title: An improved process for development and testing of vena caval filters: the percutaneous steel Greenfield filter.
abstract: BACKGROUND
  The purpose of this study was to develop a reduced profile stainless steel Greenfield filter with an over-the-wire delivery system and to compare its performance with the existing Food and Drug Administration-approved Greenfield filters. In addition, we wanted to standardize a system for evaluating filter prototypes.
  
  
  METHODS
  Percutaneous stainless steel filters with various hook configurations were evaluated for efficacy and safety in four in vitro modules designed to reproduce potential liabilities experimentally. Animal studies to assess thrombus capture and resolution, filter stability, migration, and hemodynamics were completed in 4 dogs and 38 sheep.
  
  
  RESULTS
  Mathematical modeling suggested that hook angle was the most relevant factor in improving resistance to migration. Prototypes that varied with respect to hook length and angle were evaluated in both the in vitro testing unit and in sheep. The stainless steel filter with two downward directed hooks provided clot capture comparable with the current Greenfield filter, maintenance of flow, and resistance to fatigue and corrosion while providing significant resistance to migration and penetration (p < 0.05).
  
  
  CONCLUSIONS
  The percutaneous stainless steel Greenfield filter with the alternating hook design provides a reduced profile device that can be placed over a wire to improve positioning. The use of a standardized testing system reduced both the time and cost of bringing this new device to the market.
authors.affiliation: Department of Surgery, University of Michigan, Ann Arbor 48109-0346, USA.
authors.forename: L J
authors.initials: LJ
authors.lastname: Greenfield
authors.forename: M C
authors.initials: MC
authors.lastname: Proctor
authors.forename: K R
authors.initials: KR
authors.lastname: Roberts
mesh_terms: D000818:Animals; D004285:Dogs; D004867:Equipment Design; D005374:Filtration / Q000295:instrumentation*; D005548:Foreign-Body Migration / Q000209:etiology; D066298:In Vitro Techniques; D008955:Models, Cardiovascular; D010690:Phlebography; D019736:Prostheses and Implants / Q000009:adverse effects; D011655:Pulmonary Embolism / Q000517:prevention & control*; D012756:Sheep; D013232:Steel; D014684:Venae Cavae / Q000000981:diagnostic imaging / Q000601:surgery*
chemical_list: D013232:Steel