Isometric tension developed during heating of collagenous tissues. Relationships with collagen cross-linking

Algorithm-controlled RF power output for enhanced margin precision in liver cancer radiofrequency ablation

BackgroundPercutaneous radiofrequency ablation (RFA) is a common method for treating liver cancer. Compared to other treatment modalities, RFA has a higher local tumor recurrence rate due to incomplete ablation. On the other hand, to ensure complete tumor removal, multiple ablations may be necessary, but this can lead to excessive thermal damage. Therefore, improving the precision of the ablation margin control is crucial.ObjectiveThis study aims to investigate an algorithm-controlled ablation mode that can precisely control the tumor treatment margins. This mode uses temperature and impedance as feedback parameters to adaptively adjust the RF power output, ensuring both effective tumor ablation and enhanced safety.MethodsThe study conducted finite element analyses and ex-vivo bovine liver experiments comparing traditional constant power ablation and the algorithm-controlled ablation mode. Simulations primarily analyzed the temperature changes and ablation area in biological tissue, assessing the effectiveness of the two ablation modes. In the ex-vivo bovine liver experiments, temperature and impedance were monitored in real-time to validate the feasibility of the algorithmic ablation mode.ResultsThe findings indicate that the algorithm-controlled ablation mode effectively controls the rise in tissue impedance, preventing carbonization and charring. For ablation diameters of 10 mm and 20 mm, it precisely maintained the boundary temperatures within the range of 50-60°C, ensuring effective damage at the ablation margins while avoiding excessive damage to normal tissue.ConclusionThis study developed an adaptive radiofrequency ablation algorithm for treating liver cancer, using temperature and impedance as feedback parameters. Preliminary results from finite element analysis and ex-vivo bovine liver experiments suggest that for small tumors with diameters of 10 mm and 20 mm, this algorithm may provide more precise control of the ablation zone, improving efficiency and safety compared to traditional constant power ablation.

Contribution of intramuscular connective tissue and its structural components on meat tenderness-revisited: a review

The tenderness of meat influences consumers' perceptions of its quality. Meat tenderness is a key quality characteristic that influences consumer satisfaction, repeat purchases, and willingness to pay higher prices for meat. Muscle fibers, connective tissues, and adipocytes are the main structural components of meat that contribute to its tenderness and texture. In the present review, we have focused on the role of connective tissue and its components in meat tenderness, specifically perimysial intramuscular connective tissue (IMCT) and its concept as an immutable "background toughness." The collagen contribution to cooked meat toughness can be altered by animal diet, compensatory growth, slaughter age, aging, and cooking. As well, progressive thickening of the perimysium leads to a progressive increase in shear force values in beef, pork, chicken, and this may occur prior to adipocyte formation as cattle finish in feedlots. Conversely, adipocyte accumulation in the perimysium can decrease cooked meat shear force, suggesting that the contribution of IMCT to meat toughness is complex and driven by both collagen structure and content. This review provides a theoretical foundation of information to modify IMCT components to improve meat tenderness.

Shrinkage Properties and Their Relationship with Degradation of Proteins Linking the Endomysium and Myofibril in Lamb Meat Submitted to Heating or Air Drying

The shrinkage of the connective tissue and myofiber of lamb meat submitted to heat treatment or air drying at different storage stages (1, 5 and 7 days) was evaluated herein. The longitudinal and transverse shrinkage of heated lamb meat was significantly influenced by storage time and water bath heating temperature (50 °C, 70 °C and 90 °C) (p < 0.001). In contrast, the shrinkage of air-dried lamb meat was not influenced by storage time (p > 0.05). The microstructure of heated lamb meat, namely, the distance between muscle fascicles, the distance between myofibril networks, the area of myofibril networks, and the endomysium circumference, was significantly influenced by storage time (p < 0.05). During storage, the proportion of muscle fibers completely detached from endomysium increased, which could be due to the progressive degradation of proteins linking the endomysium and myofibril, including β-dystroglycan, α-dystroglycan, integrin-β1, and dystrophin. However, degradation of such proteins did not influence the shrinkage of lamb meat stored for five days or longer, since the decreased distance between myofibril networks indicated a higher shrinkage ratio of the endomysium compared to myofibers in samples air-dried at 35 °C or heated at 90 °C. The effect of these proteins on the shrinkage of heated lamb meat (raw meat stored for 1 day or less time) requires further elucidation.

Effect of testing temperature on the nanostructural response of tendon to tensile mechanical overload

Despite many in vitro mechanical experiments of tendon being conducted at room temperature, few assessments have been made to determine how the structural response of tendon to mechanical overload may vary with ambient temperature. We explored whether damage to the collagen nanostructure of tendon resulting from tensile rupture varies with temperature. Use of bovine tail tendons in combination with NaBH₄ crosslink stabilization treatment allowed us to probe the mechanisms underlying the observed changes. Untreated tendons and NaBH₄-stabilized tendons were pulled to rupture at temperatures of 24, 37, and 55 °C. Of nine mechanical parameters measured from the resulting stress-strain curves, only yield stress differed between the tendons tested at 37 and 24 °C. When tested at 55 °C, untreated tendons showed large reductions in ultimate strength and toughness, while NaBH₄-stabilized tendons showed smaller reductions. Differential scanning calorimetry was used to assess damage to the collagen fibril nanostructure of tendons resulting from rupture, with samples from the ruptured tendons compared to samples from the same tendons removed prior to loading. While there was indication that overload-induced molecular packing disruption to collagen fibrils may be heightened at 37 °C, statistical increases in damage compared to that occurring at 24 °C were only seen when testing was conducted at 55 °C. The results show that the temperature sensitivity of tendon to ramp loading depends on crosslinking within the tissue. In poorly crosslinked tissues, collagen may be more susceptible to mechanical damage when tested at physiologic temperature compared to room temperature. For tendons with a high density of thermally stable crosslinks, such as the human Achilles or patellar tendons, testing at room temperature should produce comparable results to testing at physiologic temperature.

