Comparison of water, hydroxyproline, uronic acid and elastin contents of bovine knee ligaments and patellar tendon and their relationships with biomechanical properties

Physicochemical and Functional Properties of Yanbian Cattle Bone Gelatin Extracted Using Acid, Alkaline, and Enzymatic Hydrolysis Methods

Yanbian cattle, a high-quality indigenous breed in China, were selected due to their unique biological characteristics, underutilized bone byproducts, and potential as a halal-compliant gelatin source, addressing the growing demand for alternatives to conventional mammalian gelatin in Muslim-majority regions. This study investigates the physicochemical and functional properties of gelatin extracted from Yanbian cattle bones using three different methods: acid, alkaline, and papain enzymatic hydrolysis. The extraction yields and quality of gelatin were evaluated based on hydroxyproline content, gel strength, viscosity, amino acid composition, molecular weight distribution, and structural integrity. Specifically, A gelatin, prepared using 0.075 mol/L hydrochloric acid, achieved the highest yield (18.64%) among the acid-extraction methods. B gelatin, extracted with 0.1 mol/L sodium hydroxide, achieved the highest yield (21.06%) among the alkaline-extraction methods. E gelatin, obtained through papain hydrolysis, exhibited the highest yield (25.25%) among the enzymatic methods. Gelatin extracted via papain enzymatic hydrolysis not only retained better protein structure but also exhibited higher hydroxyproline content (19.13 g/100 g), gel strength (259 g), viscosity (521.67 cP), and superior thermal stability. Structural analyses conducted using SDS-PAGE, GPC, FTIR, XRD, and CD spectroscopy confirmed that papain extraction more effectively preserved the natural structure of collagen. Furthermore, amino acid composition analysis revealed that gelatin extracted via papain hydrolysis contained higher levels of essential residues, such as glycine, proline, and hydroxyproline, emphasizing the mild and efficient nature of enzymatic treatment. These findings suggest that, compared with acid and alkaline extraction methods, enzymatic hydrolysis has potential advantages in gelatin production. Yanbian cattle bone gelatin shows promise as an alternative source for halal gelatin production. This study also provides insights into optimizing gelatin production to enhance its functionality and sustainability.

The human patellar tendon is mechanically homogenous at its mid-substance

The human patellar tendon contains distinct fascicle bundles across its mediolateral and anteroposterior regions. Studies have suggested region-specific behaviour during in vivo actions, but it is unclear whether such regional differences result from localized variation in composition and mechanical properties within the tendon itself. Furthermore, the viscoelastic properties of any region of the human patellar tendon have not been well described previously. Here, a comprehensive investigation of the composition and material properties of six regions (three mediolateral × two anteroposterior) of the human patellar tendon was performed on tendons harvested from eight cadaver knees. Thorough viscoelastic (stress relaxation and sinusoidal) and elastic (failure) mechanical tests were conducted on dumbbell-shaped samples. Uronic acid (proteoglycan), hydroxyproline (collagen), and water contents were measured from the samples after mechanical testing. No systematic between-region differences were found for any measured biomechanical or biochemical parameter. However, the phase difference between stress and strain decreased as a function of increasing sinusoidal frequency (from 0.1 Hz to 5 Hz), suggesting the human patellar tendon behaves more elastically at higher strain rates. These results indicate the human patellar tendon is a homogenous material at its mid-substance and that other factors, such as geometrical constraints, enthesis properties, and insertion points, may be responsible for any region-specific behaviour in vivo. Additionally, the more elastic behaviour of the human patellar tendon as strain rate increases likely supports improved joint control and enhanced movement economy during fast actions such as sprinting.

