Modifications on Collagen Structures Promoted by 1,4-Dioxane Improve Thermal and Biological Properties of Bovine Pericardium as a Biomaterial

Biomechanics of the fresh and conserved bovine pericardium

The use of biological membranes in surgeries is a reality for years, and one of the most used is the bovine pericardium, so the purpose of this research is to describe the bovine pericardium's biomechanics by comparing two directions of a test, one parallel to the longitudinal heart axis and one perpendicular. 20 adult bovine pericardium were tested for the maximum rupture force and rupture elongation, collecting four samples of each pericardium direction. In phase 2, eight pericardia were conserved for 4 months in a 98% glycerine solution, and the solution in which they were submerged was microbiologically analysed monthly. The Mann-Whitney test was used; there was a very significant difference between the perpendicular and parallel groups (p = .0001). The T test showed no significant difference for the rupture elongation (p = .0938). In pericardium preserved in glycerine, the outliers were removed regarding the maximum rupture force, and a Boxcox transformation was performed (λ = 0.25). Outliers were removed for the rupture elongation, and Bartlett's test (p = .7836), and Cramer-Von Mises (p = .5033) were performed and then, the analysis of variance (p < .0001), followed by the Tukey test at 5%. In the microbiological analysis, there was no presence of microorganisms during conservation. The research has shown that the pericardium collection direction influences its resistance and it can be stored in glycerine for 4 months without losing biomechanical characteristics.

In Vivo Comparative Evaluation of Biocompatibility and Biodegradation of Bovine and Porcine Collagen Membranes

Mechanical barriers prevent the invasion of the surrounding soft tissues within the bone defects. This concept is known as Guided Bone Regeneration (GBR). The knowledge about the local tissue reaction and the time of degradation of absorbable membranes favors the correct clinical indication. This study aimed to evaluate the biocompatibility and biodegradation of a bovine collagen membrane (Lyostypt^®, São Gonçalo, Brazil) and compare it to a porcine collagen membrane (Bio-Gide^®) implanted in the subcutaneous tissue of mice, following ISO 10993-6:2016. Thirty Balb-C mice were randomly divided into three experimental groups, LT (Lyostypt^®), BG (Bio-Gide^®), and Sham (without implantation), and subdivided according to the experimental periods (7, 21, and 63 days). The BG was considered non-irritant at seven days and slight and moderate irritant at 21 and 63 days, respectively. The LT presented a small irritant reaction at seven days, a mild reaction after 21, and a reduction in the inflammatory response at 63 days. The biodegradation of the LT occurred more rapidly compared to the BG after 63 days. This study concluded that both membranes were considered biocompatible since their tissue reactions were compatible with the physiological inflammatory process; however, the Bio-Gide^® was less degraded during the experimental periods, favoring the guided bone regeneration process.

The Role of Stiffness in Cell Reprogramming: A Potential Role for Biomaterials in Inducing Tissue Regeneration

The mechanotransduction is the process by which cells sense mechanical stimuli such as elasticity, viscosity, and nanotopography of extracellular matrix and translate them into biochemical signals. The mechanotransduction regulates several aspects of the cell behavior, including migration, proliferation, and differentiation in a time-dependent manner. Several reports have indicated that cell behavior and fate are not transmitted by a single signal, but rather by an intricate network of many signals operating on different length and timescales that determine cell fate. Since cell biology and biomaterial technology are fundamentals in cell-based regenerative therapies, comprehending the interaction between cells and biomaterials may allow the design of new biomaterials for clinical therapeutic applications in tissue regeneration. In this work, we present the most relevant mechanism by which the biomechanical properties of extracellular matrix (ECM) influence cell reprogramming, with particular attention on the new technologies and materials engineering, in which are taken into account not only the biochemical and biophysical signals patterns but also the factor time.

