To meet the increasing demand for bone scaffolds, advancements in 3D printing have significantly impacted bone tissue engineering. However, the materials used must closely mimic the biological components and structural characteristics of natural bone tissue. Additionally, constructing complex, oblique structures presents considerable challenges. To address these issues, we explored 3D bioceramic printing using a sanitizer-based hydrogel. Collagen, a primary component of the bone extracellular matrix (ECM), was combined with alpha-tricalcium phosphate (α-TCP) to create the bioceramic ink. The sanitizer-based hydrogel was chosen as the gel bath due to its carbopol content, which provides hydrogel-like support, and ethanol, which coagulates collagen and maintains the integrity of the 3D-printed structure. The α-TCP/collagen bioceramic ink was printed within the sanitizer-based hydrogel, then collected, immersed in ethanol, and finally submerged in phosphate-buffer saline to initiate a self-setting reaction that converted α-TCP into calcium-deficient hydroxyapatite. The results demonstrated that complex ceramic/ECM structures could be successfully printed in the sanitizer bath, exhibiting excellent mechanical characteristics. Additionally, scaffolds printed in the sanitizer bath showed higher levels of cell growth and osteogenic activity compared to those produced with only α-TCP in an open-air environment. This bioceramic printing approach has a strong potential for constructing complex scaffolds with enhanced osteogenic potential for bone regeneration.

To improve the properties of the hydrogel-based bioinks, a calcium phosphate phase transition was applied, and the products were examined. We successfully enhanced the mechanical properties of the hydrogels by adding small amounts (< 0.5 wt%) of alpha-tricalcium phosphate (α-TCP) to photo-crosslinkable gelatin methacrylate (GelMA). As a result of the hydrolyzing calcium phosphate phase transition involving α-TCP, which proceeded for 36 h in the cell culture medium, calcium-deficient hydroxyapatite was produced. Approximately 18 times the compressive modulus was achieved for GelMA with 0.5 wt% α-TCP (20.96 kPa) compared with pure GelMA (1.18 kPa). Although cell proliferation decreased during the early stages of cultivation, both osteogenic differentiation and mineralization activities increased dramatically when the calcium phosphate phase transition was performed with 0.25 wt% α-TCP. The addition of α-TCP improved the printability and fidelity of GelMA, as well as the structural stability and compressive modulus (approximately six times higher) after three weeks of culturing. Therefore, we anticipate that the application of calcium phosphate phase transition to hydrogels may have the potential for hard tissue regeneration.

Developments in three-dimensional (3D) printing technologies have led to many potential applications in various biomedical fields, especially artificial bone substitutes (ABSs). However, due to the characteristics of artificial materials, biocompatibility and infection remain issues. Here, multifunctional ABSs have been designed to overcome these issues by the inclusion of a biochemical modality that allows simultaneous detection of an infection biomarker by osteo-friend 3D scaffolds. The developed multifunctional scaffolds consist of calcium-deficient hydroxyapatite (CDHA), which has a similar geometric structure and chemical composition to human bone, and gold nanoparticles (Au NPs), which assists osteogenesis and modulates the fluorescence of labels in their microenvironment. The Au NPs were subsequently conjugated with fluorescent dye-labeled probe DNA, which allowed selective interaction with a specific target biomarker, and the fluorescent signal of the dye was temporally quenched by the Au NP-derived Förster resonance energy transfer (FRET). When the probe DNA unfolded to bind to the target biomarker, the fluorescence signal was recovered due to the increased distance between the dye and Au NPs. To demonstrate this sensing mechanism, a microbial oligonucleotide was selected as a target biomarker. Consequently, the multifunctional scaffold simultaneously facilitated osteogenic proliferation and the detection of the infection biomarker.