Multiscale correlations between joint and tissue-specific biomechanics and anatomy in postmortem ovine stifles

Joint stability depends on various properties that include the bone anatomy, joint capsule geometry and stiffness, and soft tissues within. The multiscale biomechanical relationships between the whole joint and individual tissues are useful in estimating the physiological condition of the knee. To better understand these relationships, we evaluated multiple structural and mechanical parameters in healthy ovine stifles, specifically joint laxity, joint morphology, individual tissue T2* relaxation and mechanical properties of ligaments (ACL, PCL, MCL, LCL), patellar tendon, menisci, and cartilage. By combining mechanical testing at two length scales and magnetic resonance imaging (MRI) scans, we quantify the strength of correlation coefficients between measured metrics, among joint size, whole joint and individual tissue properties. We observe positive correlations between joint laxity forces and the inter-epicondylar distance. Further, the viscoelastic properties of the tendons and ligaments correlate positively with joint laxity forces; however, no such correlations were observed for the cartilage and menisci. We also found weak inverse correlation between tissue viscoelasticity and T2* for MCL; and positive correlations for cartilage and menisci, LCL and PCL respectively. These results provide useful insights into the role of individual tissues that are crucial in measuring whole joint responses as key indicators of knee health.

Are Collagen Protons Visible with the Zero Echo Time (ZTE) Magnetic Resonance Imaging Sequence: A D2O Exchange and Freeze-Drying Study

It is known that ultrashort echo time (UTE) magnetic resonance imaging (MRI) sequences can detect signals from water protons but not collagen protons in short T2 species such as cortical bone and tendons. However, whether collagen protons are visible with the zero echo time (ZTE) MRI sequence is still unclear. In this study, we investigated the potential of the ZTE MRI sequence on a clinical 3T scanner to directly image collagen protons via D2O exchange and freeze-drying experiments. ZTE and UTE MRI sequences were employed to image fully hydrated bovine cortical bone (n = 10) and human patellar tendon (n = 1) specimens. Then, each specimen was kept in a 30 mL syringe filled with D2O solution for two days. Fresh D2O was flushed every 2 h to reach a more complete D2O-H2O exchange. Later, the samples were lyophilized for over 40 h and then sealed in tubes. Finally, the samples were brought to room temperature and visualized using the identical 3D ZTE and UTE sequences. All hydrated bone and tendon specimens showed high signals with ZTE and UTE sequences. However, all specimens showed zero signal after the D2O exchange and freeze-drying procedures. Therefore, similar to UTE imaging, the signal source in ZTE imaging is water. The ZTE sequence cannot directly detect signals from collagen protons in bone and tendons.

Process Optimization and Characterization of Polysaccharides with Potential Antioxidant and Hypoglycemic Activity from Cissus repens

Ultrasound-assisted extraction of Cissus repens polysaccharides (CRPs) was optimized through response surface methodology (RSM) based on Box-Behnken design (BBD). The maximum CRPs yield (16.18 %) was achieved under the optimum extraction conditions: extraction time 72 min, extraction temperature 74 °C, extraction power 240 W. Then three-phase partitioning (TPP) method combined with gradient alcohol precipitation was used to obtained CRP20, CRP40, CRP60 and CRP80 from CRPs, and CRP80 has a higher purity than others. The primary chemical and structural characteristics of CRP80 were investigated by UV, FT-IR, high-performance liquid chromatography (HPLC) and high-performance gel-permeation chromatography (HPGPC). CRP80 is mainly composed of glucose, galactose, arabinose and mannose, with a molecular weights of approximately 2.95 kDa. Furthermore, the antioxidant activity and hypoglyceamic activity of CRP80 in vitro were evaluated. The results showed that CRP80 had strong scavenging activities on ABTS, hydroxyl and DPPH radicals, as well as high scavenging activities on α-glucosidase and α-amylase. Our research provided an efficient method for the extraction of polysaccharides from C. repens and CRP80 has potential as a promising source of natural antioxidants and hypoglycemic agent for the functional food and medicinal industries.

Three-year follow-up of the grip concept: an open, prospective, observational registry study on biomechanically calculated abdominal wall repair for complex incisional hernias

PURPOSE

We studied the effectiveness of biomechanically calculated abdominal wall reconstructions for incisional hernias of varying complexity in an open, prospective observational registry trial.

