Biomedical subjects

K A Mann

Publications and source records attributed to K A Mann.

29 records · Page 2Linked to original sources

PubMed1995

A dynamic biomechanical study of scapholunate ligament sectioning.

A biomechanical study was performed on fresh cadaver forearms to investigate the role of the scapholunate interosseous ligament in carpal stability. Scaphoid and lunate motion and radiocarpal and ulnocarpal pressure patterns were continually monitored while the wrist was moved physiologically. Prior to ligament sectioning, it was found that the position of the scaphoid and lunate were dependent on both the wrist position and the direction of wrist motion. Sectioning the scapholunate interosseous ligament caused increased scaphoid flexion, scaphoid pronation, and lunate extension. Pressure in the radiocarpal and ulnocarpal joint was redistributed following ligament sectioning. These findings support the clinical impression that the scapholunate interosseous ligament is an important stabilizer of the scaphoid and lunate.

Biomechanical Phenomena↗

PubMed1994

Mixed mode fracture characterization of hydroxylapatite-titanium alloy interface.

Cantilever beam and four-point bend specimen geometries were used to experimentally determine the critical energy release rates for a plasma sprayed hydroxylapatite-titanium alloy (HA-Ti alloy) interface. A locus of energy release rates as a function of crack tip phase angle was determined where a 0 degree phase angle represented tensile opening (mode I) loading and a 90 degree phase angle represented in-plane shear (mode II) loading. Energy release rates were found to increase substantially with an increase in phase angle. An energy release rate of 0.108 N/mm was determined for a phase angle of 0 degrees (mode I). Energy release rates of 0.221, 0.686, and 1.212 N/mm were determined for phase angles of 66 degrees, 69 degrees, and 72 degrees, respectively. The experimental data was matched to a phenomenological model for which crack propagation depended on mode I loading alone indicating that crack propagation at the Ha-Ti alloy interface is dominated by the mode I loading component. Therefore, regions of HA coated implants that experience compressive or shear loading across the HA-Ti alloy interface may be much less likely to debond than regions that experience tensile loading.

Alloys↗

PubMed1993

Nonaffinity purification of recombinant gp120 for use in AIDS vaccine development.

The gene encoding the major envelope glycoprotein of the HIV-SF2 isolate was engineered for the secretion of recombinant gp120 (rgp120SF2) from permanent Chinese hamster ovary (CHO) cell lines. Cellular production methods were scaled up and a method for purification of the secreted glycoprotein was devised. Mild purification conditions were selected in order to preserve the native structure of the protein. rgp120SF2 exhibits a molecular weight of 120 kDa in reduced or nonreduced SDS gels; thus the polypeptide chain is intact. Deglycosylated rgp120SF2 has the predicted molecular weight of the polypeptide backbone, 54 kDa. Gel-filtration HPLC in a nondenaturing buffer at neutral pH yields a molecular weight estimate of approximately 120 kDa. Purified rgp120 closely resembles authentic viral gp120 by several physical, chemical, and immunochemical tests. rgp120SF2 reacts strongly with human HIV-positive sera, monoclonal antibodies reactive with HIV-SF2 and HIV-MN viral envelope, and a human virus-neutralizing monoclonal antibody that maps to a conserved discontinuous epitope on HIV-1 gp120. Purified rgp120SF2 forms a 1:1 molecular complex with soluble recombinant human CD4 (rCD4) receptor, as demonstrated by gel-filtration HPLC; binding is high affinity (Kd approximately 2 x 10(-9) M).

AIDS Vaccines↗

PubMed1991

Mechanical characteristics of the stem-cement interface.

The mechanical characteristics of the interface between a metallic stem and the surrounding poly(methyl methacrylate) bone cement were determined from experimental tests and finite element analyses. Push-through-stem tests of straight and tapered titanium alloy stems, surrounded by cement columns, were performed and the resulting load-displacement behavior and strain distribution on the surface of the cement column were measured for loading, unloading, and reloading. Test geometries were modelled using nonlinear, axisymmetric, finite element analyses, which incorporated Coulomb friction elements at the titanium alloy-cement interface. Initial residual stresses, due to curing of the cement column, were modeled by thermal contraction of the cement. Good agreement was obtained between load-displacement curves and surface strains predicted from the nonlinear analysis and those obtained from experiments, when a coefficient of friction of 0.3 was assumed for the stem-cement interface. These results show that, in the absence of chemical adhesion, the load-displacement behavior of a stem-cement composite can be described completely in terms of the friction at the interface and the residual stresses normal to the interface.

