Investigation of Physical Properties of a Polycaprolactone Dermal Filler when Mixed with Lidocaine and Lidocaine/Epinephrine

INTRODUCTION: In esthetic treatments with dermal fillers, increasing numbers of physicians are using the technique of mixing an anesthetic agent into the dermal filler before treatment to increase the comfort of the patients. This study aimed at evaluating the effects on the physical properties of a polycaprolactone (PCL)-based dermal filler after mixing with lidocaine. METHODS: A range of 2.0% lidocaine and 2.0% lidocaine/epinephrine concentrations was mixed with the PCL dermal filler to evaluate the changes in dynamic viscosity and elasticity, extrusion force, pH, and needle jam rates. The number of passes back to forth for optimal homogeneity of lidocaine and PCL dermal filler was determined. RESULTS: With 15 mixing strokes the lidocaine solution can effectively be mixed into dermal filler resulting in a homogenous blend. The viscosity, elasticity, and the extrusion force decrease with increasing lidocaine volume. The viscosity and elasticity of the dermal filler is sufficient to keep the PCL microspheres in suspension. There were no needle jams. The pH of the PCL dermal filler mixed with lidocaine solution is equivalent to that of the original dermal filler. CONCLUSION: It is concluded that mixing of lidocaine into the PCL-based dermal filler can safely be performed without harmful changes in the physical properties of the original dermal filler.