Changes In Viscoelastic Properties Research Articles

Influence of Hydroxyapatite Content on Physical and Rheological Properties of Chitosan-based Scaffold

Chitosan-based scaffolds offer significant potential in tissue engineering and regenerative medicine. Whilst exhibiting great bio-regenerative and biocompatible properties, their mechanical properties remain quite poor. The presented research is focused on the modification of macroporous chitosan scaffolds with various amounts of bioactive ceramics (hydroxyapatite) and its influence on the physical and rheological properties of the composite scaffold. Chitosan/hydroxyapatite composite scaffolds with a highly porous microstructure have been prepared by suspending hydroxyapatite (HAp) particles into the chitosan matrix. According to SEM imaging, homogeneous dispersion of the inorganic phase in a chemically-crosslinked chitosan matrix had been achieved. The obtained composite scaffolds exhibited lower swelling capacity with respect to pure chitosan after 24 h of incubation in Hanks’ balanced salt solution. Rheological measurements show an increase in storage and loss modulus indicating an improvement in mechanical properties under shear stress. Furthermore, no significant change in loss factor (tanδ) was observed indicating no change in composite viscoelastic properties with an increase in HAp content.

Structural properties of immune complexes formed by viral antigens and specific antibodies shape the inflammatory response of macrophages

Data on the course of viral infections revealed severe inflammation as a consequence of antiviral immune response. Despite extensive research, there are insufficient data on the role of innate immune cells in promoting inflammation mediated by immune complexes (IC) of viral antigens and their specific antibodies. Recently, we demonstrated that antigens of human polyomaviruses (PyVs) induce an inflammatory response in macrophages. Here, we investigated macrophage activation by IC. We used primary murine macrophages as a cell model, virus-like particles (VLPs) of PyV capsid protein as antigens, and a collection of murine monoclonal antibodies (mAbs) of IgG1, IgG2a, IgG2b subclasses. The inflammatory response was investigated by analysing inflammatory chemokines and activation of NLRP3 inflammasome. We observed a diverse pattern of chemokine secretion in macrophages treated with different IC compared to VLPs alone. To link IC properties with cell activation status, we characterised the IC by advanced optical and acoustic techniques. Ellipsometry provided precise real-time kinetics of mAb-antigen interactions, while quartz crystal microbalance measurements showed changes in conformation and viscoelastic properties during IC formation. These results revealed differences in mAb-antigen interaction and mAb binding parameters of the investigated IC. We found that IC-mediated cell activation depends more on IC characteristics, including mAb affinity, than on mAb affinity for the activating Fc receptor. IC formed by the highest affinity mAb showed a significant enhancement of inflammasome activation. This may explain the hyperinflammation related to viral infection and vaccination. Our findings demonstrate that IC promote the viral antigen-induced inflammatory response depending on antibody properties.

Synthesis and real-time characterization of self-healing, injectable, fast-gelling hydrogels based on alginate multi-reducing end polysaccharides (MREPs)

Polysaccharide-based hydrogels are promising for many biomedical applications including drug delivery, wound healing, and tissue engineering. We illustrate herein self-healing, injectable, fast-gelling hydrogels prepared from multi-reducing end polysaccharides, recently introduced by the Edgar group. Simple condensation of reducing ends from multi-reducing end alginate (M-Alg) with amines from polyethylene imine (PEI) in water affords a dynamic, hydrophilic polysaccharide network. Trace amounts of acetic acid can accelerate the gelation time from hours to seconds. The fast-gelation behavior is driven by rapid Schiff base formation and strong ionic interactions induced by acetic acid. A cantilever rheometer enables real-time monitoring of changes in viscoelastic properties during hydrogel formation. The reversible nature of these crosslinks (imine bonds, ionic interactions) provides a hydrogel with low toxicity in cell studies as well as self-healing and injectable properties. Therefore, the self-healing, injectable, and fast-gelling M-Alg/PEI hydrogel holds substantial promise for biomedical, agricultural, controlled release, and other applications.

