Biomedical subjects

Ari Karchin

Publications and source records attributed to Ari Karchin.

8 recordsLinked to original sources

PubMed2006

Matricellular hevin regulates decorin production and collagen assembly.

Matricellular proteins such as SPARC, thrombospondin 1 and 2, and tenascin C and X subserve important functions in extracellular matrix synthesis and cellular adhesion to extracellular matrix. By virtue of its reported interaction with collagen I and deadhesive activity on cells, we hypothesized that hevin, a member of the SPARC gene family, regulates dermal extracellular matrix and collagen fibril formation. We present evidence for an altered collagen matrix and levels of the proteoglycan decorin in the normal dermis and dermal wound bed of hevin-null mice. The dermal elastic modulus was also enhanced in hevin-null animals. The levels of decorin protein secreted by hevin-null dermal fibroblasts were increased by exogenous hevin in vitro, data indicating that hevin might regulate both decorin and collagen fibrillogenesis. We also report a decorin-independent function for hevin in collagen fibrillogenesis. In vitro fibrillogenesis assays indicated that hevin enhanced fibril formation kinetics. Furthermore, cell adhesion assays indicated that cells adhered differently to collagen fibrils formed in the presence of hevin. Our observations support the capacity of hevin to modulate the structure of dermal extracellular matrix, specifically by its regulation of decorin levels and collagen fibril assembly.

Animals↗

PubMed2005

Fibro-porous meshes made from polyurethane micro-fibers: effects of surface charge on tissue response.

The purpose of this research was to evaluate the influence of surface charge on fibrous encapsulation, cell nuclei density, and vessel ingrowth into small-fiber, fibro-porous, biomaterial meshes. Meshes electrospun from polyurethane with mean fiber diameters of 5.8 microm and mean fiber spacing of 64.9 microm were plasma coated with films of different relative surface charge: Hexafluoropropylene (HF) (neutral), N,N-dimethylaminoethyl methacrylate (NN) (positive charge), and methacrylic acid (MA) (negative charge). Samples were implanted in rat subcutaneous dorsum for 5 weeks then fibrous capsule presence around the implants, cell nuclei density, and vessel number were assessed. Results showed that within the resolution of the histological analysis methods used, no implant experienced fibrous encapsulation. There was no significant difference between cell nuclei density and coating for the four groups: uncoated, HF-coated, NN-coated, and MA-coated. HF-coated and NN-coated samples had lower vessel numbers than uncoated samples (p = 0.055 and 0.032, respectively). MA-coated samples had vessel numbers not significantly different from uncoated polyurethane (slightly negatively charged) samples (p = 0.879). The results suggest that negatively charged surfaces may facilitate vessel ingrowth into fibro-porous mesh biomaterials.

Animals↗

PubMed2005

Tension in a double loop tendon anterior cruciate graft during a simulated open chain knee extension exercise.

Concerns exist regarding the tension developed in a reconstructed anterior cruciate ligament (ACL) during open chain knee extension exercises used to rehabilitate the knee. Therefore, the primary objective was to measure tension in an ACL graft during a simulated open chain knee extension exercise as a function of ankle weight. A secondary objective was to determine whether the graft tension was reduced with relatively high stiffness fixation. The open chain exercise was simulated in seven cadaveric specimens in which the ACL had been reconstructed with double loop tendon grafts. Graft tension was measured at 15 degrees of flexion as the effective ankle weight was increased from 22.5 to 67.5 and then to 112.5 N for three different fixation stiffnesses (25, 125, and 225 N/mm). The initial tension was set to restore the 225 N anterior limit of motion to that of the intact knee at 30 degrees of flexion. Increasing the ankle weight caused the graft tension to increase significantly (p<0.0001), but the increase with the highest ankle weight was only 62 N on average. Increasing the fixation stiffness caused the graft tension to decrease significantly (p<0.0001) because the initial tension decreased by 107 N as the fixation stiffness increased. Because the graft tension with the highest ankle weight was limited to 112 N on average, high stiffness fixation methods, which are also resistant to lengthening in the region of the fixation, may reduce the risk of graft construct lengthening during open chain knee extension exercises.

Aged↗

PubMed2004

Testing of elastomeric liners used in limb prosthetics: classification of 15 products by mechanical performance.

