Tuning mechanical performance of poly(ethylene glycol) and agarose interpenetrating network hydrogels for cartilage tissue engineering

Abstract

Hydrogels are attractive for tissue engineering applications due to their incredible versatility, but they can be limited in cartilage tissue engineering applications due to inadequate mechanical performance. In an effort to address this limitation, our team previously reported the drastic improvement in the mechanical performance of interpenetrating networks (IPNs) of poly(ethylene glycol) diacrylate (PEG-DA) and agarose relative to pure PEG-DA and agarose networks. The goal of the current study was specifically to determine the relative importance of PEG-DA concentration, agarose concentration, and PEG-DA molecular weight in controlling mechanical performance, swelling characteristics, and network parameters. IPNs consistently had compressive and shear moduli greater than the additive sum of either single network when compared to pure PEG-DA gels with a similar PEG-DA content. IPNs withstood a maximum stress of up to 4.0 MPa in unconfined compression, with increased PEG-DA molecular weight being the greatest contributing factor to improved failure properties. However, aside from failure properties, PEG-DA concentration was the most influential factor for the large majority of properties. Increasing the agarose and PEG-DA concentrations as well as the PEG-DA molecular weight of agarose/PEG-DA IPNs and pure PEG-DA gels improved moduli and maximum stresses by as much as an order of magnitude or greater compared to pure PEG-DA gels in our previous studies. Although the viability of encapsulated chondrocytes was not significantly affected by IPN formulation, glycosaminoglycan (GAG) content was significantly influenced, with a 12-fold increase over a three-week period in gels with a lower PEG-DA concentration. These results suggest that mechanical performance of IPNs may be tuned with partial but not complete independence from biological performance of encapsulated cells.

Chondroinduction from Naturally Derived Cartilage Matrix: A Comparison Between Devitalized and Decellularized Cartilage Encapsulated in Hydrogel Pastes

“…Moreover, DVC consistently outperformed all TGF-b 3 -exposed groups in aggrecan and collagen II gene expression, which may present significant advantages in cost and regulatory approval of chondroinductive strategies for cartilage regeneration because of eliminating the need for costly growth factors. 41 Certainly, future work will need to address improving the mechanical properties of these networks, whereby choosing a higher mechanically performing hydrogel, such as an interpenetrating network hydrogel, [42][43][44][45][46] could be considered. In addition, overall matrix production will need to be addressed, where in vivo studies will be paramount because immunogenicity as well as how biomechanical stimulation of DCC and DVC may affect chondroinductivity and therefore, hyaline-like cartilage regeneration can be tested.…”

Photochemical Production of Interpenetrating Polymer Networks; Simultaneous Initiation of Radical and Cationic Polymerization Reactions

“…Hydrogels have received a considerable attention for use in tissue engineering scaffolds (with gelatin methacrylamide/PEG [72], silk fibroin/poly(vinyl alcohol) [73], silk fibroin/gelatin [74] or others [75]), cartilage tissue engineering (with poly (ethylene glycol)/agarose [76]), vascular tissue engineering (dextran/gelatin [77]). Mechanically enhanced properties (e.g., Young's moduli) rivaling those of natural load-bearing tissues was found in a poly (acrylic acid)/end-linked poly (ethylene glycol) crosslinked material [78].…”

Hydrogels and bioreactors for cartilage research and functional tissue engineering

“…Accordingly, their suitability for cell encapsulation, direction of tissue-specific cell differentiation, ECM accumulation, as well as enzymatic degradation remains largely unexplored [194]. Only a few instances of cell-laden double-network gels have been reported [195][196][197][198]; however, most of these studies only demonstrated short-term cytocompatibility, while a functional assessment of neotissue formation and mechanical properties has rarely been performed.…”

“…Although the potential of DN gels for tissue engineering applications has been emphasized in previous studies, surprisingly, only short-term cytocompatibility has been demonstrated [195][196][197][198] and functional assessment of their suitability for cellbased tissue engineering applications has rarely been performed [195]. This may stem from the synthetic nature of most previously described DN gels which allow for fabrication of composites with extreme stiffness and ultimate mechanical strength [193,194,357], but often lack bioactivity and do not allow for cell-encapsulation due to harsh crosslinking conditions, thus making them better candidates for substitutes of load-bearing tissues rather than true tissue engineering scaffolds.…”

“…This may stem from the synthetic nature of most previously described DN gels which allow for fabrication of composites with extreme stiffness and ultimate mechanical strength [193,194,357], but often lack bioactivity and do not allow for cell-encapsulation due to harsh crosslinking conditions, thus making them better candidates for substitutes of load-bearing tissues rather than true tissue engineering scaffolds. Only a few instances of cell-laden DN gels have been reported [195][196][197][198], most of which were based on a combination of biopolymers, or a blend of a bio-and synthetic polymers. Although an improvement of mechanical properties compared to singlenetwork gels was achieved, the ultimate strength of synthetic DN gels is often significantly higher (compressive failure stress of 5.3 -6.9 MPa [197,358] vs. 17.2…”