METHODS

From July 1st, 2017 to December 31st, 2020, four hospitals affiliated with the University of Heidelberg recruited 198 patients with complex incisional hernias. Hernias were repaired using biomechanically calculated reconstructions and materials classified on their gripping force towards cyclic load. This approach determines the required strength preoperatively based on the hernia size, using the Critical Resistance to Impacts related to Pressure. The surgeon is supported in reliably determining the Gained Resistance, which is based on the mesh-defect-area-ratio, as well as other mesh and suture factors, and the tissue stability. Tissue stability is defined as a maximum distension of 1.5 cm upon a Valsalva maneuver. In complex cases, a CT scan of the abdomen can be used to assess unstable tissue areas both at rest and during Valsalva's maneuver.

RESULTS

Larger and stronger gripping meshes were required for more complex cases to achieve a durable repair, especially for larger hernia sizes. To achieve durable repairs, the number of fixation points increased while the mesh-defect area ratio decreased. Performing these repairs required more operating room time. The complication rate remained low. Less than 1% of recurrences and low pain levels were observed after 3 years.

CONCLUSIONS

Biomechanical stability, defined as the resistance to cyclic load, is crucial in preventing postoperative complications, including recurrences and chronic pain.

The alteration of the structure and macroscopic mechanical response of porcine patellar tendon by elastase digestion

Background: The treatment of patellar tendon injury has always been an unsolved problem, and mechanical characterization is very important for its repair and reconstruction. Elastin is a contributor to mechanics, but it is not clear how it affects the elasticity, viscoelastic properties, and structure of patellar tendon. Methods: The patellar tendons from six fresh adult experimental pigs were used in this study and they were made into 77 samples. The patellar tendon was specifically degraded by elastase, and the regional mechanical response and structural changes were investigated by: (1) Based on the previous study of elastase treatment conditions, the biochemical quantification of collagen, glycosaminoglycan and total protein was carried out; (2) The patellar tendon was divided into the proximal, central, and distal regions, and then the axial tensile test and stress relaxation test were performed before and after phosphate-buffered saline (PBS) or elastase treatment; (3) The dynamic constitutive model was established by the obtained mechanical data; (4) The structural relationship between elastin and collagen fibers was analyzed by two-photon microscopy and histology. Results: There was no statistical difference in mechanics between patellar tendon regions. Compared with those before elastase treatment, the low tensile modulus decreased by 75%-80%, the high tensile modulus decreased by 38%-47%, and the transition strain was prolonged after treatment. For viscoelastic behavior, the stress relaxation increased, the initial slope increased by 55%, the saturation slope increased by 44%, and the transition time increased by 25% after enzyme treatment. Elastin degradation made the collagen fibers of patellar tendon become disordered and looser, and the fiber wavelength increased significantly. Conclusion: The results of this study show that elastin plays an important role in the mechanical properties and fiber structure stability of patellar tendon, which supplements the structure-function relationship information of patellar tendon. The established constitutive model is of great significance to the prediction, repair and replacement of patellar tendon injury. In addition, human patellar tendon has a higher elastin content, so the results of this study can provide supporting information on the natural properties of tendon elastin degradation and guide the development of artificial patellar tendon biomaterials.

Proteoglycans in Mechanobiology of Tissues and Organs: Normal Functions and Mechanopathology

Proteoglycans (PGs) are a diverse class of glycoconjugates that serve critical functions in normal mechanobiology and mechanopathology. Both the protein cores and attached glycosaminoglycan (GAG) chains function in mechanically-sensitive processes, and loss of either can contribute to development of pathological conditions. PGs function as key components of the extracellular matrix (ECM) where they can serve as mechanosensors in mechanosensitive tissues including bone, cartilage, tendon, blood vessels and soft organs. The mechanical properties of these tissues depend on the presence and function of PGs, which play important roles in tissue elasticity, osmolarity and pressure sensing, and response to physical activity. Tissue responses depend on cell surface mechanoreceptors that include integrins, CD44, voltage sensitive ion channels, transient receptor potential (TRP) and piezo channels. PGs contribute to cell and molecular interplay in wound healing, fibrosis, and cancer, where they transduce the mechanical properties of the ECM and influence the progression of various context-specific conditions and diseases. The PGs that are most important in mechanobiology vary depending on the tissue and its functions and functional needs. Perlecan, for example, is important in the mechanobiology of basement membranes, cardiac and skeletal muscle, while aggrecan plays a primary role in the mechanical properties of cartilage and joints. A variety of techniques have been used to study the mechanobiology of PGs, including atomic force microscopy, mouse knockout models, and in vitro cell culture experiments with 3D organoid models. These studies have helped to elucidate the tissue-specific roles that PGs play in cell-level mechanosensing and tissue mechanics. Overall, the study of PGs in mechanobiology is yielding fundamental new concepts in the molecular basis of mechanosensing that can open the door to the development of new treatments for a host of conditions related to mechanopathology.

