Enhancement of properties of a cell-laden GelMA hydrogel-based bioink via calcium phosphate phase transition.

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 involvingα-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 ofα-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.

142Development of an alginate-gelatin bioink enhancing osteogenic differentiation by gelatin release.

Hydrogels are natural bioink options for cellular printing due to their high-water content and permeable three-dimensional (3D) polymeric structure, which are favorable for cellular anchoring and metabolic activities. To increase the functionality of hydrogels as bioinks, biomimetic components are often incorporated, such as proteins, peptides, and growth factors. In this study, we aimed to enhance the osteogenic activity of a hydrogel formulation by integrating both the release and retention of gelatin so that gelatin serves as both an indirect support for released ink component on cells nearby and a direct support for encapsulated cells inside a printed hydrogel, thereby fulfills two functions. Methacrylate-modified alginate (MA-alginate) was chosen as the matrix because it has a low cell adhesion effect due to the absence of ligands. The gelatin-containing MA-alginate hydrogel was fabricated, and gelatin was found to remain in the hydrogel for up to 21 days. The gelatin remaining in the hydrogel had positive effects on encapsulated cells, especially on cell proliferation and osteogenic differentiation. The gelatin released from the hydrogel affected the external cells, showing more favorable osteogenic behavior than the control sample. It was also found that the MA-alginate/gelatin hydrogel could be used as a bioink for printing with high cell viability. Therefore, we anticipate that the alginate-based bioink developed in this study could potentially be used to induce osteogenesis in bone tissue regeneration.

Support-less ceramic 3D printing of bioceramic structures using a hydrogel bath.

Volumetric bone tissue defects are beyond the intrinsic regenerative capacity of bone tissue. With the recent development of ceramic 3D printing, various bioceramic scaffolds that can induce bone regeneration are being actively developed. However, hierarchical bone is complex, with overhanging structures that require additional sacrificial support during ceramic 3D printing. Not only can this increase the overall process time and material consumption, but breaks and cracks may occur when sacrificial supports are removed from fabricated ceramic structures. In this study, a support-less ceramic printing (SLCP) process using a hydrogel bath was developed to facilitate the manufacture of complex bone substitutes. A hydrogel bath, consisting of pluronic P123 with temperature-sensitive properties, mechanically supported the fabricated structure when the bioceramic ink was extruded into the bath and promoted the cement reaction to cure the bioceramic. SLCP enables the fabrication of complex bone constructs with overhanging structures, such as the mandible and maxillofacial bones, with reduced overall processing time and material consumption. Scaffolds fabricated by SLCP showed more cell adhesion, higher cell growth rate, and osteogenic protein expression due to their rougher surface than conventionally printed scaffolds. Hybrid scaffolds were fabricated by SLCP to co-print cells and bioceramics, and SLCP provided a cell-friendly environment, exhibiting high cell viability. SLCP enables control of the shape of various cells, bioactive substances, and bioceramics and thus can be used as an innovative 3D bioprinting technique to manufacture complex hierarchical bone structures.

Selective Detection of an Infection Biomarker by an Osteo-Friend Scaffold: Development of a Multifunctional Artificial Bone Substitute.

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.

Pore characteristics for improving luminous efficacy of phosphor-in-glass.

Pores formed during the sintering of a glass/phosphor mixture affect the scattering and path of light within the resulting phosphor-in-glass (PIG) plate. An investigation of the interactions between blue light from an LED chip and pores within a PIG plate is therefore needed to understand the effect of light scattering on the optical properties. To this end, various glass compositions based on SiO2-B2O3-ZnO were prepared so as to better understand the effect of modifiers (i.e., Li2O, Na2O, La2O3, WO3) on the viscosity and pore properties at different sintering temperatures. This study found that PIGs sintered within a given viscosity range exhibit different optical properties depending on their pore size and overall porosity; a higher luminous efficacy observed in the case of intermediate scattering length values was due to an improved interaction between pores and light. This is a significant finding, as ensuring suitable PIG pore characteristics is an important factor in achieving a desired spectrum and high efficacy from white LEDs.