Abstract
Hydrogels for load-bearing biomedical applications, such as soft tissue replacement, are required to be tough and biocompatible. In this sense, alginate-methacrylate hydrogels (H-ALGMx) are well known to present modulable levels of elasticity depending on the methacrylation degree; however, little is known about the role of additional structural parameters. In this work, we present an experimental-computational approach aimed to evaluate the effect of the molecular conformation and electron density of distinct methacrylate groups on the mechanical properties of photocrosslinked H-ALGMx hydrogels. Three alginate-methacrylate precursor macromers (ALGMx) were synthesized: alginate-glycidyl methacrylate (ALGM1), alginate-2-aminoethyl methacrylate (ALGM2), and alginate-methacrylic anhydride (ALGM3). The macromers were studied by Fourier-transform infrared spectroscopy (FTIR), proton nuclear magnetic resonance (1H-NMR), and density functional theory method (DFT) calculations to assess their molecular/electronic configurations. In parallel, they were also employed to produce H-ALGMx hydrogels, which were characterized by compressive tests. The obtained results demonstrated that tougher hydrogels were produced from ALGMx macromers presenting the C=C reactive bond with an outward orientation relative to the polymer chain and showing free rotation, which favored in conjunction the covalent crosslinking. In addition, although playing a secondary role, it was also found that the presence of acid hydrogen atoms in the methacrylate unit enables the formation of supramolecular hydrogen bonds, thereby reinforcing the mechanical properties of the H-ALGMx hydrogels. By contrast, impaired mechanical properties resulted from macromer conditions in which the C=C bond adopted an inward orientation to the polymer chain accompanied by a torsional impediment.
Highlights
Hydrogels are a special class of biomaterials that has attracted great interest in research and clinical communities for their use in the biomedical field, in particular for advanced applications such as tissue engineering and regenerative medicine (TERM) [1]
Hydrogels for biomedical applications can be produced from natural polysaccharides [6], such as cellulose [7], chitosan (CH) [3,4], sodium alginate (ALG) [5,8], and dextran [9], and from some synthetic polymers such as poly(acrylamide) (PAM) [10], poly(ethylene glycol) (PEG) [11,12], and poly(vinyl alcohol) (PVA) [13], among others
The study presented here portrays an experimental-computational characterization by which differences in compressive strength and toughness of photocrosslinked ALG-methacrylate hydrogels were assessed and explained
Summary
Hydrogels are a special class of biomaterials that has attracted great interest in research and clinical communities for their use in the biomedical field, in particular for advanced applications such as tissue engineering and regenerative medicine (TERM) [1]. Hydrogels are hydrophilic networks formed upon crosslinking of polymer chains, capable of absorbing water or biological fluids while maintaining their crosslinked structure [2]. The interest in these materials, both as 2D and 3D systems, stems from the fact that they closely resemble the natural environment of cells, allowing them to replicate and unravel diverse cell-extracellular matrix (cell-ECM) interactions [3,4,5]. Examples of physical crosslinking processes include molecular entanglements of polymeric chains and/or interplay of secondary forces like ionic attraction and hydrogen bonding, as well as hydrophobic interactions [15]. Last but not least, photocrosslinked hydrogels can be designed to degrade via hydrolytic or enzymatic processes and, more importantly, to present biofunctional moieties within their structure to control cellular responses and/or initiate organ-specific tissue formation [18]
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