Chemorheological Kinetic Modeling of Uncatalyzed Hydroxyl‐Terminated Polybutadiene and Isophorone Diisocyanate

AbstractCatalysts are often employed to enable nonisothermal reaction kinetic studies when tracking cure progression of polyurethane reactions. However, when quickly reacting, catalyzed materials are prepared through mixing followed by the addition of fillers or additives, subsequent processing of the partially reacted material becomes difficult. Here, chemorheology is used to track changes in viscoelastic properties of uncatalyzed polybutadiene‐diisocyanate reactions for multiple days, which quantifies the degree of cure during polymerization. Viscosity profiles are accurately captured by the two‐stage Arrhenius model (r2>0.95), and conversion progress is adequately represented by the Kamal–Sourour model (r2>0.76). Transition state analysis via Wynne–Jones–Eyring–Evans theory (WJEE) reveals the presence of an associative mechanism according to entropic and enthalpic activation energies ΔS# = −96.9 J K−1 and ΔH# = 36.4 kJ, respectively. These rheokinetic modeling results align with Fourier transform infrared spectroscopy findings. To the knowledge, no rheokinetic studies have tracked cure progress of this uncatalyzed system for the extended timeframe presented here. The cure profile also presents unique viscosity growth, representative of molecular weight buildup, compared to catalyzed systems. This finding emphasizes the novelty of applying previously developed chemorheological models to multiday thermosetting reactions within a flow field in a manner that is generalizable to many long‐term curing systems.

Light responsive microstructural transitions in photo-responsive wormlike micelle mediated viscoelastic material based on cationic surfactant and photo-responsive organic acids

Designing smart materials with fine-tunable structures and stimuli-tunable characteristics within a single molecule is a challenging task for the scientific community. This kind of materials circumvent limitations of conventional materials and are applicable in the formation of soft robotics, actuators, tissue engineering, optical devices, molecular switches and biosensors. In our efforts to design photo-responsive materials, herein we have designed photo-responsive wormlike micelle mediated viscoelastic materials (WMMVMs) through the synergistic interactions between the cetyltrimethylammonium bromide (CTAB) with photo-responsive organic acids (P-OA), i.e.,trans-cinnamic acid (t-CA) and p-coumaric acid (p-CA). Upon exposing the WMMVMs to UV light of 270 nm, drastic drop in viscoelasticity was observed because of the conversation of wormlike micelles in to rodlike micelles as the P-OAs are transformed from its trans form to cis form, confirmed through rheology and SANS. Further, the morphology of the system before and after UV irradiation was confirmed through SEM and TEM images. The irreversible photo-responsive character of the P-OA contributed to the irreversible photo-responsive behavior of the investigated systems. These systems bear good rheological behavior; specifically, Maxwell behavior. Additionally, these viscoelastic materials are also having excellent stretchability (20 times than its original length), self-healing (2 min) ability and higher thermal stability (>262 0C). WMMVMs also exhibited pH (below pKa) and temperature induced (CTAB/t-CA and CTAB/p-CA at 42 °C and 40 °C, respectively) reversible change in viscoelastic properties. We believe that the studied WMMVMs can serve as a useful model in understanding the process of photo-responsiveness and in various applications.

The effect of cyclic stretch on aortic viscoelasticity and the putative role of smooth muscle focal adhesion.

