Biomedical subjects

W A Naimark

Publications and source records attributed to W A Naimark.

4 recordsLinked to original sources

PubMed1999

A computer-controlled system for mechanostimulation of tissues in culture: a preliminary study of protein synthesis in the pericardium.

During pericardial development or disease, changes in diastolic filling pressure and chamber volumes lead to changes in pericardial stress/strain state. These changes may be transduced into altered cellular synthesis of connective tissue proteins. To study the underlying mechanisms, we have constructed a system in which tissue strips may be subjected to a range of physiologically relevant load-elongation waveforms while being maintained under optimal tissue culture conditions. One sample grip is attached to a 500 g load cell and the other to a linear stepper motor. Load or stroke waveforms and feedback control are achieved under computer control. For preliminary studies, strips of fetal ovine pericardium (127-132 days gestation) and juvenile bovine pericardium (6 months) were subjected to ramp-and-hold loading for 24 hr in culture medium containing tritiated proline. At the end of the experiment, pericardial collagen and elastin were purified biochemically and assessed for tritium content. Preliminary results indicate that loading produced a significant 16% decrease in collagen synthesis (p < 0.02, cpm/mg wet weight) but no change in elastin synthesis. This novel system is a valuable tool for further studies of mechanotransduction in developing, normal, and pathological cardiac tissues.

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PubMed1995

A multi-sample denaturation temperature tester for collagenous biomaterials.

The temperature at which collagen denatures from a triple helix to a random coil structure is a useful measure of the degree of crosslinking. A new multi-sample denaturation temperature tester (DTT) has been constructed for rapid determination of the collagen denaturation temperature of natural tissues and collagenous biomaterials. To validate the system, the denaturation temperatures measured for the DTT are compared with results from differential scanning calorimetry (DSC). Data are presented for bovine pericardium in three states with denaturation temperatures ranging from 68 to 85 degrees C: fresh, or crosslinked with glutaraldehyde or the epoxide reagent Denacol EX-512 poly (glycidyl ether). Denaturation temperatures measured by DTT were not significantly different from those measured by differential scanning calorimetry (DSC); however, DSC onset systematically occurred at a slightly lower temperature than that measured by DTT. This result, seen only for fresh tissue is in agreement with earlier experiments using hydrothermal isometric tension (HIT) testing. By contrast, DTT and DSC onset were identical for the exogenously crosslinked materials. Since the measured transition temperature was independent of initial load, this variable may be chosen to yield sharper force-temperature transitions with a given sample geometry. This instrument allows accurate assessment of collagen denaturation temperatures for multiple samples in a fraction of the time required by other methods.

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PubMed1992

Correlation of structure and viscoelastic properties in the pericardia of four mammalian species.

Although the pericardium is recognized as having important contributions to ventricular function, the relationship between its functional role and structural composition remains poorly understood. Conflicting evidence from low strain rate experiments has shown that differences exist between the mechanical properties of canine, human, and bovine pericardium but with no structural explanation for these differences. This paper examines the pericardia of calves, dogs, pigs, and sheep using a structural/mechanical approach with techniques novel to the pericardial literature. High strain rate mechanical testing for stress-strain response, stress relaxation, and forced vibration response has shown the pericardium to be much more viscoelastic than previously believed under large deformations, but to be quite elastic in small vibrations. The thinner canine and porcine pericardia were found to be significantly stiffer than the thicker bovine and ovine tissues, but equivalently viscoelastic. Biochemical analysis shows these thinner tissues to have significantly higher levels of type III collagen combined with a higher degree of cross-linking. This is the first structural explanation for differences in mechanical properties between the pericardia of different species.

Animals↗

PubMedDate not supplied

Thermomechanical analysis of collagen crosslinking in the developing lamb pericardium.

In a developing lamb model, we have used hydrothermal isometric tension (HIT) techniques to assess collagen crosslink stability and its contribution to the mechanical properties of the pericardium. Strip samples of tissue were either: (i) heated to a 90 degrees C isotherm or (ii) heated in 5 degrees C increments between 60-90 degrees C and then 93 and 97 degrees C isotherms. The half-life of stress relaxation associated with peptide bond hydrolysis (t1/2) was calculated at each isotherm. The activation energy, Eact, for the hydrolysis-associated relaxation process was also calculated using the data from the stepwise HIT tests--a technical improvement which significantly reduces the experimental time required to develop statistically valid measurements. Crosslinking in the pericardium increased during development and was demonstrated both by thermoelasticity and by resistance to enzymatic solubilization. We observed greater conversation to thermally stable crosslinks upon maturation, the ratio of the NaBH4-stabilized/unstabilized half-lives peaking at 21 days postnatal. Whereas tissue from lambs (119 day fetal, and 3 day and 21 day postpartum) showed an early maximum and rapid decay of force, NaBH4 stabilization significantly increased thermal stability and yielded profiles similar to those in adult tissue.

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