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J Thorac Cardiovasc Surg 2002;123:161-167
© 2002 The American Association for Thoracic Surgery

General Thoracic Surgery

New tubular bioabsorbable knitted airway stent: Biocompatibility and mechanical strength

From the Department of Thoracic and Cardiovascular Surgery,^a the Division of Surgical Pathology,^b Kansai Medical University, Moriguchi, and the Division of Surgical Pathology,^c International Center for Diagnostic Pathology, Kobe, Japan.

Received for publication April 3, 2001. Revisions requested May 14, 2001; revisions received June 4, 2001. Accepted for publication July 3, 2001. Address for reprints: Yukihito Saito, MD, Associate Professor, Department of Thoracic and Cardiovascular Surgery, Kansai Medical University, 10-15 Fumizonocho, Moriguchi, Osaka 570-8507, Japan (E-mail: saitoy@ takii.kmu.ac.jp).

Objective: This study examines the biocompatibility and suitability of a new tubular bioabsorbable knitted stent made of poly-L-lactic acid in normal rabbit airways and examines the mechanical strength of this stent in vitro.
Methods: A tubular knitted airway stent (group B, n = 15) made of poly-L-lactic acid wire was implanted operatively in New Zealand White rabbits intratracheally; silicone stents served as controls (group A, n = 8). The cervical trachea was exposed, and the stent was implanted. Up to 40 weeks after stent implantation, the rabbits were killed, at which time bronchoscopy, histologic examination, and scanning electron microscopic study was done. We tested poly-L-lactic acid stents and silicone stents for their mechanical strength in vitro. We subjected stents to area loads and measured their mechanical strengths.
Results: In group A, which received silicone stents, 3 (37.5%) rabbits died within 4 weeks of stent implantation as a result of airway obstruction by secretions inside the stent lumen. In group B, poly-L-lactic acid stents, 1 (6.7%) rabbit died 3 weeks after implantation because of weakness caused by anorexia. In the remaining animals, except for 1 animal with stent trouble, the bronchial lumen was fully open until the 40th week after implantation. After 40 weeks of follow-up, the stents disappeared, except for nonabsorbable suture in the bronchial wall. None of the animals in group B died of airway complication. Histologic examination and scanning electron microscopic examination of the group A silicone stents showed marked regression of ciliated cells under the stent. In group B the ciliated epithelium was preserved, and there were numerous capillary blood vessels in the submucosa. In scanning electron microscopy of the group B poly-L-lactic acid stents, the ciliated cells were preserved between the mesh holes of the stent. For diameters between 4 and 6 mm, the mechanical strength of silicone stents was greater than that of poly-L-lactic acid stents. However, the mechanical strength of poly-L-lactic acid stents increased as a function of their diameter.
Conclusion: A new tubular bioabsorbable stent made of poly-L-lactic acid is biocompatible in normal rabbit airways, indicating that poly-L-lactic acid is a promising material for airway stents for clinical use.

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