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Biomedical subjects

S W Shalaby

Publications and source records attributed to S W Shalaby.

16 recordsLinked to original sources
PubMed2001

Long-term gamma irradiation effects on ultrahigh molecular weight polyethylene.

Effects of gamma irradiation, irradiation environment, and long-term postirradiation aging on thermal behavior, crystallinity, mechanical properties, and weight change of ultrahigh molecular weight polyethylene (UHMWPE) were investigated. The gamma irradiation was conducted at 2.5 Mrad under four different environments, i.e., air, nitrogen, acetylene, and vacuum. The postirradiation aging effects were monitored over a period of 5.5 years. The results showed that gamma irradiation, irradiation environments, and postirradiation aging significantly changed the properties of UH-MWPE. After gamma irradiation, the melting temperature and crystallinity of UHMWPE were increased in all cases, with the highest increase at longest postirradiation aging time. Gamma irradiation and postirradiation aging caused weight gain of UHMWPE in all conditions. The tensile and flexural properties were significantly affected by gamma irradiation. At 5.5 years postirradiation, tensile-tested UHMWPE specimens fractured in brittle form, indicating dramatic reduction in the material's toughness. This kind of behavior may be detrimental to UHMWPE load-bearing orthopedic devices for their intended long-term applications.

Crystallization↗
PubMed2001

The growth of chondrocytes into a fibronectin-coated biodegradable scaffold.

Porous scaffolds made from a biodegradable copolymer of trimethylene carbonate and glycolide were evaluated for tissue-engineered medical products. We examined the scaffold coated with cell adhesion protein and fibronectin and cultured under a dynamic mixing condition to enhance the growth of chondrocytes. Our hypothesis was that the combination of coating and dynamic mixing would be beneficial to the viability of the chondrocytic cells. Fibronectin was selected as the model protein because of its availability and routine assaying methods. Sterile samples of scaffolds of about 1 mm in thickness were coated with fibronectin at 37 degrees C for 1.5 h. Four groups of scaffolds were used: uncoated static or dynamic, and coated static or dynamic. Scaffold samples were placed in either a Petri dish or a spinner flask (static vs. dynamic groups) after inoculation with rat chondrocytes of an initial cell density of 1.29 x 10(5) cell/mL. After 7, 14, 21, and 28 days, each sample was fixed, embedded, and sectioned at 5 micro thickness. The sections were double-label immunostained using antibodies against cellular fibronectin synthesized by adherent cells as a measure of cell viability. A Hoechst 33258 nuclear stain was used to measure the number of cells attached to the scaffold at each time interval. The slides were examined using a fluorescence microscope to determine the cell ingrowth. At least 25 fields/treatment group (except the 7 day group) were measured. The data showed that cell in-growths into the porous scaffolds were higher at all time periods for the coated dynamic group than those for the other three groups.

Animals↗
PubMed2000

Bone formation into surface phosphonylated polymeric implants.

Through the use of two animal models, the present study demonstrates the ability of phosphonylated surfaces to bind bone. In one model, surface-treated polypropylene (PP) and polyethylene (PE) were implanted in the medial cortex of the goat tibia. In the second model, surface-treated poly(ether-ether ketone) (PEEK) and carbon fiber-reinforced PEEK (CFR-PEEK) were implanted through both cortices of the goat mandible. Selected rods of all material types were microtextured using crystallization induced microphase separation, a method for the formation of continuous, open-cell microporous surfaces in thermoplastic polymers. Microtextured and smooth rods were phosphonylated, and calcium was subsequently introduced to the phosphonylated surface by incubating the samples in a saturated solution of calcium oxide. For all substrate materials tested, phosphonylation and calcium posttreatment resulted in an increased propensity for bone binding and apposition, as measured by push out test. Microtextured PP, PE, and CFR-PEEK surfaces that were further phosphonylated and calcium treated resulted in test samples with an increased interfacial strength.

Animals↗
PubMed1998

Study of creep behavior of ultra-high-molecular-weight polyethylene systems.

