Structural Features of Connective Tissue Formed around Resin Implants Subcutaneously Embedded in Dairy Cows

Simple Summary The relation between implant components, foreign body reactions to implant materials, and the formation of connective tissue (CNT) in host animals is crucial for developing effective xenotransplantation techniques. This study demonstrated that dairy cows produce several large, dense, collagen-based CNTs following subcutaneous implantation of acrylic resin-based implants. We elucidated the process of CNT formation within the implants. The implants used in this study, comprising an outer cylinder, a core rod, and caps at both ends, were composed of acrylic resin created using a three-dimensional (3D) printer. No abnormalities, such as chronic inflammation, were observed. An advantage of 3D printing technology in the medical field is its ability to produce implants with complex shapes for surgical applications. Therefore, the combination of acrylic resin and 3D printer design holds promise for researching foreign body reaction and clinical applications in future studies.Abstract Foreign body reactions (FBRs) are inadvertently observed in invading or artificially embedded materials, triggering inflammation and subsequent fibrotic processes to occur in situ. Here, we assessed the spatiotemporal formation of connective tissue around implanted materials to establish a technique using connective tissue formed by FBRs as xenografts. An acrylic resin implant, comprising a columnar inner rod and a tubular outer cylinder (OC) with several slits, was embedded in adult dairy cows. Tissues formed in the inner rod and OC groups were histologically analyzed at weeks 2, 4, 8, and 12. Edematous tissues with non-collagenous fibers formed for 2 weeks and showed increased cellularity after 4 weeks. The weight, thickness, amounts of total protein, collagen, DNA, and quantitative scores of alpha-smooth muscle actin-positive myofibroblasts or elastic fibers notably increased after 8 weeks, with condensed collagen fibers showing orientation. Inflammatory cells were primarily localized in tissues close to the OC, and their numbers increased, with the count of CD204+ cells peaking at 8 weeks and declining at 12 weeks. The count of Ki67+ proliferating cells slightly increased in tissues close to the OC; however, the number and lumen of CD31+ vessels increased. These results may help understand FBR-related tissue remodeling.

Automated summary

This study demonstrated the formation of connective tissue in dairy cows following subcutaneous implantation of acrylic resin-based implants created using 3D printing technology. The results provide insights into the tissue remodeling process related to foreign body reactions.