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PubMed2000

A cell-based constitutive relation for bio-artificial tissues.

By using a combination of continuum and statistical mechanics we derive an integral constitutive relation for bio-artificial tissue models consisting of a monodisperse population of cells in a uniform collagenous matrix. This constitutive relation quantitatively models the dependence of tissue stress on deformation history, and makes explicit the separate contribution of cells and matrix to the mechanical behavior of the composite tissue. Thus microscopic cell mechanical properties can be deduced via this theory from measurements of macroscopic tissue properties. A central feature of the constitutive relation is the appearance of "anisotropy tensors" that embody the effects of cell orientation on tissue mechanics. The theory assumes that the tissues are stable over the observation time, and does not in its present form allow for cell migration, reorientation, or internal remodeling. We have compared the predictions of the theory to uniaxial relaxation tests on fibroblast-populated collagen matrices (FPMs) and find that the experimental results generally support the theory and yield values of fibroblast contractile force and stiffness roughly an order of magnitude smaller than, and viscosity comparable to, the corresponding properties of active skeletal muscle. The method used here to derive the tissue constitutive equation permits more sophisticated cell models to be used in developing more accurate representations of tissue properties.

Animals↗
PubMed2006

Different effects of oral conjugated estrogen and transdermal estradiol on arterial stiffness and vascular inflammatory markers in postmenopausal women.

AIMS: We compared the effects of oral conjugated equine estrogen (CEE) therapy and transdermal estradiol therapy on pulse wave velocity (PWV) and circulating levels of vascular inflammatory markers in postmenopausal women and we also explored the interrelationship between the change in PWV and the changes in vascular inflammatory markers. METHODS AND RESULTS: In a randomized 12-month trial, 28 postmenopausal women received a continuous oral CEE plus cyclic medroxyprogesterone acetate (MPA), 28 received a continuous transdermal estradiol patch plus cyclic MPA, and 27 did not receive either therapy. In each subject, we measured the brachial-ankle PWV (baPWV) using an automated device, the blood pressure, and the circulating levels of vascular inflammatory markers (C-reactive protein [CRP], cell adhesion molecules [CAMs], monocyte chemoattractant protein-1 [MCP-1], and matrix metalloproteinase [MMP-9]) before and 12 months after the start of the study. Oral CEE therapy did not change the baPWV but significantly increased the CRP and MMP-9 levels (P<0.05, each) and significantly decreased the CAMs and MCP-1 levels (P<0.05, each). Transdermal estradiol therapy significantly decreased the baPWV, and the CAMs and MCP-1 levels (P<0.05, each) but had no effect on the CRP or MMP-9 levels. No significant changes were seen in the control group. The blood pressures of the subjects remained unchanged. In the transdermal estradiol group, the change in baPWV was not significantly correlated with the changes in vascular inflammatory markers. CONCLUSION: Transdermal estradiol, but not oral CEE therapy, may have antiatherosclerotic effects by improving arterial stiffness. The reduction in baPWV may contribute to the direct effect of estrogen, but not to the decrease in estrogen-induced vascular inflammatory markers.

Administration, Cutaneous↗
PubMed1985

Structure and polymorphism of bipolar isopranyl ether lipids from archaebacteria.

