The objective of this study was to develop a thermoresponsive gel system for high efficiency skin regeneration with multiple routes of action and exploit synergistic interactions between polymers and polypeptides.
Growth factors are multifunctional, biological proteins involved in the complex signaling pathways that regulate cell processes such as growth, differentiation, proliferation, and survival. They have many inferred applications within regenerative medicine, and have shown promising results in skin care treatments. Epidermal growth factors (EGF) have been shown to play a large role in collagen biosynthesis resulting in anti-ageing benefits along with further potential in resolving skin scarring, acne, and other skin disorders. The efficacy of growth factors into topical cosmeceutical formulations is greatly hindered by their relatively large size and short half-life. These polypeptides require immobilization and encapsulation to enhance stability and transdermal delivery. Additionally, with an increased demand from consumers for more natural products, the need for sustainable drug delivery systems for growth factor formulations is unavoidable. Chitosan and alginate have proven regenerative properties with topical skin treatments as well. Chitosan has inherent pH responsiveness, an efficient EGF release profile, and is cationic. Conversely, alginate is anionic with a high EGF encapsulation efficiency. Using these polyelectrolytes in conjunct with EGF reinforce natural signaling pathways and mimic the dermal microenvironment. Additionally, methyl cellulose is incorporated to invoke a thermal response. The resulting gel mixture will have a novel sensory feel being more gel-like at low temperatures and increasingly fluid-like as the temperature rises. Structural disruption upon application at skin temperature could allow EGF and the natural polymers to potentially better penetrate into the skin.
Alginic acid sodium salt from brown algae with medium viscosity and chitosan with a degree of acetylation ≥ 75% were both obtained from Sigma-Aldrich Inc. Methyl cellulose from Alfa Aesar with a defined 2% aqueous solution viscosity of 400 cP at 20 °C was used. Alginate or chitosan with added methyl cellulose content were simultaneously stirred into a solution of deionized water or 0.1M acetic acid, respectively. To begin to optimally tune the gel properties, the alginate and chitosan concentrations were held constant at 1% w/v while methyl cellulose concentration varied: 1%, 1.5%, and 2% w/v. Epidermal growth factor was obtained from Skin Actives Scientific. The peptide gels were formulated at 3.33 mg/mL and incorporated prior to mixing. The Discovery Hybrid Rheometer (DHR-3) from TA Instruments was employed to determine the rheological properties of the alginate-methyl cellulose and chitosan-methyl cellulose systems both with and without EGF peptides. A stainless steel, 40 mm cone plate with a 2-degree angle and 50 mm gap was used to conduct all rheological experiments on the temperature-controlled Peltier plate. Flow sweeps were carried out between the shear rate range of 0.1 to 5000 1/s at a constant temperature of 25°C. This encompasses the storage, spreading, pumping, and rubbing processes during product utilization. Temperature sweeps evaluated the thermosensitivity as the gels approach and surpass the skin’s surface temperature of 37.5 °C. A constant shear rate of 10 1/s was applied to the sample, and temperature was increased by 1°C/min between 25°C and 50°C.
This study collected and analyzed viscosity, pseudoplastic behavior, and thermoresponse trends for various alginate-methyl cellulose and chitosan-methyl cellulose systems along with the impact of EGF addition
The results of this study concluded that chitosan and alginate interact with methyl cellulose when in a gel mixture in a way that builds viscosity further than any individual component. The thermoresponsiveness is enhanced in the gel mixtures, and the magnitude is intensified with increasing methyl cellulose concentration. EGF interacts with the alginate-methyl cellulose network and slightly decreases gel viscosity, and the temperature response is further enhanced with EGF incorporation.
The future work to be carried out for this study includes exploring the impact of polyelectrolyte concentration, EGF concentration, and pH variations on the gel system. The complexity of the interactions can be further investigated with microrheology and zeta potential measurements. Raman spectroscopy analysis under temperature and shear stressors can give better indication of structural changes happening in the system correlating to drug delivery and stability.
We acknowledge the contribution of TA Instruments for making this study and our future work possible.
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