The thermal shrinkage force in perimysium from different beef muscles is not affected by post-mortem ageing

Differences in the thermal shrinkage and collagen solubility between bovine Semitendinosus (ST) and Pectoralis profundus (PP) muscles and their interactions with ageing were evaluated by studying collagen solubility, hydrothermal isometric tension and thermal denaturation properties of intramuscular connective tissue after 5-20days post-mortem storage at 4°C. Collagen solubility was higher in ST than in PP muscle at 5-13days, but the differences between the two muscles decreased at longer ageing times. A small decrease in the peak denaturation temperature of perimysium occurred with increasing ageing times in both muscles. Maximum force in isometrically-heated perimysium was broadly equivalent in both muscles. Although the amount and solubility of collagen varies between muscles and ageing decreases the stability of some of the collagen, thermal shrinkage forces in heated perimysium are not significantly diminished by ageing. These findings support the idea of one collagen fraction easily degraded by ageing and heat, and another more resistant fraction that determines the physical properties of the tissue after ageing and cooking.

Pregnancy-induced remodeling of heart valves

Recent studies have demonstrated remodeling of aortic and mitral valves leaflets under the volume loading and cardiac expansion of pregnancy. Those valves' leaflets enlarge with altered collagen fiber architecture, content, and cross-linking and biphasic changes (decreases, then increases) in extensibility during gestation. This study extends our analyses to right-sided valves, with additional compositional measurements for all valves. Valve leaflets were harvested from nonpregnant heifers and pregnant cows. Leaflet structure was characterized by leaflet dimensions, and ECM composition was determined using standard biochemical assays. Histological studies assessed changes in cellular and ECM components. Leaflet mechanical properties were assessed using equibiaxial mechanical testing. Collagen thermal stability and cross-linking were assessed using denaturation and hydrothermal isometric tension tests. Pulmonary and tricuspid leaflet areas increased during pregnancy by 35 and 55%, respectively. Leaflet thickness increased by 20% only in the pulmonary valve and largely in the fibrosa (30% thickening). Collagen crimp length was reduced in both the tricuspid (61%) and pulmonary (42%) valves, with loss of crimped area in the pulmonary valve. Thermomechanics showed decreased collagen thermal stability with surprisingly maintained cross-link maturity. The pulmonary leaflet exhibited the biphasic change in extensibility seen in left side valves, whereas the tricuspid leaflet mechanics remained largely unchanged throughout pregnancy. The tricuspid valve exhibits a remodeling response during pregnancy that is significantly diminished from the other three valves. All valves of the heart remodel in pregnancy in a manner distinct from cardiac pathology, with much similarity valve to valve, but with interesting valve-specific responses in the aortic and tricuspid valves.

Repeated subrupture overload causes progression of nanoscaled discrete plasticity damage in tendon collagen fibrils

A critical feature of tendons and ligaments is their ability to resist rupture when overloaded, resulting in strains or sprains instead of ruptures. To treat these injuries more effectively, it is necessary to understand how overload affects the primary load-bearing elements of these tissues: collagen fibrils. We have investigated how repeated subrupture overload alters the collagen of tendons at the nanoscale. Using scanning electron microscopy to examine fibril morphology and hydrothermal isometric tension testing to look at molecular stability, we demonstrated that tendon collagen undergoes a progressive cascade of discrete plasticity damage when repeatedly overloaded. With successive overload cycles, fibrils develop an increasing number of kinks along their length. These kinks-discrete zones of plastic deformation known to contain denatured collagen molecules-are accompanied by a progressive and eventual total loss of D-banding along the surface of fibrils, indicating a loss of native molecular packing and further molecular denaturation. Thermal analysis of molecular stability showed that the destabilization of collagen molecules within fibrils is strongly related to the amount of strain energy dissipated by the tendon after yielding during tensile overload. These novel findings raise new questions about load transmission within tendons and their fibrils and about the interplay between crosslinking, strain-energy dissipation ability, and molecular denaturation within these structures.

Relationship between meat toughness and properties of connective tissue from cows and young bulls heat treated at low temperatures for prolonged times

The aim of the current study was to elucidate whether cows and young bulls require different combinations of heating temperature and heating time to reduce toughness of the meat. The combined effect of heating temperature and time on toughness of semitendinosus muscle from the two categories of beef was investigated and the relationship to properties of connective tissue was examined. Measurements of toughness, collagen solubility, cathepsin activity and protein denaturation of beef semitendinosus heated at temperatures between 53°C and 63°C for up to 19 1/2 h were conducted. The results revealed that slightly higher temperatures and prolonged heating times were required to reduce toughness of semitendinosus from cows to the same level as in young bulls. Reduced toughness of semitendinosus as a result of low temperature for prolonged time is suggested to result from weakening of the connective tissue, caused partly by denaturation or conformational changes of the proteins and/or by solubilization of collagen.

