## 3 Fn Application and Involvement in Biomaterials and Medical Device Engineering
### Fn 2D Molecular Coatings  
#### 3.1.1 Fn Covalent Binding  
The covalent binding of Fn presents many advantages such as the strong and stable linkage of molecules to the surface. Nevertheless, the grafting process is delicate, as it should proceed in mild conditions to preserve the protein structure and requires the presence of functional groups at the surface of the biomaterial able to react with reactive protein groups, which often requires a preliminary activation step at the surface. The following section describes the main published papers regarding surface activation and Fn-grafting modes on various substrates, which are summarized in Table 1. \begin{table}
\begin{tabular}{c c c c} \hline
**Surface Activation/Fn Grafting** & **Substrate** & **Biological Activity** & **References** \\ \hline Modification with isocyanates & Polyvinyl alcohol (PVA) & Increasing cell adhesion and proliferation in rabbit corneal epithelial cells & [27, 28, 29] \\ \hline Carbonyl dimidazole activation & PVA & Enhancing cell adhesion and proliferation in murine (NHST3) and human fibroblasts, murine chondrocytes, and porcine radial arterial and endothelial cells & [30, 31, 32, 33] \\ \hline Arvidin– biotin & Polyethylene glycolacrylate (PECDA)/polyacrylamideamide (PA) & Improving cell adhesion and supporting long-term survival of rat astrogolina cells & [34] \\ \hline Hydrazine hydrate activation & PA & Leading to higher cell adhesion of human marrow stromal cells (nMSCs); enhancing the secretion of promgigeotic factors & [35] \\ \hline Polydopamine coating & Poloxamine & Enhancing cell adhesion and the proliferation of human dermal fibroblasts & [36] \\ \hline Modification with cyanate ester & Nanocellulose & Increasing cell adhesion and proliferation in static and dynamic culture  conditions of human saphenous vein endothelial and endothelial & [37] \\ \hline \multirow{3}{*}{Carbodimide cross-linker} & Chitosan & [38] \\  & Fibrinogen & Increasing cell adhesion and proliferation in osteoblasts, murine & [39] \\  & PEGDA/PA & myoblasts (C2C12), hMSCs, NHST3, and pancreatic tumor cells & [40] \\  & Poly(N-isopropylacrylamide) & & [41] \\ \hline \multirow{3}{*}{Polymer modification PEG–NHS} & PEG & Improving cell adhesion and proliferation in human aortic smooth muscle cells and human umbilical vein endothelial cells (HUVPCs) & [43] \\ \cline{2-5}  & PEGDA & Increasing cell proliferation and metabolic activity in porcine hepatocyte cells; enhancing albumin secretion & [44] \\ \hline \multirow{3}{*}{Modification with Sulfo-SANPAH} & PA & Enhancing osteoblast differentiation in bone marrow stromal cells; influencing translocation of yes-associated protein (VAS) in hMSCs. & [45] \\ \cline{2-5}  & PVA & Enhancing optimal migratory behavior in human hepatocytes & [47] \\ \hline GA cross-linking & Plasma-treated silica and polytetrafluoroethylene (TTFE) & Increasing CBD accessibility and bovine aortic endothelial cell adhesion & [48, 49] \\ \hline Modification with phosphonate & Titanium & Increasing dermal fibroblast adhesion, spreading, and proliferation; enhancing the strength of adhesion to bioengineered dermal tissue & [50] \\ \hline \end{tabular}
\end{table} 
Table 1: Fn surface functionalization of different substrates using different strategies and related biological activities. One of the first approaches to Fn-covalent immobilization was reported by [PERSON] and [PERSON] on polyvinyl alcohol (PVA) hydrogels for contact lens applications [29]. In this case, PVA, known to be a highly bio-inactive polymer, was modified by the addition of isocyanate groups able to react with the amino and hydroxyl groups of Fn to form urea and urethane bonds, respectively [29]. The resulting Fn-functionalized PVA enhanced the adhesion of corneal epithelial cells and their proliferation [27, 28]. PVA chains can also be activated via a three-step reaction: the linkage of alkyl chains containing acids group followed by acid-group activation with carbonyl diimidazole (CDI) and, finally, a PVA-CDI reaction with Fn amine groups [30, 31, 32, 33].