scholarly journals Effect of Preconditioning and Stress Relaxation on Local Collagen Fiber Re-Alignment: Inhomogeneous Properties of Rat Supraspinatus Tendon

2012 ◽  
Vol 134 (3) ◽  
Author(s):  
Kristin S. Miller ◽  
Lena Edelstein ◽  
Brianne K. Connizzo ◽  
Louis J. Soslowsky
Keyword(s):  
Mechanical Properties ◽  
Stress Relaxation ◽  
Mechanical Testing ◽  
Collagen Fiber ◽  
Mechanical Test ◽  
Optical Transition ◽  
Insertion Site ◽  
Polarized Light ◽  
Supraspinatus Tendon ◽  
Circular Variance

Repeatedly and consistently measuring the mechanical properties of tendon is important but presents a challenge. Preconditioning can provide tendons with a consistent loading history to make comparisons between groups from mechanical testing experiments. However, the specific mechanisms occurring during preconditioning are unknown. Previous studies have suggested that microstructural changes, such as collagen fiber re-alignment, may be a result of preconditioning. Local collagen fiber re-alignment is quantified throughout tensile mechanical testing using a testing system integrated with a polarized light setup, consisting of a backlight, 90 deg-offset rotating polarizer sheets on each side of the test sample, and a digital camera, in a rat supraspinatus tendon model, and corresponding mechanical properties are measured. Local circular variance values are compared throughout the mechanical test to determine if and where collagen fiber re-alignment occurred. The inhomogeneity of the tendon is examined by comparing local circular variance values, optical moduli and optical transition strain values. Although the largest amount of collagen fiber re-alignment was found during preconditioning, significant re-alignment was also demonstrated in the toe and linear regions of the mechanical test. No significant changes in re-alignment were seen during stress relaxation. The insertion site of the supraspinatus tendon demonstrated a lower linear modulus and a more disorganized collagen fiber distribution throughout all mechanical testing points compared to the tendon midsubstance. This study identified a correlation between collagen fiber re-alignment and preconditioning and suggests that collagen fiber re-alignment may be a potential mechanism of preconditioning and merits further investigation. In particular, the conditions necessary for collagen fibers to re-orient away from the direction of loading and the dependency of collagen reorganization on its initial distribution must be examined.

Collagen Fiber Re-Alignment and Mechanical Properties in a Mouse Supraspinatus Tendon Model: Examining Changes With Age and Location

2012 ◽  
Author(s):  
Kristin S. Miller ◽  
Brianne K. Connizzo ◽  
Elizabeth Feeney ◽  
Louis J. Soslowsky
Keyword(s):  
Mechanical Properties ◽  
Collagen Fiber ◽  
Mechanical Load ◽  
Mechanical Test ◽  
Insertion Site ◽  
Supraspinatus Tendon ◽  
Tissue Response ◽  
Mechanical Stimuli ◽  
Fiber Alignment ◽  
Collagen Fiber Alignment

One postulated mechanism of tendon structural response to mechanical load is collagen fiber re-alignment. Recently, where collagen fiber re-alignment occurs during a tensile mechanical test has been shown to vary by tendon age and location in a postnatal developmental mouse supraspinatus tendon (SST) model [1]. It is thought that as the tendon matures and its collagen fibril network, collagen cross-links and collagen-matrix interactions develop, its ability to respond quickly to mechanical stimuli hastens [1]. Additionally, the insertion site and midsubstance of postnatal SST may develop differently and at different rates, providing a potential explanation for differences in fiber re-alignment behaviors at the insertion site and midsubstance at postnatal developmental time points [1]. However, collagen fiber re-alignment behavior, in response to mechanical load at a mature age and in comparison to developmental ages, have not been examined. Therefore, the objectives of this study are to locally measure: 1) fiber re-alignment during preconditioning and tensile mechanical testing and 2) to compare local differences in collagen fiber alignment and corresponding mechanical properties to address tissue response to mechanical load in the mature and postnatal developmental mouse SST. We hypothesize that 1) 90 day tendons will demonstrate the largest shift in fiber re-alignment during preconditioning, but will also re-align during the toe- and linear-regions. Additionally, we hypothesize that 2) mechanical properties and initial collagen fiber alignment will be greater in the midsubstance of the tendon compared to the tendon-to-bone insertion site at 90 days, 3) that mechanical properties will increase with age, and that 4) collagen fiber organization at the insertion site will decrease with age.

scholarly journals Effect of Age and Proteoglycan Deficiency on Collagen Fiber Re-Alignment and Mechanical Properties in Mouse Supraspinatus Tendon

