A preliminary technical study on sodium dodecyl sulfate-induced changes of the nano-structural and macro-mechanical properties in human iliotibial tract specimens

Time-dependent effects of ethanol-glycerin embalming on iliotibial band biomechanics

When conducting biomechanical testing or clinical training using embalmed human soft tissues, it is essential to understand their impact on biomechanical properties and their time dependence. Previous studies have investigated this influence, but specific variations over different embalming durations have not been thoroughly addressed to date. Ninety-seven human iliotibial band specimens were obtained from nine donors. All specimens were embalmed in ethanol-glycerin for varying durations: one day, eight days, and fourteen days. Prior to the mechanical trials, the specimens underwent osmotic water adjustment, tapering and standardized clamping. Uniaxial tensile tests were conducted to determine elastic modulus, ultimate tensile strength, and ultimate strain. Surface strain measurements were performed using a digital image correlation system. Ethanol-glycerin embalming of soft tissues significantly affects ultimate strain after one day of submersion time, elastic modulus after eight days, and the ultimate tensile strength after fourteen days. For applications requiring consistent and reliable material properties reflecting a (supra-)vital state, caution is advised against using embalmed tissues even following short submersion durations in ethanol-glycerin.

Is there a duration-characteristic relationship for trypsin exposure on tendon? A study on anterior cruciate ligament reconstruction in a rabbit model

Background

Decellularized allograft tendons are highly regarded for their accessibility and the reduced risk of immune rejection, making them a promising choice for grafting due to their favorable characteristics. However, effectively integrating reconstructed tendons with host bone remains a significant clinical challenge.

Purpose

This study aims to investigate the relationship between the duration of tendon exposure to trypsin and its impact on tendon biomechanical properties and healing capacity.

Methods

Morphological assessments and biochemical quantifications were conducted. Allograft tendons underwent heterotopic transplantation into the anterior cruciate ligament (ACL) in a rabbit model, with specimens harvested 6 weeks post-surgery for a comparative analysis of cell adhesion strength and mechanical performance. Duration-response curves were constructed using maximum stress and cell adhesion quantity as primary indicators.

Results

The trypsin treatment enhanced cell adhesion on the tendon surface. Adhesion rates in the control group vs. the experimental groups were as follows: 3.10 ± 0.56% vs. 4.59 ± 1.51%, 5.36 ± 1.24%, 6.12 ± 1.98%, and 8.27 ± 2.34% (F = 6.755, p = 0.001). However, increasing treatment duration led to a decline in mechanical properties, with the ultimate load (N) in the control vs. experimental groups reported as 103.30 ± 10.51 vs. 99.59 ± 4.37, 93.15 ± 12.38, 90.42 ± 7.87, and 82.68 ± 6.89, F = 4.125 (p = 0.013).

Conclusion

The findings reveal an increasing trend in adhesion effectiveness with prolonged exposure duration, while mechanical strength declines. The selection of the optimal processing duration should involve careful consideration of the benefits derived from both outcomes.

Properties of the iliotibial band and their relationships with gait parameters among patients with knee osteoarthritis

This study aimed to determine the thickness and stiffness of the iliotibial band (ITB) in patients with knee osteoarthritis (KOA) and to identify the gait parameters that are associated with ITB properties. Eighteen female patients with radiographically diagnosed medial KOA and knee pain (age: 69.7 ± 5.9 years, body mass index: 23.0 ± 3.1 kg/m² ) and 22 age-matched female individuals without knee pain (age: 69.1 ± 7.0 years, body mass index: 21.6 ± 3.6 kg/m² ) were included. Shear wave elastography images were obtained at the height of the proximal pole of the patella with the participants in the supine position, and the ITB thickness and shear wave velocity, which is a surrogate measure of stiffness, were calculated. In patients with KOA, the knee and hip joint angles and moments during walking were calculated using a motion analysis system. The shear wave velocity was significantly higher in patients with KOA than in asymptomatic adults (11.3 ± 1.0 vs. 10.0 ± 1.8 m/s, respectively; p = 0.010); however, the thickness did not differ between them (2.1 ± 0.3 vs. 2.0 ± 0.3 mm, respectively; p = 0.705). The time-integral value of the knee adduction moment (β = 0.507, p = 0.032) and maximum value of the hip flexion moment (β = 0.498, p = 0.036) were associated with the shear wave velocity. Meanwhile, no parameters were associated with the thickness. The ITB was stiffer in patients with KOA than in asymptomatic adults; such a stiffer ITB was associated with greater knee adduction and hip flexion moments during walking. Clinical Significance: Greater mechanical loading was associated with a stiffer ITB in patients with KOA.

