Shape-Shifting Technology of High-Molecular-Weight Hyaluronic Acid Realizing Youthful Skin
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Presented by: Mika Fujii
Introduction: Hyaluronic acid (HA) is essential to maintain youthful skin because it is involved in many biological processes such as cell proliferation, cell migration and cell differentiation. Because HA amounts in the epidermis diminish with aging, providing additional HA is necessary for maintaining the skin condition. However, it shows low skin permeability when introduced to the skin through non-invasive methods due to its high-molecular-weight (HMW). Injecting HA can provide HA into the dermis topically, but it has pain and could not provide HA to a whole face. Moreover, the half-life of HA in the skin is extremely short (approximately 1 day). Thus, to maintain youthful skin, there is a need to develop the methods for providing HA non-invasively in daily care. In this study, we developed novel technologies that deliver HMW-HA to epidermis without decreasing their original function. In addition, we investigated the effect of HA penetration on skin properties such as stratum corneum (SC) softness, transparency and skin surface contour.
Methods: Sodium hyaluronate with 1100-1600 kDa was used as the HMW-HA. Its size and volume were evaluated by multi-angle light scattering (MALS), partial specific volume (PSV) measurements and molecular dynamics (MD) simulations. The HA penetration was evaluated by the quantitation of HA using the ELISA method and the observation of skin cross section with fluorescence microscopy. The softness and transparency of ex vivo human SC sheets were measured with a rheometer and a haze meter. The water retention capacity of HA was measured through differential scanning calorimetry (DSC) and SC water contents using a corneometer. Skin surface contour was evaluated to measure the skin texture using a Handy Skin Sensor after applying formulations to panels for 4 weeks.
Results and Discussion: First, the volume of the HA molecules before and after adding MgCl2 was measured through MALS and PSV measurements. The volumes of the individual HA molecules decreased and became more compact from the addition of MgCl2. This led to a corresponding decrease in the overall volume of the structure. Moreover, MD simulation of short HA units revealed that the chain bending frequency was increased after adding of MgCl2. The Mg2+ electrostatically shield the carboxyl groups, resulting in the compaction of HA chains and overall volume of structure. Compacted HA also showed drastically increased skin penetration, and was able to penetrate the viable epidermis. This volume changes are suggested improved skin penetration of HMW-HA. Next the effect of this compacted HA on the softness and transparency of SC sheets was evaluated by rheometer and haze meter. While the SC sheet became softer and more transparent after exposure to compacted HA, aqueous HA did not elucidate a similar change. This suggests that, although standard HA could not penetrate the sheet, compacted HA could both penetrate and improve physical properties. Meanwhile, based on DSC and corneometer measurements, the water retention capacity of standard HA was inhibited by Mg2+ due to the inhibiting dissociation of carboxyl groups, which plays an important role in water retention capacity. After screening several candidates for recovering water retention capacity, it was discovered that sodium metaphosphate (SMP) was able to both recover that capacity and expand the overall volume of compacted HA structure. From these results, SMP appears to be a good candidate for capturing Mg2+ and separating them from HA so that the compacted HA can be returned to a larger size. This expansion method improved the skin texture of panels over 4 weeks of continuous use. The results can be attributed to the recovery of the original water retention capacity of HA by SMP.
Conclusion: We developed compaction and expansion methods for HMW-HA. The compaction method increased the skin penetration of HMW-HA and improved the physical properties of SC sheets. The expansion method allowed compacted HA to be returned to a larger size, and recovery of its original water retention capacity. These shape control methods made it possible not only to provide HMW-HA to the epidermis, but also to improve the function of the original HA. This technology is highly expected to utilize the novel cosmetics that maintain youthful skin as a non-invasive delivery method into the skin for HA, which diminishes in the epidermis with aging.
Methods: Sodium hyaluronate with 1100-1600 kDa was used as the HMW-HA. Its size and volume were evaluated by multi-angle light scattering (MALS), partial specific volume (PSV) measurements and molecular dynamics (MD) simulations. The HA penetration was evaluated by the quantitation of HA using the ELISA method and the observation of skin cross section with fluorescence microscopy. The softness and transparency of ex vivo human SC sheets were measured with a rheometer and a haze meter. The water retention capacity of HA was measured through differential scanning calorimetry (DSC) and SC water contents using a corneometer. Skin surface contour was evaluated to measure the skin texture using a Handy Skin Sensor after applying formulations to panels for 4 weeks.
Results and Discussion: First, the volume of the HA molecules before and after adding MgCl2 was measured through MALS and PSV measurements. The volumes of the individual HA molecules decreased and became more compact from the addition of MgCl2. This led to a corresponding decrease in the overall volume of the structure. Moreover, MD simulation of short HA units revealed that the chain bending frequency was increased after adding of MgCl2. The Mg2+ electrostatically shield the carboxyl groups, resulting in the compaction of HA chains and overall volume of structure. Compacted HA also showed drastically increased skin penetration, and was able to penetrate the viable epidermis. This volume changes are suggested improved skin penetration of HMW-HA. Next the effect of this compacted HA on the softness and transparency of SC sheets was evaluated by rheometer and haze meter. While the SC sheet became softer and more transparent after exposure to compacted HA, aqueous HA did not elucidate a similar change. This suggests that, although standard HA could not penetrate the sheet, compacted HA could both penetrate and improve physical properties. Meanwhile, based on DSC and corneometer measurements, the water retention capacity of standard HA was inhibited by Mg2+ due to the inhibiting dissociation of carboxyl groups, which plays an important role in water retention capacity. After screening several candidates for recovering water retention capacity, it was discovered that sodium metaphosphate (SMP) was able to both recover that capacity and expand the overall volume of compacted HA structure. From these results, SMP appears to be a good candidate for capturing Mg2+ and separating them from HA so that the compacted HA can be returned to a larger size. This expansion method improved the skin texture of panels over 4 weeks of continuous use. The results can be attributed to the recovery of the original water retention capacity of HA by SMP.
Conclusion: We developed compaction and expansion methods for HMW-HA. The compaction method increased the skin penetration of HMW-HA and improved the physical properties of SC sheets. The expansion method allowed compacted HA to be returned to a larger size, and recovery of its original water retention capacity. These shape control methods made it possible not only to provide HMW-HA to the epidermis, but also to improve the function of the original HA. This technology is highly expected to utilize the novel cosmetics that maintain youthful skin as a non-invasive delivery method into the skin for HA, which diminishes in the epidermis with aging.