Citation: Olevsky, L.M.; Anup, A.; Jacques, M.; Keokominh, N.; Holmgren, E.P.; Hixon, K.R. Direct Integration of 3D Printing and Cryogel Scaffolds for Bone Tissue Engineering. Bioengineering 2023, 10, 889. https://doi.org/10.3390/ bioengineering10080889 Academic Editor: Ólafur E. Sigurjónsson Received: 30 June 2023 Revised: 21 July 2023 Accepted: 24 July 2023 Published: 27 July 2023 Copyright: © 2023 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/). bioengineering Article Direct Integration of 3D Printing and Cryogel Scaffolds for Bone Tissue Engineering Levi M. Olevsky 1 , Amritha Anup 1 , Mason Jacques 2 , Nadia Keokominh 2 , Eric P. Holmgren 3 and Katherine R. Hixon 1,3, * 1 Thayer School of Engineering, Dartmouth College, Hanover, NH 03755, USA; levi.olevsky.th@dartmouth.edu (L.M.O.); amritha.anup.th@dartmouth.edu (A.A.) 2 College of Engineering and Physical Sciences, University of New Hampshire, Durham, NH 03824, USA; mason.jacques@dartmouth.edu (M.J.); nadia.keokominh@unh.edu (N.K.) 3 Geisel School of Medicine, Dartmouth College, Hanover, NH 03755, USA; eric.p.holmgren@hitchcock.org * Correspondence: katherine.r.hixon@dartmouth.edu Abstract: Cryogels, known for their biocompatibility and porous structure, lack mechanical strength, while 3D-printed scaffolds have excellent mechanical properties but limited porosity resolution. By combining a 3D-printed plastic gyroid lattice scaffold with a chitosan–gelatin cryogel scaffold, a scaffold can be created that balances the advantages of both fabrication methods. This study compared the pore diameter, swelling potential, mechanical characteristics, and cellular infiltration capability of combined scaffolds and control cryogels. The incorporation of the 3D-printed lattice demonstrated patient-specific geometry capabilities and significantly improved mechanical strength compared to the control cryogel. The combined scaffolds exhibited similar porosity and relative swelling ratio to the control cryogels. However, they had reduced elasticity, reduced absolute swelling capacity, and are potentially cytotoxic, which may affect their performance. This paper presents a novel approach to combine two scaffold types to retain the advantages of each scaffold type while mitigating their shortcomings. Keywords: tissue engineering; cryogel; 3D printing; scaffold; gyroid; bone graft substitute; bone healing 1. Introduction Bone disorders caused by infection, trauma, or tumor resection are highly prevalent, highlighting the need for improved treatments to induce bone regeneration; current treat- ment for a defect less than 6 cm is bone grafting [1,2]. Harvesting bone from a donor site can lead to associated complications such as pain, infection, and nerve damage [3,4]. Additionally, the limited supply of donor tissue can be a significant challenge, particularly in cases requiring multiple grafts or repeat surgeries [3]. Furthermore, bone grafts may fail to fully integrate with the surrounding tissue, leading to poor mechanical stability and the need for additional surgeries [5]. These limitations have motivated the development of alternative treatments for bone regeneration [6]. These novel approaches aim to address the limitations of bone grafting by providing a biocompatible and mechanically stable envi- ronment for bone tissue regeneration while promoting the differentiation and proliferation of bone cells [6]. Tissue engineering is an interdisciplinary field that involves the integration of bioma- terial scaffolds, cells, and bioactive factors to promote targeted growth and regeneration of new tissue [7]. Therefore, the implementation of a tissue-engineered scaffold framework that supports cell proliferation, migration, and attachment could present a promising sub- stitute for bone grafting. While the clinical and economic advantages of tissue engineering are recognized, there are still areas that require attention to enhance translation from bench to bedside [6,7]. In particular, the optimization of patient-specific biomaterials to mimic Bioengineering 2023, 10, 889. https://doi.org/10.3390/bioengineering10080889 https://www.mdpi.com/journal/bioengineering