Adaptation of Fibril-Reinforced Poroviscoelastic Properties in Rabbit Collateral Ligaments 8 Weeks After Anterior Cruciate Ligament Transection

Ligaments of the knee provide stability and prevent excessive motions of the joint. Rupture of the anterior cruciate ligament (ACL), a common sports injury, results in an altered loading environment for other tissues in the joint, likely leading to their mechanical adaptation. In the collateral ligaments, the patterns and mechanisms of biomechanical adaptation following ACL transection (ACLT) remain unknown. We aimed to characterize the adaptation of elastic and viscoelastic properties of the lateral and medial collateral ligaments eight weeks after ACLT. Unilateral ACLT was performed in six rabbits, and collateral ligaments were harvested from transected and contralateral knee joints after eight weeks, and from an intact control group (eight knees from four animals). The cross-sectional areas were measured with micro-computed tomography. Stepwise tensile stress-relaxation testing was conducted up to 6% final strain, and the elastic and viscoelastic properties were characterized with a fibril-reinforced poroviscoelastic material model. We found that the cross-sectional area of the collateral ligaments in the ACL transected knees increased, the nonlinear elastic collagen network modulus of the LCL decreased, and the amount of fast relaxation in the MCL decreased. Our results indicate that rupture of the ACL leads to an early adaptation of the elastic and viscoelastic properties of the collagen fibrillar network in the collateral ligaments. These adaptations may be important to consider when evaluating whole knee joint mechanics after ACL rupture, and the results aid in understanding the consequences of ACL rupture on other tissues.

Long-term anti-inflammatory effects of injectable celecoxib nanoparticle hydrogels for Achilles tendon regeneration

The treatment of chronic Achilles tendonitis (AT) often requires prolonged therapy and invasive therapeutic methods such as surgery or therapeutic endoscopy. To prevent the progression of chronic AT, excessive inflammation must be alleviated at an early stage. Corticosteroids or nonsteroidal anti-inflammatory drugs are generally prescribed to control inflammation; however, the high doses and long therapeutic periods required may lead to serious side effects. Herein, a local injectable poly(organophosphazene) (PPZ) - celecoxib (CXB) nanoparticle (PCNP) hydrogel system with long-term anti-inflammatory effects was developed for the treatment of tendonitis. The amphiphilic structure and thermosensitive mechanical properties of PPZ means that the hydrophobic CXB can be easily incorporated into the hydrophobic core to form PCNP at 4 °C. Following the injection of PCNP into the AT, PCNP hydrogel formed at body temperature and induced long-term local anti-inflammatory effects via sustained release of the PCNP. The therapeutic effects of the injectable PCNP system can alleviate excessive inflammation during the early stages of tissue damage and boost tissue regeneration. This study suggests that PCNP has significant potential as a long-term anti-inflammatory agent through sustained nonsteroidal anti-inflammatory drugs (NSAIDs) delivery and tissue regeneration boosting. STATEMENT OF SIGNIFICANCE: In the treatment of Achilles tendinitis, a long-term anti-inflammatory effect is needed to alleviate excessive inflammation and induce regeneration of the damaged Achilles tendon. Injectable poly(organophosphazene)(PPZ)-celecoxib(CXB) nanoparticles (PCNP) generated a long-term, localized-anti-inflammatory effect in the injected region, which successfully induced the expression of anti-inflammatory cytokines and suppressed pro-inflammatory cytokines, while the PCNPs degraded completely. Accordingly, regeneration of the damaged Achilles tendon was achieved through the long-term anti-inflammatory effect induced by a single PCNP injection. The PCNP system therefore has great potential in long-term NSAIDs delivery for various tissue engineering applications.

