Mechanical properties of porcine spinal dura mater and pericranium.

BACKGROUND: The objective of this study was to characterize and compare the mechanical properties of porcine pericranium and spinal dura mater, to evaluate the mechanical suitability of pericranium as a dural graft. METHOD: Eighty-eight spinal dura (cervical, thoracic, and lumbar regions, in ventral longitudinal, dorsal longitudinal and circumferential orientations) and eighteen pericranium samples (ventral-dorsal, and lateral orientations) from four pigs, were harvested and subjected to uniaxial loading while hydrated. The stiffness, strain at toe-linear regions transition, strain at linear-yield regions transition and other structural and mechanical properties were measured. Stress-strain curves were fitted to a one-term Ogden model and Ogden parameters were calculated. Linear regression models with cluster-robust standard errors were used to assess the effect of region and orientation on material and structural properties. RESULTS: Both spinal dura and pericranium exhibited distinct anisotropy and were stiffer in the longitudinal direction. The tissues exhibited structural and mechanical similarities especially in terms of stiffness and strains in the linear region. Stiffness ranged from 1.28 to 5.32 N/mm for spinal dura and 2.42-3.90 N/mm for pericranium. In the circumferential and longitudinal directions, the stiffness of spinal dura specimens was statistically similar to that of pericranium in the same orientation. The strain at the upper bound of the linear region of longitudinal pericranium (28.0%) was statistically similar to that of any spinal dura specimens (24.4-32.9%). CONCLUSIONS: Autologous pericranium has advantageous physical properties for spinal duraplasty. The present study demonstrated that longitudinally oriented pericranium is mechanically compatible with spinal duraplasty procedures. Autologous pericranium grafts will likely support the mechanical loads transmitted from the spinal dura, but further biomechanical analyses are required to study the effect of the lower yield strain of circumferential pericranium compared to spinal dura. Finally, the Ogden parameters calculated for pericranium, and the spinal dura at each spinal level, will be useful for computational models incorporating these soft tissues.

A novel analytical approach for determining the frictional moments and torques acting on modular femoral components in total hip replacements.

A three dimensional analytical approach was developed to determine the frictional moment vector generated by the relative sliding of the head-cup bearing couple of a total hip replacement. The frictional moment projection onto the femoral neck was also determined over the loading cycle. Predicted frictional moments for nine combinations of bearing materials and diameters were in close agreement with existing in vitro data. The analytical method was then applied to simplified gait (lubrication conditions of dry and serum), ISO standard gait and physiological level gait loading cycles. ISO standard gait had a total contact force of about two fold of physiological level gait and there was a corresponding increase in the maximum frictional torque on neck from 0.66×BW%m to 0.88×BW%m. For the ISO standard gait, the maximum frictional torque occurred at the same instance of maximum frictional moment and the maximum contact force. In contrast, for the physiological level gait, the frictional torque did not occur at the same instance as the peak load. This suggests that the neck frictional torque is a function of other parameters, such as angle between neck axis and frictional moment vector, as well as the magnitude of the contact force and frictional moment. The developed methodology was able to predict the maximum magnitude and change of directions of moments and the variation of torque at the head neck interface. The data will be useful for experimental studies assessing the fretting behaviour of the head neck junction, by providing appropriate loading data.

Polymer Brushes Containing Sulfonated Sugar Repeat Units: Synthesis, Characterization and In Vitro Testing of Blood Coagulation Activation.

A new polymer brush chemistry containing sulfonated carbohydrate repeat units has been synthesized from silicon substrates using ATRP methods and characterized both in bulk and using surface analysis. The polymer brush was designed to act as a mimic for the naturally occurring sulfonated glycosaminoglycan, heparin, commonly used for modifying blood-contacting surfaces both in vitro and in vivo. Surface analysis showed conversion of brush saccharide precursor chemistry to the desired sulfonated polymer product. The sulfonated polymer brush surface was further analyzed using three conventional in vitro tests for blood compatibility -- plasma recalcification times, complement activation, and thrombin generation. The sulfonated polymer brush films on silicon oxide wafers exhibited better assay performance in these blood component assays than the unsulfonated sugar functionalized polymer brush in all tests performed.

Successful transplantation of 50 single unit pediatric kidneys ages 11 to 48 months into adult recipients.

There is currently an imbalance between the need for cadaveric kidneys for transplantation and the supply. The medical criteria for accepting cadaveric donors are changing and organs that were originally thought to be unacceptable have functioned well. Previous reports have discussed the problems with transplanting pediatric allografts less than 4 years old into adult recipients, and the results have not been encouraging. From 1986 to 1991 a total of 50 kidneys ages 11 to 48 months were transplanted as single units into adult recipients (Group A). Ninety-one adult donor cadaveric transplants were used as controls (Group B). The cadaveric transplants were 2nd or 3rd transplants in 7 of the Group A and 12 of the Group B patients. Renal preservation, storage times, and demographics were the same. Prednisone, cyclosporine, and either Minnesota ALG or OKT3 were used for immunosuppression in both groups. Imuran was added in immunologically high-risk patients. The 1-year actuarial patient and allograft survivals for Group A versus Group B were 89.5% versus 94.2% (p=0.49) and 71.3% versus 87.8% (p=0.01), respectively. There was no difference in allograft or patient survival in kidneys from donors 11-24 months of age or 25-48 months (p=0.56). Renal growth, as measured by sonography, occurred while on cyclosporine A. Excretory and hormonal function as measured by creatinine and hematocrit both improved. Seventy percent of the Group A patients and 76% of the Group B patients were free from rejection in the first 2 months post transplantation (p=0.45).(ABSTRACT TRUNCATED AT 250 WORDS)

Determination of pH with acid-base indicators: Implications for optical fibre probes.

Results are presented which clearly illustrate the possibilities and limitations of the use of indicators immobilized on optical fibres, in the determination of pH.