3d bioprinting 3D printing bioink Bioprinting Extrusion-based bioprinting gelMA hydrogel Nanyang Technological University regenHU research paper Science & Technology Singapore tissue engineering ultraviolet light

UV-Assisted Extrusion-Based Bioprinting to Make GelMA Hydrogels for Soft Tissue Engineering

It’s troublesome to manufacture complicated tissue constructs with the required mechanical properties and structure integrity once you’re with bioprinting in tender tissue engineering. Sometimes, scientists will use materials, like PCL, to reinforce the within of 3D bioprinting constructs, however the lengthy degradation interval just isn’t great. However a workforce of researchers – Pei Zhuang, Wei Long Ng, Jia An, Chee Kai Chua, and Lay Poh Tan – from Singapore’s Nanyang Technological College have proposed a novel UV-assisted, extrusion-based (UAE) 3D bioprinting technique that would assist fabricate mushy tissue constructs with the specified structural integrity. The group lays out their work in a paper titled “Layer-by-layer ultraviolet assisted extrusion-based (UAE) bioprinting of hydrogel constructs with high aspect ratio for soft tissue engineering applications.”

The abstract reads, “Herein, we present a facile bioprinting strategy that combines the rapid extrusion-based bioprinting technique with an in-built ultraviolet (UV) curing system to facilitate the layer-by-layer UV curing of bioprinted photo-curable GelMA-based hydrogels to achieve soft yet stable cell-laden constructs with high aspect ratio for soft tissue engineering. GelMA is supplemented with a viscosity enhancer (gellan gum) to improve the bio-ink printability and shape fidelity while maintaining the biocompatibility before crosslinking via a layer-by-layer UV curing process. This approach could eventually fabricate soft tissue constructs with high aspect ratio (length to diameter) of ≥ 5. The effects of UV source on printing resolution and cell viability were also studied. As a proof-of-concept, small building units (3D lattice and tubular constructs) with high aspect ratio are fabricated. Furthermore, we have also demonstrated the ability to perform multi-material printing of tissue constructs with high aspect ratio along both the longitudinal and transverse directions for potential applications in tissue engineering of soft tissues.”

Schematic drawing of layer-by-layer UV-assisted bioprinting strategy. The gellam gun in the bio-ink serves as a viscosity enhancer to enhance the bio-ink printability (by way of formation of ionic bonds between GelMA chain and gellan gum) through the extrusion printing process prior to additional UV crosslinking (to type chemical bond between adjoining GelMA chains) of each particular person printed layer. This layer-by-layer UV-assisted bioprinting strategy is repeated to ultimately achieve fabrication of complicated 3D buildings with high facet ratio.

Using 3D bioprinting to exactly deposit cells and biomaterials can actually assist facilitate interactions between them, which allows tissue maturation. A very good microenvironment is important for regulation, however as beforehand mentioned, when it comes to gentle tissue engineering, it’s troublesome to achieve this. Whereas there are numerous bioprinting approaches, extrusion-based appears greatest due to its compatibility with bioinks, ease of operation, and fast fabrication velocity.

“An ideal bio-ink should exhibit good printability, biocompatibility and compliant tissue stiffness,” the researchers defined. “Most of the existing bio-inks are modified from natural biomaterials such as gelatin ([30–34]) and collagen ([35–37]) to form new composite bio-inks with tunable properties. Particularly, gelatin methacryloyl (GelMA) has been identified as a promising bio-ink owing to its excellent biological properties and tunable physical properties ([38, 39]).”

The bioprinting part includes characterization of rheological properties, willpower of appropriate UV scanning velocity and number of appropriate bio-inks.
A) Rheological properties of 30 totally different GelMA-GG bio-inks at a continuing shear fee of 100s−1 at 25°C indicated greater bio-ink viscosity with growing polymer concentrations. B) An summary of the totally different GelMA-GG bio-inks when it comes to printability and cell encapsulation. C) Representative pictures of printed constructs to distinguish among the many three totally different classifications; (Prime) poor printability, (Center) good printability, (Bottom) over-gelation. D) Affect of bio-ink on printing resolution, a more viscous bio-ink leads to greater printing resolution due to significantly much less spreading of the shear-thinning bio-inks upon contact with the substrate surface.

Bioinks based mostly in GelMA are sometimes used in regenerative drugs and tissue engineering, but when there are high concentrations of this materials, limited cell activity can occur due to high crosslinking density, in addition to stiffness of the photo-crosslinked constructs; low concentrations may cause poor shape constancy and low printing decision.