2013 ◽  
Vol 135 (2) ◽  
Author(s):  
Brianne K. Connizzo ◽  
Joseph J. Sarver ◽  
Renato V. Iozzo ◽  
David E. Birk ◽  
Louis J. Soslowsky
Keyword(s):  
Mechanical Properties ◽  
Collagen Fiber ◽  
Mechanical Test ◽  
Insertion Site ◽  
Supraspinatus Tendon ◽  
Matrix Proteins ◽  
Wild Type ◽  
Structural Alterations ◽  
A Site ◽  
Effect Of Age

Collagen fiber realignment is one mechanism by which tendon responds to load. Re-alignment is altered when the structure of tendon is altered, such as in the natural process of aging or with alterations of matrix proteins, such as proteoglycan expression. While changes in re-alignment and mechanical properties have been investigated recently during development, they have not been studied in (1) aged tendons, or (2) in the absence of key proteoglycans. Collagen fiber re-alignment and the corresponding mechanical properties are quantified throughout tensile mechanical testing in both the insertion site and the midsubstance of mouse supraspinatus tendons in wild type (WT), decorin-null (Dcn-/-), and biglycan-null (Bgn-/-) mice at three different ages (90 days, 300 days, and 570 days). Percent relaxation was significantly decreased with age in the WT and Dcn-/- tendons, but not in the Bgn-/- tendons. Changes with age were found in the linear modulus at the insertion site where the 300 day group was greater than the 90 day and 570 day group in the Bgn-/- tendons and the 90 day group was smaller than the 300 day and 570 day groups in the Dcn-/- tendons. However, no changes in modulus were found across age in WT tendons were found. The midsubstance fibers of the WT and Bgn-/- tendons were initially less aligned with increasing age. The re-alignment was significantly altered with age in the WT tendons, with older groups responding to load later in the mechanical test. This was also seen in the Dcn-/- midsubstance and the Bgn-/- insertion, but not in the other locations. Although some studies have found changes in the WT mechanical properties with age, this study did not support those findings. However, it did show fiber re-alignment changes at both locations with age, suggesting a breakdown of tendon's ability to respond to load in later ages. In the proteoglycan-null tendons however, there were changes in the mechanical properties, accompanied only by location-dependent re-alignment changes, suggesting a site-specific role for these molecules in loading. Finally, changes in the mechanical properties did not occur in concert with changes in re-alignment, suggesting that typical mechanical property measurements alone are insufficient to describe how structural alterations affect tendon's response to load.

Effect of Preconditioning on Collagen Fiber Recruitment: Inhomogeneous Properties of Rat Supraspinatus Tendon

2010 ◽  
Author(s):  
Kristin S. Miller ◽  
Lena Edelstein ◽  
Louis J. Soslowsky
Keyword(s):  
Mechanical Properties ◽  
Collagen Fiber ◽  
Insertion Site ◽  
Supraspinatus Tendon ◽  
Fiber Alignment ◽  
Rigorous Evaluation ◽  
Structural Alterations ◽  
Testing Protocol ◽  
Inhomogeneous Properties ◽  
Collagen Fiber Alignment

Cyclic preconditioning is a commonly accepted initial component of any tendon testing protocol. Preconditioning provides tendons with a consistent “history” and stress-strain results become repeatable allowing for rigorous evaluation and comparison. While it is widely accepted that preconditioning is important, changes that occur during preconditioning are not well understood. Micro-structural alterations, such as re-arrangement of collagen fibers, is one proposed mechanism of preconditioning [1,4]. However, this mechanism has not been examined. Therefore, the objective of this study is to locally measure: 1) fiber re-alignment during preconditioning, stress relaxation and tensile testing and 2) corresponding mechanical properties, to address mechanisms of preconditioning as well as tissue nonlinearity and inhomogeneity in the rat supraspinatus tendon. We hypothesize that 1) fiber re-alignment will be greatest in the toe region, but will also occur during preconditioning and 2) mechanical properties and initial collagen fiber alignment will be greater in the midsubstance location of the tendon compared to the tendon-to-bone insertion site.

scholarly journals Examining Differences in Local Collagen Fiber Crimp Frequency Throughout Mechanical Testing in a Developmental Mouse Supraspinatus Tendon Model

2012 ◽  
Vol 134 (4) ◽  
Author(s):  
Kristin S. Miller ◽  
Brianne K. Connizzo ◽  
Elizabeth Feeney ◽  
Jennica J. Tucker ◽  
Louis J. Soslowsky
Keyword(s):  
Mechanical Testing ◽  
Collagen Fiber ◽  
Mechanical Test ◽  
Nonlinear Behavior ◽  
Supraspinatus Tendon ◽  
Behavior Changes ◽  
Developmental Age ◽  
Sst Model ◽  
Custom Software ◽  
Number Of Cycles