Near infrared spectroscopic evaluation of biochemical and crimp properties of knee joint ligaments and patellar tendon

Knee ligaments and tendons play an important role in stabilizing and controlling the motions of the knee. Injuries to the ligaments can lead to abnormal mechanical loading of the other supporting tissues (e.g., cartilage and meniscus) and even osteoarthritis. While the condition of knee ligaments can be examined during arthroscopic repair procedures, the arthroscopic evaluation suffers from subjectivity and poor repeatability. Near infrared spectroscopy (NIRS) is capable of non-destructively quantifying the composition and structure of collagen-rich connective tissues, such as articular cartilage and meniscus. Despite the similarities, NIRS-based evaluation of ligament composition has not been previously attempted. In this study, ligaments and patellar tendon of ten bovine stifle joints were measured with NIRS, followed by chemical and histological reference analysis. The relationship between the reference properties of the tissue and NIR spectra was investigated using partial least squares regression. NIRS was found to be sensitive towards the water (R2_CV = .65) and collagen (R2_CV = .57) contents, while elastin, proteoglycans, and the internal crimp structure remained undetectable. As collagen largely determines the mechanical response of ligaments, we conclude that NIRS demonstrates potential for quantitative evaluation of knee ligaments.

The dispersion of viscoelastic properties of fascicle bundles within the tendon results from the presence of interfascicular matrix and flow of body fluids

In this work, we investigate differences in the mechanical and structural properties of tendon fascicle bundles dissected from different areas of bovine tendons. The properties of tendon fascicle bundles were investigated by means of uniaxial tests with relaxation periods and hysteresis, dynamic mechanical analysis (DMA), as well as magnetic resonance imaging (MRI). Uniaxial tests with relaxation periods revealed greater elastic modulus, hysteresis, as well as stress drop during the relaxation of samples dissected from the posterior side of the tendon. However, the normalized stress relaxation curves did not show a statistically significant difference in the stress drop between specimens cut from different zones or between different strain levels. Using dynamic mechanical analysis, we found that fascicle bundles dissected from the anterior side of the tendon had lower storage and loss moduli, which could result from altered fluid flow within the interfascicular matrix (IFM). The lower water content, diffusivity, and higher fractional anisotropy of the posterior part of the tendon, as observed using MRI, indicates a different structure of the IFM, which controls the flow of fluids within the tendon. Our results show that the viscoelastic response to dynamic loading is correlated with fluid flow within the IFM, which was confirmed during analysis of the MRI results. In contrast to this, the long-term relaxation of tendon fascicle bundles is controlled by viscoplasticity of the IFM and depends on the spatial distribution of the matrix within the tendon. Comparison of results from tensile tests, DMA, and MRI gives new insight into tendon mechanics and the role of the IFM. These findings may be useful in improving the diagnosis of tendon injury and effectiveness of medical treatments for tendinopathies.

Elastase treatment of tendon specifically impacts the mechanical properties of the interfascicular matrix

The tendon interfascicular matrix (IFM) binds tendon fascicles together. As a result of its low stiffness behaviour under small loads, it enables non-uniform loading and increased overall extensibility of tendon by facilitating fascicle sliding. This function is particularly important in energy storing tendons, with previous studies demonstrating enhanced extensibility, recovery and fatigue resistance in the IFM of energy storing compared to positional tendons. However, the compositional specialisations within the IFM that confer this behaviour remain to be elucidated. It is well established that the IFM is rich in elastin, therefore we sought to test the hypothesis that elastin depletion (following elastase treatment) will significantly impact IFM, but not fascicle, mechanical properties, reducing IFM resilience in all samples, but to a greater extent in younger tendons, which have a higher elastin content. Using a combination of quasi-static and fatigue testing, and optical imaging, we confirmed our hypothesis, demonstrating that elastin depletion resulted in significant decreases in IFM viscoelasticity, fatigue resistance and recoverability compared to untreated samples, with no significant changes to fascicle mechanics. Ageing had little effect on fascicle or IFM response to elastase treatment.