“Hence, further optimization is required to improve the stability and printability of GelMA bio-inks. A plethora of methods have been explored to improve the rheological behavior of GelMA, such as the addition of various materials like nanosilicates ([46]), partial crosslinking GelMA with enzymes ([33]), or through cooling process,” said the researchers. “Among these methods, gellan gum, which is a non-toxic polysaccharide, has been discovered as a promising rheological modifier to improve the rheological property of the bio-ink.”

The staff selected to use the minimum needed amount of gellan gum (GG) so as to stability biocompatibility and “endow the enhanced printability of GelMA-GG,” while they used layer-by-layer UAE bioprinting when making thick cell-laden tissue constructs in order to reinforce resolution and structure stability.

“As such, we have demonstrated the ability to fabricate bioprinted constructs with high aspect ratio via a layer-by-layer UAE bioprinting strategy,” the researchers defined.

“The study offers a new bioprinting strategy to generate stable 3D structures with compliant mechanical property and high aspect ratio using GelMA-based (GelMA-GG) bio-inks for engineering of soft tissue constructs.”

They investigated 30 totally different mixtures of GelMA-GG bio-inks in three levels:

  1. Bioink preparation part
  2. Bioprinting part
  3. Submit-printing part

A) Left: Printed grid construct with no layer-by-layer UV curing using 7.5-Zero.2 group. Proper: Printed grid pattern with the 6 selected GelMA-GG bio-inks. B) a. Printed grid assemble. b. Aspect view of the printed assemble. c-e. Tubular buildings printed with GelMA-GG bio-ink (7.5-0.2) with totally different AR, which is bioprintable and cell permissive. f-h. Multiple supplies deposition with layer-by-layer UV curing.

The group loaded the cells into the composite bioinks to evaluate their potential sedimentation and ease of cell encapsulation. The bioinks have been then printed using the UAE technique so as to evaluate accuracy and printability of the constructs. The researchers adjusted the print parameters in order to “achieve structures with high aspect ratio,” and then investigated the “UV effects on printing resolution and cell behavior,” before finally evaluating the 3D printed constructs for their corresponding cell conduct and material properties.

The staff used a regenHU bioprinter, with a temperature of 25 ± 1°C and 27G needle, for its experiments, and fabricated GelMA-GG constructs in a rectangular form.

“To optimize the printing process, 2D structures were first printed to determine the bio-ink printability and then further tests were conducted to determine the optimal printing pressure and feed rate. Additionally, UV scanning speed has shown critical effects on printing resolution and cell viability,” the researchers wrote. “To study the influence of UV scanning speed on printing resolution, C2C12 encapsulated GelMA-GG constructs with 1, 3, 5, 7, 9 and 11 layers were printed into grid pattern under fixed printing speed and pressure. The width of the printed filaments were measured to determine the change of printing resolution overtime. Meanwhile, Live/dead staining and ImageJ was used to analyse the cell viability in the printed constructs. Cells in the bottom layer of the constructs were by imaged by fluorescent microscope to determine the UV influence on cell viability by cell counting analysis. After which, 3D grid and tubular constructs of different aspect ratio at varying diameter were printed with layer-by-layer UV curing approach using the identified optimal printing parameters with all the printable bio-inks.”

C2C12 cell viability and proliferation research of cell printing on Day 1,four and seven; scale bar is 500 μm.

C2C12 cells have been also printed, so that the workforce might research how materials stiffness and microstructure influenced cell conduct. They have been in a position to easily choose composite bio-inks for specific tissue engineering purposes by performing a guide casting strategy.

“The GelMA-based bio-inks have exhibited great biocompatibility for cells due to the presence of RGD peptides,” the researchers concluded.

“To strike a stability between printability and biocompatibility, minimum very best amount of gellan gum was added to enforce the printability of the bioinks with out compromising the biocompatibility. In-depth characterization and evaluation on the totally different composite GelMA-GG bio-inks have been performed to choose an appropriate range of GelMA-GG bio-inks via our proposed parametric research.

“From our work, a suitable range of bio-ink viscosity lower than 0.124 Pa·s at 37°C was found to be suitable for cell encapsulation and to achieve a homogeneous cell-laden bio-inks. Material viscosity of 0.2-1.0 Pa·s at a printing temperature of 25°C is recommended for printing of complex 3D cell-laden constructs with high aspect ratio using our layer-by-layer UV-assisted bioprinting strategy. The critical role of UV source in printing process has been investigated, specifically, the UV influence on printing resolution and cell survival rate. In addition, a strong correlation between material microstructure and stiffness has been shown in our study and their synergistic influence on cell behavior has been investigated.”

The researchers stated their technique could possibly be tailored for all light-curable supplies.

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