Long-Term In Vivo Response of a Polyurethane Gastric Implant for Treating Gastro-Oesophageal Reflux Diseases: A Comparison of Different Surface Treatments

Abstract

Gastro oesophagael reflux disease (GORD) is common in the Western hemisphere. Patients with regurgitated reflux are typically treated with fundoplication surgery. We present a newly designed polyurethane implant which passively aids the sphincter in reducing gastric fluids within the oesophagus. The gastric implant has an open porous inner side which allows for tissue ingrowth from the oesophagus and thus allows for fixation around the sphincter. In addition, a device for minimally invasive surgery of this implant was developed and used in a pig model. The unmodified GORD implant was placed around the pig’s oesophagus with unsatisfactory results, leading to insufficient fixation at the implantation site and scarring tissue leading to dysphagia. In addition, two surface modifications, plasma activation and TiO2 deposition were used to improve the implant’s host tissue response. The biocompatibility effects of the surface treatments and sterilisation method on the implant were investigated in vitro and in vivo. In vitro tests found that the plasma activation and TiO2 deposition have effectively enhanced the surface hydrophilicity and, consequently, the cell response to the implant. In addition, the gamma sterilisation harmed the plasma-activated implant. The plasma activation was more effective than TiO2 deposition as a surface treatment method for improving the tissue response of this implant in vivo. In addition, the in vivo experiment proved tissue ingrowth as deep as 1 mm into the porous structure of the implant. The GORD implants were encapsulated wholly in fibrous tissue; however, the capsule thickness diminished over time. Finally, the TiO2-coated implants showed the poorest histocompatibility, contradictory to the in vitro findings. This study shows that it is possible to produce a plasma-treated porous polyurethane gastric implant that allows for fibrous tissue ingrowth, reduced in vivo encapsulation, and enhanced chemical properties.Graphical Model of the implant with an inner porous and an outer non-porous surface. The hypothesis was that the porous surface allows for fibroblastic infiltration into the porous structure (A) and fixation by scarring at the point of implantation, the lower oesophageal sphincter (LOS). The outer side is smooth (B), which hinders neighbouring tissue attachments. In addition, a Nitinol ring (C) aids the implant in exerting pressure around the LOS, thus reducing sphincter volume. In addition, this metal ring aids visualisation with, e.g. X-ray or CT during post-therapy follow-ups. The open, flexible design eases the freeing of the ring in a stretched position and placement around the cardia (D-F). The internal diameter of 28 mm prevents stenosis but markedly reinforces the lower oesophagal sphincter. In addition, its size allows for minimally invasive surgery.