This study offers a first insight into the functional importance of elastin in regional specific tendon mechanics. It highlights the important contribution of elastin to IFM mechanical properties, demonstrating that maintenance of a functional elastin network within the IFM is essential to maintain IFM and thus tendon integrity.

Statement of significance

Developing effective treatments or preventative measures for musculoskeletal tissue injuries necessitates the understanding of healthy tissue function and mechanics. By establishing the contribution of specific proteins to tissue mechanical behaviour, key targets for therapeutics can be identified. Tendon injury is increasingly prevalent and chronically debilitating, with no effective treatments available.

Here, we investigate how elastin modulates tendon mechanical behaviour, using enzymatic digestion combined with local mechanical characterisation, and demonstrate for the first time that removing elastin from tendon affects the mechanical properties of the interfascicular matrix specifically, resulting in decreased recoverability and fatigue resistance. These findings provide a new level of insight into tendon hierarchical mechanics, important for directing development of novel therapeutics for tendon injury.

Structure, composition and fibril-reinforced poroviscoelastic properties of bovine knee ligaments and patellar tendon

Tissue-level stress-relaxation of ligaments and tendons in the toe region is characterized by fast and long-term relaxations and an increase in relaxation magnitude with strain. Characterizing the compositional and structural origins of these phenomena helps in the understanding of mechanisms of ligament and tendon function and adaptation in health and disease. A three-step tensile stress-relaxation test was conducted on dumbbell-shaped pieces of bovine knee ligaments and patellar tendon (PT) (n = 10 knees). Their mechanical behaviour was characterized by a fibril-reinforced poroviscoelastic material model, able to describe characteristic times and magnitudes of fast and long-term relaxations. The crimp angle and length of tissues were measured with polarized light microscopy, while biochemical contents were determined by colorimetric biochemical methods. The long-term relaxation time was longer in the anterior cruciate ligament (ACL) and PT compared with collateral ligaments (p < 0.05). High hydroxyproline content predicted greater magnitude and shorter time of both fast and long-term relaxation. High uronic acid content predicted longer time of long-term relaxation, whereas high crimp angle predicted higher magnitude of long-term relaxation. ACL and PT are better long-term stabilizers than collateral ligaments. The long-term relaxation behaviour is affected or implied by proteoglycans and crimp angle, possibly relating to slow structural reorganization of the tissue.

Comparison of material models for anterior cruciate ligament in tension: from poroelastic to a novel fibril-reinforced nonlinear composite model

Computational models of the knee joint are useful for evaluating stresses and strains within the joint tissues. However, the outcome of those models is sensitive to the material model and material properties chosen for ligaments, the collagen reinforced tissues connecting bone to bone. The purpose of this study was to investigate different compositionally motivated material models and further to develop a model that can accurately reproduce experimentally measured stress-relaxation data of bovine anterior cruciate ligament (ACL). Tensile testing samples were extracted from ACLs of bovine knee joints (N = 10) and subjected to a three-step stress-relaxation test at the toe region. Data from the experiments was averaged and one average finite element model was generated to replicate the experiment. Poroelastic and different fibril-reinforced poro(visco)elastic material models were applied, and their material parameters were optimized to reproduce the experimental force-time response. Material models with only fluid flow mediated relaxation were not able to capture the stress-relaxation behavior (R² = 0.806, 0.803 and 0.938). The inclusion of the viscoelasticity of the fibrillar network improved the model prediction (R² = 0.978 and 0.976), but the complex stress-relaxation behavior was best captured by a poroelastic model with a nonlinear two-relaxation-time strain-recruited viscoelastic fibrillar network (R² = 0.997). The results suggest that in order to replicate the multi-step stress-relaxation behavior of ACL in tension, the fibrillar network formulation should include the complex nonlinear viscoelastic phenomena.