Effects of treatment protocols and subcutaneous implantation on bovine pericardium: a Raman spectroscopy study

Characteristics of Collagen Changes in Small Intestine Anastomoses Induced by High-Frequency Electric Field Welding

High-frequency electric field welding-induced tissue fusion has been explored as an advanced surgical method for intestinal anastomoses; however, intrinsic mechanisms remain unclear. The aim of this study was to investigate microcosmic changes of collagen within the fusion area, with various parameters. Ex vivo small intestine was fused with mucosa-mucosa. Four levels of compressive pressure (100 kPa, 150 kPa, 200 kPa, 250 kPa) were applied for 10 s in order to fuse the colons under a power level of 140 W. Then, collagen fibers of the fusion area were examined by fibrillar collagen alignment and TEM. Three levels of power (90 W, 110 W, 140 W) and three levels of time (5 s, 10 s, 20 s) were applied in order to fuse colons at 250 kPa, and then collagen within the fusion area was examined by Raman spectroscopy. Fibrillar collagen alignment analysis showed that with the increase in compression pressure, alignment of the collagen in the fusion area gradually increased, and the arrangement of collagen fibers tended to be consistent, which was conducive to the adhesion of collagen fibers. TEM showed that pressure changed the distribution and morphology of collagen fibers. Raman spectroscopy showed that increased power and time within a certain range contributed to collagen cross linking. Peak positions of amide I band and amide III band changed. These results suggested that higher power and a longer amount of time resulted in a decrease in non-reducible cross links and an increase in reducible cross links. Compression pressure, power, and time can affect the state of collagen, but the mechanisms are different. Compressive pressure affected the state of collagen by changing its orientation; power and time denatured collagen by increasing temperature and improved the reducible cross linking of collagen to promote tissue fusion.

Temperature Distribution of Vessel Tissue by High Frequency Electric Welding with Combination Optical Measure and Simulation

In clinical surgery, high frequency electric welding is routinely utilized to seal and fuse soft tissues. This procedure denatures collagen by electrothermal coupling, resulting in the formation of new molecular crosslinks. It is critical to understand the temperature distribution and collagen structure changes during welding in order to prevent thermal damage caused by heat generated during welding. In this study, a method combining optical measurement and simulation was presented to evaluate the temperature distribution of vascular tissue during welding, with a fitting degree larger than 97% between simulation findings and measured data. Integrating temperature distribution data, strength test data, and Raman spectrum data, it is discovered that optimal parameters exist in the welding process that may effectively prevent thermal damage while assuring welding strength.

FLIm-Guided Raman Imaging to Study Cross-Linking and Calcification of Bovine Pericardium

Bovine pericardium (BP) is a vascular biomaterial used in cardiovascular surgery that is typically cross-linked for masking antigenicity and enhance stability. There is a need for biochemical evaluation of the tissue properties prior to implantation to ensure that quality and reliability standards are met. Here, engineered antigen removed BP (ARBP) that was cross-linked with 0.2% and 0.6% glutaraldehyde (GA), and further calcified in vitro to simulate graft calcifications upon implantation was characterized nondestructively using fluorescence lifetime imaging (FLIm) to identify regions of interest which were then assessed by Raman spectroscopy. We observed that the tissue fluorescence lifetime shortened, and that Raman bands at 856, 935, 1282, and 1682 cm-1 decreased, and at 1032 and 1627 cm-1 increased with increasing GA cross-linking. Independent classification analysis based on fluorescence lifetime and on Raman spectra discriminated between GA-ARBP and untreated ARBP with an accuracy of 91% and 66%, respectively. Pearson's correlation analysis showed a strong correlation between pyridinium cross-links measured with high-performance liquid chromatography and fluorescence lifetime measured at 380-400 nm (R = -0.76, p = 0.00094), as well as Raman bands at 856 cm-1 for hydroxy-proline (R = -0.68, p = 0.0056) and at 1032 cm-1 for hydroxy-pyridinium (R = 0.74, p = 0.0016). Calcified areas of GA cross-linked tissue showed characteristic hydroxyapatite (959 and 1038 cm-1) bands in the Raman spectrum and fluorescence lifetime shortened by 0.4 ns compared to uncalcified regions. FLIm-guided Raman imaging could rapidly identify degrees of cross-linking and detected calcified regions with high chemical specificity, an ability that can be used to monitor tissue engineering processes for applications in regenerative medicine.

