Depth-dependent anisotropies of amides and sugar in perpendicular and parallel sections of articular cartilage by Fourier transform infrared imaging

Effects of Polarizer-Analyzer Configurations for FTIR Spectroscopy: Implications for Multiple Polarization Algorithms

Polarized Fourier transform infrared (p-FTIR) spectroscopy is a widely used technique for determining orientational information in thin organic materials. Conventionally, a single polarizer is placed in the path of the incident light (termed the polarizer). Occasionally, a second polarizer is also placed after the sample (referred to as the analyzer). However, this polarizer-analyzer configuration has the potential to induce polarization-dependent variances in the final spectra beyond those that are expected, i.e., the squared-cosine relationship of absorptance with respect to polarization angle is no longer accurate. These variances are due to changes in the polarization state of the transmitted light induced by the sample and have yet to be explored in the context of p-FTIR. Consequently, this study employs both theoretical and experimental approaches to identify the effects of including a second polarizer in p-FTIR analyses of anisotropic organic samples. For thin samples, the most significant spectral variance arising from only birefringence is observed on the shoulders of the dichroic peaks. By adopting a crossed polarizer configuration, it is shown that there is potential to identify anisotropy of samples that are generally considered too thick for p-FTIR analysis by exploiting this feature. Furthermore, the squared-cosine relationship of absorptance with respect to the polarization angle is also shown to be inapplicable when a second parallel-oriented polarizer is included. Accordingly, a function that accounts for the second polarizer is proposed for multiple polarization techniques.

Linearly Polarized Infrared Spectroscopy for the Analysis of Biological Materials

The analysis of biological samples with polarized infrared spectroscopy (p-IR) has long been a widely practiced method for the determination of sample orientation and structural properties. In contrast to earlier works, which employed this method to investigate the fundamental chemistry of biological systems, recent interests are moving toward "real-world" applications for the evaluation and diagnosis of pathological states. This focal point review provides an up-to-date synopsis of the knowledge of biological materials garnered through linearly p-IR on biomolecules, cells, and tissues. An overview of the theory with special consideration to biological samples is provided. Different modalities which can be employed along with their capabilities and limitations are outlined. Furthermore, an in-depth discussion of factors regarding sample preparation, sample properties, and instrumentation, which can affect p-IR analysis is provided. Additionally, attention is drawn to the potential impacts of analysis of biological samples with inherently polarized light sources, such as synchrotron light and quantum cascade lasers. The vast applications of p-IR for the determination of the structure and orientation of biological samples are given. In conclusion, with considerations to emerging instrumentation, findings by other techniques, and the shift of focus toward clinical applications, we speculate on the future directions of this methodology.

Construction and properties detection of 3D micro-structure scaffolds base on decellularized sheep kidney before and after crosslinking

Decellularized extracellular matrix is one form of natural material in tissue engineering. The process of dECM retains the tissue microstructure, provides good cell adhesion sites, maintains most of biological signals that promotes the survival and differentiation ability of cells. In this study, sheep kidney was decellularized followed by histochemical staining, elemental analysis and scanning electron microscopy characterizations. The dECM scaffold was prepared with different sequences of freeze drying technology, crosslinking and the water absorption, porosity, mechanical strength with subsequent thermogravimetric analysis, Infrared spectroscopy and biocompatibility tests. Our results indicated that these decellularized treatments of sheep kidney can effectively remove DNA and retain uniform pore size distribution. After crosslinking the scaffold's water absorption decreased from 987.56 ± 40.21% to 934.39 ± 39.61%, the porosity decreased from 89.64 ± 3.2% to 85.09 ± 17.63%, and the compression modulus increased from 304.32 ± 25.43 kPa to 459.53 ± 38.92 kPa, with thermal process the percentage of weight loss decreased from 66.57% to 44.731%, in addition, the composition didn't change significantly, crosslinking could also promote the stability. In terms of biocompatibility, the number of viable cells increased significantly with the days. In conclusion, the crosslinked decellularized sheep kidney extracellular matrix scaffold reduced water absorption and porosity slightly, but has a significant increase in mechanical properties, and presented excellent biocompatibility which are beneficial to cell adhesion, growth and differentiation.

Chronic inflammation deteriorates structure and function of collagen fibril in rat temporomandibular joint disc

Collagen is the building component of temporomandibular joint (TMJ) discs and is often affected by inflammation in temporomandibular disorders. The macromechanical properties of collagen are deteriorated by chronic inflammation. However, the mechanism by which inflammation influences disc function remains unknown. The relationship between the ultrastructure and nanomechanical properties of collagen in inflamed discs should be clarified. Seven-week-old female Sprague-Dawley rats were randomly divided into two groups. Chronic TMJ inflammation was induced by intra-articular injection of complete Freund's adjuvant, and samples were harvested after 5 weeks. Picrosirius staining revealed multiple colours under polarized light, which represented alternative collagen bundles in inflamed discs. Using atomic force microscopy scanning, the magnitude of Young's modulus was reduced significantly accompanied with disordered collagen fibril arrangement with porous architecture of inflamed discs. Transmission electron microscopy scanning revealed a non-uniform distribution of collagen fibres, and oversized collagen fibrils were observed in inflamed discs. Fourier transform infrared microspectroscopy revealed a decrease in 1 338 cm^-1/amide II area ratio of collagen in different regions. The peak positions of amide I and amide II bands were altered in inflamed discs, indicating collagen unfolding. Our results suggest that sustained inflammation deteriorates collagen structures, resulting in the deterioration of the ultrastructure and nanomechanical properties of rat TMJ discs.

