15502-m-pleumeekers

INTRODUCTION Serious auricular defects such as anotia and microtia, along with auricle damage caused by cancer and trauma, demand an effective treatment for auricular cartilage reconstruction. For such cases, the field of tissue engineering (TE) provides a promising potential alternative therapy to the conventional and complex surgical reconstruction of auricular cartilage by using ear-shaped autologous costal and nasoseptal cartilage [124, 310, 311]. Bacterial nanocellulose (BNC), a novel biomaterial with excellent biocompatibility and remarkable tissue integration capability [312-316], has been evaluated for several TE strategies and has shown to support adhesion, proliferation and differentiation of different cell types [317-323]. BNC is a natural biopolymer synthesized by various bacteria species, particularly Gluconacetobacter xylinus [90, 324]. Its three-dimensional (3D) and interconnected network is composed of highly hydrated nanofibrils ranging from 70 to 140 nm in width, similar to collagen fibrils found in extracellular matrix (ECM) of several tissues, with high tensile strength [319, 325]. BNC is considered a hydrogel since it is mostly composed of water in its native state (99%). All together, these outstanding properties make BNC an exceptional biomaterial for many biomedical applications [326-328], including auricular cartilage reconstruction [316, 322, 329]. Although several groups have attempted to engineer auricular cartilage [124], few successful outcomes have been reported [330-332]. Development of artificial auricular grafts with adequate mechanical properties has been identified as a key factor for successful auricular cartilage TE [333]. Most studies that have used biodegradable scaffold materials have resulted in poor structural integrity (i.e. shape and size stability) of the auricular scaffold after implantation; caused by the short-lived chemical and mechanical stability [136, 334-337]. On the other hand, recent studies that have investigated the use of non-degradable biomaterials for auricular cartilage reconstruction have reported a better structural integrity of the implant [330, 332, 338] - likely caused by the chemical stability of the support biomaterial, which translates into long-lasting mechanical properties even after implantation. As opposed to the many biodegradable scaffolds previously evaluated for auricular cartilage TE, the long-term structural integrity of BNC scaffolds should not be compromised after implantation since humans do not produce enzymes capable of breaking down cellulose [339]. Besides being a chemically stable material, BNC with increased cellulose content of 17% (densified hydrogel) is a competitive scaffold material for repair, reconstruction or regeneration of auricular cartilage since it matches the elastic mechanical properties (e.g. equilibrium modulus) of human auricular cartilage [329], can be fabricated in patient-specific auricular shapes [340] and exhibits excellent biocompatibility in vivo - causing a minimal foreign body response [316]. When densified, BNC hydrogel is a mechanically and biologically appropriate biomaterial for use in auricular cartilage reconstruction [316, 329]. However, its dense nanocellulose network prevents cells from penetrating the material. To circumvent this problem, several techniques have been developed to support cell ingrowth in BNC scaffolds by tuning pore size and pore interconnectivity during biosynthesis of BNC [341], via laser ablation [318] and freeze-dry processing [342, 343]. Such macroporous BNC scaffolds have been shown to provide an adequate environment that supports ingrowth and differentiation 149 NOVEL BILAYER BNC: AN ECM-INSPIRED SCAFFOLD 8