Effects of avocado and soya bean lipidic non-saponifiables on the components of skin connective tissue after topical application in the hairless rat: biophysical and biomechanical determination

Synopsis The non-saponifiable lipidic fractions of avocado and soya bean applied percutaneously to hairless rats for 15 days had been shown to produce biochemical modifications of dermal connective tissue components: increases of soluble collagen and of the ratio soluble collagen/insoluble collagen. In this present study, we tried to show whether these biochemical modifications could be confirmed by biophysical analytical methods and could affect the biochemical properties of the skin. The experiments were carried out on three groups of rats treated by application to the dorsal skin, either with 0.9% NaCl (control), or sweet almond oil (vehicle), or with a mixture of 2/3 soya bean and 1/3 avocado in solution at 5% of sweet almond oil (treated group). After 15 days treatment, the rats were killed and the skin of the treated area dissected. X-ray diffraction diagrams were recorded by varying the position of previously dried samples in controlled conditions. Results indicated that the vehicle decreased the orientation degree of collagen fibres, acting on their reticulation. The addition of the non-saponifiable fraction did not significantly add to the vehicle effect. The study of thermostability of the cutaneous collagen by differential scanning calorimetry showed that non-saponifiables increased the slope of the rise of temperature of denaturation. The quantity of heat absorbed during the denaturation (enthalpy variation) reached around 0.04 J mg(-1) of collagen in the control groups and did not exceed 0.03 J mg(-1) of collagen in the treated ones. Taken in conjunction with previous work it is probable that the non-saponifiables increase the proportion of soluble collagen. The elasticity of whole skin, determined by a static method using an Instron exten-siometer was significantly modified by treatment with non-saponifiables. They produced a decrease of the elasticity module. These results correspond to a decrease of collagen reticulation degree.

Interrelationships amongst carcass and meat quality characteristics of sheep

The relationships between various carcass and meat quality characteristics of sheep were studied. Relationships were determined by regression, using data obtained from sheep belonging to a wide range of breeds, sex types and slaughter weight (32-62 kg). The chilling rate of the M. longissimus dorsi (LD) post-mortem was negatively correlated with carcass weight (r=-0.42, P<0.01), back fat thickness (r=-0.54, P<0.001) and the cooking loss of the M. infraspinatus (IS) muscle (r=-0.44, P<0.001). Correlation between chilling rate and shear force of the IS muscle was not significant, which was also the case between chilling rate and the cooking loss and shear force of the LD and M. triceps brachii muscles. A positive relationship was observed between total collagen and cooking loss (r=0.34, P<0.05) and between heat-insoluble collagen and cooking loss of the LD muscle (r=0.37, P<0.01). Generally collagen content was positively correlated with lean content and negatively with fat content. Carcass weight was significantly (P<0.001) correlated with intramuscular fat (r=0.61), moisture (r=-0.76), cooking loss (r=-0.49), shear force (r=-0.41) and hue angle (r=-0.41). Shear force was positively associated with cooking loss (r=0.42, P<0.001), but negatively with intramuscular fat content (r=-0.55, P<0.001). Cooking loss was positively correlated with moisture content (r=0.55, P<0.001).

Changes in Collagen With Aging Maintain Molecular Stability After Overload: Evidence From an In Vitro Tendon Model

Soft tissue injuries are poorly understood at the molecular level. Previous work using differential scanning calorimetry (DSC) has shown that tendon collagen becomes less thermally stable with rupture. However, most soft tissue injuries do not result in complete tissue rupture but in damaging fiber overextension. Covalent crosslinking, which increases with animal maturity and age, plays an important role in collagenous fiber mechanics. It is also a determinant of tissue strength and is hypothesized to inhibit the loss of thermal stability of collagen due to mechanical damage. Controlled overextension without rupture was investigated to determine if overextension was sufficient to reduce the thermal stability of collagen in the bovine tail tendon (BTT) model and to examine the effects of aging on the phenomenon. Baseline data from DSC and hydrothermal isometric tension (HIT) techniques were compared between two groups: steers aged 24–30 months (young group), and skeletally mature bulls and oxen aged greater than five years (old group). Covalent crosslinks were quantified by ion exchange chromatography. Overextension resulted in reduced collagen thermal stability in the BTT model. The Young specimens, showing detectably lower tissue thermomechanical competence, lost more thermal stability with overextension than did the old specimens. The effect on old specimens, while smaller, was detectable. Multiple overextension cycles increased the loss of stability in the young group. Compositional differences in covalent crosslinking corresponded with tissue thermomechanical competence and therefore inversely with the loss of thermal stability. HIT testing gave thermal denaturation temperatures similar to those measured with DSC. The thermal stability of collagen was reduced by overextension of the tendon—without tissue rupture—and this effect was amplified by increased cycles of overextension. Increased tissue thermomechanical competence with aging seemed to mitigate the loss of collagen stability due to mechanical overextension. Surprisingly, the higher tissue thermomechanical competence did not directly correlate with the concentration of endogenous enzymatically derived covalent crosslinking on a mole per mole of collagen basis. It did, however, correlate with the percentage of mature and thermally stable crosslinks. Compositional changes in fibrous collagens that occur with aging affect fibrous collagen mechanics and partially determine the nature of mechanical damage at the intermolecular level. As techniques develop and improve, this new information may lead to important future studies concerning improved detection, prediction, and modeling of mechanical damage at much finer levels of tissue hierarchy than currently possible.

