Mechatronics, Additive Fabrication and Medical Devices
As engineering research surges forward, providing manufacturers with an increasingly comprehensive toolkit to keep them on the leading edge, many disciplines that were once separate are now intrinsically linked. Mechatronics, the result of many such mergers, is a term coined back in 1960s to establish a synergy between mechanical, electrical/electronic and software technologies in order to design and realize products, systems and processes which are more cost effective, efficient and intelligent than their predecessors.
It is not only a multi-disciplinary engineering field, but also a concurrent design approach going beyond classical sequential design and system development approaches, taking into account interactions between the system components, concepts, and design and operation parameters. As a design optimization method, it takes all parameters, interactions, technologies, operation variables into consideration from the beginning in order to achieve an optimal design. The concurrent and integrated mechatronic design approach can be applied to any system, including additive fabrication tools that many manufacturers have turned to.
Additive Bio Fabrication – 3D BioPrinting
Put simply, additive fabrication (AF) takes a 3D computer model of a structure and splits it into slices. These 2D slices, or layers, are then automatically printed in sequence onto a build platform until the complete set of slices has been recombined into a physical likeness of the original 3D model.
This technology is fast becoming an economically feasible alternative method of producing complex components in established manufacturing industries. It is the potential for production of highly complex structures using multiple materials that makes AF so attractive to medical industries. Additive Bio Fabrication (AdBioFab) takes the established principles of AF and applies them to bio-materials. This enables the fabrication of bio-compatible structures and devices at resolutions relevant to biology, i.e. sub 100μm feature details, which would be impossible to produce by any other means.
Some immediate examples of where additive fabrication has been directly used for medical research include collaborations between our research team and other partners in the development of, batch production of custom bio-compatible labware, equipment to enable microscopy analysis of living cells over extended periods of time, and glaucoma implant prototypes for live implantation trials.
These studies have been undertaken using commercially available bio-compatible build materials, namely MED610 supplied by Stratasys. The production of devices using more functional materials is also a reality. Current research focuses on the production of structures from materials such as hydrogels through to bio-compatible polymers.
Bio-compatible polymers such as Polycaprolactone (PCL) are amenable to AF due to their melt properties which are ideal for hot melt extrusion printing. We have recently shown where multiple materials can be extruded simultaneously in a co-axial format to produce multilayer scaffold structures that can have PCL outer sheaths protecting hydrogel inner cores. These structures have potential for use as controlled drug delivery mechanisms or as conductive pathways to stimulate cell differentiation and growth.
The effective integration of biology and electronics to create medical bionic devices is being facilitated by mechatronics and to further develop AdBioFab.
The addition of functional materials to the structural components discussed above further increases the impact of 3D fabrication. For example, we have been involved in the development of 3D fabrication strategies that enable organic conductors, controlled delivery sites and even living cells to be integrated and distributed during fabrication.
Living Cells: Spatial distribution of living cells within an appropriate biopolymer/gel matrix presents unprecedented opportunities for creation of new medical devices. Recently we have formulated a bio ink that provides protection to living cells, in the ink drug delivery and after printing. We have also demonstrated the ability to create 3D structures containing living cells .
Controlled Delivery of Bioactive Molecules:The automatic response of those involved in developing drug or other bio active delivery structures to the question of release profile has been - synthesise a new material!!Simple examples from our own laboratory indicate this is not always necessary. Strategic distribution of bioactive molecules throughout a known polymer structure of a given composition can realise control over the delivery profiles achieved (Figure 1).
Figure 1. Printed structures to engineer bioactive release profiles. Adapted from International Journal of Pharmaceutics 2012, 422, 254-263.
Organic Conductors:The last two decades has seen the emergence of novel organic materials and structures that are electronically conducting. While fascinating from an electronics point of view the impact on our ability to communicate with the human system is still virtually untapped. The development of “ink formulations” for both 2D and 3D printing means we can now integrate these fascinating materials into new medical device platforms (Figure 2).
