Tough PEG‐only hydrogels with complex 3D structure enabled by digital light processing of “all‐PEG” resins

Abstract

Digital light processing (DLP) of structurally complex poly(ethylene glycol) (PEG) hydrogels with high mechanical toughness represents a long‐standing challenge in the field of 3D printing. Here, we report a 3D printing approach for the high‐resolution manufacturing of structurally complex and mechanically strong PEG hydrogels via heat‐assisted DLP. Instead of using aqueous solutions of photo‐crosslinkable monomers, PEG macromonomer melts were first printed in the absence of water, resulting in bulk PEG networks. Then, post‐printing swelling of the printed networks was achieved in water, producing high‐fidelity 3D hydrogels with complex structures. By employing a dual‐macromonomer resin containing a PEG‐based four‐arm macrophotoinitiator, “all‐PEG” hydrogel constructs were produced with compressive toughness up to 1.3 MJ m−3. By this approach, porous 3D hydrogel scaffolds with trabecular‐like architecture were fabricated, and the scaffold surface supported cell attachment and the formation of a monolayer mimicking bone‐lining cells. This study highlights the promises of heat‐assisted DLP of PEG photopolymers for hydrogel fabrication, which may accelerate the development of 3D tissue‐like constructs for regenerative medicine.

Advanced Biomaterials for 3D Printing via a Synergistic Dual-Photopolymer Design

“…Recently, we developed a new approach for the high-resolution DLP fabrication of tough PEG-only hydrogels with complex structure. 48 It is based on a two-step print-swelling strategy using heat-assisted DLP in combination with an "all-PEG" dual-photopolymer resin formulation.…”

“…This improvement is more significant in compression testing: the 90/10 and 80/20 hydrogels exhibited compression toughnesses of 1.0 and 1.3 MJ m −3 , respectively, while the values for PEGDMA 10000 and PEGDA 700 were both less than 0.4 MJ m −3 (Figure 6c). 48 Subsequently, various PEG hydrogels with complex structures were 3D-printed based on the dual-photopolymer design (Figure 6d), showing high resolution with a minimal horizontal feature size down to ∼80 μm and a vertical layer thickness of ∼80 μm. In addition, a bone-mimicking structure was successfully fabricated based on a trabecular model (ϕ 3.20 mm × h 2.03 mm) with microchannels derived from the CT scan profile of a horse femur (Figure 6e).…”

“…Interestingly, some cells spread on the scaffold surface and formed osteoblastlike morphologies, arranging themselves into a monolayer reminiscent of the cellular lining found in bone tissue. 48 Indeed, the dual-photopolymer design further expanded its application from elastomers to hydrogels. On the basis of combinatorial polyurethane chemistry, Grijpma and co-workers systematically investigated the dual-polymer networks consisting of one PEG polymer (3900 or 9400 g mol −1 ) and another polymer that is one of PCL 3900 or 7800 g mol −1 , poly(propylene glycol) 4100 or 8000 g mol −1 , or PTMC 4100 g mol −1 .…”

“…While the double-network strategy developed by Gong and co-workers has been successful in achieving strong and tough 3D-printed hydrogels, − SLA or DLP printing of mechanically strong and biologically relevant hydrogels with complex structures has proven challenging, especially for those based on poly(ethylene glycol) (PEG). − This is because conventional DLP-printed PEG hydrogels manufactured with commercial acrylated PEG oligomers (e.g., PEGDA 700) are too brittle for practical applications, while PEG hydrogels made from high-MW PEG photopolymer solutions have very weak mechanical properties. Recently, we developed a new approach for the high-resolution DLP fabrication of tough PEG-only hydrogels with complex structure . It is based on a two-step print-swelling strategy using heat-assisted DLP in combination with an “all-PEG” dual-photopolymer resin formulation.…”

“…To tackle this issue, different strategies have been attempted to develop mechanically advanced degradable biomaterials for vat photopolymerization, such as the synthesis of star photopolymers, , the introduction of extra linkages, , side group engineering, the preparation of block photopolymers, , stereochemistry control and thiol–ene chemistry, − and dispersity control . Most recently, a dual-photopolymer formulation approach has emerged as a straightforward strategy for 3D-printing tough and elastic biomaterials. ,− Based on the combination of a longer polymer and a shorter polymer, robust bimodal networks can be formed, benefiting from high chain flexibility from the former and high cross-linking ability from the latter (Figure ). By adjustment of the ratio and chemical structure of the two photopolymers, the mechanical performance of the 3D-printed products can be finely tuned.…”