Differences in collagen cross-linking between the four valves of the bovine heart: a possible role in adaptation to mechanical fatigue

Hydrothermal isometric tension (HIT) testing and high-performance liquid chromatography were used to assess the molecular stability and cross-link population of collagen in the four valves of the adult bovine heart. Untreated and NaBH4-treated tissues under isometric tension were heated in a water bath to a 90°C isotherm that was sustained for 5 h. The denaturation temperature (Td), associated with hydrogen bond rupture and molecular stability, and the half-time of load decay ( t1/2), associated with peptide bond hydrolysis and intermolecular cross-linking, were calculated from acquired load/temperature/time data. An unpaired group of samples of the same population was biochemically assayed for the types and quantities of enzymatic cross-links present. Tissues known to endure higher in vivo transvalvular pressures had lower Td values, suggesting that molecular stability is inversely related to in vivo loading. The treated inflow valves (mitral and tricuspid) had significantly lower t1/2 values than did treated outflow valves (aortic and pulmonary), suggesting lower overall cross-linking in the inflow valves. Inflow valves were also found to fail during HIT testing significantly more often than outflow valves, also suggestive of a decreased cross-link population. Inflow valves may be remodeling at a faster rate and may be at an earlier state of molecular “maturity” than outflow valves. At the molecular level, the thermal stability of collagen is associated with in vivo loading and may be influenced by the mature, aldimine-derived cross-link, histidinohydroxylysinonorleucine. We conclude that the valves of the heart utilize differing, location-specific strategies to resist biomechanical fatigue loading.

Performance, slaughter characteristics and meat quality of young bulls from Belgian Blue, Limousin and Aberdeen Angus breeds fattened with a sugar-beet pulp or a cereal-based diet

Thirty-six young fattening bulls from three breeds (Belgian Blue, Limousin and Aberdeen Angus) were fattened over 5 months with fattening diets based either on sugar-beet pulp or on cereals. Fattening performance as well as carcass and meat characteristics were measured. There were few relevant effects of the diets on the parameters. The breeds also showed similar fattening features. However, the BB had higher killing-out proportion and their carcasses presented better scores in terms of conformation and fattening. The meat quality of the breeds differed, especially in terms of luminosity, redness and cooking losses. There were also significant influences of breed on the chemical composition of meat; fat content was lowest in Belgian Blue and highest in Aberdeen Angus. Such specificities could help to allocate breeds in appropriate niches in Belgium.

Comparison of composition and quality traits of meat from young finishing bulls from Belgian Blue, Limousin and Aberdeen Angus breeds

Thirty-six young finishing bulls from three breeds (Belgian Blue, Limousin and Aberdeen Angus) were fattened over five months with finishing diets based either on sugar-beet pulp or on cereals. Nutritional quality traits of meat - fat content and fatty acid composition with emphasis on the n-6 and n-3 polyunsaturated fatty acids - along with some organoleptic quality traits were measured. The Belgian Blue bulls had the lowest intramuscular fat content associated with lower saturated and monounsaturated fatty acid contents. The polyunsaturated fatty acid content did not differ to a large extent between the breeds, the Aberdeen Angus bulls showing slightly higher values. Relative to energy intake, the overall contribution of meat to the n-3 fatty acid recommended intake was small, whatever the breed. By contrast, the contribution of meat to daily fat intake was of greater importance, especially for the Aberdeen Angus bulls. The quality traits of meat varied also according to the breed: compared to the Aberdeen Angus, the Belgian Blue bull meat had the stablest colour, the highest drip and the lowest cooking losses. The meat of Limousin bulls had intermediate characteristics for all the parameters.

A review of the general aspects of radiofrequency ablation

As an alternative to standard surgical resection for the treatment of malignant tumors, radiofrequency ablation (RFA) has rapidly evolved into the most popular minimally invasive therapy. To help readers gain the relevant background knowledge and to better understand the other reviews in this Feature Section on the clinical applications of RFA in different abdominal organs, the present report covers the general aspects of RFA. After an introduction, we present a simple definition of the energy applied during RFA, a brief historical review of its technical evolution, and an explanation of the mechanism of action of RFA. These basic discussions are substantiated with descriptions of RFA equipment including those commercially available and those under preclinical development. The size and geometry of induced lesions in relation to RFA efficacy and side effects are discussed. The unique pathophysiologic process of thermal tissue damage and the corresponding histomorphologic manifestations after RFA are detailed and cross-referenced with the findings in the current literature. The crucial role of imaging technology during and after RFA is also addressed, including some promising new developments. This report finishes with a summary of the key messages and a perspective on further technologic refinements and identifies some specific priorities.

