Bioactive Materials 6 (2021) 3947–3961 Contents lists available at ScienceDirect Bioactive Materials journal homepage: www.sciencedirect.com/journal/bioactive-materials Tuning gelatin-based hydrogel towards bioadhesive ocular tissue engineering applications Sina Sharifi a, Mohammad Mirazul Islam a, Hannah Sharifi a, Rakibul Islam b, Darrell Koza c, Felisa Reyes-Ortega g, David Alba-Molina g, Per H. Nilsson b,d, Claes H. Dohlman a, Tom Eirik Mollnes b,e,f,h, James Chodosh a, Miguel Gonzalez-Andrades a,g,* a Massachusetts Eye and Ear and Schepens Eye Research Institute, Department of Ophthalmology, Harvard Medical School, Boston, MA, USA b Department of Immunology, Oslo University Hospital, Rikshospitalet, University of Oslo, Oslo, Norway c Department of Physical Sciences, Eastern Connecticut State University, Willimantic, CT, USA d Linnaeus Center for Biomaterials Chemistry, Linnaeus University, Kalmar, Sweden e Research Laboratory, Nordland Hospital, Bodø, Norway f Centre of Molecular Inflammation Research, Norwegian University of Science and Technology, Trondheim, Norway g Maimonides Biomedical Research Institute of Cordoba (IMIBIC), Department of Ophthalmology, Reina Sofia University Hospital and University of Cordoba, Cordoba, Spain h Faculty of Health Sciences, K.G. Jebsen TREC, University of Tromsø, Norway ARTICLE INFO ABSTRACT Keywords: Gelatin based adhesives have been used in the last decades in different biomedical applications due to the Natural-based hydrogel excellent biocompatibility, easy processability, transparency, non-toxicity, and reasonable mechanical properties Gelatin to mimic the extracellular matrix (ECM). Gelatin adhesives can be easily tuned to gain different viscoelastic and Biocompatible mechanical properties that facilitate its ocular application. We herein grafted glycidyl methacrylate on the Biomimetic gelatin backbone with a simple chemical modification of the precursor, utilizing epoxide ring-opening reactions Bioadhesive Cornea and visible light-crosslinking. This chemical modification allows the obtaining of an elastic protein-based hydrogel (GELGYM) with excellent biomimetic properties, approaching those of the native tissue. GELGYM can be modulated to be stretched up to 4 times its initial length and withstand high tensile stresses up to 1.95 MPa with compressive strains as high as 80% compared to Gelatin-methacryloyl (GeIMA), the most studied derivative of gelatin used as a bioadhesive. GELGYM is also highly biocompatible and supports cellular adhesion, proliferation, and migration in both 2 and 3-dimensional cell-cultures. These characteristics along with its super adhesion to biological tissues such as cornea, aorta, heart, muscle, kidney, liver, and spleen suggest widespread applications of this hydrogel in many biomedical areas such as transplantation, tissue adhesive, wound dressing, bioprinting, and drug and cell delivery. 1. Introduction macromolecular microsphere composites (MMC) [9], nanocomposite physical hydrogels [10], double crosslinked polymeric networks [11], Hydrogels are three-dimensional (3D) networks of crosslinked tetrahedron-like structures with homogeneous spacers [12], slide-ring polymers, engineered to structurally and biologically support cellular connected materials [13], and dynamically crosslinked systems [14, growth, migration, and tissue formation [1,2]. Although their bio­ 15] are among the approaches to enhance the mechanical properties of mimetic behaviors including biocompatibility [3], biodegradation [4], hydrogels. These approaches often require the incorporation of syn­ and responsiveness to an external stimulus [5] can be controlled, their thetic materials such as polyacrylic acid (PAA) [6,8], polyacrylamide [7, relatively low mechanical and adhesion characteristics pose crucial 11], poly-ethylene glycol (PEG), PAA/polystyrene/poly butyl acrylate challenges, obstructing their translation into clinical medicine. [9], hybrid silica nano-particles (VSNPs)/PAA [10], Multicomponent interpenetration polymer networks (mIPNs) [6–8], Tetrahydroxyl-Terminated PEG [12], Polyrotaxane (PR) [13], and Peer review under responsibility of KeAi Communications Co., Ltd. * Corresponding author. 20 Staniford St, Boston, MA, 02114, USA. E-mail addresses: [email protected], [email protected] (M. Gonzalez-Andrades). https://doi.org/10.1016/j.bioactmat.2021.03.042 Received 29 January 2021; Received in revised form 26 March 2021; Accepted 26 March 2021 Available online 17 April 2021 2452-199X/© 2021 The Authors. Publishing services by Elsevier B.V. on behalf of KeAi Communications Co. Ltd. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/). S. Sharifi et al. Bioactive Materials 6 (2021) 3947–3961 stearyl methacrylate (C18)/dodecyl acrylate copolymer [14] along with hydrogel [27,31]. However, the methacrylation degree of gelatin has carboxyl-functionalized polystyrene [15] into natural-based hydrogels been constrained by the low abundance of nucleophilic amino acids matrices, involving covalent and non-covalent (i.e. electrostatic forces, (mostly primary amine bearing amino acids such as lysine and hydrophobic interactions, hydrogen bonding, van der Waals forces) or hydroxylysine), which can undergo a single methacrylation reaction to combinations of these interactions in reinforcement process [6]. form amide bond [27]. To extend the functionalization degree to a wider However, such incorporation may alter the chemical composition of range, we functionalized gelatin with glycidyl methacrylate that un­ the hydrogel and adversely impact their biological properties. On the dergoes epoxide ring-opening reaction and forms a secondary amine other hand, many biomedical applications of hydrogels, including tissue that can also react with another glycidyl methacrylate (Fig. 1a), gener­ repair [16], drug delivery [17], wound dressings [18], and biomedical ating the precursor of Gelatin-glycidyl-methacrylate hydrogel (abbre­ devices [19] require strong adhesion between the hydrogel and the viated or called as GELGYM). This GELGYM precursor potentially hold dynamic surface of the host tissue. Thus, the incorporation of such twice the methacrylate groups compared to GelMA (two glycidyl adhesion properties into the hydrogel structure is crucial and can methacrylate per each amine bearing amino acid). significantly facilitate hydrogel translation into clinical medicine [20]. GELGYM precursor generates a hydrogel after crosslinking under One of the most widely used biomaterials for hydrogel low-intensity visible light. This simple modification of GelMA formed manufacturing, because of its cheapness and high-biocompatibility, is from grafting functional crosslinkable moieties onto a gelatin backbone gelatin and its derivatives. Gelatin is a polydisperse protein produced facilitates the tuning of the mechanical and adhesive properties of from irreversible hydrolysis of collagen fibrils into lower molecular gelatin scaffolds. To validate that hypothesis, GELGYM was tuned based weight polypeptides. Although the chemical composition of gelatin is on functional degree, precursor concentration, and crosslinking time, to similar to those of the parent collagen, it possesses better solubility and optimize its corneal application. The corneal model was used because of lesser antigenicity [21,22]. These render gelatin as an excellent its high optical and mechanical requirements, in addition to the component for stimulating cellular attachment and growth, including complexity of combining different cell populations. Finally, we obtained the possibility of regulating matrix metalloproteinase degradation. robust biomaterials and strong adhesion to biological tissues, in addition Despite the development of various crosslinking strategies to generate to maintaining the highly biocompatible nature of the hydrogel to gelatin-based hydrogels [23–26], adequate mechanical and adhesion support cellular adhesion, growth, and migration. The tuning of gelatin- characteristics have yet to be realized. For instance, gelatin meth­ based hydrogels described here might benefit various fields of biomed­ acryloyl (GelMA), the most studied derivative of gelatin [27], demon­ ical engineering and regenerative medicine including ophthalmology. strated maximum elastic modulus and ultimate tensile strength 180 ± 34, 53 ± 17 KPa, respectively [28], which are almost 2 orders of 2. Materials and methods magnitude lower than those reported for the human cornea (i.e. 15.86 ± 1.95 and 3.29 ± 1.95 MPa, respectively) [29]. A recent modificationin 2.1. Materials the crosslinking of GelMA was reported to increase the elastic modulus and tensile strength up to 224.4 ± 32.3 and 45.3 ± 4.1 KPa, respectively All chemicals were used as received from Sigma-Aldrich (St. Louis, [30], yet fall short of those reported for human tissues. MO) without further modification unless otherwise noted. Human It has been shown that enhancing the degree of methacrylation or FD donated corneas were kindly provided by VisionGift (Boston, MA) for significantly enhances the mechanical properties of the resulting research purposes only. Each donated cornea was obtained from Fig. 1. Synthesis, and chemical characterization of GELGYM. a) Schematic of chemical synthesis of GELGYM via epoxide ring-opening reaction of glycidyl meth­ acrylate with gelatin and its crosslinking with a visible LED in the presence of E (0.05 mM), TEA 0.04%, and VC (0.04%) to form a 3-dimensional network