A new multi-scale x-ray micro computed tomography machine to enable (image-guided) non-destructive inspections of decellularised tissue

Tissue engineering - aimed at developing "lab-grown" organs and tissue by combining appropriate scaffolds and cells - could solve one of the biggest medical problems of our times, the shortage of donor organs. While the pool of scaffold materials is large (e.g. natural/synthetic biomaterials), there is consensus that the extracellular matrix (ECM) of the target tissue is an excellent choice as it possesses native structural and biomechanical properties. ECMs can be derived from cadaver tissue (e.g. from animals) through a process called decellularization, by which the tissue undergoes several cycles of flushing with detergents and enzymes. A successfully decellularised tissue is characterised by the absence of cellular material and the presence of an intact ECM. Imaging, for assessing the ECM, is an extremely important tool for the development of decellularisation methods that are simultaneously gentle and effective.

This project is about developing a new imaging tool for characterising decellularised tissue based on x-ray micro computed tomography (CT). Since micro-CT is a non-destructive technique, the inspected samples can be used further in longitudinal studies or be implanted into animals to test their performance in vivo. In comparison, the current gold standard techniques for inspecting ECMs (histology, electron microscopy) require that samples are sliced, sectioned and/or stained in preparation for being imaged, prohibiting using them in any further studies.

A number of substantial developments will be needed before micro-CT can become a valuable tool for validating decellularisation techniques and other methodologies in tissue engineering. Currently, micro-CT fails to meet the complex imaging needs of this field, which often requires multi-scale and multi-contrast approaches. First, a micro-CT machine with zooming in capabilities would be required to inspect the multi-level structure of ECMs. Second, decellularised tissue generally exhibits weak x-ray attenuation; hence, the micro-CT machine should provide access to phase contrast alongside attenuation contrast, which is known to provide a much better visualisation of tissue scaffolds than the latter.

The micro-CT machine proposed here will have both these functionalities. It will exploit an innovative imaging mechanism that is underpinned by the idea to structure the x-ray beam into an array of narrow (micrometric) beamlets via a mask placed immediately upstream of the sample. This provides flexibility in terms of spatial resolution, as this metric - unlike in conventional micro-CT scanners - is not defined by the blur of the source and detector. Instead, resolution is driven by the beamlet width, which can be made smaller than the intrinsic system blur, bearing unique potential for fast resolution switching and multi-scale imaging. Second, it provides access to complementary contrast channels (phase, ultra-small angle x-ray scattering). These channels result from small x-ray photon deviations which occur alongside attenuation when x-rays interact with matter. While most conventional micro-CT scanners are blind to these effects, the machine proposed here will enable their detection, allowing to reconstruct three sets of complementary tomographic images for each sample. While the phase channel can provide a much higher contrast-to-noise ratio than the attenuation channel, the ultra-small angle x-ray scattering channel encodes the presence of sub-resolution features in a sample. The latter bears unique potential for image-guided zooming in.

The project will culminate in the design, construction and test of an experimental prototype for image-guided multi-scale and multi-contrast imaging with a field of view of up to 10 cm by 10 cm, which may be expanded to larger dimensions in the future. A broad range of decellularised tissues will be scanned, and the results benchmarked against the current gold standard (histology or electron microscopy).

Impact will arise from the transformative detection capabilities that this project will deliver; these are very important in tissue engineering, but also urgently needed in a variety of other disciplines. Virtually anyone who relies on high-resolution, highly sensitive CT scanning will benefit; this includes both academic researchers, as well as industry scientists, R&D teams, manufacturing companies, biomedical engineers, medics etc. Since the new technique can become a vehicle for driving breakthroughs in all these areas, a breadth of benefits for UK society and Plc can be expected.

Initially, the vision is that the project will greatly benefit tissue engineers, who lack appropriate tools for validating novel tissue decellularisation techniques. The proposed x-ray micro-CT machine would solve this gap in technology; since it is a non-destructive technique, it would allow using inspected decellularised tissue in longitudinal studies in vitro, ex vivo and in vivo, which will substantially ease the transition to more advanced and preclinical studies. This is a vital step in the development of new treatments, bearing significant benefits for UK society and the NHS. A key targeted area (through my collaborator Prof. Paolo De Coppi, who specialises in this field) is the tissue engineering based treatment of congenital esophageal atresia, a condition that occurs in about 1 of 3000 live births. The images delivered by my machine would critically inform the development of decellularisation protocols to generate esophageal scaffolds with an intact extracellular matrix.

Although this project is targeted at tissue engineering initially, impact on a much broader scale can be expected. For example, my micro-CT machine will offer opportunities for highly sensitive non-destructive testing (NDT) in materials science and manufacturing, and underpin many areas of the UK's Industrial Strategy. A particular high-impact area, where the new functionalities offered by my machine would push the boundaries of what is currently possible, is the NDT of composite materials. In these materials, the option for image-guided zooming in would enable the detection of otherwise invisible micro-damage. An advanced NDT tool would also inform the development of more efficient and reliable industrial techniques in general and, thus, be instrumental in achieving the government's goal of in increasing national productivity.

To reap these multi-sector benefits, my micro-CT machine will be made available to external users. Our group at UCL has recently secured major funding through which we will be able to grow our labs into a user-oriented facility, the vision being to create a hub for advanced x-ray imaging and tomography. My micro-CT machine will add complementary imaging capabilities to the hub that would otherwise not be available, broadening its scope and raising its profile.

Opportunities for commercialisation of my research will be explored with two major companies in the x-ray domain, Nikon X-Tek Systems and PerkinElmer Inc. For both, the new functionalities provided by my method could imply a new revenue stream and an advantageous edge over competitors in the fast growing sector of industrial x-ray CT, a market that is forecast to triple over the next five years.

Finally, the project provides excellent opportunities for training as well as for inspiring the next generation of scientists. Student training is a key pathway to impact, and applications to the relevant EPSRC supported Centres for Doctoral Training (CDTs) at UCL will be made. Direct societal impact will be generated through inspiring outreach and engagement activities (such as an Imaging Week, during which the developed technology will be made accessible to the general public, especially children), enabling non-scientists to experience, discuss and take part in imaging science.