Due to its viscoelastic properties, the aorta aids in dampening blood pressure pulsatility. At the level of resistance-arteries, the pulsatile flow will be transformed into a continuous flow to allow for optimal perfusion of end organs such as the kidneys and the brain. In this study, we investigated the ex vivo viscoelastic properties of different regions of the aorta of healthy C57Bl6/J adult mice as well as the interplay between (altered) cyclic stretch and viscoelasticity. We demonstrated that the viscoelastic parameters increase along the distal aorta and that the effect of altered cyclic stretch is region dependent. Increased cyclic stretch, either by increased pulse pressure or pulse frequency, resulted in decreased aortic viscoelasticity. Furthermore, we identified that the vascular smooth muscle cell (VSMC) is an important modulator of viscoelasticity, as we have shown that VSMC contraction increases viscoelastic parameters by, in part, increasing elastin fiber tortuosity. Interestingly, an acute increase in stretch amplitude reverted the changes in viscoelastic properties induced by VSMC contraction, such as a decreasing contraction-induced elastin fiber tortuosity. Finally, the effects of altered cyclic stretch and VSMC contraction on viscoelasticity were more pronounced in the abdominal infrarenal aorta, compared to both the thoracic ascending and descending aorta, and were attributed to the activity and stability of VSMC focal adhesion. Our results indicate that cyclic stretch is a modulator of aortic viscoelasticity, acting on VSMC focal adhesion. Conditions of (acute) changes in cyclic stretch amplitude and/or frequency, such as physical exercise or hypertension, can alter the viscoelastic properties of the aorta.

Fatigue Behaviour of Additively Manufactured Short Fibre Reinforced Polyamide

Additive manufacturing of Short Fibre Reinforced Polymers (SFRPs) combines good mechanical properties with high design flexibility. In this work, fatigue tests were performed on SFRP specimens with 0°/90° and ±45° raster orientations. Thermal and mechanical fatigue regimes were both observed. In thermal fatigue, self-heating, softening and changes in viscoelastic properties occurred. In mechanical fatigue, the material progressively stiffened, and dissipative effects due to viscoelasticity were reduced. Such a behaviour is unusual for composites, but mainly seen in neat polymers. These results suggest the fatigue behaviour of this material to be dominated by the polyamide matrix.

Using uniaxial tensile testing to evaluate the biomechanical properties of bladder tissue after spinal cord injury in rat model

To investigate the biomechanical properties of rat bladder tissue after spinal cord injury (SCI) using uniaxial tensile testing.Evidence suggests the bladder wall undergoes remodeling following SCI. There is limited data describing the biomechanical properties of bladder wall after SCI. This study describes the changes in elastic and viscoelastic mechanical properties of bladder tissue using a rat model after SCI.Seventeen adult rats received mid-thoracic SCI. Basso, Beattie, and Bresnahan (BBB) locomotor testing was performed on the rats 7–14 days after injury quantifying the degree of SCI. Bladder tissue samples were collected from controls and spinal injured rats at 2- and 9-weeks post-injury. Tissue samples underwent uniaxial stress relaxation to determine instantaneous and relaxation modulus as well as monotonic load-to failure to determine Young’s modulus, yield stress and strain, and ultimate stress.SCI resulted in abnormal BBB locomotor scores. Nine weeks post-injury, instantaneous modulus decreased by 71.0% (p = 0.03) compared to controls. Yield strain showed no difference at 2 weeks post-injury but increased 78% (p = 0.003) in SCI rats at 9 weeks post-injury. Compared to controls, ultimate stress decreased 46.5% (p = 0.05) at 2 weeks post-injury in SCI rats but demonstrated no difference at 9 weeks post-injury.The biomechanical properties of rat bladder wall 2 weeks after SCI showed minimal difference compared to controls. By week 9, SCI bladders had a reduction in instantaneous modulus and increased yield strain. The findings indicate biomechanical differences can be identified between control and experimental groups at 2- and 9-week intervals using uniaxial testing.