Surface coating and speckling of the human iliotibial tract does not affect its load-deformation properties

Stochastic surface patterns form an important requirement to facilitate digital image correlation and to subsequently quantify material properties of various tissues when loaded and deformed without artefacts arising from material slippage. Depending on the samples' natural colour, a surface pattern is created by speckling with colour or dye only, or it requires combined surface coating and speckling before to enhance the contrast, to facilitate high-quality data recording for mechanical evaluation. However, it is unclear to date if the colours deployed for coating and speckling do significantly alter the biomechanical properties of soft tissues. The given study investigated the biomechanical properties of 168 human iliotibial tract samples as a model for collagen-rich soft tissues, separated into four groups: untreated, graphite speckling only, water-based coating plus graphite speckling and solvent-based coating plus graphite speckling following a standardized approach of application and data acquisition. The results reveal that elastic modulus, ultimate tensile strength and strain at maximum force of all groups were similar and statistically non-different (p ≥ 0.69). Qualitatively, the speckle patterns revealed increasing contrast differences in the following order: untreated, graphite speckling only, water-based coating plus graphite speckling and solvent-based coating plus graphite speckling. Conclusively, both coating by water- and solvent-based paints, as well as exclusive graphite speckling, did not significantly influence the load-deformation parameters of the here used human iliotibial tract as a model for collagen-rich soft tissues. In consequence, water- and solvent-based coating paints seem equally suitable to coat collagen-rich soft tissues for digital image correlation, resulting in suitable speckle patterns and unbiased data acquisition.

What is Considered a Variation of Biomechanical Parameters in Tensile Tests of Collagen-Rich Human Soft Tissues? - Critical Considerations Using the Human Cranial Dura Mater as a Representative Morpho-Mechanic Model

Background and Objectives: Profound knowledge on the load-dependent behavior of human soft tissues is required for the development of suitable replacements as well as for realistic computer simulations. Regarding the former, e.g., the anisotropy of a particular biological tissue has to be represented with site- and direction-dependent particular mechanical values. Contrary to this concept of consistent mechanical properties of a defined soft tissue, mechanical parameters of soft tissues scatter considerably when being determined in tensile tests. In spite of numerous measures taken to standardize the mechanical testing of soft tissues, several setup- and tissue-related factors remain to influence the mechanical parameters of human soft tissues to a yet unknown extent. It is to date unclear if measurement extremes should be considered a variation or whether these data have to be deemed incorrect measurement outliers. This given study aimed to determine mechanical parameters of the human cranial dura mater as a model for human soft tissues using a highly standardized protocol and based on this, critically evaluate the definition for the term mechanical "variation" of human soft tissue. Materials and Methods: A total of 124 human dura mater samples with an age range of 3 weeks to 94 years were uniformly retrieved, osmotically adapted and mechanically tested using customized 3D-printed equipment in a quasi-static tensile testing setup. Scanning electron microscopy of 14 samples was conducted to relate the mechanical parameters to morphological features of the dura mater. Results: The here obtained mechanical parameters were scattered (elastic modulus = 46.06 MPa, interquartile range = 33.78 MPa; ultimate tensile strength = 5.56 MPa, interquartile range = 4.09 MPa; strain at maximum force = 16.58%, interquartile range = 4.81%). Scanning electron microscopy revealed a multi-layered nature of the dura mater with varying fiber directions between its outer and inner surface. Conclusions: It is concluded that mechanical parameters of soft tissues such as human dura mater are highly variable even if a highly standardized testing setup is involved. The tissue structure and composition appeared to be the main contributor to the scatter of the mechanical parameters. In consequence, mechanical variation of soft tissues can be defined as the extremes of a biomechanical parameter due to an uncontrollable change in tissue structure and/or the respective testing setup.