The increase in denaturation temperature following cross-linking of collagen is caused by dehydration of the fibres

Differential scanning calorimetry (DSC) was used to study the thermal stability of native and synthetically cross-linked rat-tail tendon at different levels of hydration, and the results compared with native rat-tail tendon. Three cross-linking agents of different length between functional groups were used: malondialdehyde (MDA), glutaraldehyde and hexamethylene diisocyanate (HMDC). Each yielded the same linear relation between the reciprocal of the denaturation temperature in Kelvin, T(max), and the water volume fraction, epsilon (1/T(max)=0.000731epsilon+0.002451) up to a critical hydration level, the volume fraction of water in the fully hydrated fibre. Thereafter, water was in excess, T(max) was constant and the fibre remained unchanged, no matter how much excess water was added. This T(max) value and the corresponding intrafibrillar volume fraction of water were as follows: 84.1 degrees C and 0.48 for glutaraldehyde treated fibres, 74.1 degrees C and 0.59 for HMDC treated fibres, 69.3 degrees C and 0.64 for MDA treated fibres, and 65.1 degrees C and 0.69 for untreated native fibres. Borohydride reduction of the native enzymic aldimines did not increase the denaturation temperature of the fibres. As all samples yielded the same temperature at the same hydration, the temperature could not be affected by the nature of the cross-link other than through its effect on hydration. Cross-linking therefore caused dehydration of the fibres by drawing the collagen molecules closer together and it was the reduced hydration that caused the increased temperature stability. The cross-linking studied here only reduced the quantity of water between the molecules and did not affect the water in intimate contact with, or bound to, the molecule itself. The enthalpy of denaturation was therefore unaffected by cross-linking. Thus, the "polymer-in-a-box" mechanism of stabilization, previously proposed to explain the effect of dehydration on the thermal properties of native tendon, explained the new data also. In this mechanism, the configurational entropy of the unfolding molecule is reduced by its confinement in the fibre lattice, which shrinks on cross-linking.

Altered Mechanical Behavior of Epicardium Under Isothermal Biaxial Loading

Most soft tissues that are treated clinically via heating experience multiaxial states of stress and strain in vivo and are subject to complex constraints during treatment. Remarkably, however, there are no prior data on changes in the multiaxial mechanical behavior of a collagenous tissue subjected to isometric constraints during heating. This paper presents the first biaxial stress-stretch data on a collagenous membrane (epicardium) before and after heating while subjected to various biaxial isometric constraints. It was found that isometric heating does not allow the increase in stiffness at low strains that occurs following isotonic heating. Moreover, increasing the degree of stretch prior to heating increased the thermal stability of the tissue consistent with the concept that mechanical loading primarily affects the activation entropy, not the activation energy.

Denaturation of collagen via heating: an irreversible rate process

Heating therapies are increasingly used in cardiology, dermatology, gynecology, neurosurgery, oncology, ophthalmology, orthopedics, and urology, among other medical specialties. This widespread use of heating is driven primarily by the availability of new technology, not by a detailed understanding of the biothermomechanics. Without basic quantification of the underlying physical and chemical processes in terms of parameters that can be controlled clinically, identification of preferred interventions will continue to be based primarily on trial and error, thus necessitating large clinical studies and years of accumulative experience. Perusal of the literature reveals that much has been learned over the past century about the response of cells, proteins, and tissues to supra-physiologic temperatures; yet, the associated findings are reported in diverse journals and the underlying basic processes remain unidentified. In this review, we seek to contrast various findings on the kinetics of the thermal denaturation of collagen and to encourage investigators to consider the many open problems in part via a synthesis of results from the diverse literatures.

Glenohumeral translation after arthroscopic thermal capsuloplasty with a radiofrequency probe

The purpose of this study was to determine whether there are changes in anterior and posterior glenohumeral translation after arthroscopic thermal capsuloplasty with a radiofrequency probe. Anteriorly directed loads of 15 N and 20 N were sequentially applied to the humerus of each of 5 cadaveric glenohumeral joints, and anterior translation on the glenoid was measured through use of a customized translation apparatus and an electromagnetic tracking device. The tests were then repeated with posteriorly directed forces, and posterior translation was measured. During testing, the glenoid was rigidly fixed and the glenohumeral joint was positioned to simulate 90 degrees of shoulder abduction and 90 degrees of external rotation. By means of the radiofrequency probe, thermal energy was then applied to the anteroinferior capsuloligamentous structures; anterior and posterior translation measurements were repeated. The results showed a significant reduction in anterior and posterior translations after thermal capsuloplasty (P < .05). Anterior translation decreased from 6.8 to 4.0 mm (a 41% decrease) with the 15-N load and from 8.6 to 4.9 mm (a 42% decrease) with the 20-N load. Posterior translation decreased from 9.3 to 5.8 mm (a 36% decrease) with the 15-N load and from 10.4 to 6.5 mm (a 35% decrease) with the 20-N load. The results of this study indicate that the radiofrequency probe can be used to decrease both anterior and posterior glenohumeral translation in vitro. The biological effect on heat-treated tissues over time needs to be studied to prove that this is a satisfactory treatment for glenohumeral instability.

Radiofrequency thermal ablation of hepatocellular carcinomas

Although surgical resection remains the best option as potentially curative therapy for hepatocellular carcinoma, radiofrequency thermal ablation has begun to receive much attention as an effective minimally invasive technique for the local control of unresectable malignant hepatic tumors. Most recent radiofrequency devices equipped with a powerful generator and larger needle electrode permit larger thermal lesions, up to 5 cm in diameter, with a single ablation. In this article, the author reviews the technical developments and early clinical results obtained with radiofrequency ablation techniques.

Changes of biochemical and biomechanical properties in Dupuytren disease

BACKGROUND

The major biochemical characteristic of Dupuytren disease is the progressive and irreversible deposition of excess fibrous collagen characterized by an enhanced type III collagen proportion.

OBJECTIVE

To investigate the influence of changes of the collagen spectrum on the biophysical properties of the palmar aponeurosis.

