Thiol-Ene Photo-Click Collagen-PEG Hydrogels: Impact of Water-Soluble Photoinitiators on Cell Viability, Gelation Kinetics and Rheological Properties

Abstract

Thiol-ene photo-click hydrogels were prepared via step-growth polymerisation using thiol-functionalised type-I collagen and 8-arm poly(ethylene glycol) norbornene-terminated (PEG-NB), as a potential injectable regenerative device. Type-I collagen was thiol-functionalised by a ring opening reaction with 2-iminothiolane (2IT), whereby up to 80 Abs. % functionalisation and 90 RPN% triple helical preservation were recorded via 2,4,6-Trinitrobenzenesulfonic acid (TNBS) colorimetric assay and circular dichroism (CD). Type, i.e., either 2-Hydroxy-1-[4-(2-hydroxyethoxy) phenyl]-2-methyl-1-propanone (I2959) or lithium phenyl-2,4,6-trimethylbenzoylphosphinate (LAP), and concentration of photoinitiator were varied to ensure minimal photoinitiator-induced cytotoxicity and to enable thiol-ene network formation of collagen-PEG mixtures. The viability of G292 cells following 24 h culture in photoinitiator-supplemented media was largely affected by the photoinitiator concentration, with I2959-supplemented media observed to induce higher toxic response (0.1 → 0.5% (w/v) I2959, cell survival: 62 → 2 Abs. %) compared to LAP-supplemented media (cell survival: 86 → 8 Abs. %). In line with the in vitro study, selected photoinitiator concentrations were used to prepare thiol-ene photo-click hydrogels. Gelation kinetics proved to be largely affected by the specific photoinitiator, with LAP-containing thiol-ene mixtures leading to significantly reduced complete gelation time (τ: 187 s) with respect to I2959-containing mixtures (τ: 1683 s). Other than the specific photoinitiator, the photoinitiator concentration was key to adjusting the hydrogel storage modulus (G'), whereby 15-fold G' increase (232 → 3360 Pa) was observed in samples prepared with 0.5% (w/v) compared to 0.1% (w/v) LAP. Further thiol-ene formulations with 0.5% (w/v) LAP and varied content of PEG-NB were tested to prepare photo-click hydrogels with porous architecture, as well as tunable storage modulus (G': 540-4810 Pa), gelation time (τ: 73-300 s) and swelling ratio (SR: 1530-2840 wt %). The photoinitiator-gelation-cytotoxicity relationships established in this study will be instrumental to the design of orthogonal collagen-based niches for regenerative medicine.

Precisely Controlled Delivery of Abaloparatide through Injectable Hydrogel to Promote Bone Regeneration

“…It can turn the solutions into gel much quicker than other photo initiators such as 1173, I‐2959, I‐250, and I‐260. In addition, it was found to be less harmful to cells compared with other photo initiators …”

A UV-cured nanofibrous membrane of vinylbenzylated gelatin-poly(ɛ-caprolactone) dimethacrylate co-network by scalable free surface electrospinning

“…The synthesis of the covalent gelatin-PCL co-network was carried out in the fibrous state via UV-initiated radical crosslinking reaction in the presence of (2-hydroxy-4-(2-hydroxyethoxy)-2methylpropiophenone) (I2959) as water-soluble, UV-compatible photoinitiator [68][69][70][71]. I2959 was selected since no toxic response was detected during cell culture with either bovine chondrocytes, human fetal osteoblasts or osteosarcoma cells with up to 0.5 mg·ml -1 I2959 [72][73][74]. To establish defined process-structure relationships, viscosity, surface tension, and electrical conductivity of the electrospinning solutions were measured and linked to fibre characteristics.…”

A hydroxamic acid–methacrylated collagen conjugate for the modulation of inflammation-related MMP upregulation

“…SDS-PAGE was used to both elucidate the chemical composition of reacted products and to explore the triple helix organisation of methacrylated and HA-conjugated products. Retention of the triple helix architecture of collagen is key to enable resulting materials with chemotactic functionality, enhanced mechanical properties and decreased swellability [39]. Although we previously confirmed that collagen methacrylation had minimal effect on the collagen triple helix structure [40], the reaction of collagen-based polypetides with hydroxylamine has been reported to catalyse the chemical cleavage of peptide bonds between asparagine and glycine residues [58][59][60], which is likely to induce a denaturation of collagen triple helices.…”

“…polyacrylates [32] and respective hydroxamic acid-bearing derivatives [26], have been proposed as proof-of-concept anti-MMP substrates, due to the presence of ionically-charged and metal-chelating groups, respectively, along the polymeric backbone. [37][38][39]. UV-cured covalent networks made of functionalised collagen triple helices have also been presented with integrated MMP-chelating functions, whose swelling and compression properties can be controlled in a relatively independent fashion, via variation of e.g.…”