Motivated by these results, we further produced the bone-mimicking hydrogel scaffolds printed from PEGDMA 10k -PEGDA 700 (90/10, w/w), and evaluated their bioactivity for tissue engineering applications (Figure ). The scaffolds were scanned by micro-computed tomography (micro-CT) at high resolution (17 µm). A biomimetic porous architecture (Figures and) with a pore size in the range of 100-500 µm was achieved. We reasoned that a small amount of the residual methacrylate groups (5-10%) on a pre-formed hydrogel should be enough for covalent fixation of cell adhesive motifs, despite the high double bone conversion of PEGDMA (Figures and). To this, fibronectinderived cysteine-containing arginylglycylaspartic acid (RGD) peptides (N-C: CGRGDS) were conjugated to the scaffold surface via Michael addition between thiols and the residual methacrylates at a concentration of 10 mM (Figure ), using a reported method. After surface functionalization, the scaffolds were thoroughly washed to remove unreacted RGD since soluble RGD has been shown to inhibit cell adhesion. For cell seeding experiments, human mesenchymal stem cells (hMSC) were selected as the precursor for in vitro bone tissue formation. However, initial attempts for direct hMSC seeding atop PEG scaffolds were unsuccessful since cells rapidly sedimented to the bottom through the pore space due to gravity. To better control the spatial distribution of cells in the scaffolds, we used type I collagen hydrogel as a temporal supportive matrix. Notably, we found that an optimal concentration of collagen is the key to efficient cell penetration and spatial distribution within the scaffold. A cell seeding using a soft collagen (1.0 mg mL -1 ) enabled efficient cell penetration into the pore space. Initially, cells were embedded in a 3D environment. Over time, they migrated out and attached to the scaffold surface (Figures and). Moreover, increasing the cell seeding density from 0.7 Mio mL -1 to 3 Mio mL -1 promoted faster migration of the cells from the collagen matrix. A live-dead assay confirmed that the cells after seeding at such high density were highly viable at day 7 (95.3% ± 4.4%, Figure ), indicating excellent cell-compatibility of the scaffolds. Some of the cells spread on the scaffold surface, exhibited osteoblast-like morphologies, and lined up to form a monolayer that mimics bone-lining cells (Figure ). This was also observed in the confocal microscopic image of seeded cells stained for actin and nuclei (Figure ).