Biomaterials 26 (2005) 3113–3121 Fibrin as a cell carrier in cardiovascular tissue engineering applications Anita Mol a,Ã , Marjolein I. van Lieshout a , Christa G. Dam-de Veen a , Stefan Neuenschwander b , Simon P. Hoerstrup b , Frank P.T. Baaijens a , Carlijn V.C. Bouten a a Department of Biomedical Engineering, Eindhoven University of Technology, PO Box 513, 5600 MB Eindhoven, The Netherlands b Clinic for Cardiovascular Surgery, University Hospital Zu¨rich, Raemistrasse 100, CH 8091 Zu¨rich, Switzerland Received 2 April 2004; accepted 10 August 2004 Available online 25 September 2004 Abstract In cardiovascular tissue engineering approaches, efficient seeding methods are essential. To achieve this and to save time, cells can be encapsulated in gels. Combining the advantages of a gel as a cell carrier with the advantages of a fiber-based scaffold, providing structural integrity to the developing tissue, might offer several advantages. In this study, seeding by using fibrin as a cell carrier is compared to the conventional static seeding method with regard to tissue development. Seeding with fibrin resulted in less loss of soluble collagen into the medium and a more mature extracellular matrix in a shorter period of time. The use of fibrin degradation inhibitors was shown to inhibit extracellular matrix formation, although it did not hamper cell proliferation. The use of fibrin as a cell carrier to seed cells into a fiber-based scaffold may represent a promising, timesaving approach in cardiovascular tissue engineering applications. r 2004 Elsevier Ltd. All rights reserved. Keywords: Scaffold; Non-woven fabric; Fibrin; Cell encapsulation; ECM 1. Introduction In tissue engineering, the seeding method of the scaffold influences the final outcome of engineered tissues to a large extent. The initial distribution of the cells throughout the scaffold and the amount of cells lost during seeding influences ultimate tissue development and organization. Currently, several seeding methods are used, being either static or dynamic in nature. Static seeding is performed by injecting a concentrated cell suspension into the scaffold. Dynamic seeding proce- dures involve stirring or agitation of cells in suspension together with the scaffold. The dynamic seeding methods render a more uniform cell distribution throughout the scaffold with larger cell yields when compared to static seeding [1,2]. In these comparison studies, however, the static seeding method involved only a single seeding step, while static seeding using multiple seeding steps has shown to render large cell yields and acceptable cell distribution as well [3]. Using this multiple-step static seeding procedure lowers the risk of destroying nascent cell-polymer interactions by physical forces created by dynamic seeding methods [4]. In cardiovascular tissue engineering, static seeding methods are most commonly used. Seeding of a scaffold is a complex and time- consuming process as several seeding steps are necessary for proper static seeding. For more efficient and less time-consuming seeding, involving only one single seed- ing step, cells can be encapsulated in gels, for example collagen and fibrin gels. The gel can subsequently be ARTICLE IN PRESS www.elsevier.com/locate/biomaterials 0142-9612/$ - see front matter r 2004 Elsevier Ltd. All rights reserved. doi:10.1016/j.biomaterials.2004.08.007 Ã Corresponding author. Tel.: +31402473048; fax: +31402447355. E-mail address: a.mol@tue.nl (A. Mol).