Live monitoring of foreign-body response in animals by diffuse Raman spectroscopy

Lead Research Organisation: University of Nottingham
Department Name: Sch of Physics & Astronomy


A broad range of biomaterials are being developed for medical applications, from regenerative medicine and medical devices to vaccine adjuvants and drug delivery platforms. Foreign body response (FBR) to implanted biomaterials is the leading cause of medical device failure. Assessing FBR is not only an integral part of biomaterials development but also it is required for regulatory approval of new materials and medical devices. These studies heavily rely on in vivo animal models and involve end stage methodologies such as histology and immunohistochemistry.
The main goal of this proposal is to develop a new portable device based on diffuse Raman spectroscopy (DRS) to monitor FBR in live animal models. This will allow longitudinal measurements of FBR on the same animal (rather than sacrificing animals at specific time points). Although a range of in-vivo animal imaging are available, they lack the molecular specificity, sensitivity or resolution to monitor FBR. DRS relies on diffuse photon migration in connective tissue. Using near-infrared light (785-1000 nm wavelength), DRS is ideally-suited for probing deeper in and under skin to measure the biomolecular processes during FBR. In our previous work we showed that Raman spectroscopy can detect inflammation in skin and monitor changes in collagen density, two main hallmarks of FBR. However, the main challenge in this project is to optimise the design of the DRS instrument in order to achieve a detection limit and accuracy to allow quantification of these changes in-vivo. This project builds on our latest results using modelling of light propagation in tissue that show that this high level of performance can be achieved by optimising the design of the DRS probe and integration with high optical throughput spectrometers and detectors.
While DRS is a platform technology, the focus of this project is on a mouse model used for investigation FBR triggered by subcutaneous implantation of polymer biomaterials. Although FBR induces a range of biomolecular changes in tissue, in this project we will focus on two key read-outs, for which we already have demonstrated proof-of-principle, and which are the main parameters obtained from histology: the thickness of the fibrotic capsule from quantification of collagen concentration, and inflammation from quantification of DNA signals.
If successful, this new technology would allow scientists and engineers to follow FBR non-invasively, on the same animal, without having to sacrifice animals at each time point. This will provide unique high quality data, with unmatched time resolution and molecular sensitivity, with ethical and economic benefits by reducing the number of animals used in research.The technology has the potential to reduce the number of animals in research by a minimum 50% (typical two end-points studies). However, the need for better understanding of the time-dependent molecular changes in FBR, more and more studies require four and more time end points. In such cases we envisage that reduction by 75-80% may be achieved.

Technical Summary

Implantable medical devices are widely used in healthcare. However, foreign body response (FBR) can lead to chronic inflammation, tissue damage, and fibrosis, resulting in device rejection and failure. The standard method for evaluating FRB in animal models is histological assessment of ex-vivo skin tissue surrounding the implant. Because histology is an end point technique, understanding the time-dependent changes caused by FBR require a large number of animals to be sacrificed and each time point.
Spatially-offset Raman Spectroscopy (SORS) was shown to be able to probe deeper in tissue and measure detailed molecular information of skin and connective tissue in-vivo. Our recent studies using phantom samples and rat cadavers showed that SORS was able to detect differences in collagen concentrations similar to those involved in bone healing. We also showed that Raman spectroscopy can detect changes in ex-vivo skin tissue caused by inflammation. However, the current SORS probes have limited sensitivity levels when measuring the small changes in tissue, such as those involved in FBR.
In this proposal we will develop a portable device based on diffuse Raman spectroscopy (DRS) for in-vivo monitoring of FBR. We will use modelling of light propagation in tissue to maximise the spectral contrast between the regions adjacent to the implant and surrounding tissue. This will be achieved by increasing the number of the laser excitation and detection points and optimising their spatial configuration on the surface of skin. Based on the optimised configuration, we will build a portable device equipped with a fibre optic handheld probe matching the high-throughput spectrometer and CCD, which will be suitable for in-vivo measurements on animal models. The ability to follow FBR on the same animal will provide higher quality data at high temporal resolution while reducing the number of animals used in research.


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