Research Article Tissue Engineering of Large Full-Size Meniscus Defects by a Polyurethane Scaffold: Accelerated Regeneration by Mesenchymal Stromal Cells Matthias Koch, 1 Felix P. Achatz, 1 Siegmund Lang , 1 Christian G. Pfeifer , 1 Girish Pattappa, 1,2 Richard Kujat , 1,2 Michael Nerlich, 1 Peter Angele , 1,3 and Johannes Zellner 1 1 Department of Trauma Surgery, University Medical Centre Regensburg, Franz-Josef-Strauss-Allee 11, 93053 Regensburg, Germany 2 Laboratory of Experimental Trauma Surgery, Department of Trauma Surgery, University Regensburg Medical Centre, Regensburg, Germany 3 Sporthopaedicum Regensburg/Straubing, Hildegard-von-Bingen-Str. 1, 93053 Regensburg, Germany Correspondence should be addressed to Johannes Zellner; johannes.zellner@ukr.de Received 24 November 2017; Revised 6 March 2018; Accepted 4 April 2018; Published 7 May 2018 Academic Editor: Mikel Sánchez Copyright © 2018 Matthias Koch et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. The endogenous healing potential of avascular meniscal lesions is poor. Up to now, partial meniscectomy is still the treatment of choice for meniscal lesions within the avascular area. However, the large loss of meniscus substance predisposes the knee for osteoarthritic changes. Tissue engineering techniques for the replacement of such lesions could be a promising alternative treatment option. Thus, a polyurethane scaffold, which is already in clinical use, loaded with mesenchymal stromal cells, was analyzed for the repair of critical meniscus defects in the avascular zone. Large, approximately 7 mm broad meniscus lesions affecting both the avascular and vascular area of the lateral rabbit meniscus were treated with polyurethane scaffolds either loaded or unloaded with mesenchymal stromal cells. Menisci were harvested at 6 and 12 weeks after initial surgery. Both cell- free and cell-loaded approaches led to well-integrated and stable meniscus-like repair tissue. However, an accelerated healing was achieved by the application of mesenchymal stromal cells. Dense vascularization was detected throughout the repair tissue of both treatment groups. Overall, the polyurethane scaffold seems to promote the vessel ingrowth. The application of mesenchymal stromal cells has the potential to speed up the healing process. 1. Introduction Lesions of the meniscus are amongst the most frequent knee injuries in orthopedic surgery [1, 2]. In many cases, partial meniscectomy has to be performed due to the poor endoge- nous healing capacity of avascular parts of the meniscus [2–4]. However, the loss of meniscus continuity predisposes for the development of osteoarthritic changes, which corre- lates with the amount of resected meniscus substance [5–7]. The meniscus has a decisive functional and biomechani- cal relevance for an intact knee joint [8, 9]. The knee menisci provide essential qualities in load bearing and shock absorption as well as in stabilization, lubrication, and propri- oception of the knee joint [10–14]. (Partial) Meniscectomy causes severe changes in the biomechanics of the knee joints. The effect is directly proportional to the amount of lost tissue [15] and results in drastically increased contact pressure [16]. Therefore, it is of importance to restore as much meniscus tissue as possible. Successful repair strategies for lesions in the vascular zone of the meniscus like suturing have already been devel- oped [17, 18]. However, up to now, there is still no estab- lished curative therapy for lesions within the avascular parts of the meniscus in clinical practice [19–21]. Hindawi Stem Cells International Volume 2018, Article ID 8207071, 11 pages https://doi.org/10.1155/2018/8207071