Tough, Resorbable Polycaprolactone‐Based Bimodal Networks for Vat Polymerization 3D Printing

Abstract

Vat polymerization allows for the accurate and fast fabrication of personalized implants and devices. While the technology advances rapidly and more materials become available, the fabrication of flexible yet tough resorbable materials for biomedical applications remains a challenge. Here, a formulation that can be 3D printed with high accuracy using vat polymerization, yielding materials that are tough, degradable, and non-toxic is presented. This unique combination of properties is obtained by combining a long-chain polycaprolactone macromonomer with a small molecule cross-linker. A wide range of properties is achieved by tuning the ratio of these components. The use of benzyl alcohol as a non-volatile, benign solvent enables fabrication on a lowcost desktop 3D printer, with an exposure time of 8 s per 50-micron layer. The 3D-printed networks are tough and elastic with a tensile strength of 11 MPa at 116% elongation at break. Cells attach and proliferate on the networks with a viability of >91%. The networks are fully degradable to soluble products. This new 3D printable material opens up a range of opportunities in biomedical engineering and personalized medicine.

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

“…Recently, Melchels and co-workers reported another dualphotopolymer system based on a linear PCL methacrylate with a MW of 10000 g mol −1 (PCL-MA 10000). 47 Instead of using a biodegradable oligomer, pentaerythritol tetraacrylate (PETA), a commercial cross-linker, was employed as the low-MW part (Figure 5a). Because PCL is a semicrystalline solid with a melting point around 50 °C, benzyl alcohol was used as a nonvolatile, benign solvent for the resin formulation (55 wt %).…”

“…(Figure 5e, bottom) with metabolic activity comparable to that of the positive control at day 7, despite the differences in the growth rate of the cells on different material surfaces. 47 Overall, advanced biodegradable materials for 3D printing have been obtained from dual-photopolymer resins by synergistically combining long and short biodegradable photopolymers, ranging from amorphous PTMC-MA and poly(CLco-LA)-MA to semicrystalline PCL-MA. The bimodal polymer networks enabled efficient tuning of the mechanical strength and elasticity of the 3D-printed biodegradable elastomers by simply adjusting the polymer weight ratio, showing great potential in personalized implants and devices, as evidenced by both in vitro and in vivo studies.…”

“…For example, 3D-printed biodegradable networks employing homopolymers often exhibit a yield point. 45,47 This is observed even with the use of amorphous polymers, such as PTMC. Consequently, these materials may experience irreversible deformation, posing a challenge when they are implemented in medical devices, where maintaining shape integrity is crucial.…”

“…Recently, Melchels and co-workers reported another dual-photopolymer system based on a linear PCL methacrylate with a MW of 10000 g mol –1 (PCL-MA 10000) . Instead of using a biodegradable oligomer, pentaerythritol tetraacrylate (PETA), a commercial cross-linker, was employed as the low-MW part (Figure a).…”

“…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.…”