Animals↗

PubMed1991

Functional and immunological characterization of SIV envelope glycoprotein produced in genetically engineered mammalian cells.

Retroviral envelope glycoproteins interact with cell receptors and are targets for antiviral immune responses in infected hosts. Macaque simian immunodeficiency virus (SIVmac) is a T-lymphocytopathic lentivirus which causes an AIDS-like disease in rhesus macaques. The envelope gene of SIVmac encodes a precursor glycoprotein (gp160) which is cleaved into an external domain (gp130) and a transmembrane domain (gp32). To investigate the functional and immunological properties of the SIV external envelope glycoprotein, we have used genetically engineered mammalian cells to produce recombinant gp130 (rgp130). The rgp130 has the appropriate molecular weight, is glycosylated, and has native conformation as determined by binding to the cell receptor for SIV, the CD4 antigen. Rhesus macaques immunized with purified rgp130 formulated in muramyl dipeptide adjuvant generated high titers of antienvelope antibodies. Antibodies from these macaques were tested for in vitro virus neutralization; very low or undetectable levels of neutralization were observed. In contrast, neutralizing antibodies were readily detected in sera from goats immunized with rgp130. With respect to cell-mediated immunity, proliferative responses to rgp130 were demonstrated in peripheral blood monocyte cells (PBMC) from macaques immunized with the recombinant glycoprotein as well as in PBMC from SIV-infected animals. These results show that rgp130 is functional and immunogenic; the potential of rgp130 for protective immunization remains to be determined.

Animals↗

PubMed1991

Effects of sodium hyaluronate on tendon healing and adhesion formation in horses.

Sodium hyaluronate reduces adhesions after tendon repair in rodents and dogs, and has been used in limited clinical trials in people. To evaluate its effect on tendon healing and adhesion formation in horses and to compare these effects with those of a compound of similar visco-elastic properties, a study was performed in horses, using a model of collagenase injection in the flexor tendons within the digital sheath. Eight clinically normal horses were randomly allotted to 2 groups. Adhesion formation between the deep digital flexor tendon and the tendon sheath at the pastern region was induced in the forelimbs of all horses. Using tenoscopic control, a 20-gauge needle was inserted into the deep digital flexor tendon of horses under general anesthesia and 0.2 ml of collagenase (2.5 mg/ml) was injected. The procedure was repeated proximally at 2 other sites, spaced 1.5 cm apart. A biopsy forceps was introduced, and a 5-mm tendon defect was created at each injection site. Group-A horses had 120 mg of sodium hyaluronate (NaHA) gel injected into the tendon sheath of one limb. Group-B horses had methylcellulose gel injected at the same sites. The contralateral limbs of horses in both groups served as surgical, but noninjected, controls. Horses were euthanatized after 8 weeks of stall rest. Ultrasonographic evaluation revealed improved tendon healing after NaHa injection, but no difference in peritendinous adhesion formation. Tendon sheath fluid volume and hyaluronic acid (HA) content were greater in NaHA-treated limbs. Gross pathologic examination revealed considerably fewer and smaller adhesions when limbs were treated with NaHA. However, significant difference in pull-out strengths was not evident between NaHA-treated and control limbs. Histologically, the deep digital flexor tendon from the NaHA-treated limbs had reduced inflammatory cell infiltration, improved tendon structure, and less intratendinous hemorrhage. Treatment with methylcullulose had no significant effect on tendon healing, adhesion size, quantity, or strength or on the volume and composition of the tendon sheath fluid. Sodium hyaluronate, administered intrathecally, appears to have a pharmaceutically beneficial action in this collagenase-induced tendinitis and adhesion model in horses.

Animals↗

PubMed1990

A biomechanical investigation of short segment spinal fixation for burst fractures with varying degrees of posterior disruption.

