Mechanical and biochemical mapping of human auricular cartilage for reliable assessment of tissue-engineered constructs Luc Nimeskern a , Mieke M. Pleumeekers b , Duncan J. Pawson a , Wendy L.M. Koevoet b , Iina Lehtoviita a , Michael B. Soyka c , Christof Röösli c , David Holzmann c , Gerjo J.V.M van Osch b,d , Ralph Müller a , Kathryn S. Stok a,n a Institute for Biomechanics, ETH Zürich, Zürich, Switzerland b Department of Otorhinolaryngology, Head and Neck Surgery, Erasmus MC, University Medical Center, Rotterdam, The Netherlands c Department of Otorhinolaryngology and Head and Neck Surgery, University Hospital Zürich, Zürich, Switzerland d Department of Orthopaedics, Erasmus MC, University Medical Center, Rotterdam, The Netherlands article info Article history: Accepted 14 May 2015 Keywords: Ear cartilage Auricle pinna Ear reconstruction Biomechanical properties abstract It is key for successful auricular (AUR) cartilage tissue-engineering (TE) to ensure that the engineered cartilage mimics the mechanics of the native tissue. This study provides a spatial map of the mechanical and biochemical properties of human auricular cartilage, thus establishing a benchmark for the eva- luation of functional competency in AUR cartilage TE. Stress-relaxation indentation (instantaneous modulus, E in ; maximum stress, s max ; equilibrium modulus, E eq ; relaxation half-life time, t 1/2 ; thickness, h) and biochemical parameters (content of DNA; sulfated-glycosaminoglycan, sGAG; hydroxyproline, HYP; elastin, ELN) of fresh human AUR cartilage were evaluated. Samples were categorized into age groups and according to their harvesting region in the human auricle (for AUR cartilage only). AUR cartilage displayed significantly lower E in , s max , E eq , sGAG content; and significantly higher t 1/2 , and DNA content than NAS cartilage. Large amounts of ELN were measured in AUR cartilage ( 415% ELN content per sample wet mass). No effect of gender was observed for either auricular or nasoseptal samples. For auricular samples, significant differences between age groups for h, sGAG and HYP, and significant regional variations for E in , s max , E eq , t 1/2 , h, DNA and sGAG were measured. However, only low correlations between mechanical and biochemical parameters were seen (R o0.44). In conclusion, this study established the first comprehensive mechanical and biochemical map of human auricular cartilage. Regional variations in mechanical and biochemical properties were demon- strated in the auricle. This finding highlights the importance of focusing future research on efforts to produce cartilage grafts with spatially tunable mechanics. & 2015 Elsevier Ltd. All rights reserved. 1. Introduction Surgical reconstruction with autologous cartilage or alloplastic implants is the only existing treatment for auricular defects. The current gold-standard technique – autologous ear reconstruction (Rotter et al., 2008) – is a multi-staged time-consuming procedure (Brent, 1992; Nagata, 1993), that ranks among the most complicated of reconstructive surgeries (Walton and Beahm, 2002). In short, autologous cartilage is harvested from the ribs, shaped appro- priately and implanted subcutaneously. Auricular (AUR) cartilage tissue-engineering (TE) is a potential alternative that endeavors to circumvent the resulting donor-site morbidity by engineering rat- her than harvesting cartilage (Arevalo-Silva et al., 2000; Bichara et al., 2012; Cao et al., 1998; Cao et al., 1997; Haisch et al., 2002; Isogai et al., 2004, 2008; Kamil et al., 2004, 2003; Kusuhara et al., 2009; Liu et al., 2010; Neumeister et al., 2006; Ruszymah et al., 2011; Saim et al., 2000; Shieh et al., 2004; Xu et al., 2005). Ideally tissue-engineered AUR cartilage should possess similar mechanical properties to the native tissue in order to withstand daily load (e.g. wearing spectacles, helmets, ear phones, etc.) and without causing discomfort (Nimeskern et al., 2014). Selecting autologous material for ear cartilage surgical reconstruction is difficult, where donations come from the nasal septum, auricle and rib. Whether the graft qualifies mechanically for surgical implantation is usually made Contents lists available at ScienceDirect journal homepage: www.elsevier.com/locate/jbiomech www.JBiomech.com Journal of Biomechanics http://dx.doi.org/10.1016/j.jbiomech.2015.05.019 0021-9290/& 2015 Elsevier Ltd. All rights reserved. n Correspondence to: Wolfgang-Pauli-Strasse 14, HPI F 26, CH-8093 Zurich. Tel.: þ41 44 632 45 80; fax: þ41 44 633 11 24. E-mail address: kas@ethz.ch (K.S. Stok). Journal of Biomechanics 48 (2015) 1721–1729