Strain Assessment of Deep Fascia of the Thigh During Leg Movement: An in situ Study

Fascia is a fibrous connective tissue present all over the body. At the lower limb level, the deep fascia that is overlying muscles of the outer thigh and sheathing them (fascia lata) is involved in various pathologies. However, the understanding and quantification of the mechanisms involved in these sheathing effects are still unclear. The aim of this study is to observe and quantify the strain field of the fascia lata, including the iliotibial tract (ITT), during a passive movement of the knee. Three fresh postmortem human subjects were studied. To measure hip and knee angles during knee flexion-extension, passive movements from 0° to around 120° were recorded with a motion analysis system and strain fields of the fascia were acquired using digital image correlation. Strains were computed for three areas of the fascia lata: anterior fascia, lateral fascia, and ITT. Mean principal strains showed different strain mechanisms depending on location on the fascia and knee angle. For the ITT, two strain mechanisms were observed depending on knee movement: compression is observed when the knee is extended relative to the reference position of 47°, however, tension and pure shear can be observed when the knee is flexed. For the anterior and lateral fascia, in most cases, minor strain is higher than major strain in absolute value, suggesting high tissue compression probably due to microstructural fiber rearrangements. This in situ study is the first attempt to quantify the superficial strain field of fascia lata during passive leg movement. The study presents some limitations but provides a step in understanding strain mechanism of the fascia lata during passive knee movement.

Water-content related alterations in macro and micro scale tendon biomechanics

Though it is known that the water content of biological soft tissues alters mechanical properties, little attempt has been made to adjust the tissue water content prior to biomechanical testing as part of standardization procedures. The objective of this study was to examine the effects of altered water content on the macro and micro scale mechanical tissues properties. Human iliotibial band samples were obtained during autopsies to osmotically adapt their water content. Macro mechanical tensile testing of the samples was conducted with digital image correlation, and micro mechanical tests using atomic force microscopy. Analyses were conducted for elastic moduli, tensile strength, and strain at maximum force, and correlations for water content, anthropometric data, and post-mortem interval. Different mechanical properties exist at different water concentrations. Correlations to anthropometric data are more likely to be found at water concentrations close to the native state. These data underline the need for adapting the water content of soft tissues for macro and micro biomechanical experiments to optimize their validity. The osmotic stress protocol provides a feasible and reliable standardization approach to adjust for water content-related differences induced by age at death, post-mortem interval and tissue processing time with known impact on the stress-strain properties.

Migrating Myofibroblastic Iliotibial Band-Derived Fibroblasts Represent a Promising Cell Source for Ligament Reconstruction

The iliotibial band (ITB) is a suitable scaffold for anterior cruciate ligament (ACL) reconstruction, providing a sufficient mechanical resistance to loading. Hence, ITB-derived fibroblasts attract interest for ligament tissue engineering but have so far not been characterized. This present study aimed at characterizing ITB fibroblasts before, during, and after emigration from cadaveric ITB explants to decipher the emigration behavior and to utilize their migratory capacity for seeding biomaterials. ITB and, for comparison, ACL tissues were assessed for the content of alpha smooth muscle actin (αSMA) expressing fibroblasts and degeneration. The cell survival and αSMA expression were monitored in explants used for cell isolation, monolayer, self-assembled ITB spheroids, and spheroids seeded in polyglycolic acid (PGA) scaffolds. The protein expression profile of targets typically expressed by ligamentocytes (collagen types I-III, elastin, lubricin, decorin, aggrecan, fibronectin, tenascin C, CD44, β1-integrins, vimentin, F-actin, αSMA, and vascular endothelial growth factor A [VEGFA]) was compared between ITB and ACL fibroblasts. A donor- and age-dependent differing percentage of αSMA positive cells could be detected, which was similar in ITB and ACL tissues despite the grade of degeneration being significantly higher in the ACL due to harvesting them from OA knees. ITB fibroblasts survived for several months in an explant culture, continuously forming monolayers with VEGFA and an increased αSMA expression. They shared their expression profile with ACL fibroblasts. αSMA decreased during the monolayer to spheroid/scaffold transition. Using self-assembled spheroids, the migratory capacity of reversible myofibroblastic ITB cells can be utilized for colonizing biomaterials for ACL tissue engineering and to support ligament healing.