The short- and long-term creep behaviors of ultra-high-molecular-weight polyethylene (UHMWPE) systems (compression-molded UHMWPE sheets and self-reinforced UHMWPE composites) have been investigated. The short-term (30-120 min) creep experiment was conducted at a load of 1 MPa and a temperature range of 37-62 degrees C. Based on short-term creep data, the long-term creep behavior of UHMWPE systems at 1 MPa and 37 degrees C was predicted using time-temperature superposition and analytical formulas. Compared to actual long-term creep experiments of up to 110 days, the predicted creep values were found to well describe the creep properties of the materials. The creep behaviors of the UHMWPE systems were then evaluated for a creep time of longer than 10 years, and it was found that most creep deformation occurs in the early periods. The shift factors associated with time-temperature superposition were found to increase with increasing temperature, as per the Arrhenius equation. The effects of temperature, materials, and load on the shift factors could be explained by the classical free volume theory.

Hot Temperature↗
PubMed1997

Modulation of surface and bulk properties of biomedical polymers.

The surface and bulk modulation of polymeric biomedical devices allows the full range of material properties to be exercised as demanded by custom applications. Polymeric biomaterials are finding greater use as relatively inert and even transient options and so therefore will require thorough processing analyses and the transfer of technology from nonbiomedical applications to the biomedical industry.

Biocompatible Materials↗
PubMed1997

Efficacy of hyaluronic acid/nonsteroidal anti-inflammatory drug systems in preventing postsurgical tendon adhesions.

Tendon adhesion is acknowledged to be a function of both an overwhelming inflammatory response at the surgical site and the loss of physical separation that is normally present between the tendons and the synovial sheath. Adhesions bind the flexor tendons to each other and to surrounding structures, interfering with their normal gliding function. The clinical result of adhesion formation following flexor tendon surgery is poor digital function. This study investigated the effect of intraoperative treatments of high viscosity absorbable gels made of various combinations of hyaluronic acid and nonsteroidal anti-inflammatory drugs, on adhesion formation in a leghorn chicken flexor tendon model. Forty-eight mature, white leghorn chickens were used to verify the surgical model and to test five different gel treatments. The gels were formed from: 2% sodium hyaluronate in phosphate buffered saline alone or combined with 1 mg/mL tolmetin sodium; 1 mg/mL naproxen sodium; 0.216 g/mL calcium acetate; or 0.216 g/mL calcium acetate plus 1 mg/mL naproxen sodium. The gels were applied by injecting 0.2 mL of the specified composition into the intrasheath space near the conclusion of the surgical procedure. Gross and histological evaluations were conducted to analyze the efficacy. All of the treatments significant reduced the extent and severity of postsurgical tendon adhesion in this animal model as compared with the control (no gel treatment) (p < 0.05). The combination of naproxen sodium and calcium acetate in a high viscosity sodium hyaluronate carrier was the most effective composition. The combination of a high viscosity gel and nonsteroidal anti-inflammatory drugs appears to maintain the natural separation between the tendons and their sheaths and decrease the tissue inflammatory response through mediating two of the major stimuli in adhesion formation.

Animals↗
PubMed1997

Water fugacity in absorbing polymers.

Absorbable biomaterials, as dynamic systems, require special handling, processing, and characterization techniques beyond those of the traditional nonabsorbable materials. As the material degrades or absorbs, in vitro or in vivo, it undergoes structural, physical, and chemical changes. These changes in the base material may significantly impact the performance of a particular biomedical device; hence, it is important that the investigator consider the full range of properties that constitute the lifetime of a given absorbable material. The long term degradation study presented here sought to identify one such property, the change in water retention of a degrading oriented polylactide film. The investigation found through differential scanning calorimetry that later stages of degradation are often characterized by a stronger retention of water, potentially due to a higher number of polar carboxyl groups within the relatively hydrophobic polymer matrix.

Biocompatible Materials↗
PubMed1997

Performance of modified cyanoacrylate composition as tissue adhesives for soft and hard tissues.

