Microfluidic-Generated Injectable Bulking Agents with Biocompatible Surfaces and Their Mid-term Outcomes in a Rat Model with Anal Sphincter Injury

Bulking agents have gained attention as new, minimally invasive treatments for fecal incontinence. Various materials and surface treatment techniques have been extensively studied to ensure good biocompatibility and long-term stability. Despite significant improvements in biocompatibility, the nonuniform particle size of existing materials has led to other challenges, such as the induction of phagocytosis or reduction of injectability during in vivo tests. This study aimed to conduct a preclinical test of the midterm stability of bulking agents with newly formulated particles with uniform size. To this end, the particles were fabricated using microfluidics, resulting in a narrow size dispersity of less than 5% as the coefficient of variation, which is essentially distinct from conventional bulking agents. The microfluidic fabrication resulted in uniformly sized particles larger than the in vivo migratory limit of 80 μm and in a reduction in maximum injection pressure. Histological staining and microscopic observations confirmed proper positioning of the filler materials in vivo and a negligible immune response for up to 6 months, indicating successful midterm stability.