The mechanical properties of 15 elastomeric liner products used in limb prosthetics were evaluated under compressive, frictional, shear, and tensile loading conditions. All testing was conducted at load levels comparable to interface stress measurements reported on transtibial amputee subjects. For each test configuration, materials were classified into four groups based on the shapes of their response curves. For the 15 liners tested, there were 10 unique classification sets, indicating a wide range of unique materials. In general, silicone gel liners classified within the same groups thus were quite similar to each other. They were of lower compressive, shear, and tensile stiffness than the silicone elastomer products, consistent with their lightly cross-linked, high-fluid content structures. Silicone elastomer products better spanned the response groups than the gel liners, demonstrating a wide range of compressive, shear, and tensile stiffness values. Against a skin-like material, a urethane liner had the highest coefficient of friction of any liner tested, although coefficients of friction values for most of the materials were higher than interface shear:pressure ratios measured on amputee subjects using Pelite liners. The elastomeric liner material property data and response groupings provided here can potentially be useful to prosthetic fitting by providing quantitative information on similarities and differences among products.

Artificial Limbs↗

PubMed2004

Initial tension and anterior load-displacement behavior of high-stiffness anterior cruciate ligament graft constructs.

BACKGROUND: Because the tension that exists in an anterior cruciate ligament graft when the knee is unloaded (the initial tension) affects the surgical outcome and because high initial tension has a number of adverse consequences, the primary purpose of this study was to determine quantitatively how much less initial tension was required for a high-stiffness construct than for a low-stiffness construct. A secondary purpose was to determine how the stiffness of the graft construct affects the anterior load-displacement behavior of the knee from 0 degrees to 90 degrees of flexion. METHODS: Anterior-posterior load-displacement was measured in each of ten intact cadaveric knee specimens, the anterior cruciate ligament was excised, and the anterior cruciate ligament was reconstructed with a double-loop bovine tendon graft. Graft constructs of different stiffness were created with use of six springs, ranging in stiffness from 25 to 275 N/mm to simulate the fixation stiffness. After adjusting the initial tension of the graft so that the anterior-posterior laxity of the reconstructed knee matched that of the intact knee, the 0-N posterior limit and the 225-N anterior limit were measured at 0 degrees, 30 degrees, 60 degrees, and 90 degrees of flexion. RESULTS: The highest stiffness fixation (275 N/mm) required an average of 73 N of initial tension, which was more than three times less than the average of 242 N of initial tension required by the lowest stiffness fixation (25 N/mm). The 225-N anterior limit was overconstrained an average of 1.0 mm with the highest stiffness fixation (275 N/mm), which was 3.6 mm less than the overconstraint with the lowest stiffness fixation (25 N/mm). Likewise, the posterior limit was overconstrained an average of 2.6 mm with the highest stiffness fixation (275 N/mm), which was 3.8 mm less than the overconstraint with the lowest stiffness fixation (25 N/mm). CONCLUSIONS: The initial tension for a high-stiffness graft construct is more than three times less than that for a low-stiffness construct. The initial tension for a high-stiffness graft construct better restores both the 225-N anterior limit and the 0-N posterior limit to normal than the initial tension for a low-stiffness graft construct over the range of flexion from 0 degrees to 90 degrees.

Adult↗

PubMed2003

Cricoid ring integrity: implications for cricothyrotomy.