Species-Independent Modeling of High-Frequency Ultrasound Backscatter in Hyaline Cartilage

Apparent integrated backscatter (AIB) is a common ultrasound parameter used to assess cartilage matrix degeneration. However, the specific contributions of chondrocytes, proteoglycan and collagen to AIB remain unknown. To reveal these relationships, this work examined biopsies and cross sections of human, ovine and bovine cartilage with 40-MHz ultrasound biomicroscopy. Site-matched estimates of collagen concentration, proteoglycan concentration, collagen orientation and cell number density were employed in quasi-least-squares linear regression analyses to model AIB. A positive correlation (R(2) = 0.51, p < 10(-4)) between AIB and a combination model of cell number density and collagen concentration was obtained for collagen orientations approximately perpendicular (>70°) to the sound beam direction. These findings indicate causal relationships between AIB and cartilage structural parameters and could aid in more sophisticated future interpretations of ultrasound backscatter.

Structure-function relations and rigidity percolation in the shear properties of articular cartilage

Among mammalian soft tissues, articular cartilage is particularly interesting because it can endure a lifetime of daily mechanical loading despite having minimal regenerative capacity. This remarkable resilience may be due to the depth-dependent mechanical properties, which have been shown to localize strain and energy dissipation. This paradigm proposes that these properties arise from the depth-dependent collagen fiber orientation. Nevertheless, this structure-function relationship has not yet been quantified. Here, we use confocal elastography, quantitative polarized light microscopy, and Fourier-transform infrared imaging to make same-sample measurements of the depth-dependent shear modulus, collagen fiber organization, and extracellular matrix concentration in neonatal bovine articular cartilage. We find weak correlations between the shear modulus |G(∗)| and both the collagen fiber orientation and polarization. We find a much stronger correlation between |G(∗)| and the concentration of collagen fibers. Interestingly, very small changes in collagen volume fraction vc lead to orders-of-magnitude changes in the modulus with |G(∗)| scaling as (vc - v0)(ξ). Such dependencies are observed in the rheology of other biopolymer networks whose structure exhibits rigidity percolation phase transitions. Along these lines, we propose that the collagen network in articular cartilage is near a percolation threshold that gives rise to these large mechanical variations and localization of strain at the tissue's surface.

Fourier-transform infrared spectroscopic imaging of articular cartilage and biomaterials: A review

Fourier transform infrared spectroscopy (FTIR) has the potential to mark up the chemical changes of the materials, as almost all the materials contain their signatures in infrared region. Spectroscopy combined with spatial resolution enables the possibility of characterizing samples up to microscopic level. The emerging development of instrumentation to provide spatial information for infrared (IR) spectroscopy, termed as IR microscopy, provides an opening for newer applications in terms of image analysis, novel data processing tools, etc. Characterization of biomaterials using IR spectroscopy has a trace back to 1950s. The advent of FTIR with imaging capability made characterization possible in cartilage tissue and other biological systems. Extensive analysis of chemical constituents of cartilage and tendon, collagen orientation and polarization property of cartilage using FTIR imaging (FTIRI) has been actively explored during the last two decades. Also, studies using specialized instrumentations like synchrotron FTIR imaging have been attempted to understand the characteristics of biological samples like cartilage. This review covers most of those investigations on cartilage with FTIRI to characterize the same in terms of component characteristics and quantification, collagen orientation, zonal boundary determination, influence of mechanical compression on tissue nature and its correlation to other techniques in last 20 years.

Quantitative determination of morphological and territorial structures of articular cartilage from both perpendicular and parallel sections by polarized light microscopy

In order to investigate the three-dimensional structure of the collagen fibrils in articular cartilage, full-thickness canine humeral cartilage was microtomed into perpendicular sections that included both the articular surface and the subchondral bone and approximately 100 successive parallel sections that were each 6 microm thick and from a different cartilage depth. Each section was imaged using polarized light microscopy with a 5x objective (2.0 microm pixel size), generating two quantitative images (angle and retardation). Selected sections were also imaged using a 40x objective (0.25 microm pixel size). At an increased depth from the articular surface, the angle and retardation results in the perpendicular sections showed the well-known 90 degrees change in fibril orientation between the surface and the deep cartilage. In contrast, the retardation results of the parallel sections decreased from the articular surface and remained approximately 0 through most of the radial zones, while the angle results of the parallel sections only changed about 30 degrees. The territorial matrix morphology surrounding 61 chondrocyte clusters was quantified by its length, aspect ratio, and orientation. The cellular clusters in the surface cartilage were ellipsoidal in both parallel and perpendicular sections. In the radial zone, the cellular clusters were oriented in vertical columns in the perpendicular sections and as circular groupings in the parallel sections. This orthogonal imaging technique could provide a better understanding of the three-dimensional territorial and interterritorial fibrils in articular cartilage, the disturbance of which could signify the onset of degenerative cartilage diseases such as osteoarthritis.