Utilization of 3D printing technology to facilitate and standardize soft tissue testing

Three-dimensional (3D) printing has become broadly available and can be utilized to customize clamping mechanisms in biomechanical experiments. This report will describe our experience using 3D printed clamps to mount soft tissues from different anatomical regions. The feasibility and potential limitations of the technology will be discussed. Tissues were sourced in a fresh condition, including human skin, ligaments and tendons. Standardized clamps and fixtures were 3D printed and used to mount specimens. In quasi-static tensile tests combined with digital image correlation and fatigue trials we characterized the applicability of the clamping technique. Scanning electron microscopy was utilized to evaluate the specimens to assess the integrity of the extracellular matrix following the mechanical tests. 3D printed clamps showed no signs of clamping-related failure during the quasi-static tests, and intact extracellular matrix was found in the clamping area, at the transition clamping area and the central area from where the strain data was obtained. In the fatigue tests, material slippage was low, allowing for cyclic tests beyond 10⁵ cycles. Comparison to other clamping techniques yields that 3D printed clamps ease and expedite specimen handling, are highly adaptable to specimen geometries and ideal for high-standardization and high-throughput experiments in soft tissue biomechanics.

Tenogenesis of Decellularized Porcine Achilles Tendon Matrix Reseeded with Human Tenocytes in the Nude Mice Xenograft Model

Cultivation of autologous human tenocytes in a cell-free xenogenic extracellular tendon matrix (xECM) could present an approach for tendon reconstruction. The aim of this study was to achieve tendon-like tissue formation by implanting decellularized porcine Achilles tendons recellularized with human hamstring tendon-derived tenocytes into nude mice. The structure of decellularized xECM was histologically monitored before being dynamically reseeded with human tenocytes. After 6⁻12 weeks in vivo, construct quality was monitored using macroscopical and histological scoring systems, vitality assay and quantitative DNA and glycosaminoglycan (GAG) assays. For comparison to tendon xECM, a synthetic polyglycolic acid (PGA) polymer was implanted in a similar manner. Despite decellularized xECM lost some GAGs and structure, it could be recellularized in vitro with human tenocytes, but the cell distribution remained inhomogeneous, with accumulations at the margins of the constructs. In vivo, the xECM constructs revealed in contrast to the PGA no altered size, no inflammation and encapsulation and a more homogeneous cell distribution. xECM reseeded with tenocytes showed superior histological quality than cell-free implanted constructs and contained surviving human cells. Their DNA content after six and 12 weeks in vivo resembled that of native tendon and xECM recellularized in vitro. Results suggest that reseeded decellularized xECM formed a tendon-like tissue in vivo.

The Challenge in Using Mesenchymal Stromal Cells for Recellularization of Decellularized Cartilage

Some decellularized musculoskeletal extracellular matrices (ECM)s derived from tissues such as bone, tendon and fibrocartilaginous meniscus have already been clinical use for tissue reconstruction. Repair of articular cartilage with its unique zonal ECM architecture and composition is still an unsolved problem, and the question is whether allogenic or xenogeneic decellularized cartilage ECM could serve as a biomimetic scaffold for this purpose.Hence, this survey outlines the present state of preparing decellularized cartilage ECM-derived scaffolds or composites for reconstruction of different cartilage types and of reseeding it particularly with mesenchymal stromal cells (MSCs).The preparation of natural decellularized cartilage ECM scaffolds hampers from the high density of the cartilage ECM and lacking interconnectivity of the rather small natural pores within it: the chondrocytes lacunae. Nevertheless, the reseeding of decellularized ECM scaffolds before implantation provided superior results compared with simply implanting cell-free constructs in several other tissues, but cartilage recellularization remains still challenging. Induced by cartilage ECM-derived scaffolds MSCs underwent chondrogenesis.Major problems to be addressed for the application of cell-free cartilage were discussed such as to maintain ECM structure, natural chemistry, biomechanics and to achieve a homogenous and stable cell recolonization, promote chondrogenic and prevent terminal differentiation (hypertrophy) and induce the deposition of a novel functional ECM. Some promising approaches were proposed including further processing of the decellularized ECM before recellularization of the ECM with MSCs, co-culturing of MSCs with chondrocytes and establishing bioreactor culture e.g. with mechanostimulation, flow perfusion pressure and lowered oxygen tension. Graphical Abstract Synopsis of tissue engineering approaches based on cartilage-derived ECM.