DESIGN

Variably affected palmar regions from 30 individuals with Dupuytren disease were classified according to histologic test results and clinical stage. Biochemical, biomechanical, and thermal contracture studies were performed.

RESULTS

The relative type III collagen content increased with increasing tissue involvement and was found to correlate with calorimetric and biomechanical properties with the exception of the Young modulus. In experiments on the thermal isometric contracture, the collagen denaturation temperature decreased with increasing type III collagen content, ie, increasing involvement. To study the dependence of biophysical properties from the collagen type distribution independent of structural changes, as seen in Dupuytren disease, we investigated rat skins from animals of an age range characterized by dramatic changes in type III collagen content (0-18 months). Biomechanical data also correlated significantly with type III collagen content in rat skin with the exception of the time constant of stress relaxation.

CONCLUSION

In light of these results, we suggest that structural changes, such as reduced collagen fibril diameters, associated with alterations in the type III collagen proportion may influence biophysical properties of connective tissues in the involved palmar aponeurosis in addition to alterations of the cross-linking pattern.

Differential scanning calorimetry, biochemical, and biomechanical analysis of human skin from individuals with diabetes mellitus

The aim of this work was to compare biochemical, two-dimensional biomechanical and calorimetric parameters of diabetic skin vs. control skin. Skin specimens taken from the palms and backs of the hands of aged persons with non-insulin-dependent diabetes mellitus (NIDDM) and of controls (CO) were compared (age range 68-85 years). Only skin specimens from individuals with diabetes mellitus (DM) showed an increased fluorescence specific for the formation of advanced glycation end-products (AGEs) and the presence of tissue AGEs, such as N(e)-(Carboxymethyl)lysine (CML). Differential scanning calorimetry (DSC) revealed an elevation of the heat flow per unit mass during collagen denaturation in diabetic skin samples. However, the temperatures of the heat flow maximum and the onset of the phase transformation were not uniformly altered. Young's moduli were found to be increased in diabetic skin and correlated with AGE-fluorescence and tissue AGEs. The ratio between the Young's moduli, which defines a measure for the degree of anisotropy, was higher for dorsal skins from hands. In dorsal skin specimens from diabetic subjects the degree of anisotropy was more pronounced than in healthy controls. In general, neither of the measured parameters showed any correlation with age. However, E(1) moduli were clearly associated with the duration of diabetes.

Monopolar radiofrequency energy effects on joint capsular tissue: potential treatment for joint instability. An in vivo mechanical, morphological, and biochemical study using an ovine model

The purpose of this study was to evaluate the thermal effect of monopolar radiofrequency energy, a potential treatment means for joint instability, on the mechanical, morphologic, and biochemical properties of joint capsular tissue in an in vivo ovine model. The energy was applied arthroscopically to the synovial surface of the femoropatellar joint capsule of 24 sheep. The sheep were sacrificed at 0, 2, 6, and 12 weeks after surgery (6 per group). Monopolar radiofrequency energy initially caused a significant decrease in tissue stiffness and an increase in tissue relaxation properties, followed by gradual improvement in the tissue's mechanical properties by 6 weeks after surgery. Microscopic examination illustrated that radiofrequency energy initially caused collagen hyalinization and cell necrosis, followed by active tissue repair. Biochemical analysis revealed that treated collagen was significantly more trypsin-susceptibile than untreated collagen at 0 and 2 weeks after surgery, indicating early collagen denaturation. This study demonstrated that this treatment initially caused a significantly deleterious effect on the mechanical properties of the joint capsule, which was associated with partial denaturation of joint capsular tissue. This was followed by gradual improvement of the mechanical, morphologic, and biochemical properties of the tissue over time.

Determinants of mechanical properties in the developing ovine thoracic aorta

We previously reported changes in mechanical properties and collagen cross-linking of the ovine thoracic aorta during perinatal development and postnatal maturation, and we now report changes in biochemical composition (elastin, collagen, and DNA contents per mg wet wt) over the same developmental intervals. A comparison of results from the present and previous studies has yielded novel and important observations concerning the relationship between aortic mechanics and composition during maturation. Developmental changes in aortic incremental elastic modulus at low tensile stress (E(low)) closely followed changes in relative elastin content (i.e., per mg wet wt). An 89% increase in E(low) during the perinatal period was associated with a 69% increase in relative elastin content, whereas neither variable changed during postnatal life. Incremental elastic modulus at high tensile stress (E(high)) did not change during the perinatal period but increased 88% during postnatal life. This pattern closely paralleled changes in collagen cross-linking index, which did not change perinatally but almost doubled postnatally. In contrast, relative collagen content (per mg wet wt) increased only slightly from fetal to adult life, a trend that was unrelated to aortic mechanics. Substantial, progressive decreases in measures of wall viscosity (pressure wave attenuation coefficient and viscoelastic phase angle) from fetal to adult life followed the pattern observed for relative DNA (smooth muscle cell) content (per mg wet wt). Our findings suggest that accumulation of elastin per milligram wet weight contributes most to developmental changes in E(low), change in collagen cross-linking is the primary determinant of developmental changes in E(high), and cell accumulation contributes most to developmental changes in wall viscosity.