We describe in this work the structure and polymorphism of a variety of lipids extracted from Sulfolobus solfataricus, an extreme thermoacidophilic archaebacterium growing at about 85 degrees C and pH 2. These lipids are quite different from the usual fatty acid lipids of eukaryotes and prokaryotes: each molecule consists of two C40 omega-omega' biphytanyl residues (with 0 to 4 cyclopentane groups per residue), ether linked at both ends to two (variably substituted) glycerol or nonitol groups. Four lipid preparations were studied; the total and the polar lipid extracts, and two hydrolytic fractions, the symmetric glycerol dialkyl glycerol tetraether and the asymmetric glycerol dialkyl nonitol tetraether, as a function of water content and temperature, using X-ray scattering techniques. The main conclusions from the study of the four lipid preparations can be summarized as follows. (1) As with other lipids, a remarkable number and variety of phases are observed over a temperature-concentration range close to "physiological" conditions. The possibility is discussed that this polymorphism reflects a fundamental property of lipids, closely related to their physiological rôle. (2) As in other lipids, two types of chain conformations are observed: a disordered one (type alpha) at high temperature; at lower temperature, a more ordered packing of stiff chains, all parallel to each other (type beta'). At temperatures and degrees of hydration approaching the conditions prevailing in the living cell, the conformation is of type alpha. (3) In all the phases with chains in the alpha conformation, the unsubstituted glycerol headgroups, whose concentration is high in these lipids, segregate in the hydrocarbon matrix, away from the other polar groups. This property may have interesting biological consequences: for example, the chains of a fraction of the bipolar lipid molecules can span hydrocarbon gaps as wide as 75 A. (4) Two cubic phases are observed in the total and the polar lipid extracts, which display a remarkable degree of metastability, most unusual in lipid phase transitions involving structures with chains in the alpha conformation. This phenomenon can be explained by the interplay of the physical structure of the cubic phases (the two contain two intertwined and unconnected three-dimensional networks of rods) and the chemical structure of the lipid molecules: the two headgroups of most molecules being anchored on each of the two networks of rods, the migration of the lipid molecules is hindered by the two independent diffusion processes and by the entanglement of the chains.(ABSTRACT TRUNCATED AT 400 WORDS)

Archaea↗
PubMed1993

Stress-sharing between the fluid and solid components of articular cartilage under varying rates of compression.

This paper investigates the factors affecting the mechanical behavior of the articular cartilage matrix with special emphasis on the effect of compressive strain-rate on the short and long term responses of the fluid and the solid components. The relationships expressed in the general theory of one-dimensional consolidation are generalized to account for strain-rate in the deformation process with the result that the stiffness due to the fluid and the solid components, and a parameter representing the degree of drag, can be calculated explicitly.

Animals↗
PubMed2003

Matrix metalloproteinase-3 genotype contributes to age-related aortic stiffening through modulation of gene and protein expression.

Matrix metalloproteinases (MMPs) include most major constituents of the arterial wall as substrates. A common promotor polymorphism (5A/6A) is associated with differences in MMP-3 (stromelysin-1) activity, and associations with certain forms of vascular disease have been shown. This study investigated whether the MMP-3 5A/6A promoter polymorphism contributes to age-related large artery stiffening. MMP-3 5A/6A genotype was determined in 203 (135 male) low cardiovascular risk, unmedicated individuals who were divided prospectively into two groups (30 to 60 years, n=126; > or =61 years, n=77). Noninvasive large artery stiffness was measured as ascending aortic input impedance from brachial blood pressure, carotid tonometry, and Doppler ascending aortic blood flow. In the older group, homozygotes had higher aortic input (P<0.01) and characteristic (P<0.01) impedance, ie, higher stiffness, than heterozygotes after correction for the effects of age, gender, and mean arterial pressure. There was no such difference in the younger group. Gene expression was subsequently investigated in dermal biopsies in randomly selected older men from the same cohort with real-time PCR (n=40). In 5A homozygotes, gene expression was 4-fold higher (P<0.05), and in 6A homozygotes, 2-fold lower (P<0.05) compared with the heterozygotes. Differences in gene expression were associated with corresponding significant changes in MMP-3 protein levels. Concordance between dermal and aortic gene and protein expression was shown in a separate cohort of postmortem aortic samples (n=7). We conclude that MMP-3 genotype may be an important determinant of vascular remodeling and age-related arterial stiffening, with the heterozygote having the optimal balance between matrix accumulation and deposition.

Adult↗
PubMed1992

The interglobular domain of cartilage aggrecan is cleaved by PUMP, gelatinases, and cathepsin B.

