USING 3D PRINTING TO HELP IMPROVE HEALTHCARE
Constructs – *Biomimetic Heterogenous Elastic Tissue Development; in-situ 3D Printed Substitutes (in association with University College London)
The world needs artificial tissue to address current limitations with donor organs and problems with donor site morbidity. Despite the success with sophisticated tissue engineering endeavours, which employs cells as building blocks, they are limited to dedicated labs suitable for cell cultures, with associated high costs and Long tissue maturation times before being available for clinical applications. Direct 3D printing can present rapid, bespoke solutions for skull and bone repair but has not adequately addressed the need for elastic tissue, which is a major constituent of many organs. Direct 3D printing of biocompatible thermoplastic polyurethane (TPU) can expeditiously and economically produce biomimetic elastic tissue.
Fluid Deposition Modelling (FDM) is one of the most widely used 3D printing techniques, which utilises thermoplastic filaments that are extruded through a nozzle to three dimensionally build an object as instructed through a coded computer assisted design (CAD). They are relatively economic and does not require tight safety regulations and specialised staff as associated with other processes such as SLS.
Despite the theoretical ability to produce a limitless range of TPU elastomers, practical and commercial considerations dictate that in reality only a small percentage of the potential material grades are commercially available. In the case of medical device applications, the percentage is further limited by the use of additives and processing aids in the polymer manufacturing, which affect both biocompatibility and function. This is evidenced by the very limited number of new medical grades of TPU entering the market over the last decade.
Here we have custom synthesised a polyester (polycaprolactone) polyol based (TPU 80) and a polyether polyol based (TPU 90) formulation in a ‘designed in’ rather than ‘engineered out’ approach to demonstrate the unique opportunities with TPU in developing tissue substitutes. Both polymers were synthesised using a precisely controlled step addition (prepolymer approach) process using an aromatic diisocyanate and a short linear diol chain extender, which were subsequently extruded into 1.75mm filaments and then 3D printed. We used two different types of commercially available FDM printers to evaluate the efficacy of fabrication of TPU filaments. The models used for 3D printing were designed and sliced to incorporate micropatterns using open source software, Blender™ and slic3r™ respectively.
This method can expeditiously and economically produce heterogenous, biomimetic elastic tissue substitutes with controlled porosity to potentially facilitate vascularisation. The flexibility of this application is shown here with tubular constructs as exemplars. We demonstrate how these 3D printed constructs can be post-processed to incorporate bioactive molecules. This efficacious strategy, when combined with the privileges of digital healthcare, can be used to produce bespoke elastic tissue substitutes in-situ, independent of extensive cell culture and may be developed as a point-of-care therapy approach.
The Tubes were printed with either 20, 40, 60 or 80% infill in either a linear or hexagonal pattern using TPU 90 or TPU 80. The structures were printed at a rate of 20mm/s at a temperature of 225°C.