Decellularized Iliotibial Band Recolonized with Allogenic Homotopic Fibroblasts or Bone Marrow-Derived Mesenchymal Stromal Cells

Decellularized scaffolds present promising biomimetic approaches in various fields of tissue engineering. Different tissues have been selected for decellularization, among them extracellular matrix (ECM)-rich tissues such as tendons, ligaments and cartilage. The dense ECM of ligaments is particularly challenging to achieve a completely non-immunogenic ECM void of any cells. Here, the methods for decellularization adapted to ligamentous tissue of the iliotibial band (ITB) are presented along with cell isolation and several recolonization techniques using allogenic ITB-derived fibroblasts or mesenchymal stromal cells (MSCs).

Tensile properties of the hip joint ligaments are largely variable and age-dependent - An in-vitro analysis in an age range of 14-93 years

INTRODUCTION

Hip joint stability is maintained by the surrounding ligaments, muscles, and the atmospheric pressure exerted via these structures. It is unclear whether the ligaments are capable of preventing dislocation solely due to their tensile properties, and to what extent they undergo age-related changes. This study aimed to obtain stress-strain data of the hip ligaments over a large age range.

METHODS

Stress-strain data of the iliofemoral (IL), ischiofemoral (IS) and pubofemoral ligament (PF) were obtained from cadavers ranging between 14 and 93 years using a highly standardized setting. Maximum strains were compared to the distances required for dislocation.

RESULTS

Elastic modulus was 24.4 (IL), 22.4 (IS) and 24.9N/mm² (PF) respectively. Maximum strain was 84.5%, 86.1%, 72.4% and ultimate stress 10.0, 7.7 and 6.5N/mm² for the IL, IS and PF respectively. None of these values varied significantly between ligaments or sides. The IS' elastic modulus was higher and maximum strain lower in males. Lower elastic moduli of the PF and higher maximum strains for the IS and PF were revealed in the ≥55 compared to the <55 population. Maximum strain exceeded the dislocation distance of the IS without external hip joint rotation in females, and of the IS and cranial IL under external rotation in both genders.

DISCUSSION

Tensile and failure load properties of the hip joint ligaments are largely variable. The IS and PF change age-dependently. Though the hip ligaments contribute to hip stability, the IS and cranial IL may not prevent dislocation due to their elasticity.

Acellularization-Induced Changes in Tensile Properties Are Organ Specific - An In-Vitro Mechanical and Structural Analysis of Porcine Soft Tissues

Introduction

Though xenogeneic acellular scaffolds are frequently used for surgical reconstruction, knowledge of their mechanical properties is lacking. This study compared the mechanical, histological and ultrastructural properties of various native and acellular specimens.

Materials and Methods

Porcine esophagi, ureters and skin were tested mechanically in a native or acellular condition, focusing on the elastic modulus, ultimate tensile stress and maximum strain. The testing protocol for soft tissues was standardized, including the adaption of the tissue’s water content and partial plastination to minimize material slippage as well as templates for normed sample dimensions and precise cross-section measurements. The native and acellular tissues were compared at the microscopic and ultrastructural level with a focus on type I collagens.

Results

Increased elastic modulus and ultimate tensile stress values were quantified in acellular esophagi and ureters compared to the native condition. In contrast, these values were strongly decreased in the skin after acellularization. Acellularization-related decreases in maximum strain were found in all tissues. Type I collagens were well-preserved in these samples; however, clotting and a loss of cross-linking type I collagens was observed ultrastructurally. Elastins and fibronectins were preserved in the esophagi and ureters. A loss of the epidermal layer and decreased fibronectin content was present in the skin.

Discussion

Acellularization induces changes in the tensile properties of soft tissues. Some of these changes appear to be organ specific. Loss of cross-linking type I collagen may indicate increased mechanical strength due to decreasing transverse forces acting upon the scaffolds, whereas fibronectin loss may be related to decreased load-bearing capacity. Potentially, the alterations in tissue mechanics are linked to organ function and to the interplay of cells and the extracellular matrix, which is different in hollow organs when compared to skin.