FT-IR imaging spectroscopy of genetically modified bovine chondrocytes

Monitoring the Progression of Spontaneous Articular Cartilage Healing with Infrared Spectroscopy

OBJECTIVE

Evaluation of early compositional changes in healing articular cartilage is critical for understanding tissue repair and for therapeutic decision-making. Fourier transform infrared imaging spectroscopy (FT-IRIS) can be used to assess the molecular composition of harvested repair tissue. Furthermore, use of an infrared fiber-optic probe (IFOP) has the potential for translation to a clinical setting to provide molecular information in situ. In the current study, we determined the feasibility of IFOP assessment of cartilage repair tissue in a rabbit model, and assessed correlations with gold-standard histology.

DESIGN

Bilateral osteochondral defects were generated in mature white New Zealand rabbits, and IFOP data obtained from defect and adjacent regions at 2, 4, 6, 8, 12, and 16 weeks postsurgery. Tissues were assessed histologically using the modified O'Driscoll score, by FT-IRIS, and by partial least squares (PLS) modeling of IFOP spectra.

RESULTS

The FT-IRIS parameters of collagen content, proteoglycan content, and collagen index correlated significantly with modified O'Driscoll score (P = 0.05, 0.002, and 0.02, respectively), indicative of their sensitivity to tissue healing. Repair tissue IFOP spectra were distinguished from normal tissue IFOP spectra in all samples by PLS analysis. However, the PLS model for prediction of histological score had a high prediction error, which was attributed to the spectral information being acquired from the tissue surface only.

CONCLUSION

The strong correlations between FT-IRIS data and histological score support further development of the IFOP technique for clinical applications, although further studies to optimize data collection from the full sample depths are required.

Applications of ATR-FTIR spectroscopic imaging to biomedical samples

FTIR spectroscopic imaging in ATR (Attenuated Total Reflection) mode is a powerful tool for studying biomedical samples. This paper summarises recent advances in the applications of ATR-FTIR imaging to dissolution of pharmaceutical formulations and drug release. The use of two different ATR accessories to obtain chemical images of formulations in contact with water as a function of time is demonstrated. The innovative use of the diamond ATR accessory allowed in situ imaging of tablet compaction and dissolution. ATR-FTIR imaging was also applied to obtain images of the surface of skin and the spatial distribution of protein and lipid rich domains was obtained. Chemical images of cross-section of rabbit aorta were obtained using a diamond ATR accessory and the possibility of in situ imaging of arterial samples in contact with aqueous solution was demonstrated for the first time. This experiment opens an opportunity to image arterial samples in contact with solutions containing drug molecules. This approach may help in understanding the mechanisms of treatment of atherosclerosis.

The use of FT-IR imaging as an analytical tool for the characterization of drug delivery systems

FT-IR imaging spectroscopy is well suited for studying dynamic processes occurring in multi-component systems. Each component is resolved spatially based on the spectral response at each detector element. Additionally, the sequential collection of images tracks the movement of each component over time. In this study, the delivery characteristics of the drug, testosterone, suspended in a poly(ethylene oxide) (PEO) matrix was observed using this technique. Drug release occurred as the hydrophilic, erodible polymer underwent controlled dissolution, exposing the drug to the aqueous environment. The subsequent conversion of the drug into the therapeutic aqueous form completed the delivery process. Qualitative evaluation of the false color composite infrared images led to the elucidation of two distinct delivery mechanisms, dependent on the degree of drug loading. The spatially embedded spectral features led to the quantification of the drug release rates as well as the rates of polymer dissolution. The rates for both polymer dissolution and drug release were evaluated using well-established models. Additionally, the homogeneity of the drug dispersion for different loadings was characterized. The roles of chemical interactions across the solvent interface of species were also investigated. Changes in each component from the bulk to the solvated region were investigated, revealing changes in concentration and polymer orientation as well as inter-species interactions.

New opportunities in micro- and macro-attenuated total reflection infrared spectroscopic imaging: spatial resolution and sampling versatility

New opportunities exist to obtain chemical images using attenuated total reflection infrared (ATR-IR) spectroscopy. This paper shows the feasibility of obtaining FT-IR images with a spatial resolution of at least 3-4 microm using a Ge ATR objective coupled with an infrared microscope. The improved spatial resolution compared to FT-IR images obtained by the transmission method is due to the high refractive index of the ATR crystal, which gives a high numerical aperture and hence, a higher spatial resolution. FT-IR imaging with a conventional diamond ATR accessory has been investigated. This is the first time that FT-IR imaging is reported using such a versatile accessory based on a diamond ATR crystal. These results showed that a spatial resolution up to 13 microm can be achieved without the use of infrared microscope objectives. One advantage of the diamond element is that it allows pressure to be applied and hence, good contact to be obtained over the whole field of view.