# Genipin Attachment of Conjugated Gold Nanoparticles to a Decellularized Tissue Scaffold
## 1 Introduction  
Tissue engineering has advanced as a promising solution for the repair of damaged or diseased tissues with the goal of creating functional scaffolds that mimic native tissue and can be colonized by the host's cells. Decellularized tissue has shown promise in this regard, and there are numerous surgical scaffolds in clinic use today utilizing both allogenic and xenogeneic decellularized tissue including, urinary bladder, small intestine, dermis, mesothelium, heart valves, and pericardium [1]. In addition, researchers are working towards the use of three-dimensional scaffolds created through whole organ decellularization as a treatment for end-stage organ failure without the risk of chronic rejection and the morbidity associated with immunosuppression [2; 3; 4]. Biological tissue is better able to mimic the full complexity of the tissue architecture while also being a source of signaling molecules and growth factors creating a superb environment for cellular attachment and proliferation [5; 6]. Although decellularized tissue has numerous promising characteristics, it is not without its drawbacks. These concerns include decellularization weakening mechanical properties, inherent heterogeneity, high immunogenicity, rapid biodegradation, and slow integration [7; 8; 9]. This is specifically true with ligament grafts. Decellularized ligament and tendon use is limited due to a prolonged inflammatory period and delayed graft remodeling [10]. A potential solution to some of these concerns is the utilization of gold nanoparticles. Gold nanoparticles (AuNPs), conjugated to decellularized tissue, can mitigate some of the concerns with decellularized tissue grafts. First, AuNPs have long been utilized for their anti-inflammatory properties, which is believed to be the result of free radical scavenging [11; 12; 13]. Secondly, gold nanoparticle attachment modify the surface structure and encourage cellular attachment and proliferation [14; 15]. The increased surface energy of AuNPs may promote the attachment of proteins including those necessary for cellular attachment [16]. In addition, conjugation of the AuNPs to the tissue is believed to block collagenase attachment and thereby slow down scaffold degradation [15]. AuNPs can also be used to direct the differentiation of stem cells into specific cell types. [PERSON] et al. demonstrated that AuNPs promote the osteogenic differentiation of mesenchymal stem cells by activating the p38 mitogen-activated protein kinase pathway, and [PERSON] et al. demonstrated the addition of AuNPs promotes osteogenic differentiation of adipose-derived stem cells and results in significantly higher new bone formation in a rabbit model [17; 18]. With all the promise of nanoparticles, their attachment to tissue remains challenging. The commonly used methods have cytotoxic byproducts and require multiple washes to remove them [19; 20]. In addition, the current conjugation protocols only enable a rather rough estimate of the amount of attached gold as many of the agents only react for a limited period of time [21; 22]. There is a need to find a biocompatible, stable, crosslinking agent to facilitate the attachment of nanoparticles. Genipin is a potential solution to this problem. Genipin is a chemical compound extracted from the fruits of _Gardenia jasminoides_. It is a natural crosslinking agent, and it spontaneously reacts with amino-group-containing compounds such as proteins, collagens, and gelatins to form mono- to tetramer crosslinks, and has an exceptionally low cytotoxicity [23; 24]. Genipin also has the added benefit of acting as an anti-inflammatory agent and simultaneously reducing the immunogenicity of the scaffold [8; 25; 26]. In this study, it is hypothesized that genipin is a viable agent to conjugate gold nanoparticles to a decellularized tendon scaffold quickly and efficiently.