The action of three matrix metalloproteinases (MMPs), 72- and 95-kDa gelatinases (MMP-2 and MMP-9) and PUMP (MMP-7), and a cysteine proteinase, cathepsin B, were investigated on aggrecan the major proteoglycan of cartilage. All the enzymes cleaved aggrecan although the activity of the 95-kDa gelatinase was very low. Specific cleavage sites were investigated following incubation with a purified aggrecan G1-G2 domain fragment (150 kDa). Both gelatinases produced 110-kDa G2 and 56-kDa G1 products by a single cleavage at an Asn-Phe bond within the interglobular domain close to the G1 domain. This was similar to the action of stromelysin (MMP-3) (Fosang, A. J., Neame, P. J., Hardingham, T. E., Murphy, G., and Hamilton, J. A. (1991) J. Biol. Chem. 266, 15579-15582). Cathepsin B also produced two fragments from a single cleavage at a Gly-Val bond only three amino acids C-terminal to the metalloproteinase cleavage site. PUMP cleaved at the metalloproteinase Asn-Phe site, but in addition produced a low yield of a smaller G2 fragment (56 kDa) corresponding to cleavage between Asp441 and Leu442 (human sequence), within the interglobular domain, close to the G2 domain. The apparent difference in size between the two G2 fragments released by PUMP (110 and 56 kDa) was much greater than predicted from the peptide length between the cleavage sites (100 amino acids). However, keratanase digestion greatly reduced the size of the 110-kDa G2 fragment, while producing only a small reduction in size of the 56-kDa product, showing that there was approximately 30-40 kDa of keratan sulfate attached to the interglobular domain between the PUMP cleavage sites. This new structural information on aggrecan may account for the previously observed stiffness of the interglobular domains when viewed by rotary shadowing electron microscopy (Paulsson, M., Morgelin, M., Wiedemann, H., Beardmore-Gray, M., Dunham, D. G., Hardingham, T. E., Heinegard, D., Timpl, R., and Engel, J. (1987) Biochem. J. 245, 763-772). These results show that in spite of a high keratan sulfate content the interglobular domain provides important sites for cleavage by different proteinases, including several members of the matrix metalloproteinase family.

Aggrecans↗
PubMed2004

Response of the osteocyte syncytium adjacent to and distant from linear microcracks during adaptation to cyclic fatigue loading.

Cyclic loading induces fatigue in bone and initiates a complex, functionally adaptive response. We investigated the effect of a single period of fatigue on the histologic structure and biomechanical properties of bone. The ulnae of 40 rats were subjected to cyclic fatigue (-6000 microepsilon) unilaterally until 40% loss of stiffness developed, followed by 14 days of adaptation. The contralateral ulna served as a treatment control (n = 20 rats), and a baseline loaded/non-loaded group (n = 20 rats/group) was included. Bones from 10 rats/group were examined histologically and the remaining bones (10 rats/group) were tested mechanically. The following measurements were collected: volumetric bone mineral density (vBMD); ultimate force (Fu); stiffness (S); energy-to-failure (U); cortical area (Ct.Ar); microcrack density (Cr.Dn); microcrack mean length (Cr.Le); microcrack surface density (Cr.S.Dn); osteocyte density (Ot.N/T.Ar and Ot.N/TV); bone volume fraction (B.Ar/T.Ar); resorption space density (Rs.N/Ct.Ar); and maximum and minimum area moments of inertia (IMAX and IMIN). Using confocal microscopy, the bones were examined for diffuse matrix injury, canalicular disruption, and osteocyte disruption. The adapted bones had increased B.Ar, IMAX, and IMIN in the mid-diaphysis. Fatigue loading decreased structural properties and induced linear microcracking. At 14 days, adaptation restored structural properties and microcracking was partially repaired. There was a significant nonlinear relationship between Ot.N/T.Ar and B.Ar/T.Ar during adaptation. Disruption of osteocytes was observed adjacent to microcracks immediately after fatigue loading, and this did not change after the period of adaptation. In fatigue-loaded bone distant from microcracks, diffuse matrix injury and canalicular disruption were often co-localized and were increased in the lateral (tension) cortex. These changes were partially reversed after adaptation. Loss of canalicular staining and the presence of blind-ends in regions with matrix injury were suggestive of rupture of dendritic cell processes. Taken together, these data support the general hypothesis that the osteocyte syncytium can respond to cyclic loading and influence targeted remodeling during functional adaptation. Changes in the appearance of the osteocyte syncytium were found in fatigue-loaded bone with and without linear microcracks. We hypothesize that the number of dendritic cell processes that experience load-related disruption may determine osteocyte metabolic responses to loading and influence targeted remodeling.

Adaptation, Physiological↗
PubMed1996

Connective tissue and joint disease in diabetes mellitus.