STUDY OBJECTIVES: The rapid 4-step technique for cricothyrotomy was originally described as making use of a single traction hook on the cricoid ring. However, it is possible that such hook placement could lead to damage of the cricoid ring. As an alternative, a double-hook device was developed to augment the rapid 4-step technique by dispersing forces applied to the cricoid ring. The objectives of this study were to compare the requisite forces for intubation and the structural tolerances of the cricoid ring between the single- and double-hook techniques. METHODS: We randomized 56 human cadaver specimens to undergo either cricothyrotomy with intubation followed by cricoid ring breakage or cricoid ring breakage alone. We randomized those cadaver specimens undergoing cricothyrotomy with intubation with respect to the initial hook technique used and then crossed over to the alternate technique for repeat intubation and subsequent cricoid ring breakage. We performed all cricothyrotomies in a similar manner with a consistent technique. We measured the intubation and breakage forces for the single- and double-hook techniques and calculated 95% confidence intervals (CIs). RESULTS: The mean force to intubate with the single-hook technique was 18 N (95% CI 14 to 22 N), and the mean force to intubate with the double-hook technique was 23 N (95% CI 17 to 29 N). There was a significant difference between the mean forces required to break the cricoid ring with the single-hook technique (54 N; 95% CI 47 to 62 N) versus with the double-hook technique (101 N; 95% CI 89 to 113 N; difference in means 47 [95% CI 34 to 60 N]). CONCLUSION: When applying the rapid 4-step technique for cricothyrotomy, the force required to intubate with either the single- or double-hook technique is small. The cricoid ring, however, tolerates significantly more force without breakage when the double-hook technique is used.

Airway Obstruction↗

PubMed2002

Experimental optimization of pivot point height for swing-arm type rear suspensions in off-road bicycles.

Towards the ultimate goal of designing dual suspension off-road bicycles which decouple the suspension motion from the pedaling action, this study focused on determining experimentally the optimum pivot point height for a swing-arm type rear suspension such that the suspension motion was minimized. Specific objectives were (1) to determine the effect of interaction between the front and rear suspensions on the optimal pivot point height, (2) to investigate the sensitivity of the optimal height to the pedaling mechanics of the rider in both the seated and standing postures, (3) to determine the dependence of the optimal height on the rider posture. Eleven experienced subjects rode a custom-built adjustable dual suspension off-road bicycle, [Needle, S., and Hull, M. L., 1997, "An Off-Road Bicycle With Adjustable Suspension Kinematics," Journal of Mechanical Design 119, pp. 370-375], on an inclined treadmill. The treadmill was set to a constant 6 percent grade at a constant velocity of 24.8 km/hr. With the bicycle in a fixed gear combination of 38 x 14, the corresponding cadence was 84 rpm. For each subject, the pivot point height was varied randomly while the motions across both the front and rear suspension elements were measured. Subjects rode in both the seated and standing postures and with the front suspension active and inactive. It was found that the power loss from the rear suspension at the optimal pivot point height was not significantly dependent on the interaction between the front and rear suspensions. In the seated posture, the optimal pivot point height was 9.8 cm on average and had a range of 8.0-12.3 cm. The average optimal pivot point height for the seated posture corresponded to an average power loss for the rear suspension that was within 10 percent of the minimum power loss for each subject for 8 of the 11 subjects. In the standing posture, the average height was 5.9 cm and ranged from 5.1-7.2 cm. The average heightfor the standing posture was within 10 percent of the minimum power loss for each subject for 9 of the 11 subjects. While the optimum height was relatively insensitive to pedaling mechanics in both the seated and standing postures, the choice of the optimal pivot point height in production bicycles necessitates some compromise in performance given the disparity in the averages between the seated and standing postures.

Adult↗

PubMedDate not supplied

A noncontact sensor for measurement of distal residual-limb position during walking.

A simple noncontact device was implemented for measuring the position of the distal residual limb relative to the prosthetic socket during ambulation. The device was a small and lightweight photoelectric sensor positioned within a frame mounted immediately beneath the socket. Calibration tests showed that the sensor had a displacement range of 60.0 mm. The root-mean-square error for all sources of error considered (different reflective surfaces, peak-to-peak signal noise, drift, nonlinearity, different surface tilt angles, surface curvature, and wetness [simulating sweating]) was <1.95% full-scale output. We used the sensor in a preliminary study on a unilateral, transtibial amputee with diabetes to assess pistoning during ambulation. Results showed an average 41.7 mm proximal displacement during swing phase relative to stance phase. When the subject was walking on a flat surface, pistoning was significantly less (p = 0.000) with a supracondylar strap compared with no supracondylar strap, although the difference was not substantial (0.8 mm). A 5 min rest period caused the limb to displace proximally in the socket approximately 4.8 mm during subsequent walking trials, possibly reflecting limb enlargement and thus a more proximal position in the socket after the rest period. The device can potentially be used in prosthetics research for evaluating clinical features that may affect limb position and pistoning and thus fit.

Amputation Stumps↗