Investigating lipids as a source of chemical exchange-induced MRI frequency shifts

While magnetic susceptibility is a major contributor to NMR resonance frequency variations in the human brain, a substantial contribution may come from the chemical exchange of protons between water and other molecules. Exchange-induced frequency shifts f_e have been measured in tissue and protein solutions, but relatively lipid-rich white matter (WM) has a larger f_e than gray matter, suggesting that lipids could contribute. Galactocerebrosides (GC) are a prime candidate as they are abundant in WM and susceptible to exchange. To investigate this, f_e was measured in a model of WM lipid membranes in the form of multilamellar vesicles (MLVs), consisting of a 1:2 molar ratio of GC and phospholipids (POPC), and in MLVs with POPC only. Chemical shift imaging with 15% volume fraction of dioxane, an internal reference whose protons are assumed not to undergo chemical exchange, was used to remove susceptibility-induced frequency shifts in an attempt to measure f_e in MLVs at several lipid concentrations. Initial analysis of these measurements indicated a necessity to correct for small unexpected variations in dioxane concentration due to its effect on the water frequency shift. To achieve this, the actual dioxane concentration was inferred from spectral analysis and its additional contribution to f_e was removed through separate experiments which showed that the water-dioxane frequency shift depended linearly on the dioxane concentration at low concentrations with a proportionality constant of -0.021 ± 0.002 ppb/mM in agreement with published experiments. Contrary to expectations and uncorrected results, for GC + POPC vesicles, the dependence of the corrected f_e on GC concentration was insignificant (0.023 ± 0.037 ppb/mM; r²  = 0.085, p > 0.57), whereas for the POPC-only vesicles a small but significant linear increase with POPC concentration was found: 0.044 ± 0.008 ppb/mM (r²  = 0.877, p < 0.01). These findings suggest that the exchange-induced contribution of lipids to frequency contrast in WM may be small. Published 2016. This article is a U.S. Government work and is in the public domain in the USA.

A novel photochemical cross-linking technology to improve luminal gain, vessel compliance, and buckling post-angioplasty in porcine arteries

Development of substituted 1,8-naphthalimides for photochemical cross-linking of biomolecules is the focus of this research. This study describes limited cross-linking of collagen in the artery wall to control recoil and buckling in arteries following balloon angioplasty. Isolated porcine arteries were overstretched (25%) with balloon angioplasty (BA) +/- light-activated naphthalimide treatment (NVS). Lumen size and recoil were measured as retention of stretch after angioplasty. Cross-sectional compliance and distensibility coefficients were measured as slope of cross-sectional area versus increasing hydrostatic pressure. Buckling was measured, with 30% axial pre-stretch and 200 mmHg, as deviation from the center line. Electron microscopy evaluation of collagen fibers was conducted.

RESULTS

Uninjured arteries have low compliance and low levels of buckling, whereas the BA-injured arteries demonstrated much greater compliance and buckling behavior. Treatment of the injured artery with NVS reduced buckling and demonstrated compliance midway between the two groups while retaining the increased luminal diameter imparted by angioplasty compared to untreated vessels. In summary, limited collagen cross-linking with NVS treatment resulted in lumen retention, as well as improved compliance without the accompanying rigidity and stiffness of conventional stent therapy or current cross-linking materials. This treatment shows great promise for dilation, repair and strengthening of arteries damaged by injury or vascular disease.

1,4-Dioxane enhances properties and biocompatibility of polyanionic collagen for tissue engineering applications

Polyanionic collagen obtained from bovine pericardial tissue submitted to alkaline hydrolysis is an acellular matrix with strong potential in tissue engineering. However, increasing the carboxyl content reduces fibril formation and thermal stability compared to the native tissues. In the present work, we propose a chemical protocol based on the association of alkaline hydrolysis with 1,4-dioxane treatment to either attenuate or revert the drastic structural modifications promoted by alkaline treatments. For the characterization of the polyanionic membranes treated with 1,4-dioxane, we found that (1) scanning electron microscopy (SEM) shows a stronger reorientation and aggregation of collagen microfibrils; (2) histological evaluation reveals recovering of the alignment of collagen fibers and reassociation with elastic fibers; (3) differential scanning calorimetry (DSC) shows an increase in thermal stability; and (4) in biocompatibility assays there is a normal attachment, morphology and proliferation associated with high survival of the mouse fibroblast cell line NIH3T3 in reconstituted membranes, which behave as native membranes. Our conclusions reinforce the ability of 1,4-dioxane to enhance the properties of negatively charged polyanionic collagen associated with its potential use as biomaterials for grafting, cationic drug- or cell-delivery systems and for the coating of cardiovascular devices.