Connective tissue is ubiquitous and subject to alterations that result in changes in the extracellular matrix of vessels and tissues leading to the long-term complications of diabetes. This article reviews only those abnormalities of interstitial connective tissue involving skeleton, joints, skin, and periarticular tissues. Abnormalities in the skin and periarticular tissues result in syndromes limiting joint movement, including limited joint mobility, Dupuytren disease, flexor tenosynovitis, carpal tunnel syndrome, stiff-hand syndrome, and shoulder-hand reflex dystrophy. Of these, only limited joint mobility and stiff-hand syndrome occur exclusively in patients with diabetes. In all of these conditions, advanced glycation end products are thought to form as a result of nonenzymatic reaction of glucose with proteins, causing stiffening.

Adult↗
PubMed2006

Developmental changes in passive stiffness and myofilament Ca2+ sensitivity due to titin and troponin-I isoform switching are not critically triggered by birth.

The giant protein titin, a major contributor to myocardial mechanics, is expressed in two main cardiac isoforms: stiff N2B (3.0 MDa) and more compliant N2BA (>3.2 MDa). Fetal hearts of mice, rats, and pigs express a unique N2BA isoform ( approximately 3.7 MDa) but no N2B. Around birth the fetal N2BA titin is replaced by smaller-size N2BA isoforms and N2B, which predominates in adult hearts, stiffening their sarcomeres. Here we show that perinatal titin-isoform switching and corresponding passive stiffness (STp) changes do not occur in the hearts of guinea pig and sheep. In these species the shift toward "adult" proportions of N2B isoform is almost completed by midgestation. The relative contributions of titin and collagen to STp were estimated in force measurements on skinned cardiac muscle strips by selective titin proteolysis, leaving the collagen matrix unaffected. Titin-based STp contributed between 42% and 58% to total STp in late-fetal and adult sheep/guinea pigs and adult rats. However, only approximately 20% of total STp was titin based in late-fetal rat. Titin-borne passive tension and the proportion of titin-based STp generally scaled with the N2B isoform percentage. The titin isoform transitions were correlated to a switch in troponin-I (TnI) isoform expression. In rats, fetal slow skeletal TnI (ssTnI) was replaced by adult carciac TnI (cTnI) shortly after birth, thereby reducing the Ca2+ sensitivity of force development. In contrast, guinea pig and sheep coexpressed ssTnI and cTnI in fetal hearts, and skinned fibers from guinea pig showed almost no perinatal shift in Ca2+ sensitivity. We conclude that TnI-isoform and titin-isoform switching and corresponding functional changes during heart development are not initiated by birth but are genetically programmed, species-specific regulated events.

Actin Cytoskeleton↗
PubMed2001

Advanced glycation endproducts: activators of cardiac remodeling in primary fibroblasts from adult rat hearts.

BACKGROUND: Cardiovascular diseases are the leading cause of death in the Western world, especially in the elderly. Myocardial fibrosis induced by activated cardiac fibroblasts is thought to play a key role in the pathogenesis of cardiovascular disease. Accumulation of advanced glycation endproducts (AGEs), products of nonenzymatic glycation of proteins, correlate with the stiffness of the heart and large vessels. To elucidate a potential role of AGEs as a trigger of fibrosis, the effects of AGEs on primary fibroblasts from hearts of adult rats were investigated. MATERIAL AND METHODS: The activation of intracellular signaling pathways was shown by Western blotting. In addition, the expression of genes of the extracellular matrix proteins, metalloproteases (MMPs), their inhibitors, and TGF-beta were analyzed by semiquantitative PCR. Activation of MMPs were controlled by Zymography. RESULTS: It was shown that treatment of cardiac fibroblasts with AGEs leads to an activation of different signaling molecules, such as the p38MAP-kinase, the extracellular regulated kinases (ERKs), the jun kinase (JNK), as well as transcription factors like ATF-2 and NF-kappaB. In addition, the expression and activation of MMP-2, MMP-9, and MMP-13 were induced, which may be responsible for tissue remodeling followed by fibrosis. CONCLUSION: Due to their effects on the expression and activation of metalloproteases, AGEs should be regarded as a potential therapeutic target for the prevention of pathologic remodeling.

Animals↗
PubMed2026

FBN1-related connective tissue disorders: unraveling cardiovascular, skeletal, and ocular complications through TGF-&#x3b2; signaling dysregulation and genotypic correlations.

