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Project

Aerosol Jet Printing of Fibrillar Collagens for the Replication of Dense Collagenous Tissues

Bioprinting, or the use of additive manufacturing techniques to produce scaffolds for tissue engineering, has recently been established as a useful tool in tissue engineering and regenerative medicine. However, a major limitation of bioprinting has been the mechanical properties of the printed constructs. While there are many tissues where this may not be treated as a priority, mechanical strength is a particularly important property for any construct aiming to replicate connective tissues, such as the cornea and cartilage. The strength of these tissues is often attributed to the overwhelming presence of the fibrillar collagens in their extracellular matrix, the long uninterrupted triple helix secondary structure of the fibrillar collagens, and the ability of these triple helices to align and assemble into densely packed fibrils. While fibrillar collagens, particularly collagen type I, have been bioprinted using some bioprinting techniques, the mechanical properties of the resultant constructs are typically very weak. The overall intent of this dissertation is to perform a fundamental study on aerosol jet printing of fibrillar collagens and develop it as a method for generating mechanically strong collagen hydrogels.

Aerosol jet® printing is a relatively recent electronic printing technology developed to print electronics onto a wider variety of surfaces than possible using pre-existing electronic printing technologies. It achieves its enhanced deposition characteristics by accelerating aerosol droplets of the ink towards the substrate while confined in a coaxial flow of dry gas. This allows the aerosol ink droplets to continue their intended path for a greater distance thereby allowing deposition onto rough substrates. The aerosol ink droplets also dry out remarkably quickly due to the high surface-area-to-volume ratio of an aerosol droplet. This method of drying out the ink is particularly attractive to collagen printing since it allows a relatively dilute solution to be processed into highly concentrated collagen scaffolds with a lower risk of thermal denaturation, and without the use of toxic solvents. However, by transitioning straight from solution to solid in this way, it is unlikely for collagen fibrils to assemble. In order to generate an aerosol, it is also necessary to exert high shear forces on the bulk solution to produce the tiny aerosol droplets. Hence, before exalting aerosol jet printing as a method to print collagen it is necessary to establish whether the printed material is stable, and whether the shear forces of aerosolization damage the collagen structure.

Aerosol jet printing was investigated as a method to produce mechanically strong collagen scaffolds using one recombinant collagen (recombinant human collagen type III, RHCIII), and two animal-derived collagens; bovine Achilles’ tendon-derived collagen type I, and porcine articular cartilage-derived collagen type II. The accuracy and stability of aerosol jet printed collagen was investigated via microscope examination of printed scaffolds. The effect of the shear forces of aerosolization on the structure of each collagen used was determined by sodium dodecyl sulphate-polyacrylamide gel electrophoresis (SDS-PAGE), circular dichroism (CD) spectroscopy, and in one case Fourier transform infra-red (FTIR) spectroscopy. The mechanical properties of the printed collagen scaffolds were measured via ferrule-topped nanoindentation. The structural properties of the aerosol jet printed collagen scaffolds were investigated via swelling ratio measurements and scanning electron microscopy (SEM).

Date:11 Jan 2016 →  3 Jun 2022
Keywords:3D-printen, Additive Manufacturing, Biomaterialen
Disciplines:Ceramic and glass materials, Materials science and engineering, Semiconductor materials, Other materials engineering
Project type:PhD project