Electrothermally-assisted capsular shift

The marriage of biomedical instrumentation and patient care has once again proven itself successful. The ETAC is a new procedure with various potential applications. Despite its embryonic stage, this procedure is being used by a handful of shoulder surgeons who are cautiously pursuing new and improved ways to prevent the common and debilitating diagnosis of shoulder instability. Follow-up thus far is short, and the current literature lacks studies that compare the time-honored conventional standard of open stabilization to this new procedure. However, those surgeons who have been using this device are optimistic about its role in the future repair of shoulder injuries.

Heat-induced changes in the mechanics of a collagenous tissue: isothermal free shrinkage

We present data from isothermal free-shrinkage tests (i.e., performed in the absence of mechanical loads) wherein bovine chordae tendineae were subjected to temperatures from 65 to 85 degrees C for 120 to 1200 s. These data reveal four new insights into heat-induced denaturation of a collagenous tissue. First, a characteristic time for the free shrinkage appears to exhibit an Arrhenius-type relationship with temperature. Second, scaling the actual heating time via the characteristic time results in a single correlation between free shrinkage and the duration of heating; this correlation suggests a time-temperature equivalence. Third, it is the cumulative, not current, heating time that governs the free shrinkage. And fourth, heat-induced free shrinkage is partially recovered when the tissue is returned to 37 degrees C, this recovery also being time-dependent. Although these findings will help guide future experimentation and constitutive modeling, as well as the design of new heat-based clinical therapies, there is a pressing need to collect additional isothermal data, particularly in the presence of well-defined mechanical loads.

Crosslinking density and resorption of dimethyl suberimidate-treated collagen

Collagen was purified from bovine Achilles tendon and crosslinked with dimethyl suberimidate (DMS) and glutaraldehyde (GTA). Under optimal conditions, the shrinkage temperature (Ts) was raised to 74 degrees C for collagen crosslinked with DMS and to 80 degrees C for those crosslinked with GTA. Crosslinking density measurements were done on the hydrothermally denatured collagen by the method based on the Flory-Rehner equation. GTA treatment was found to introduce more number of crosslinks than DMS. The maximum tension attained during heating (after shrinkage has occurred) was greater for GTA-treated collagen than for DMS and control. The control collagen membranes broke during heating (at 73 degrees C), while for the crosslinked membranes the tension kept on increasing up to 100 degrees C. The crosslinking density correlated well with the data determined from the in vitro and in vivo degradation studies. Uncrosslinked and DMS crosslinked collagen membranes were more susceptible to degradation by enzymes in vitro, while GTA-treated collagen was highly resistant to degradation. The biocompatibility of the collagen membranes was studied by subcutaneous implantation in rats. Uncrosslinked collagen membranes degraded within 14 days with the formation of granulation tissue. DMS crosslinked membranes degraded within 21 days and the area was replaced by numerous fibroblasts and newly formed collagen. No calcification was observed. For GTA-treated membranes, necrosis was observed after 7 days implantation and by 14 days the membrane had started to calcify.

Dynamic glutaraldehyde fixation of a porcine aortic valve xenograft. I. Effect of fixation conditions on the final tissue viscoelastic properties

Sixty porcine aortic valves were fixed under dynamic conditions at specific durations, pressures and vibration rates in a 0.5% glutaraldehyde phosphate buffer (pH 7.4, 0.2 M). Tensile relaxation tests were performed at low through high extension rates (0.3, 3 and 30 mm s-1) and tissue denaturation temperatures were determined by the hydrothermal isometric tension method. Conventional statically fixed valves and fresh valves were used as controls. No differences between dynamic and static treatment were observed at pulsation rates above those expected in the physiological range (i.e. above 1.2 Hz) or at higher pressures such as 30 mmHg. However, differences in both stress relaxation rates and denaturation temperatures were delineated in milder fixation conditions, i.e. at low pressures (< 4 mmHg) and low vibration rates similar to that of the normal heart beat (approximately 1.2 Hz). In these conditions the relaxation rate of the dynamically fixed tissue (-7.4 +/- 0.7% of stress remaining per log(s)) was similar to that of the fresh tissue (-6.7 +/- 1.2% log(s-1)) and significantly higher than the statically treated tissue (-3.9 +/- 1.7% log(s-1)). The rates of stress relaxation appeared to be strain rate dependent in both radial and circumferential directions when the tissues were strained at physiological rates during testing (> approximately 15000% min-1). Dynamically treated valves showed higher denaturation temperatures (mean +/- SD) (89.4 +/- 0.5 degree C) compared with the statically fixed (82.7 +/- 1.4 degrees C) or untreated (fresh) valves (65.5 +/- 0.8 degree C). The results suggest a higher degree of internal cross-linking owing possibly to enhanced penetration of the glutaraldehyde reagent and a greater accessability of reactive cross-linking sites on the collagen molecules. Better stress relaxation rates are likely associated with an increase in potential shearing between adjacent collagen fibres thus preserving the natural stress-reducing mechanism of the fresh, untreated valves. The dynamically treated valves therefore possess characteristics that may enable them to better resist long-term mechanical fatigue and in vivo degradation.

