, such as Crohn's disease and ulcerative colitis, fibroin demonstrates therapeutic properties through anti-inflammatory and reparative mechanisms. Topical application of fibroin-based formulations in murine models of experimental colitis induced by dextran sodium sulfate (DSS) has shown significant reductions in systemic inflammatory markers, with 40-60% decreases in plasma levels of TNF-α, IL-1β and IL-6.
This incredible protein modulates local immune response through interaction with dendritic cells and macrophages present in the intestinal lamina propria, promoting a shift toward an anti-inflammatory M2 phenotype. This effect is mediated by activation of the IL-10/STAT3 signaling pathway and downregulation of NF-κB-dependent pro-inflammatory pathways. Immunofluorescence analyses have shown significant increases in infiltration of regulatory T lymphocytes (Treg) CD4+CD25+FoxP3+ in areas treated with fibroin, suggesting a role in intestinal autoimmunity modulation.
From a tissue repair perspective, fibroin also stimulates proliferation of intestinal stem cells located in the crypts of Lieberkühn through activation of the Wnt/β-catenin pathway. This process is facilitated by increased expression of Lgr5, a specific marker of intestinal stem cells, and by secretion of paracrine growth factors that accelerate epithelial turnover and reconstitution of the mucosal barrier.
Gastric coating technologies
Technologies for clinical application of gastroprotective fibroin are based on advanced drug delivery systems that guarantee controlled release and selective deposition of the material on injured mucosal surfaces. The most promising systems include biodegradable microspheres, thin films and injectable hydrogels that can be administered orally or through endoscopic procedures.
Fibroin microspheres, with diameters ranging between 10-50 μm, are prepared through spray-drying or coacervation techniques, allowing encapsulation of gastroprotective active principles such as sucralfate, bismuth or anti-Helicobacter pylori antimicrobial agents. Release kinetics can be modulated by varying the degree of microsphere crosslinking through treatments with genipin or glutaraldehyde, obtaining release profiles ranging from immediate release (30 minutes) to prolonged release (12-24 hours).
Silk protein thin films represent a particularly interesting technology for direct endoscopic applications. These devices, with thicknesses of 50-200 μm, are applied directly to the mucosal lesion through specialized catheters, adhering to the surface and forming a temporary protective barrier. The mechanical flexibility of the film (elastic modulus of 0.1-0.5 GPa) allows adaptation to the complex morphology of gastric mucosa, while controlled permeability facilitates metabolic exchanges necessary for tissue repair.
Clinical and translational perspectives
Clinical translation of gastroprotective fibroin requires the development of standardized protocols for material production, purification and sterilization according to GMP (Good Manufacturing Practice) regulations. Phase I studies currently in progress are evaluating the safety and tolerability of oral fibroin-based formulations in healthy volunteers, with particular attention to pharmacokinetic parameters and gastrointestinal side effects.
The main challenges for clinical implementation include optimization of administration methods to ensure uniform application on mucosal lesions and development of imaging systems for real-time monitoring of adhesion and permanence of the protective coating. Laser confocal endoscopy and optical coherence tomography (OCT) techniques are emerging as promising tools for non-invasive evaluation of therapeutic efficacy.
From a regulatory perspective, fibroin benefits from recognition as a natural material with a long history of use in medical applications, potentially facilitating approval pathways. However, thorough characterization of batch-to-batch variability and development of validated analytical methods for quality control of therapeutic formulations remain necessary. Integration with conventional pharmacological therapies represents an active research area, with particular interest in synergistic combinations with proton pump inhibitors and selective antimicrobial agents.
