Optimization of spider silk sphere formation processing conditions to obtain carriers with controlled characteristics.

Bioengineered spider silk is a focus of research due to its biocompatibility, biodegradability, and excellent mechanical properties. Functionalized silk can be processed into spheres and employed as selective drug delivery vehicles in targeted cancer treatment. Efficient, repeatable and controllable processing conditions are essential to drug carrier development. This study aimed to optimize the processing conditions of silk spheres formation, scale-up, and automation of the silk spheres production process. The automated micromixing system provided substantial amounts of silk spheres under repetitive production conditions. Micromixing resulted in smaller sphere sizes and narrower sphere size distributions than mixing with a pipette. Furthermore, the particle size and size distribution of silk spheres could be tailored by varying mixing process parameters, such as protein concentration, silk and salting out buffer ratio, mixing speed, and the size of the tubes and mixing zone. In addition, the implementation of ultrafiltration techniques provided a fast and efficient concentration of spheres in water. Furthermore, the shear forces introduced by micromixing did not impede the properties of the Her2 binding peptide (H2.1) since the functionalized H2.1MS1:H2.1MS2 silk spheres selectively were internalized by Her2-positive cancer cells. This study indicated that micromixing in combination with ultrafiltration enabled scale-up of the sphere production process under controllable and repeatable conditions.