© 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim 1 1 Introduction Bone is well known for its self-healing capacities [1], how- ever, the body cannot completely heal the bone defect without intervention when it is beyond the critical size [2, 3]. Large-scale bone loss resulting from tumor resections and high impact trauma is the major cause for bone repair and implantation in clinic. The availability and function- ality of bone autografts and allografts are limited to restore the normal operations. The inert implants fail over time due to repetitive loading. Therefore, tissue engineered bone, which can ideally be remodeled into new bone to restore, maintain or improve its functions is becoming increasingly attractive [4]. Research Article Bioactive nanoparticles stimulate bone tissue formation in bioprinted three-dimensional scaffold and human mesenchymal stem cells Guifang Gao 1 , Arndt F. Schilling 2 , Tomo Yonezawa 3,4 , Jiang Wang 1 , Guohao Dai 5 and Xiaofeng Cui 1,5,6 1 Stemorgan Therapeutics, Albany, NY, USA 2 Clinic for Plastic Surgery and Hand Surgery, Klinikum Rechts der Isar, Technical University Munich, Munich, Germany 3 Department of Molecular and Experimental Medicine, The Scripps Research Institute, La Jolla, CA, USA 4 Research Institute for Biomedical Sciences, Tokyo University of Science, Chiba, Japan 5 Department of Biomedical Engineering, Center for Biotechnology and Interdisciplinary Studies, Rensselaer Polytechnic Institute, Troy, NY, USA 6 School of Chemistry, Chemical Engineering and Life Sciences, Wuhan University of Technology, Wuhan, Hubei, China Bioprinting based on thermal inkjet printing is a promising but unexplored approach in bone tis- sue engineering. Appropriate cell types and suitable biomaterial scaffolds are two critical factors to generate successful bioprinted tissue. This study was undertaken in order to evaluate bioactive ceramic nanoparticles in stimulating osteogenesis of printed bone marrow-derived human mes- enchymal stem cells (hMSCs) in poly(ethylene glycol)dimethacrylate (PEGDMA) scaffold. hMSCs suspended in PEGDMA were co-printed with nanoparticles of bioactive glass (BG) and hydroxya- patite (HA) under simultaneous polymerization so the printed substrates were delivered with high- ly accurate placement in three-dimensional (3D) locations. hMSCs interacted with HA showed the highest cell viability (86.62 ± 6.02%) and increased compressive modulus (358.91 ± 48.05 kPa) after 21 days in culture among all groups. Biochemical analysis showed the most collagen pro- duction and highest alkaline phosphatase activity in PEG-HA group, which is consistent with gene expression determined by quantitative PCR. Masson’s trichrome staining also showed the most collagen deposition in PEG-HA scaffold. Therefore, HA is more effective comparing to BG for hMSCs osteogenesis in bioprinted bone constructs. Combining with our previous experience in vasculature, cartilage, and muscle bioprinting, this technology demonstrates the capacity for both soft and hard tissue engineering with biomimetic structures. Keywords: Bioprinting · Extracellular matrix · Mesenchymal stem cells · Osteogenesis · Photopolymerization Correspondence: Prof. Xiaofeng Cui, School of Chemistry, Chemical Engineering and Life Sciences, Wuhan University of Technology, 122 Luoshi Road, Wuhan 430070, China E-mail: xfc.cui@gmail.com Additional correspondence: Prof. Guohao Dai, Department of Biomedical Engineering, Center for Biotechnology and Interdisciplinary Studies, Rensselaer Polytechnic Institute, Troy, NY, USA E-mail: daig@rpi.edu Abbreviations: BG, bioactive glass; ECM, extracellular matrix; HA, hydroxy- apatite; hMSCs, human mesenchymal stem cells; PEGDMA, poly(ethylene glycol)dimethacrylate Biotechnol. J. 2014, 9 DOI 10.1002/biot.201400305 www.biotechnology-journal.com Biotechnology Journal Received 05 MAY 2014 Revised 05 JUL 2014 Accepted 07 AUG 2014 Accepted article online 11 AUG 2014