A suspected absorbable cyanoacrylate, methoxypropyl cyanoacrylate (MPC), was investigated as a component of a new modified cyanoacrylate system. Reactive modifiers based on absorbable polymeric oxalates, which act as plasticizers as well as thickening agents, were incorporated into this system. It was found that the MPC with an oxalate modifier resulted in a higher adhesive strength than isobutyl cyanoacrylate (IBC) when used to approximate soft tissue. However, the IBC was superior in hard tissue applications. This coincides with the conclusion that modulus matching of the adhesive and substrate is a key contributor to joint strength.

Animals↗
PubMed1997

Properties of self-reinforced ultra-high-molecular-weight polyethylene composites.

The physical properties of ultra-high-molecular-weight polyethylene (UHMWPE) fibre/UHMWPE matrix composites have been characterized. It was found that the tensile strength and modulus, and creep resistance, were significantly increased after incorporating UHMWPE fibres into a UHMWPE matrix. The longitudinal tensile strength of the resulting self-reinforced composite increased with fibre content, according to the law of mixtures. The transverse strength did not change for fibre content of up to 7%. The double-notch impact strength of the composites was higher than plain UHMWPE. There was no difference in wear properties between the composites and plain UHMWPE. The cross-section and tensile fracture surfaces of the composites were examined by scanning electron microscopy (SEM). Overall results indicate that the self-reinforced UHMWPE composites may be good candidates for load-bearing biomedical applications.

Chemical Phenomena↗
PubMed1997

Physicochemical changes in degrading polylactide films.

It has been suggested in the literature that 'large' size bioabsorbable aliphatic polyester devices degrade heterogeneously when exposed to an aqueous environment. That is, following saturation, the material degrades preferentially from the center to the exterior due to an auto catalytic effect. Oriented absorbable films were developed using a new solid state method in order to assess the influence of molecular orientation on degradation pattern. The method entails uniaxial deformation and thus is referred to as solid state uniaxial orientation (SS-UO). This work examines solely the physicochemical changes occurring in the degrading polylactide film and their relevance to changes in key molecular parameters, as part of a broad based study on the effect of orientation on absorption. The results indicate that the orientation has a large effect on the glass transition temperature and the heat of fusion.

Absorption↗
PubMed1996

A differential scanning calorimetry study of retrieved orthopedic implants made of ultrahigh molecular weight polyethylene.

Differential scanning calorimetry (DSC) was used to examine thermal and thermooxidative properties of ultrahigh molecular weight polyethylene (UHMW-PE) of five acetabular components of failed orthopedic implants retrieved at revision of total hip arthoplasty. The results were compared with controls (unimplanted acetabular cups, a 20-year-old slab of UHMW-PE, and raw material). Profiles of exothermic peaks indicated increased levels of oxidation in all retrieved cups. In three retrieved cups, DSC revealed an additional peak of endotherm that was not seen in control samples. The additional endotherm peaks were not artifacts due to oxidation during scanning, heat buildup during cutting of the samples, or the sterilization method after retrieval. The additional peak was associated with the bulk of the polymer that was extracted with hexane. It varied in relative area, depending on its original location of the sample in a cup, implicating local variability in the extent of changes in material property. The distribution of the changes suggests that, during implantation, tissue exposure and friction affected the level of oxidation and degree of crystallinity in the UHMW-PE to a greater degree than did loading alone. Overall results showed that DSC may be a useful tool in evaluating changes in the properties of UHMW-PE orthopedic components in vivo.

Acetabulum↗
PubMed1995

Effectiveness of cleaning surgical implants: quantitative analysis of contaminant removal.