How to predict residual stresses of curing adhesives ab initio solely using extended rheometry

ABSTRACT Prediction of residual stresses in adhesively bonded joints is a major topic among practitioners, as they significantly contribute to failure. The experimental determination of relevant material properties, like shrinkage, modulus development, and relaxation behavior, is considered highly complex. Viscoelastic and numerical models are often simplified to suit specific applications. However, most of them do not consider all relevant parameters or limited portions of the curing process. This publication addresses the lack of experimental methods to determine cure-dependent properties of reactive adhesives to use them as input for FE modelling to predict cure-induced stresses. The authors focus on extended rotational rheometry (ExRheo), to determine shrinkage, shear modulus, and relaxation in dependency of curing time for three adhesives. The relationship between change of viscoelastic properties, shrinkage, and curing degree is determined through DSC and kinetic modelling. The experimental results are modelled to be implemented in a numerical analysis in order to predict cure-induced stresses in constrained rheological experiment in ExRheo. Numerical results show very good agreement with the experiments, which validate the methodology. For the first time, shrinkage induced residual stresses are modelled ab initio over the curing process, without any assumptions, solely based upon direct experimental data using a single device.

Analysis of the Interaction between DNA Aptamers and Cytochrome C on the Surface of Lipid Films and on the MUA Monolayer: A QCM-D Study.

We analyzed the possibility of the detection of cytochrome c (cyt c) being physically adsorbed on lipid films or covalently bounded to 11-mercapto-1-undecanoic acid (MUA) chemisorbed on the gold layer using quartz crystal microbalance with dissipation monitoring (QCM-D). The negatively charged lipid film composed of a mixture of zwitterionic DMPC and negatively charged DMPG phospholipids at a molar ratio of 1:1 allowed the formation of a stable cyt c layer. Addition of DNA aptamers specific to cyt c, however, resulted in removal of cyt c from the surface. The interaction of cyt c with the lipid film and its removal by DNA aptamers were accompanied by changes in viscoelastic properties evaluated using the Kelvin-Voigt model. Cyt c covalently bound to MUA also provided a stable protein layer already at its relatively low concentrations (0.5 μM). A decrease in the resonant frequency following the addition of gold nanowires (AuNWs) modified by DNA aptamers was observed. The interaction of aptamers with cyt c on the surface can be a combination of specific and non-specific interactions due to electrostatic forces between negatively charged DNA aptamers and positively charged cyt c.

Surface modification of carbonyl iron particles using dopamine and silane coupling agent for high-performance magnetorheological elastomers

Magnetorheological elastomers (MREs) are smart materials whose mechanical properties can quickly respond to changes in the external magnetic field. This phenomenon is known as the magnetorheological (MR) effect and is the key to the application of magnetorheological elastomers. Previous studies have found that the interface between magnetic particles and elastomers is a critical factor that influencing the MR effect of MREs. To improve the interfacial interaction between silicone rubber (SR) and carbonyl iron (CI) particles, in the MREs considered in this work, CI particles were subjected to surface modification through polydopamine (PDA) deposition and n-dodecyltrimethoxysilane (DTMS) grafting. X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM) and transmission electron microscopy (TEM) confirmed the successful deposition of PDA@DTMS coating layer with a thickness of about 30.6 nm. The tensile strength of anisotropic MREs increased by 31.5% after surface modification of CI particles. The study of magnetic field induced changes in viscoelastic properties showed that CI-PDA@DTMS based MREs exhibited a superior MR effect to the CI-based MREs.

High intensity focused ultrasound atomization and erosion in healthy and tendinopathic tendons