Comparison of the effect of different inhibitors of the non-enzymatic glycation of rat tail tendons and bovine serum albumin

The biomechanical and biochemical properties of collagen are changed by non-enzymatic glycation culminating in increased cross-linking. We have previously shown that dibasic amino acids such as L-arginine inhibit in vitro the non-enzymatic glycation of soluble proteins and insoluble connective tissue macromolecules. In the present in vitro study we obtained evidence that the nucleophilic hydrazine derivative aminoguanidine and the non-steroidal anti-rheumatic drug ibuprofen inhibit the formation of fluorescent advanced glycation end products (AGEs) to a comparable extent, while arginine is ineffective as a consequence of its tendency to form AGEs itself. Periodic replacement of glycated arginine in the rat tail tendon system, however, engendered an inhibition of fluorescence similar to that obtained by the other inhibitors. Long-term glycation of rat tail tendons caused a significant increase in Young's modulus, which could also be inhibited by periodically renewed arginine. In contrast to ibuprofen, aminoguanidine and arginine-lysine inhibited the marked increase in maximum contraction force of long-term glycated rat tail tendons. As opposed to other inhibitors, aminoguanidine also reduced the thermal contraction force of native tendons, shifted the maximum contraction temperature to markedly lower values and solubilized a significant part of the rat tail tendon collagen. These findings indicate that the in vitro alterations of rat tail tendon collagen induced by non-enzymatic glycation can be prevented by arginine, arginine-lysine and aminoguanidine. However, collagen structure is seriously affected by aminoguanidine.

Heat-induced changes in the mechanical behavior of passive coronary arteries

We performed in vitro pressure-diameter and axial force-length experiments on nondiseased, passive bovine coronary arteries subjected to bath temperatures from 21 to 80 degrees C for 90 s to 4 hr. Over the strain ranges studied, we found that: (a) vessel behavior remained the same over 20 min of testing at 21 to 55 degrees C, (b) vessels stiffened multiaxially after 5 min of exposure to 60 degrees C and continued to stiffen over 20 min of testing, (c) dramatic multiaxial vessel stiffening and shrinkage occurred after 90 s of exposure to 70 and 80 degrees C, and (d) heat-induced changes at 70 degrees C depended on the intraluminal pressure during heating. Thus, passive bovine coronary arteries exhibit a complex thermomechanical behavior that depends on the temperature, duration of thermal exposure, and the mechanical loads applied during heating.

Thermal stability of cortical bone collagen in relation to age in normal individuals and in individuals with osteopetrosis

The thermal stability of cortical bone collagen was determined in iliac crest biopsies obtained from 41 normal individuals (21 women aged 20-96 years and 20 men aged 21-84 years) and 8 individuals with autosomal dominant osteopetrosis type I (4 women and 4 men aged 17-63 years). The cortical bone was decalcified and the bone matrix was cut into 80-microns-thick freeze sections parallel to the bone surface. Circular specimens punched out from the sections were used for determination of area shrinkage during gradual heating and shrinkage temperature, Ts (representing the temperature for 50% of the area shrinkage). In normal men, Ts was not found to decrease until the age of 60-65 years, but was markedly decreased in the elderly individuals. In normal women, Ts varied considerably throughout the age range tested, without relationship to age. In contrast to age-matched controls, Ts decreased with age in men with osteopetrosis, whereas Ts in affected women was neither related to age nor different from the highly variable values found in age-matched normal women. Previous findings in rats indicate that Ts decreases with the chronological age of the bone collagen. The present results agree with these findings, which imply that a reduction in turnover rate of bone results in an increasing age and a reduced Ts of the constituent collagen. Following this assumption, the turnover rate of bone seems to be more variable in women than in men and reduced in osteopetrotic men.(ABSTRACT TRUNCATED AT 250 WORDS)

Laser balloon angioplasty: potential for reduction of the thrombogenicity of the injured arterial wall and for local application of bioprotective materials

Mitigation of adverse biologic reactivity after balloon angioplasty is necessary before the incidence of restenosis can be appreciably reduced. A brief review of experimental evidence supports the hypothesis that the thrombogenicity of the injured arterial wall can be reduced by a suitable level of thermal denaturation or cross-linking of thrombogenic proteins. In addition, the concept of local pharmacologic therapy, which can be provided with laser balloon angioplasty at the site of arterial injury, is introduced. Preliminary in vitro and in vivo data suggest that guide catheter-injected albumin-heparin conjugates fabricated as water-insoluble microspheres remain adherent to the injured luminal surface and deeper arterial layers after physical trapping by the inflated balloon and subsequent laser/thermal exposure. The combination of initially adequate luminal morphology, reduction of the thrombogenicity of the injured arterial wall and application of local pharmacologic therapy with laser balloon angioplasty may eventually prove helpful in reducing the incidence of restenosis.

Some effects of gamma irradiation on patellar tendon allografts

The purpose of this study was to investigate possible causes for altered mechanical properties of patellar tendon allografts, used for reconstructive surgery, after sterilization with 2.0 Mrads gamma irradiation. The tissues were analyzed using a Hydrothermal Isometric Tension (HIT) device in conjunction with biochemical assays of soluble collagen and electron microscopy to understand the action of this processing. Gamma irradiation was found to significantly lower the shrinkage temperature and tended to increase the rate of isometric tension development. While no significant alteration in the acetic acid solubility was noted, the processing doubled the solubility of collagen to pepsin. This could mean that the predominant effect of the gamma irradiation at this dose level is polypeptide chain scission. The stiffening of the HIT curve may suggest some minor cross linking also occurred. The damaging effect of gamma irradiation, however, was not significant enough to cause any major disruption of the normal banding pattern in collagen. These data support earlier biomechanical data showing that using current processing methods, 2.0 Mrads of gamma irradiation sterilization significantly decreases the tensile strength and modulus of human patellar tendon graft tissues.