Fibrillin-1 is an extracellular matrix glycoprotein essential for microfibril integrity, mediating cell-matrix interactions, providing structural support to tissues, and serving as a scaffold for elastogenesis. Pathogenic variants in the fibrillin 1 gene (FBN1) give rise to a spectrum of autosomal dominant connective tissue disorders collectively termed type-1 fibrillinopathies, which include Marfan syndrome, geleophysic dysplasia 2, acromicric dysplasia, Weill-Marchesani syndrome 2, marfanoid-progeroid-lipodystrophy syndrome, stiff skin syndrome, MASS syndrome, and isolated ectopia lentis 1. These disorders predominantly manifest cardiovascular, skeletal, and ocular abnormalities. Among these, aortic and valvular lesions are the principal and most life-threatening complications and therefore warrant the greatest clinical attention. Skeletal anomalies are diverse and can even be diametrically opposed across different phenotypes, while ectopia lentis represents the hallmark of ocular conditions. Notably, mutant fibrillin-1 disrupts microfibril structure and/or function, leading to dysregulated transforming growth factor-&#x3b2; (TGF-&#x3b2;) signaling, which is widely recognized as a central mechanism underlying type-1 fibrillinopathies. Although numerous pathogenic FBN1 variants have been identified, the knowledge of genotype-phenotype correlations remains limited in some specific regions. This review synthesizes the current understanding of the FBN1-related molecular mechanisms linking aberrant TGF-&#x3b2; signaling to distinct phenotypic outcomes and discusses how genetically engineered animal models and human induced pluripotent stem cell models advance mechanistic insights and facilitate therapy development. Additionally, clinical manifestations and genetic characteristics across all phenotypes are elaborated to facilitate diagnosis, treatment, and management of these complex disorders.

Cardiovascular complications↗
PubMed1993

Towards a synthetic articular cartilage.

The physical and morphological properties of articular cartilage have been used as a model for the preparation of hydrogel based synthetic analogues of this complex high water content natural hydrogel. The relatively poor strength and stiffness of simple homogeneous hydrogels have been enhanced by semi-interpenetrating polymer network (semi-IPN) technology to a level which enables the mechanical properties of natural cartilage to be approached. Maintenance of chondrocytic phenotypes at the implant interface in vitro has been found to require careful control of pore size and distribution in the hydrogel matrix. The study of synthetic techniques for the fabrication of macroporous semi-IPNs has enabled hydrogel semi-IPNs with appropriate pore sizes and mechanical properties to be produced. A range of in vitro testing techniques have been developed to enable the physico-chemical properties of these materials to be optimised prior to animal studies.

Animals↗
PubMed2006

Do biophysical properties of the airway smooth muscle in culture predict airway hyperresponsiveness?

Airway hyperresponsiveness is a cardinal feature of asthma but remains largely unexplained. In asthma, the key end-effector of acute airway narrowing is the airway smooth muscle (ASM) cell. Here we report novel biophysical properties of the ASM cell isolated from the relatively hyporesponsive Lewis rat versus the relatively hyperresponsive Fisher rat. We focused upon the ability of the cytoskeleton (CSK) of the ASM cell to stiffen, to generate contractile forces, and to remodel. We used optical magnetic twisting cytometry to measure cell stiffness and traction microscopy to measure contractile forces. To measure remodeling dynamics, we quantified spontaneous nanoscale motions of a microbead tightly anchored to the CSK. In response to a panel of contractile and relaxing agonists, Fisher ASM cells showed greater stiffening, bigger contractile forces, and faster CSK remodeling; they also exhibited higher effective temperature of the CSK matrix. These physical differences measured at the level of the single cell in vitro were consistent with strain-related differences in airway responsiveness in vivo. As such, comprehensive biophysical characterizations of CSK dynamics at the level of the cell in culture may provide novel perspectives on the ASM and its contributions to the excessive airway narrowing in asthma.

Adenosine Triphosphate↗
PubMedDate not supplied

Design and application of a test system for viscoelastic characterization of collagen gels.

