| Summary: | Spatially offset Raman spectroscopy (SORS) is a method for measuring Raman signal from much deeper within a sample than is achievable with traditional Raman spectroscopy, and relies on the diffuse scattering of photons within turbid materials. This makes SORS a promising tool in the field of medical imaging.
A SORS device was built, based around a digital micro mirror device. This allowed for the detection offset to be selected in software and gave the SORS device a huge flexibility. The instrument was then applied to the study of bone regeneration.
Using phantom samples, we investigated the feasibility of using SORS as a tool for monitoring non-invasively the mineralization of bone tissue engineering scaffold in vivo. The phantom samples consisted of 3D-printed scaffolds of poly-caprolactone (PCL) and hydroxyapatite (HA) blends, with varying concentrations of HA, to mimic the mineralisation process. The scaffolds were covered by a 4 mm layer of skin to simulate real in vivo measurement conditions. At a concentration of HA approximately 1/3 that of bone (~0.6 g/cm3), the characteristic Raman band of HA (960 cm-1) was detectable when the PCL:HA layer was located at 14 mm depth within the scaffold (i.e. 8 mm below the skin surface), and concentrations of ~10% of bone were detectable at 4 mm depth.
We then investigated the feasibility of using SORS to monitor changes in collagen concentration at levels similar to those expected to occur in vivo during bone regeneration (0 – 0.84 g/cm3). A partial least squares (PLS) regression model was developed to quantify collagen concentration in plugs consisting of mixtures of collagen and hydroxyapatite (predictive power of ±0.16 g/cm3). The PLS model was then applied to SORS spectra acquired from rat cadavers after implanting the collagen:hydroxyapatite plugs in drilled skull defects. The PLS model successfully predicted the profile of collagen concentration, but with an increased predictive error of ±0.30 g/cm3. These results demonstrate the potential of SORS to quantify collagen concentrations in the range relevant to those occurring during new bone formation.
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