Crimp morphology is believed to be related to tendon mechanical behavior. While crimp has been extensively studied at slack or nondescript load conditions in tendon, few studies have examined crimp at specific, quantifiable loading conditions. Additionally, the effect of the number of cycles of preconditioning on collagen fiber crimp behavior has not been examined. Further, the dependence of collagen fiber crimp behavior on location and developmental age has not been examined in the supraspinatus tendon. Local collagen fiber crimp frequency is quantified throughout tensile mechanical testing using a flash freezing method immediately following the designated loading protocol. Samples are analyzed quantitatively using custom software and semi-quantitatively using a previously established method to validate the quantitative software. Local collagen fiber crimp frequency values are compared throughout the mechanical test to determine where collagen fiber frequency changed. Additionally, the effect of the number of preconditioning cycles is examined compared to the preload and toe-region frequencies to determine if increasing the number of preconditioning cycles affects crimp behavior. Changes in crimp frequency with age and location are also examined. Decreases in collagen fiber crimp frequency were found at the toe-region at all ages. Significant differences in collagen fiber crimp frequency were found between the preload and after preconditioning points at 28 days. No changes in collagen fiber crimp frequency were found between locations or between 10 and 28 days old. Local collagen fiber crimp frequency throughout mechanical testing in a postnatal developmental mouse SST model was measured. Results confirmed that the uncrimping of collagen fibers occurs primarily in the toe-region and may contribute to the tendon’s nonlinear behavior. Additionally, results identified changes in collagen fiber crimp frequency with an increasing number of preconditioning cycles at 28 days, which may have implications on the measurement of mechanical properties and identifying a proper reference configuration.

scholarly journals Pregnancy and Lactation Impair Subchondral Bone Leading to Reduced Rat Supraspinatus Tendon-to-Bone Insertion Site Failure Properties

2020 ◽  
Vol 142 (11) ◽  
Author(s):  
Ashley K. Fung ◽  
Snehal S. Shetye ◽  
Yihan Li ◽  
Yilu Zhou ◽  
X. Sherry Liu ◽  
...  
Keyword(s):  
Mechanical Properties ◽  
Bone Loss ◽  
Subchondral Bone ◽  
Bone Mineralization ◽  
Insertion Site ◽  
Supraspinatus Tendon ◽  
Bone Microstructure ◽  
Female Rats ◽  
Pregnancy And Lactation ◽  
Failure Properties

Abstract Pregnant women experience weight gain, gait changes, and biochemical fluctuations that impair joint function and alter the maternal skeleton. Hormonal changes increase pelvic ligament laxity in preparation for childbirth and affect peripheral joint laxity. Calcium demands also rise during pregnancy and lactation, resulting in reduced bone mineral density (BMD) and maternal bone loss. Altered tendon properties and bone loss during pregnancy and lactation may impact tendon insertion sites, such as rotator cuff tendons where insertion site ruptures are common. However, the effects of pregnancy and lactation at the tendon-to-bone interface have not been investigated. Therefore, the objective of this study was to evaluate supraspinatus tendon mechanical properties and insertion site microstructure during pregnancy, lactation, and postweaning recovery in female rats. We hypothesized that pregnancy and lactation would compromise supraspinatus tendon mechanical properties and subchondral bone microstructure. Female rats were divided into virgin, pregnancy, lactation, and recovery groups, and supraspinatus tendons were mechanically evaluated. Surprisingly, tendon mechanics was unaffected by pregnancy and lactation. However, tendon modulus decreased two-weeks postweaning. Additionally, tendons failed by bony avulsion at the insertion site, and the lactation group exhibited reduced failure properties corresponding to decreased subchondral bone mineralization. Lactation also resulted in dramatic bone loss at the epiphysis, but trabecular bone microarchitecture recovered postweaning. In conclusion, lactation following pregnancy impaired trabecular bone microstructure and subchondral bone mineralization, leading to reduced supraspinatus tendon-to-bone insertion site failure properties. These findings will contribute toward understanding the pathogenesis of tendon-to-bone disorders.

scholarly journals Characterizing local collagen fiber re-alignment and crimp behavior throughout mechanical testing in a mature mouse supraspinatus tendon model

2012 ◽  
Vol 45 (12) ◽  
pp. 2061-2065 ◽  
Author(s):  
Kristin S. Miller ◽  
Brianne K. Connizzo ◽  
Elizabeth Feeney ◽  
Louis J. Soslowsky
Keyword(s):  
Mechanical Testing ◽  
Collagen Fiber ◽  
Supraspinatus Tendon ◽  
Mature Mouse

Long Durations of Immobilization in the Rat Result in Enhanced Mechanical Properties of the Healing Supraspinatus Tendon Insertion Site