Objective. High-intensity focused ultrasound (HIFU) can induce thermal and mechanical mechanisms in a well-defined focal volume of tissues. Histotripsy is a form of mechanical HIFU that can initiate and interact with bubble(s) to cause shock scattering and perhaps atomization within the bubble(s) to fractionate most soft tissues. Ultrasonic atomization, or the ejection of fine droplets from an acoustically-excited liquid exposed to air, has been shown to erode planar soft tissue surfaces, which has led to theories that atomization is a mechanism in histotripsy. However, healthy tendons show resistance to conventional histotripsy; pre-treatment of tendons with heat increases susceptibility to histotripsy fractionation. This study investigates ultrasonic atomization and erosion from planar healthy and tendinopathic tendon surfaces as we evaluate HIFU parameters for histotripsy in tendons. Approach. Forty-six ex vivo bovine tendon-air interfaces were pre-conditioned to surface wetting, heat baths of 20 °C (unaltered), 37 °C (body temperature), and 58 °C (collagen degradation), collagenase soaks for 1, 3, 5, and 24 h (mimicking tendinopathic tendons), and phosphate buffered saline soaks for 24 h. Ejected fragments, histology, and gross analysis determined erosion success. Tissue displacement from the HIFU radiation force was monitored with high-speed photography, and tissue relaxation was pixel-tracked and fit to a Kelvin–Voigt model to evaluate changes in viscoelastic properties. Main results. Results showed that atomization produced holes in 24 h collagenase tendons and surface pitting in 58 °C, 3 h, and 5 h collagenase tendons. Increased mound heights and viscoelastic constants in pre-heated (to 58 °C) and collagenase-soaking (3+ hours) tendinopathic models caused a decrease in elasticity and/or increase in viscosity, increasing susceptibility to erosion by HIFU atomization. Significance. Therefore, tendons with chronic tendinopathies may be more susceptible than healthy tendons to histotripsy fractionation.

Protein-protein interactions explain the temperature-dependent viscoelastic changes occurring in colloidal protein gels.

Denaturation of protein solutions can be induced by higher temperatures and the presence of non-polar organic solutions. The denatured proteins form aggregates and gels through protein interactions occurring between their amino acid side chains. Depending on the involved side chains, the denaturation conditions lead to different gel properties. As model systems, a variety of food proteins were gelled through different mechanisms to cover a whole range of protein-protein interactions. Especially the temperature dependence of the viscoelastic properties in a simple rheometer method was found to be very different. These differences could be explained by the different thermodynamic properties of the involved protein-protein interactions. Electrostatic interactions were shown to weaken the resulting gel upon temperature increase whereas entropically driven interactions such as hydrophobic or covalent links were strengthened with increased temperatures. A proposed model explaining these results can be used to assess protein interactions in hydrogels in a non-invasive way and could also have applications to describe the temperature behavior of other hydrogels.

Additively manufactured thermosetting elastomer composites: small changes in resin formulation lead to large changes in mechanical and viscoelastic properties

Better resin wettability increases strength and stiffness in high solids loading composites that can be additively manufactured with high resolution.

EVALUATION OF THE EFFECT OF BOBATH THERAPY ON SPASTICITY IN CHILDREN WITH CEREBRAL PALSY USING SUBJECTIVE AND OBJECTIVE METHODS

The positive effects of Bobath therapy on spasticity are known, but studies using objective data tools that can evaluate these positive effects are limited. The purpose of this study is to examine the changes in lower extremity muscle tone and viscoelastic properties of children with spastic cerebral palsy who received Bobath therapy. Thirty-three children with CP, aged between 5 and 15 (18 girls, 15 boys) years were included in the study. Based on the evaluation parameters, initial evaluations were conducted using the Modified Ashworth Scale and Myoton®PRO Digital Palpation Device, and all children continued to receive neurodevelopmental therapy (NGT) twice a week for six weeks following the initial evaluation. Muscle tone was measured with Modified Ashworth Scale, and muscle tone, stiffness, and elasticity levels were measured with Myoton®PRO Digital Palpation Device. According to the results of this study, it has been determined that the sensitivity of the MyotonPRO digital palpation device is higher and more reliable than MAS in evaluating spasticity in patients with cerebral palsy. Therefore, it is recommended to use MyotonPRO digital palpation device, which is more objective and reliable in evaluating spasticity in children with cerebral palsy in future studies.

