University of Birmingham researchers develop SLAM 3D bioprinting method

Researchers from the University of Birmingham have developed a new 3D printing method for soft materials which could enable the manufacture of artificial medical implants.

Known as Suspended Layer Additive Manufacturing (SLAM), this technique uses a polymer-based hydrogel containing particles for a self-healing gel. Liquids or gels can be injected into this medium to build 3D forms.

“The hydrogel we have designed has some really intriguing properties that allow us to print soft materials in really fine detail,” explains Professor Liam Grover, leader of the study published in Advanced Functional Materials.

“It has huge potential for making replacement biomaterials such as heart valves or blood vessels, or for producing biocompatible plugs, that can be used to treat bone and cartilage damage.”

A 3D print scaffold created using the SLAM method. Photo via University of Birmingham.
A 3D print scaffold created using the SLAM method. Photo via the University of Birmingham.

SLAM 3D bioprinting

The team developed SLAM as an alternative to Freeform Reversible Embedding of Suspended Hydrogels (FRESH), which uses gels to form a slurry bath into which the printed material is injected. According to the University of Birmingham scientists, this method can result in frictions within the gel medium which can distort the printing process.

SLAM uses low viscosity biopolymers into a self‐healing fluid‐gel matrix. Such fluid gels are formed upon the introduction of shear stress during the sol–gel transition to produce a network of entangled gel microparticles. This differs from the idle ‘bulk’ gels used in FRESH which form polymer networks in the absence of shear.

With this process, the researchers aimed to demonstrate how particles in the gel can be sheared, or twisted “so they separate, but still retain some connection between them,”  as stated in the study. This interaction creates the self-healing effect, allowing the gel to support the printed material for objects with precise detail, and no leaking or sagging.

A) The fluid‐gel print bed is created by shear cooling a hot agarose solution throughout the sol–gel transition which is then loaded into a container of suitable dimensions to support the scaffold. B) The bioink is extruded within the self‐healing fluid bed and multiple cartridges may extrude different hydrogel layers forming an interface with the pre‐deposited bioinks for the creation of a multilayered construct. C) Crosslinking and cell media induces solidification and provides metabolites to the cell scaffold. D) Low shear washing with deionized water releases the construct. Image via the University of Birmingham.

Soft materials and additive manufacturing

3D printing soft materials have been seen as a big challenge for scientists as they require support to avoid sagging. Through SLAM tests, the team found that the agarose support bath allows for further methods of crosslinking, which includes collagen formulations.

The researchers highlight this as an advantage in regenerative medicine. “The method enabled the successful fabrication of bulk, intricate, dual-phase, and phase‐encapsulated hydrogels from a variety of biopolymer materials that are currently widely investigated in regenerative medicine.”

“Overall, SLAM is a promising technique for producing delicate soft tissues, complex soft tissue structures, and interfaced tissues.”

Fabrication of Complex Hydrogel Structures Using Suspended Layer Additive Manufacturing (SLAM)is co-authored by Jessica J. Senior, Megan E. Cooke, Liam M. Grover, and Alan M. Smith.

Fabrication of complex structures by SLAM using gellan. A) Intricate lattice prior to (left) and following extraction (right) from the fluid‐gel bed. B) T7 intervertebral disc as a CAD file (left) and demonstrating the printing of bulk structures with lateral (middle) and apical (right) views. C) Intricate bulk structure in the form of a gellan spider. D) Carotid artery as a CAD file (left) and during 3D printing (right). Image via the University of Birmingham.

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Featured image shows a 3D print scaffold created using the SLAM method. Photo via the University of Birmingham.