A biomechanical study was performed to evaluate the effectiveness of the Fixateur Interne pedicle screw system and the Syracuse I-Plate anterior fixation system. A total of 12 fresh frozen cadaver spines were tested intact, after burst fracture was created and application of a fixation device (six each), and after six serial transections of posterior ligaments and bony structures. Spines were loaded to a maximum of 10 N-m in flexion, extension, left and right lateral bending, and clockwise and counter-clockwise rotation. Results indicate that both systems reduce spinal flexibility in flexion, extension, and lateral bend loading when used to reduce and fix a classic burst fracture without posterior disruption. No decrease in flexibility was found in axial rotation for either device. After transection of all posterior elements, the I-Plate construct became much more flexible than the intact spine in flexion, extension, and axial rotation loading. The internal fixator construct retained more stability than the I-Plate construct after transection of posterior elements in flexion and extension loading, but was considerably more flexible than the intact spine in axial rotation loading. The results imply that the posterior internal fixator provides much better stabilization than the anterior I-Plate for those cases in which there is a large amount of posterior disruption in addition to an anterior burst injury. Neither device provides extensive support in axial rotation loading.

Aged↗

PubMed1989

Frequency spectrum analysis of wrist motion for activities of daily living.

A frequency spectral analysis was performed on wrist motion data for 24 activities of daily living (ADLs). Wrist motion was measured using a triaxial electrogoniometer attached to the wrist using tape (for 12 subjects) and pins (for one subject). Results show that the average predominant frequency component of these ADLs was approximately 1 Hz with 75% of the spectral energy less than 5 Hz. The taped-on electrogoniometer, when compared with the pinned electrogoniometer, was adequate for calculating the predominant frequency component and spread of spectral data, but overestimated the magnitudes of the maximum spectral density and total area of the spectral curves. This discrepancy was largest for axial rotation.

Activities of Daily Living↗

PubMed1988

Reduction of the intracanal fragment in experimental burst fractures.

An experimental investigation was carried out to create burst fractures and to evaluate the mechanisms and degree of reduction of the intracanal fragment with posterior instrumentation techniques in multisegmental human cadaver specimens. Reduction of the spinal fragment through kyphosis correction and distraction was evaluated using CT imaging. With kyphosis correction alone there was no decrease in canal compromise; in some cases there was a slight increase in canal compromise. Distraction, whether applied before or after kyphosis correction was the effective mechanism in reducing the fracture fragment. Kyphosis correction applied after distraction did not reduce the fragment further. Posterior devices that are used to treat burst fractures of the thoracolumbar spine with intracanal fragments should provide some form of distraction.

Adolescent↗

PubMed1988

Early clinical experience with the Syracuse I-Plate: an anterior spinal fixation device.

Sixteen patients were treated with a new anterior internal fixation device after thoracolumbar or lumbar decompression, and fusion with bone grafting. Ten patients had acute burst fractures, four had metastatic tumors, and two had old, healed fractures with deformity. In the acute fracture group, eight patients had neurologic deficits and seven patients experienced improvement. Six patients had lesions of the conus medullaris, all of which improved. The four patients with metastatic tumors underwent surgery for back and leg pain and all gained significant relief. Two patients had correction of old fracture deformity with satisfactory outcome. Complications were minimal. The new anterior stabilization device provided early stability, allowed early patient mobilization, was easy to insert, and has a low profile. Late collapse, non-union, and kyphotic deformity have not been noted thusfar.

Acute Disease↗

PubMed1987

An experimental study of Newtonian and non-Newtonian flow dynamics in a ventricular assist device.

The fluid dynamic behavior of a Newtonian water/glycerol solution, a non-Newtonian polymer (separan) solution, and bovine blood were compared in the Penn State Electrical Ventricular Assist Device (EVAD). Pulsed doppler ultrasound velocimetry was used to measure velocities in the near wall region (0.95-2.7 mm) along the perimeter of the pump. Mean velocity, turbulence intensity, local and convective acceleration, and shear rate were calculated from the PDU velocity measurements. Flow visualization provided qualitative information about the general flow patterns in the EVAD. Results indicate that water/glycerol does not accurately model the flow characteristics of bovine blood in the EVAD. The non-Newtonian separan solution produced results closer to those of the bovine blood than did the water/glycerol solution. Near wall velocity magnitudes for the separan were similar to those of the bovine blood, but the profile shapes differed for portions of the pump cycle. All three fluids exhibited periods of stagnation. Bovine blood results indicated the presence of a desired rotational washout pattern at midsystole, while results with the other fluids did not show this feature.

Animals↗