Characterization and control of the mechanical properties of the extracellular matrix are critical to the interpretation of results of in vitro studies of cultured tissues and cells and for the design of functional engineered constructs. In this work a viscoelastic tensile test system and custom culture chambers were developed and characterized. The system allowed quantification of strain as well as the stresses developed during cyclic viscoelastic material testing. Finite element analysis of the culture chambers indicated that the tensile strains near the actuated ends of the gel were greater than the strains experienced by material in the center of the culture chambers. However, the strain was uniformly distributed over the central substance of the gel, validating the assumption that a homogeneous strain state existed in the central region of the chamber. Viscoelastic testing was performed on collagen gels that were created with three different collagen concentrations. Results demonstrated that there was a significant increase in the dynamic stiffness of the gels with increasing equilibrium strain, collagen concentration, and frequency of applied strain. With increasing strain rate, the phase angle, representing the energy dissipated, dropped initially and then increased at higher rates. Mechanical testing of gels at different time intervals up to 7 days after polymerization demonstrated that the material properties remained stable when appropriate environmental conditions were maintained. The ability to characterize the viscoelastic properties of gels after different periods of culture will allow the quantification of alterations in gel material properties due to changes in cell cytoskeletal organization, cell-matrix interactions, and cellular activity on the matrix. Further, the test device provides a means to apply controlled mechanical loading to growing gel cultures. Finally, the results of this study will provide guidance to the design of further experiments on this substrate.

Biocompatible Materials↗
PubMed2002

Angiotensin II AT(2) receptor inhibits smooth muscle cell migration via fibronectin cell production and binding.

To explore the vascular function of the angiotensin II (ANG II) AT(2) receptor subtype (AT(2)R), we generated a vascular smooth muscle cell (SMC) line expressing the AT(2)R (SMC-vAT(2)). The involvement of AT(2)R in the motility response of SMCs was examined in SMC-vAT(2) cells and their controls (SMC-v) cultured on either laminin or fibronectin matrix proteins with the agarose drop technique. All experiments were conducted in the presence of a saturating concentration of losartan to inactivate the AT(1)R subtype. Under basal conditions, both cell lines migrated outside drops, but on laminin only. Treatment with ANG II significantly inhibited the migration of SMC-vAT(2) but not SMC-v cells, and this effect was prevented by the AT(2)R antagonist CGP-42112A. The decreased migration of SMC-vAT(2) was not associated with changes in cell growth, cytoskeleton stiffness, or smooth muscle actin, desmin, and tenascin expression. However, it was correlated with increased synthesis and binding of fibronectin. Both responses were prevented by incubation with selective AT(2)R antagonists. Addition of GRGDTP peptide, which prevents cell attachment of fibronectin, reversed the AT(2)R inhibitory effect on SMC-vAT(2) migration. These results suggest that activated ANG II AT(2)R inhibits SMC migration via cellular fibronectin synthesis and associated cell binding.

Animals↗
PubMed1995

Self-reinforced composite poly(methyl methacrylate): static and fatigue properties.

A novel material called 'self-reinforced composite poly(methyl methacrylate)' (SRC-PMMA) is described. This composite material consists of high strength, high ductility PMMA fibres embedded in a matrix of PMMA. Tensile tests, three-point flexural tests, fracture toughness tests and flexural fatigue tests were carried out on unidirectional continuous fibre SRC-PMMA materials. Commercial sheet PMMA and bone cement were also tested for comparison purposes. Two PMMA fibre sizes (40 and 120 microns diameters) with different mechanical properties were used to make the SRC-PMMA materials. The results of this study show that the tensile strength, tensile modulus and tensile strain-to-failure were significantly greater for the SRC-PMMA compared with commercial PMMA (P < 0.05). The flexural strength was not increased in the SRC-PMMA compared with PMMA alone but was greater than that in bone cement (P < 0.05). There were no differences in flexural modulus between any group. The flexural strain-to-failure (30-35% for SRC-PMMA) was about three times greater in SRC-PMMA compared with bone cement and PMMA. Fracture toughness of these SRC-PMMA materials was also significantly greater than PMMA and bone cement (P < 0.001). Fracture toughness values of 3.2 MPa m1/2 were found in the 40 microns SRC-PMMA compared with 2.3 MPa m1/2 for the 120 microns SRC-PMMA and 1.3 MPa m1/2 for PMMA and bone cement. The fatigue strength of both SRC-PMMA samples was significantly greater (P < 0.001) at 80 MPa (10(6) cycles) compared with bone cement and PMMA, both of which had fatigue strengths of about 18 MPa. Fatigue damage in the form of fibre splitting and fibre-matrix interface failure was observed in the SRC-PMMA samples while the PMMA and bone cement showed only smooth fractures. During cyclic fatigue testing, the ongoing damage processes were periodically monitored using several novel computer-based and analysis algorithms. The measured cyclic loads and displacements are used to determine the creep-fatigue displacements, the sample stiffness (or modulus) and the hysteresis damage energy as functions of the number of applied cycles associated with the fatigue loading. The hysteresis damage energy to failure was about 25 times greater in the SRC-PMMA samples (2000 J at 10(6) cycles) compared with bone cement or PMMA at the same number of cycles to failure (80 J) indicating much greater fatigue damage tolerance in these materials. This material, SRC-PMMA, may be applicable for use in several medical and/or dental applications.