In vivo evaluation of Vivere bovine pericardium valvular bioprosthesis with a new anti-calcifying treatment

The objective of this study was to evaluate the effect of chemical treatment with glutamic acid to avoid calcification of biological cardiac valves. The bovine pericardium (BP) tissues were fixed with 0.5% glutaraldehyde (BP/GA), followed by treatment with glutamic acid (BP/GA + Glu) for neutralization of the free aldehyde groups. Microscopic analysis showed that the wavy structure of collagen fibrils was preserved, but changes in elastin's integrity occurred. However, the treatment did not promote undesirable changes in the thermal and mechanical properties of the modified BPs. These samples were systematically studied in rat subcutaneous tissue: control (BP/GA) and anticalcificant (BP/GA + Glu). After 60 days, both groups induced similar inflammatory reactions. In terms of calcification, BP/GA + Glu remained more stable with a lower index (3.1 ± 0.2 μg Ca²⁺ /mg dry tissue), whereas for BP/GA it was 5.7 ± 1.3 μg Ca²⁺ /mg dry tissue. Bioprostheses made from BP/GA + Glu were implanted in the pulmonary position in sheep, and in vivo echocardiographic analyses revealed maintenance of valvar function after 180 days, with low gradients and minimal valve insufficiency. The explanted tissues of the BP/GA + Glu group had a lower average calcium content 3.8 ± 3.0 μg Ca²⁺ /mg dry tissue. The results indicated high anticalcification efficiency of BP/GA + Glu in both subcutaneous implant in rats and in the experimental sheep model, which is an advantage that should encourage the industrial application of these materials for the manufacture of bioprostheses.

Synchrotron Imaging Assessment of Bone Quality

Bone is a complex hierarchical structure, and its principal function is to resist mechanical forces and fracture. Bone strength depends not only on the quantity of bone tissue but also on the shape and hierarchical structure. The hierarchical levels are interrelated, especially the micro-architecture, collagen and mineral components; hence, analysis of their specific roles in bone strength and stiffness is difficult. Synchrotron imaging technologies including micro-CT and small/wide angle X-ray scattering/diffraction are becoming increasingly popular for studying bone because the images can resolve deformations in the micro-architecture and collagen-mineral matrix under in situ mechanical loading. Synchrotron cannot be directly applied in vivo due to the high radiation dose but will allow researchers to carry out systematic multifaceted studies of bone ex vivo. Identifying characteristics of aging and disease will underpin future efforts to generate novel devices and interventional therapies for assessing and promoting healthy aging. With our own research work as examples, this paper introduces how synchrotron imaging technology can be used with in situ testing in bone research.

Raman spectroscopic evidence of tissue restructuring in heat-induced tissue fusion

Heat-induced tissue fusion via radio-frequency (RF) energy has gained wide acceptance clinically and here we present the first optical-Raman-spectroscopy study on tissue fusion samples in vitro. This study provides direct insights into tissue constituent and structural changes on the molecular level, exposing spectroscopic evidence for the loss of distinct collagen fibre rich tissue layers as well as the denaturing and restructuring of collagen crosslinks post RF fusion. These findings open the door for more advanced optical feedback-control methods and characterization during heat-induced tissue fusion, which will lead to new clinical applications of this promising technology.

