UNCORRECTED PROOFS TERM257 JOURNAL OF TISSUE ENGINEERING AND REGENERATIVE MEDICINE RESEARCH ARTICLE J Tissue Eng Regen Med 2010; 4: 000–000. Published online in Wiley InterScience (www.interscience.wiley.com) DOI: 10.1002/term.257 Fine-tuning scaffolds for tissue regeneration: effects of formic acid processing on tissue reaction to silk fibroin Shahram Ghanaati 1# *, Carina Orth 1# , Ronald E. Unger 1 , Mike Barbeck 1 , Matthew J. Webber 2 , Antonella Motta 3 , Claudio Migliaresi 3 and C. James Kirkpatrick 1 1 Institute of Pathology, Johannes Gutenberg University, 55101 Mainz, Germany 2 Department of Biomedical Engineering, Northwestern University, Evanston, IL 60201, USA 3 Department of Materials Engineering and Industrial Technologies and BIOtech Research Centre, University of Trento, I-38050 Trento, Italy Abstract Formic acid (FA) plays a key role in the preparation of silk fibroin (SF) scaffolds from cocoons of Bombyx mori and is used for fibre distribution. In this study, we used a subcutaneous implantation model in Wistar rats to examine SF scaffolds prepared by treating the degummed cocoon with FA for either 30 or 60 min. The tissue reaction and inflammatory response to SF was assessed by qualitative histology at intervals from 3 to 180 days. Additionally, dynamic biomaterial-induced vascularization and biomaterial degradation were quantified using a technique for analysing an image of the entire implanted biomaterial. Varying the FA treatment time led to different scaffold morphologies and resulted in two distinct peri-implant tissue reactions. The 30 min-treated scaffold was integrated into the surrounding tissue beginning at day 3 after implantation and vascularization increased 10- fold from 15 to 180 days, while the scaffold was continuously degraded throughout the first 90 days. In contrast, the 60 min-treated SF scaffold appeared as bulk for the first 90 days after implantation, after which a rapid degradation and vascularization process began. After 180 days, the tissue response was similar for both scaffolds, with eventual formation of a well vascularized connective tissue integrating the SF fibres. This study indicates that by modifying the FA treatment time, the tissue reaction to SF scaffolds can be tailored for different tissue-engineering applications. The tunability and biocompatibility of SF make it an attractive scaffold for exploration in regenerative medicine and clinical tissue engineering. Copyright  2010 John Wiley & Sons, Ltd. Received 5 May 2009; Revised 9 November 2009; Accepted 24 November 2009 Keywords vascularization; biocompatibility; immune response; tissue engineering; degradation; silk fibroin 1 2 3 4 5 6 7 8 9 10 11 12 1. Introduction The ability to produce biomaterials suitable for diverse applications is paramount to the success of regenerative medicine. An optimal biomaterial should be tailored for a specific purpose and control several reaction parameters, including, in part, the degree of inflammation, the level *Correspondence to: Shahram Ghanaati, Institute of Pathology, Langenbeckstrasse 1, Johannes Gutenberg University, 55101 Mainz, Germany. E-mail: ghanaati@uni-mainz.de # These authors contributed equally to this work. 13 14 15 16 17 18 19 20 21 22 23 24 of vascularization and the degradation rate. In addition, the material should elicit an acceptable late peri-implant tissue reaction. In recent years, fibroin silk proteins from the domestic silk worm (Bombyx mori) have shown promise as biomaterials for applications in regenerative medicine. Silk from this source is a filamentous material about 1 mile long, consisting primarily of two proteins, an internal core of fibroin and an external gum of sericin. Silk fibroin can be transformed by simple methods into films, sponges, non-woven nets and solid or injectable gels (Altman et al., 2003; Vepari et al., 2007). This material also has history of use as suture threads. Copyright  2010 John Wiley & Sons, Ltd.