Linkage Groups within Thiol–Ene Photoclickable PEG Hydrogels Control In Vivo Stability

Abstract

step-growth photopolymerization based on the orthogonal reaction between thiol and norbornene has emerged as an attractive strategy for many biomedical applications. [7,8] These step-growth photoinitiated (thiol-ene) hydrogels have shown great promise in 2D and 3D cell culture and organoid development, due, in part, to the low radical concentration and physiological pH required for crosslinking. [9] In addition, thiol-ene PEG hydrogels exhibit high cytocompatibility, precise spatiotemporal control of gelation, tunable degradation, and versatile modulation of biophysical and biochemical properties. The versatility of these hydrogels is demonstrated through extensive applications, ranging from protein and drug delivery, [10][11][12][13][14][15][16][17] cartilage development, [18,19] osteogenic differentiation, [20,21] endothelial tubulogenesis, [22] brain tumor models, [23] synthetic matrix mimics, [8,[24][25][26][27][28][29][30][31][32] 2D culture substrates, [33][34][35] and islet and cell encapsulation. [36][37][38][39][40][41][42][43] However, these applications have been exclusively conducted in vitro, yielding little insight into the in vivo behavior of these hydrogels. Our initial exploratory studies with these widely used 4-arm, ester-linked, thiol-ene PEG (PEG-4eNB) hydrogels implanted into the intraperitoneal space of mice unexpectedly showed that the hydrogels undergo rapid degradation in vivo ( Figure S1, Supporting Information). Hypothesizing that the poor in vivo stability may result from the hydrolysis of the ester linkage between the PEG backbone and norbornene functional end group, we replaced this connection with a more hydrolytically stable amide linkage. Here, we describe the characterization and implementation of 4-arm, amide-linked, thiol-ene PEG (PEG-4aNB) hydrogels that retain long-term stability in both in vitro and in vivo environments. We demonstrate rapid (<24 h) in vivo degradation of PEG-4eNB and gradual (>35 days) in vitro degradation. Conversely, PEG-4aNB retains long-term in vitro and in vivo stability while maintaining high cytocompatibility, and this material can be utilized as an appropriate replacement in many biomedical applications.The ester linkage in PEG hydrogels has been reported to be hydrolytically labile over the course of many weeks in cell culture. [44] This feature has been exploited further by introducing ester-containing poly(caprolactone) linkage groups to accelerate in vitro degradation of PEG hydrogels to within a Thiol-norbornene (thiol-ene) photoclickable poly(ethylene glycol) (PEG) hydrogels are a versatile biomaterial for cell encapsulation, drug delivery, and regenerative medicine. Numerous in vitro studies with these 4-arm ester-linked PEG-norbornene (PEG-4eNB) hydrogels demonstrate robust cytocompatibility and ability to retain long-term integrity with nondegradable crosslinkers. However, when transplanted in vivo into the subcutaneous or intraperitoneal space, these PEG-4eNB hydrogels with nondegradable crosslinkers rapidly degrade within 24 h. This char...

Thiol-Methylsulfone-Based Hydrogels for Cell Encapsulation: Reactivity Optimization of Aryl-Methylsulfone Substrate for Fine-Tunable Gelation Rate and Improved Stability

“…Additionally, in comparison to other reported thiol-based cross-linking strategies with less related reaction mechanism such as the thiol-norbornene gels, our Tz system is an attractive alternative since it does not require initiation by light 28 or by enzymes combined with reducing agents. 29 The influence of the pH on the extent of the cross-linking reaction and, consequently, on the mechanical stability of the cross-linked hydrogel was examined (Figures 1E and S2A).…”

Photoclick Chemistry: A Bright Idea

“…Recent work using thiol–ene hydrogels has demonstrated the use of these materials for a variety of exciting applications for cartilage development, antimicrobial surfaces, and as controlled drug delivery vehicles (Figure ). − …”

Engineered Biomaterials for Enhanced Function of Insulin‐Secreting β‐Cell Organoids

“…[111,201] Many PEG hydrogels have also been engineered with dynamic control of biochemical and biophysical properties to engineer a dynamic microenvironment for organoid culture and development. [206][207][208] PEG chains are typically terminated with various functional groups, such as maleimide, [209] norbornene, [210,211] or acrylate, [212] that enable control over crosslinking chemistries, crosslinking efficiencies, and reaction kinetics.…”