Bone Cements↗
PubMed2001

The importance of hyaluronic acid in vocal fold biomechanics.

OBJECTIVE: This study examined the influence of hyaluronic acid (HA) on the biomechanical properties of the human vocal fold cover (the superficial layer of the lamina propria). STUDY DESIGN: Vocal fold tissues were freshly excised from 5 adult male cadavers and were treated with bovine testicular hyaluronidase to selectively remove HA from the lamina propria extracellular matrix (ECM). Linear viscoelastic shear properties (elastic shear modulus and dynamic viscosity) of the tissue samples before and after enzymatic treatment were quantified as a function of frequency (0.01 to 15 Hz) by a parallel-plate rotational rheometer at 37 degrees C. RESULTS: On removing HA from the vocal fold ECM, the elastic shear modulus (G' ) or stiffness of the vocal fold cover decreased by an average of around 35%, while the dynamic viscosity (eta') increased by 70% at higher frequencies (>1 Hz). CONCLUSION: The results suggested that HA plays an important role in determining the biomechanical properties of the vocal fold cover. As a highly hydrated glycosaminoglycan in the vocal fold ECM, it likely contributes to the maintenance of an optimal tissue viscosity that may facilitate phonation, and an optimal tissue stiffness that may be important for vocal fundamental frequency control. SIGNIFICANCE: HA has been proposed as a potential bioimplant for the surgical repair of vocal fold ECM defects (eg, vocal fold scarring and sulcus vocalis). Our results suggested that such clinical use may be potentially optimal for voice production from a biomechanical perspective.

Adult↗
PubMed2006

Commercial extracellular matrix scaffolds for rotator cuff tendon repair. Biomechanical, biochemical, and cellular properties.

BACKGROUND: We are not aware of any in vitro study comparing the biomechanical, biochemical, and cellular properties of commercial extracellular matrix materials marketed for rotator cuff tendon repair. In this study, the properties of GraftJacket, TissueMend, Restore, and CuffPatch were quantified and compared with each other. The elastic moduli were also compared with that of normal canine infraspinatus tendon. METHODS: Samples were tested from different manufacturing lots of four materials: GraftJacket (ten lots), TissueMend (six), Restore (ten), and CuffPatch (six). The Kruskal-Wallis test was used to compare thickness, stiffness, and modulus as well as hydroxyproline, chondroitin/dermatan sulfate glycosaminoglycan, hyaluronan, and DNA contents among these matrices. The moduli of the extracellular matrices were also compared with those of normal canine infraspinatus tendon. RESULTS: All four extracellular matrices required 10% to 30% stretch before they began to carry substantial load. Their maximum moduli were realized in their linear region at 30% to 80% strain. The elastic moduli of all four commercial matrices were an order of magnitude lower than that of canine infraspinatus tendon. TissueMend had significantly higher DNA content than the other three matrices (p<0.0001), although both Restore and GraftJacket also had measurable amounts of DNA. CONCLUSIONS: Our data demonstrate chemical and mechanical differences among the four commercial extracellular matrices that we evaluated. Probably, the source (dermis or small intestine submucosa), species (human, porcine, or bovine), age of the donor (fetal or adult), and processing of these matrices all contribute to the unique biophysical properties of the delivered product. The biochemical composition of commercial extracellular matrices is similar to that of tendon. However, the elastic moduli of these materials are an order of magnitude lower than that of tendon, suggesting a limited mechanical role in augmentation of tendon repair.

Animals↗