Figure 2. Extrusion printing 3D structures based on an organic conducting polymer. Adapted from Charles Mire PhD Thesis, University of Wollongong, 2010.
Bionics and Additive Fabrication
More effective interfacing of the biological world and that of man-made electronics is being achieved through the functional material platforms described above. This is turn broadened the scope of potential clinical applications for medical bionics. As well as prosthetic bionic implants such as the bionic eye, the bionic ear or implants for epilepsy detection and control, or for control of Parkinson’s and even pain management a new field of application on regenerative bionics is emerging.
Improving the fidelity of electronic communication across the electrode-cellular interface is the central challenge in all of these areas of application. Our ability to transmit information across this interface ultimately determines the performance of the overall device. The composition and structure of the electrode-cellular interface are determined by the characteristics of the implanted electrode.
The composition of the implanted electrode is critical. Consequently the emergence of novel materials: organic conductors has seen us lay the platform for enhanced performance and new applications in medical bionics. Equally the structure of the implanted electrode is important for a given composition. Surface topography is known to influence cellular interactions. Furthermore the creation of a 3D.
The advent of new materials and fabrication tools has also seen the development of strategies that enable controlled delivery of bioactives to become a fully integrated component further enhancing the performance of medical bionic devices.
Now fabrication strengths that enable such conductors and delicate biological entities to be integrated into complex 3D structures have emerged.
Mechatronic technologies and design approaches are indispensable to establish new printers or machinery for additive fabrication technologies. On the other hand, we need the additive fabrication technology to evaluate new concepts, designs and innovations, which are shaped using the integrated mechatronic design approach. It follows that mechatronics and additive fabrication create a synergy to provide cost effective, efficient, and intelligent products, processes and systems.
Multi-material, versatile and cost effective rapid prototyping tools should continuously be improved using the concurrent and integrated mechatronic design approach and technologies. Mechatronics and additive fabrication complement each other to develop and fabricate high-value components, products and systems to minimise the effects of the current manufacturing crisis in developed countries.
A recent example from our laboratories has resulted in the development of a coaxial 3D extrusion printing system (Figure 3). The key to the process was the development of a 3D printed co-axial extrusion tip. The structure was modelled and evaluated in-house using commercial computer aided design software before being produced in 316L Stainless Steel using a Realizer SLM50 selective laser melting system. The novel 3D printed extrusion tip was then integrated into a custom extrusion printing system to allow fabrication of bio-compatible scaffolds from co-axial filaments. These initial steps will enable further research towards conducting pathways for biocompatible electronics applications, selective cell stimulation and biocompatible fluidics systems which utilise hollow printed fibres.
Figure 3. Coaxial printing tips, reservoirs system and a printed 3D coaxial structure. Adapted from IEEE / ASME International Conference on Advanced Intelligent Mechatronics (AIM 2013) (Accepted).
Additive fabrication technology which is based on the synergy of digital modelling with additive manufacturing (layer by layer fabrication from 3D CAD data) is a rapid prototyping technology to fabricate components with any shape in order to build complex prototypes with no assembly. It is a much needed enabling technology to make the prototyping process more effective with a minimum cost and time. It is now much easier and quicker to realise inventions and innovations—it is ‘a powerful incentive for innovation’.
Iterative Developments in Hardware/Software and Materials Science
The arrival of AdFab gear in research labs has empowered research. Already the limitations of existing equipment and formulations is obvious and being addressed. Consider the ultimate: the ability to create 3D structures that emulate the amazing performance of nature.
Even a cursory glance at the elegant structures nature provides for energy conversion through photosynthesis or for biological functions (e.g. nerve, muscle tissue) reveals a hierarchical structure wherein control over the spatial distribution of nano to micro dimensional features is a macro scopic structure is evident.
What is needed is additive fabrication that enables multicomponent, multifunctional, multi length scale fabrication. Elements of a number of existing technologies will need to be grouped together into integrated additive fabrication systems, which means that the mechatronics research community has a critical role to play if we are to make effective and efficient progress.