In our original article, an affiliation is missing for the first author of the paper (Beatriz N. L. Costa). The correct affiliation information for Beatriz N. L. Costa is as follows: INL−International Iberian Nanotechnology Laboratory, Ultrafast Bio- and Nanophotonics Group, Av. Mestre JoséVeiga S/n 4715-330 Braga, Portugal; CMEMS-UMinho, University of Minho, DEI, Campus de Azurem, ́ Guimarães 4800-058, Portugal; Faculty of Mechanical, Maritime, and Materials Engineering (3mE), Department of Precision and Microsystems Engineering (PME), Delft University of Technology, Mekelweg 2, Delft 2628 CD, The Netherlands; Escola de Enxeñarí a de Minas e Enerxí a, University of Vigo, 36310 Vigo, Pontevedra, Spain. All other affiliations and the present address are the same as in the original article. This addition of the affiliation does not alter the conclusions, results, or interpretations presented in the original article. We regret the omission of this affiliation and apologize for any confusion or inconvenience this may have caused.

Biomimicking biological niches of healthy tissues or tumors can be achieved by means of artificial microenvironments, where structural and mechanical properties are crucial parameters to promote tissue formation and recreate natural conditions. In this work, three-dimensional (3D) scaffolds based on woodpile structures were fabricated by two-photon polymerization (2PP) of different photosensitive polymers (IP-S and SZ2080) and hydrogels (PEGDA 700) using two different 2PP setups, a commercial one and a customized one. The structures' properties were tuned to study the effect of scaffold dimensions (gap size) and their mechanical properties on the adhesion and proliferation of bone marrow mesenchymal stem cells (BM-MSCs), which can serve as a model for leukemic diseases, among other hematological applications. The woodpile structures feature gap sizes of 25, 50, and 100 μm and a fixed beam diameter of 25 μm, to systematically study the optimal cell colonization that promotes healthy cell growth and potential tissue formation. The characterization of the scaffolds involved scanning electron microscopy and mechanical nanoindenting, while their suitability for supporting cell growth was evaluated with live/dead cell assays and multistaining 3D confocal imaging. In the mechanical assays of the hydrogel material, we observed two different stiffness ranges depending on the indentation depth. Larger gap woodpile structures coated with fibronectin were identified as the most promising scaffolds for 3D BM-MSC cellular models, showing higher proliferation rates. The results indicate that both the design and the employed materials are suitable for further assays, where retaining the BM-MSC stemness and original features is crucial, including studies focused on BM disorders such as leukemia and others. Moreover, the combination of 3D scaffold geometry and materials holds great potential for the investigation of cellular behaviors in a co-culture setting, for example, mesenchymal and hematopoietic stem cells, to be further applied in medical research and pharmacological studies.