Gelation profile of laccase-crosslinked Bambara groundnut (Vigna subterranea) protein isolate

Enzymatic crosslinking has gained attention in improving plant protein heat-induced gels, which are composed of weak network structures. The aim of the study was to investigate the effect of laccase crosslinking on the rheological and microstructural properties of heat-induced Bambara groundnut protein gels. The rheological properties of laccase-modified Bambara groundnut protein isolate (BPI11BPI- Bambara groundnut protein isolate.) gel formed in situ were investigated. Changes in viscoelastic properties were monitored during heating and cooling ramps and gel structure fingerprints were analyzed by frequency sweep. Laccase addition induced an initial protein structure breakdown (G″>G′) at an enzyme dose-dependent (1–3 U/g) before gel formation and stabilization. Gel point temperatures were significantly decreased from 85°C to 29°C (∼3 folds) with increasing laccase activity (0 to 3 U/g protein, respectively). For laccase crosslinked gels, G′ was substantially greater than G” (>1 log) with no dependency on angular frequency, which suggests the formation of relatively well-structured gels. The highest gel strength (tan δ of 0.09, G* of 555.51 kPa & An of 468.04 kPa) was recorded at a laccase activity of 2 U/g protein and the gels formed at this activity appeared homogeneous with compact lath sheet-like structure. The crosslinking effects of laccase were corroborated by the decrease in thiol and phenolic contents as well as the crosslinking of amino acids in model reactions. Overall, the use of laccase improved gel properties and significantly altered the gelation profile of BPI. Laccase-modified Bambara groundnut protein gels have potential to be used in food texture improvement and development of new food products. For instance, they can be used in plant-based milk products such as yoghurt and cheese.

Dry immersion induced acute low back pain and its relationship with trunk myofascial viscoelastic changes.

Microgravity induces spinal elongation and Low Back Pain (LBP) but the pathophysiology is unknown. Changes in paraspinal muscle viscoelastic properties may play a role. Dry Immersion (DI) is a ground-based microgravity analogue that induces changes in m. erector spinae superficial myofascial tissue tone within 2 h. This study sought to determine whether bilateral m. erector spinae tone, creep, and stiffness persist beyond 2 h; and if such changes correlate with DI-induced spinal elongation and/or LBP.Ten healthy males lay in the DI bath at the Institute of Biomedical Problems (Moscow, Russia) for 6 h. Bilateral lumbar (L1, L4) and thoracic (T11, T9) trunk myofascial tone, stiffness and creep (MyotonPRO), and subjective LBP (0-10 NRS) were recorded before DI, after 1h, 6 h of DI, and 30min post. The non-standing spinal length was evaluated on the bath lifting platform using a bespoke stadiometer before and following DI.DI significantly modulated m. erector spinae viscoelastic properties at L4, L1, T11, and T9 with no effect of laterality. Bilateral tissue tone was significantly reduced after 1 and 6 h DI at L4, L1, T11, and T9 to a similar extent. Stiffness was also reduced by DI at 1 h but partially recovered at 6 h for L4, L1, and T11. Creep was increased by DI at 1 h, with partial recovery at 6 h, although only T11 was significant. All properties returned to baseline 30 min following DI. Significant spinal elongation (1.17 ± 0.20 cm) with mild (at 1 h) to moderate (at 6 h) LBP was induced, mainly in the upper lumbar and lower thoracic regions. Spinal length increases positively correlated (Rho = 0.847, p = 0.024) with middle thoracic (T9) tone reduction, but with no other stiffness or creep changes. Spinal length positively correlated (Rho = 0.557, p = 0.039) with Max LBP; LBP failed to correlate with any m. erector spinae measured parameters.The DI-induced bilateral m. erector spinae tone, creep, and stiffness changes persist beyond 2 h. Evidence of spinal elongation and LBP allows suggesting that the trunk myofascial tissue changes could play a role in LBP pathogenesis observed in real and simulated microgravity. Further study is warranted with longer duration DI, assessment of IVD geometry, and vertebral column stability.

