Enzymatic Mineralization of 3D Printable Granular Hydrogels

Many biological materials are structured as organic-inorganic composites. A paradigmatic example of this apparent dichotomy is bone, a biomineralized tissue with a polymeric matrix. Inspired by the natural design strategy, recent work has been done to encapsulate living components such as bacteria into a granular polymeric matrix to then trigger biomineralization [1]. Taking advantage of the intrinsic rheological properties of jammed microgels, organic/inorganic composites can be 3D printed. However, applications are limited if living organisms are involved.<br/>In this work, we introduce a 3D printable ink that can be mineralized to yield load-bearing composites after the 3D printing process has been completed. This is achieved by formulating enzyme-loaded hydrogels that are exclusively made of naturally sourced soft polymers as microgels. The enzyme-loaded microgels are jammed to obtain the required rheological properties. These microgel-based inks are 3D printed at room temperature through direct ink writing before they are converted into load-bearing mineralized scaffolds. We demonstrate how the local composition, mineral content, and porosity can be adjusted with the formulation of the granular ink. The obtained scaffolds are biocompatible with low cytotoxicity when tested with osteoblast cells showing great potential for tissue engineering applications such as bone reparation.<br/><br/>[1] M. Hirsch, L. Lucherini, R. Zhao, A. Clarà Saracho, and E. Amstad, “3D printing of living structural biocomposites,” <i>Materials Today</i>, vol. 62, pp. 21–32, Jan. 2023, doi: 10.1016/j.mattod.2023.02.001.