Biomedical subjects

D Abdulla

Publications and source records attributed to D Abdulla.

6 recordsLinked to original sources

PubMed1999

Biaxial mechanical/structural effects of equibiaxial strain during crosslinking of bovine pericardial xenograft materials.

We have investigated the effect of biaxial constraint during glutaraldehyde crosslinking on the equibiaxial mechanical properties of bovine pericardium. Crosslinking of cruciate samples was carried out with: (i) no applied load, (ii) an initial 25 g ( approximately 30 kPa) equibiaxial load, or (iii) an initial 200 g (approximately 250 kPa) equibiaxial load. All loading during crosslinking was done under a defined initial equibiaxial load and subsequently fixed biaxial strain. Load changes during crosslinking were monitored. Mechanical testing and constraint during crosslinking were carried out in a custom-built biaxial servo-hydraulic testing system incorporating four actuators with phase-controlled waveform synthesis, high frame-rate video dimension analysis, and computer-interfaced data acquisition. The paired biaxial stress strain responses under equibiaxial loading at 1 Hz (before and after treatment) were evaluated for changes in anisotropic extensibility by calculation of an anisotropy index. Scanning electron microscopy (SEM) was performed on freeze-fractured samples to relate collagen crimp morphology to constraint during crosslinking. Fresh tissue was markedly anisotropic with the base-to-apex direction of the pericardium being less extensible and stiffer than the circumferential direction. After unconstrained crosslinking, the extensibility in the circumferential direction, the stiffness in the base-to-apex direction, and the tissue's anisotropy were all reduced. Anisotropy was preserved in the tissue treated with an applied 25 g load; however, tissue treated with an applied 200 g load became extremely stiff and nearly isotropic. SEM micrographs correlated well with observed extensibility in that the collagen fibre morphology changed from very crimped (unconstrained crosslinking), to straight (200 g applied load). Biaxial stress-fixation may allow engineering of bioprosthetic materials for specific medical applications.

Animals↗

PubMed1996

Evaluating sol-gel ceramic thin films for metal implant applications. II. Adhesion and fatigue properties of zirconia films on Ti-6AI-4V.

The degree to which ceramic coatings or thin films applied to bone-interfacing metallic implants can improve the overall performance of these implants with respect to implant fixation, wear, or corrosion relies especially on the response of these films to loading. In this study, the adhesion and fatigue properties of sol-gel zirconia films that could be reproducibly deposited onto polished Ti-6AI-4V substrates was investigated. For zirconia films on the order of 100 nm thick, a shear lag-based strain approach indicated a shear adhesion strength of approximately 275 MPa. Small variations in film thickness and substrate surface preparation had little effect on this adhesion, which was believed to be due to alkoxide molecule interactions with free hydroxyl groups on the substrate surface as well as some limited interfacial diffusion following the 500 degrees C anneal. Subsequent fatigue testing of these films in air using novel tapered rotating beam fatigue samples demonstrated their excellent fatigue characteristics, with films surviving up to 10(7) cycles, the endurance limit of the Ti-6AI-4V (approximately 635 MPa). Overall, the exceptional mechanical properties of this ZrO2/Ti-6AI-4V system along with the inherent advantages of sol-gel processing support continued studies to utilize this technology for implant surface modification.

Alloys↗

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.

Animals↗

PubMed1986

A histological assessment of the initial healing response adjacent to porous-surfaced, titanium alloy dental implants in dogs.

We report here the results of a histological assessment of the initial healing response following implantation into the dog mandible of a porous-surfaced, titanium alloy endosseous dental implant. Two implants were placed in edentulous areas on each side of the mandible of each dog and covered with a full-thickness mucoperiosteal flap. The implant sites on one side of the mandible were allowed to head for four weeks, while those on the other side were allowed to head for eight weeks before the animals were killed. Histological specimens were obtained and assessed both qualitatively and by computer-assisted morphometry. All but one of the 24 implants were well-tolerated and healed with a variable ingrowth of bone into the porous-surface geometry. The histomorphometric measurements revealed that bone ingrowth had reached a plateau by four weeks of initial healing.

Alloys↗

PubMed1986

A clinical and radiographic assessment of a porous-surfaced, titanium alloy dental implant system in dogs.

A new endosseous dental implant system incorporating a porous-surface geometry with a tapered, truncated-cone shape was placed bilaterally in edentulous areas of dog mandibles in a two-stage procedure. All implants had been stabilized by bone ingrowth by the time of the second procedure (insertion of a transgingival collar and implant-supported bridge). The transgingival collar had a porous-surface geometry on its apical one-third, and was meant to encourage gingival connective tissue ingrowth and attachment, but in fact provided an excellent milieu for bacterial contamination. As a consequence, many of the implants showed clinical and radiographic signs of impending failure by eight months. Only those implants for which the porous coat, including that of the transgingival collar, was completely submerged in bone were observed to be successful. This study reports on the radiographic and clinical assessment of this implant system in dogs during the period of function.

Alloys↗

PubMed1982

Biologic fixation and bone modeling with an unconstrained canine total knee prosthesis.

To study the effects of dynamic loading on biologic fixation, an unconstrained type of prosthesis was designed for total replacement of the knee joint of dogs. The femoral component was fabricated from cast cobalt-based surgical alloy. The tibial component was fabricated from surgical grade, ultra-high molecular weight, high density polyethylene. Both components were designed for initial stabilization at surgery by mechanical interlock with bone. In addition, the bone-interfacing surface of the metal component was made porous and the stem of the polymer component was grooved to permit the subsequent ingrowth of tissue. Knee arthroplasty was performed on a total of six beagles. The prostheses were monitored for periods of 20 months and demonstrated an overall excellent stability and functionality. Each tibial component became stabilized by the formation of a thin, surrounding shell of osseous tissue. Interposed between this bone and the implant was usually a thin layer of fibrous tissue, suggesting micromovement during loading. Each femoral component became solidly fixed by bone growth into the porous surface. The altered stress state in the region of the implant eventually resulted in reactive bone modeling, with both bone formation and resorption occurring along the length of the implant.

Animals↗