Changes and relationships of viscoelastic and physical properties of Chinese yam during a novel multiphase microwave drying process

Changes in viscoelastic properties and physical qualities including rehydration ratio (RR), volume ratio (Vr), porosity and texture of Chinese yams during multiphase microwave drying (MMD) were studied and the intrinsic relationship between them was analyzed. Results showed that RR, Vr and porosity rose and then fell with drying time during MMD, with the endpoint of sublimation drying being the turning point. Scheme III with the highest microwave power (0.2 W/g) in sublimation drying resulted in the lowest RR, Vr and porosity but the highest hardness. The Maxwell model was well fitted to describe the viscoelastic behaviors of yams (R2 > 0.99). Enhanced stress relaxation behavior during sublimation drying was observed. In contrast, a decrease in stress decay but an increase in residual elasticity were found when MMD switched from sublimation drying to evaporation drying. Pearson's correlation analysis showed that relaxation modulus was significantly negatively correlated with RR (r = −0.981, p < 0.01) and porosity (r = −0.961), while positively correlated with hardness (r = 0.94, p < 0.05) and the brittleness (r = 0.96, p < 0.01). Principal component regression models between the viscoelastic indexes and physical features with high R2 (>0.9) values could explain their relationships well. These findings have implications for the production of high-quality products through controlling drying processes.

Viscoelastic properties of suspended cells measured with shear flow deformation cytometry.

Numerous cell functions are accompanied by phenotypic changes in viscoelastic properties, and measuring them can help elucidate higher level cellular functions in health and disease. We present a high-throughput, simple and low-cost microfluidic method for quantitatively measuring the elastic (storage) and viscous (loss) modulus of individual cells. Cells are suspended in a high-viscosity fluid and are pumped with high pressure through a 5.8 cm long and 200 µm wide microfluidic channel. The fluid shear stress induces large, ear ellipsoidal cell deformations. In addition, the flow profile in the channel causes the cells to rotate in a tank-treading manner. From the cell deformation and tank treading frequency, we extract the frequency-dependent viscoelastic cell properties based on a theoretical framework developed by R. Roscoe [1] that describes the deformation of a viscoelastic sphere in a viscous fluid under steady laminar flow. We confirm the accuracy of the method using atomic force microscopy-calibrated polyacrylamide beads and cells. Our measurements demonstrate that suspended cells exhibit power-law, soft glassy rheological behavior that is cell-cycle-dependent and mediated by the physical interplay between the actin filament and intermediate filament networks.

A Photochemical Crosslinking Approach to Enhance Resistance to Mechanical Wear and Biochemical Degradation of Articular Cartilage

ObjectiveThe objective of this study was to evaluate photochemical crosslinking using Al(III) phthalocyanine chloride tetrasulfonic acid (CASPc) and light with a wavelength of 670 nm as a potential therapy to strengthen articular cartilage and prevent tissue degradation.DesignChanges in viscoelastic properties with indentation were used to identify 2 crosslinking protocols for further testing. Crosslinked cartilage was subjected to an in vitro, accelerated wear test. The ability of the crosslinked tissue to resist biochemical degradation via collagenase was also measured. To better understand how photochemical crosslinking with CASPc varies through the depth of the tissue, the distribution of photo-initiator and penetration of light through the tissue depth was characterized. Finally, the effect of CASPc on chondrocyte viability and of co-treatment with an antioxidant was evaluated.ResultsThe equilibrium modulus was the most sensitive viscoelastic measure of crosslinking. Crosslinking decreased both mechanical wear and collagenase digestion compared with control cartilage. These beneficial effects were realized despite the fact that crosslinking appeared to be localized to a region near the articular surface. In addition, chondrocyte viability was maintained in crosslinked tissue treated with antioxidants.ConclusionThese results suggest that photochemical crosslinking with CASPc and 670 nm light holds promise as a potential therapy to prevent cartilage degeneration by protecting cartilage from mechanical wear and biochemical degradation. Limitations were also evident, however, as an antioxidant treatment was necessary to maintain chondrocyte viability in crosslinked tissue.