Tuning Physical Properties of GelMA Hydrogels through Microarchitecture for Engineering Osteoid Tissue.

Gelatin methacryloyl (GelMA) hydrogels have gained significant attention due to their biocompatibility and tunable properties. Here, a new approach to engineer GelMA-based matrices to mimic the osteoid matrix is provided. Two cross-linking methods were employed to mimic the tissue stiffness: standard cross-linking (SC) based on visible light exposure (VL) and dual cross-linking (DC) involving physical gelation, followed by VL. It was demonstrated that by reducing the GelMA concentration from 10% (G10) to 5% (G5), the dual-cross-linked G5 achieved a compressive modulus of ∼17 kPa and showed the ability to support bone formation, as evidenced by alkaline phosphatase detection over 3 weeks of incubation in osteogenic medium. Moreover, incorporating poly(ethylene) oxide (PEO) into the G5 and G10 samples was found to hinder the fabrication of highly porous hydrogels, leading to compromised cell survival and reduced osteogenic differentiation, as a consequence of incomplete PEO removal.

A vertical additive-lathe printing system for the fabrication of tubular constructs using gelatin methacryloyl hydrogel.

Reproducing both the mechanical and biological performance of native blood vessels remains an ongoing challenge in vascular tissue engineering. Additive-lathe printing offers an attractive method of fabricating long tubular constructs as a potential vascular graft for the treatment of cardiovascular diseases. Printing hydrogels onto rotating horizontal mandrels often leads to sagging, resulting in poor and variable mechanical properties. In this study, an additive-lathe printing system with a vertical mandrel to fabricate tubular constructs is presented. Various concentrations of gelatin methacryloyl (gelMA) hydrogel were used to print grafts on the rotating mandrel in a helical pattern. The printing parameters were selected to achieve the bonding of consecutive gelMA filaments to improve the quality of the printed graft. The hydrogel filaments were fused properly under the action of gravity on the vertical mandrel. Thus, the vertical additive-lathe printing system was used to print uniform wall thickness grafts, eliminating the hydrogel sagging problem. Tensile testing performed in both circumferential and longitudinal direction revealed that the anisotropic properties of printed gelMA constructs were similar to those observed in the native blood vessels. In addition, no leakage was detected through the walls of the gelMA grafts during burst pressure measurement. Therefore, the current printing setup could be utilized to print vascular grafts for the treatment of cardiovascular diseases.

3D Printing in Suspension Baths: Keeping the Promises of Bioprinting Afloat.

Extrusion-based 3D printers have been adopted in pursuit of engineering functional tissues through 3D bioprinting. However, we are still a long way from the promise of fabricating constructs approaching the complexity and function of native tissues. A major challenge is presented by the competing requirements of biomimicry and manufacturability. This opinion article discusses 3D printing in suspension baths as a novel strategy capable of disrupting the current bioprinting landscape. Suspension baths provide a semisolid medium to print into, voiding many of the inherent flaws of printing onto a flat surface in air. We review the state-of-the-art of this approach and extrapolate toward future possibilities that this technology might bring, including the fabrication of vascularized tissue constructs.

Thermoplastic PCL-b-PEG-b-PCL and HDI Polyurethanes for Extrusion-Based 3D-Printing of Tough Hydrogels.

Novel tough hydrogel materials are required for 3D-printing applications. Here, a series of thermoplastic polyurethanes (TPUs) based on poly(ɛ-caprolactone)-b-poly(ethylene glycol)-b-poly(ɛ-caprolactone) (PCL-b-PEG-b-PCL) triblock copolymers and hexamethylene diisocyanate (HDI) were developed with PEG contents varying between 30 and 70 mol%. These showed excellent mechanical properties not only when dry, but also when hydrated: TPUs prepared from PCL-b-PEG-b-PCL with PEG of Mn 6 kg/mol (PCL7-PEG6-PCL7) took up 122 wt.% upon hydration and had an E-modulus of 52 ± 10 MPa, a tensile strength of 17 ± 2 MPa, and a strain at break of 1553 ± 155% in the hydrated state. They had a fracture energy of 17976 ± 3011 N/mm² and a high tearing energy of 72 kJ/m². TPUs prepared using PEG with Mn of 10 kg/mol (PCL5-PEG10-PCL5) took up 534% water and were more flexible. When wet, they had an E-modulus of 7 ± 2 MPa, a tensile strength of 4 ± 1 MPa, and a strain at break of 147 ± 41%. These hydrogels had a fracture energy of 513 ± 267 N/mm² and a tearing energy of 16 kJ/m². The latter TPU was first extruded into filaments and then processed into designed porous hydrogel structures by 3D-printing. These hydrogels can be used in 3D printing of tissue engineering scaffolds with high fracture toughness.