Correlation of atomic force microscopy and Raman micro-spectroscopy to study the effects of ex vivo treatment procedures on human red blood cells

The effects of fixation and dehydration on the distribution of heme-based molecules inside red blood cells and the structural integrity of the cells have been investigated using Raman mapping and AFM topographic imaging. A strong correlation was observed between the thickness of the cells as determined from AFM images and the intensity of the characteristic heme bands in the Raman maps, demonstrating that heme compounds are relatively evenly distributed inside dried and fixed cells in the majority of cases. The exception occurred when cells were dried in phosphate buffered saline, where more hemichrome appears close to the periphery of the cell despite the AFM image showing a plateau like topography. Using neat formaldehyde solution as a fixative is inadequate for a complete structural preservation and results in diffusion of hemoglobin into the surrounding area. However, a mixture of formaldehyde (3%) and glutaraldehyde (0.1%) in buffer was found to be sufficient to retain the structural integrity of cells with minimal autofluorescence. This protocol was also suitable for red blood cells infected with Plasmodium falciparum parasites, and preserved the characteristic knob-like structures on the infected red blood cell surface.

In vivo molecular evaluation of guinea pig skin incisions healing after surgical suture and laser tissue welding using Raman spectroscopy

The healing process in guinea pig skin following surgical incisions was evaluated at the molecular level, in vivo, by the use of Raman spectroscopy. After the incisions were closed either by suturing or by laser tissue welding (LTW), differences in the respective Raman spectra were identified. The study determined that the ratio of the Raman peaks of the amide III (1247 cm(-1)) band to a peak at 1326 cm(-1) (the superposition of elastin and keratin bands) can be used to evaluate the progression of wound healing. Conformational changes in the amide I band (1633-1682 cm(-1)) and spectrum changes in the range of 1450-1520 cm(-1) were observed in LTW and sutured skin. The stages of the healing process of the guinea pig skin following LTW and suturing were evaluated by Raman spectroscopy, using histopathology as the gold standard. LTW skin demonstrated better healing than sutured skin, exhibiting minimal hyperkeratosis, minimal collagen deposition, near-normal surface contour, and minimal loss of dermal appendages. A wavelet decomposition-reconstruction baseline correction algorithm was employed to remove the fluorescence wing from the Raman spectra.

Spectrally resolved multiphoton imaging of in vivo and excised mouse skin tissues

The deep tissue penetration and submicron spatial resolution of multiphoton microscopy and the high detection efficiency and nanometer spectral resolution of a spectrograph were utilized to record spectral images of the intrinsic emission of mouse skin tissues. Autofluorescence from both cellular and extracellular structures, second-harmonic signal from collagen, and a narrowband emission related to Raman scattering of collagen were detected. Visualization of the spectral images by wavelength-to-RGB color image conversion allowed us to identify and discriminate tissue structures such as epidermal keratinocytes, lipid-rich corneocytes, intercellular structures, hair follicles, collagen, elastin, and dermal cells. Our results also showed morphological and spectral differences between excised tissue section, thick excised tissue, and in vivo tissue samples of mouse skin. Results on collagen excitation at different wavelengths suggested that the origin of the narrowband emission was collagen Raman peaks. Moreover, the oscillating spectral dependency of the collagen second-harmonic intensity was experimentally studied. Overall, spectral imaging provided a wealth of information not easily obtainable with present conventional multiphoton imaging systems.

Physicochemical Composition of Osteoporotic Bone in the Trichothiodystrophy Premature Aging Mouse Determined by Confocal Raman Microscopy

Although it has been established that premature aging trichothiodystrophy (TTD) mice display typical signs of osteoporosis, exact changes in physicochemical properties of these mice have not been elucidated. We used confocal Raman microscopy and histology to study femora of TTD mice. We measured femora isolated from xeroderma pigmentosum group A (XPA)/TTD double mutant mice to establish that Raman microscopy can be applied to measure differences in bone composition. Raman data from XPA/TTD mice showed remarkable changes in bone mineral composition. Moreover, we observed a severe form of osteoporosis, with strongly reduced cortical bone thickness. We used Raman microscopy to analyze bone composition in eight wild-type and eight TTD animals, and observed decreased levels of phosphate and carbonate in the cortex of femora isolated from TTD mice. In contrast, the bands representing the bone protein matrix were not affected in these mice.