Rheological study of injectable liquid implants

Introduction. Hyaluronic acid (HA) is a polysaccharide belonging to glycosaminoglycans. Due to its high biocompatibility and ability to retain moisture, HA is widely used in cosmetology and medicine. The popularity of HA-based gels is growing, especially in injection cosmetology for the correction of age-related changes, making up a significant part of aesthetic procedures. As a result of the departure of foreign manufacturers from the Russian market, there is a need to develop domestic analogues. The study of the rheological properties of gels helps to optimize formulations for medical use, ensuring the effectiveness and safety of new products.

Aim. To study how the concentration of HA and excipients affect the rheological properties of gels. The study is also aimed at identifying the relationship between these properties and clinical effectiveness.

Materials and methods. Objects of study: fillers of the Stylage® line – Stylage® HydroMax, Stylage® L, Stylage® L lidocaine, Stylage® XL, Stylage® XL lidocaine, and Repаrt® Ġ line – Repart G Normal, Repart G Deep. The samples were examined by rotational viscometry.

Results and discussion. We established a relationship between the clinical characteristics of liquid implants and their rheological properties. In the course of the studies, we determined the following optimal ranges: mucoadhesion – from 100 to 200 Pa, plastic viscosity – from 0,2 to 1,0 Pa ∙ s at a shear rate of 0–100 s^–1 at a temperature of 25 ± 1 °C, flow stress – from 50 to 150 Pa at a shear rate of 0–100 s^–1 at a temperature of 25 ± 1 °C, thixotropy – complete.

Conclusion. As a result, the study showed that viscosity is important for injection and distribution of the drug in tissues. High mucoadhesion in gynecology and urology determines the fixation of the implant in the tissues. However, excessive mucoadhesion can cause the formation of subcutaneous agglomerates, which limits the use of such products on the face. The relationship between the flow stress and the quality characteristics of the implants was not established.

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