2006 ◽  
Vol 129 (3) ◽  
pp. 400-404 ◽  
Author(s):  
J. A. Gimbel ◽  
J. P. Van Kleunen ◽  
G. R. Williams ◽  
S. Thomopoulos ◽  
L. J. Soslowsky
Keyword(s):  
Mechanical Properties ◽  
Rotator Cuff ◽  
Bone Healing ◽  
Insertion Site ◽  
Supraspinatus Tendon ◽  
Shoulder Function ◽  
Activity Level ◽  
Rotator Cuff Tears ◽  
Operative Activity ◽  
Positive Effect

Rotator cuff tears frequently occur and can lead to pain and decreased shoulder function. Repair of the torn tendon back to bone is often successful in relieving pain, but failure of the repair commonly occurs. Post-operative activity level is an important treatment component that has received minimal attention for the shoulder, but may have the potential to enhance tendon to bone healing. The objective of this study was to investigate the effect of short and long durations of various activity levels on the healing supraspinatus tendon to bone insertion site. Rotator cuff tears were surgically created in Sprague–Dawley rats by detaching the supraspinatus tendon from its insertion on the humerus and these tears were immediately repaired back to the insertion site. The post-operative activity level was controlled through shoulder immobilization (IM), cage activity (CA), or moderate exercise (EX) for durations of 4 or 16 weeks. The healing tissue was evaluated utilizing biomechanical testing and a quantitative polarized light microscopy method. We found that activity level had no effect on the elastic properties (stiffness, modulus) of the insertion site at four weeks post injury and repair, and a decreased activity level had a positive effect on these properties at 16 weeks (IM>CA=EX). Furthermore, a decreased activity level had the greatest positive effect on these properties over time (IM>CA=EX). The angular deviation of the collagen, a measure of disorganization, was decreased with a decrease in activity level at 4 weeks (IM<CA=EX), but was similar between groups at 16 weeks (IM=CA=EX). It appears from this study that decreasing the activity level by immobilizing the shoulder improves tendon to bone healing, which progresses by first increasing the organization of the collagen and then increasing the mechanical properties. Future studies in this area will investigate the effect of passive motion and remobilization on both tendon to bone healing and shoulder function.

The Effect of Return to Overuse Activity After a Supraspinatus Tear on Joint Function and Biceps Mechanical Properties in a Rat Model

2011 ◽  
Author(s):  
Stephen J. Thomas ◽  
Joseph J. Sarver ◽  
Jennica Tucker ◽  
Katherine Reuther ◽  
Lena Edelstein ◽  
...  
Keyword(s):  
Mechanical Properties ◽  
Insertion Site ◽  
Supraspinatus Tendon ◽  
Shoulder Function ◽  
Shoulder Injuries ◽  
Tendon Tear ◽  
Model Studies ◽  
Cuff Tear ◽  
Supraspinatus Tear ◽  
Long Head

Rotator cuff tendon tears are one of the most common shoulder injuries and are most prevalent in populations performing repetitive overhead activities [1]. In addition, long head of the biceps (LHB) tendon injuries occur secondary to cuff tears and may or may not lead to functional deficits [2]. Previous animal model studies have found that in the presence of a cuff tear, the biceps has decreased mechanical properties at 8 weeks [3]. Such studies, however, did not examine the effect of repetitive overhead activity on biceps properties and shoulder function in the presence of a cuff tear. Therefore, the objective of this study was to evaluate the effect of returning to overuse activity after a supraspinatus tendon tear on shoulder function and biceps structural and mechanical properties. We hypothesized that overuse activity following a supraspinatus tendon tear would not alter shoulder function, when compared to cage activity, but would decrease biceps structural and mechanical properties, particularly at the insertion site.

scholarly journals Effect of Moisture Content on the Processing and Mechanical Properties of a Biodegradable Polyester

Polymers ◽  
2021 ◽  
Vol 13 (10) ◽  
pp. 1616
Author(s):  
Vincenzo Titone ◽  
Antonio Correnti ◽  
Francesco Paolo La Mantia
Keyword(s):  
Mechanical Properties ◽  
Tensile Strength ◽  
Moisture Content ◽  
Mechanical Testing ◽  
Hydrolytic Degradation ◽  
Slight Reduction ◽  
Biodegradable Polyester ◽  
Molding Process ◽  
Elongation At Break ◽  
Effect Of Moisture

This work is focused on the influence of moisture content on the processing and mechanical properties of a biodegradable polyester used for applications in injection molding. The pellets of the biodegradable polyester were exposed under different relative humidity conditions at a constant temperature before being compression molded. The compression-molded specimens were again placed under the above conditions before the mechanical testing. With all these samples, it is possible to determine the effect of moisture content on the processing and mechanical properties separately, as well as the combined effect of moisture content on the mechanical properties. The results obtained showed that the amount of absorbed water—both before processing and before mechanical testing—causes an increase in elongation at break and a slight reduction of the elastic modulus and tensile strength. These changes have been associated with possible hydrolytic degradation during the compression molding process and, in particular, with the plasticizing action of the moisture absorbed by the specimens.

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