Surgical implants need to be free from contaminants before implantation. The effectiveness of a presently used Clemson bioengineering cleaning (CBC) protocol was evaluated for cleaning three different biomaterials (titanium, aluminum oxide, and polyethylene terephthalate, PET) contaminated with three different contaminants (calcium chloride, zinc chloride, and hexadecane). Radiolabeled tracer analysis (RTA), with the use of liquid scintillation, was used as the surface analytical technique to quantitatively determine the percent contaminant removed from the biomaterial surface. On average, the ultrasonic cleaning step removed 99.96% of all three contaminants from both titanium and aluminum oxide. The CBC protocol did not sufficiently clean PET fabric contaminated with hexadecane leaving 11.76% of the contaminant after the ultrasonic step. With the use of isopropyl alcohol in series with 1% Liquinox, the ultrasonic step cleaned the fabric soiled with hexadecane within 30 min, removing 99.85% of the hexadecane initially on the surface. RTA proved to be an excellent method of quantifying surface contamination on implant materials, and for assessing the effectiveness of cleaning protocols in question.

Alkanes↗
PubMed1994

The effect of site of implantation and animal age on properties of polydioxanone pins.

Absorbable polymeric orthopaedic pins (Orthosorb) of 2.0 mm diameter were implanted at different sites in mature (3.5 kg, > 5 months) and immature (5 weeks old) rabbits (total 36) for 2, 4, and 5 weeks. The sites of implantation were the medullary canal of the femur, muscles of the thigh and subcutaneous tissue of the dorsum. In mature rabbits, 1.3 mm diameter pins were also implanted in the medullary canal of the femur. The shear strength of the pins harvested from the rabbits, was measured at each time period using a fixture that shears the pins into three parts symmetrically about the load axis. In both mature and immature rabbits the rate of degradation in mechanical properties was higher in the medullary canal of bone than in the muscle and in the subcutaneous tissue (p < 0.05). The strength retention was lower in immature than in mature rabbits after 4 and 5 weeks. The 1.3-mm pins had higher initial strength (174.7 +/- 7 MPa), higher strength retention and slower degradation within the medullary canal of femur of mature rabbits as compared to the 2.0-mm pins (157.5 +/- 4.8). DSC and X-ray diffraction results of control and implanted pins showed higher initial crystallinity and a wider range of crystallite size in the 1.3-mm pins. After 5 weeks in vivo, the crystallinity increased indicating degradation within the amorphous phase. The smaller crystallites underwent recrystallization to form larger crystallites. The results indicate that site of implantation and age of recipient influence the degradation and associated effects on mechanical properties of absorbable implants. The size of the implant, though important in determining its properties, should be considered in association with its microstructure, which also plays an important role in determining strength and strength retention of absorbable polymeric systems.

Aging↗
PubMedDate not supplied

Change in stiffness and effect of orientation in degrading polylactide films.

The degradation pattern of the synthetic absorbable polyester is thought to occur from the center of the material outward, and the bulk degradation is therefore attributed largely to the chemical composition of the material. It was hypothesized that this pattern might be altered by changing the morphology of the material, i.e., by introducing molecular orientation into the system. A new solid state uniaxial orientation (SS-UO) process was used to orient two types of lactide polymer films. The films were exposed to a phosphate buffered solution, then chemically, mechanically, and visually analyzed after predetermined times. This paper explores the results of flexural testing which will be later correlated with microscopic degradation events, as part of the larger degradation study. The results show that, while orientation does not have an overall significant effect on the flexural modulus, there is a significant material/orientation interaction.

Absorption↗
PubMedDate not supplied

Use of a new elastin patch and glue for repair of a major duodenal injury.

Major duodenal injury with significant tissue loss causes high morbidity and mortality. Our new elastin based heterograft combined with small intestinal submucosa (SIS) and biodegradable glue could be used for repair of such defects. Twenty-four domestic pigs were anesthetized and underwent celiotomy. A 2 cm circular defect was created at the second portion of the duodenum with scissors, excising one-half of its circumference. Our elastin patch, combined with SIS, was applied to cover the defect using biodegradable cyanoacrylate glue and a few sutures. It was then covered with omentum. Animals were followed by weight gain, endoscopic evaluation, and upper GI barium studies. After 2-5 months, animals were sacrificed to obtain specimens. One failed in 3 days due to a technical problem, and one failed in 20 days due to an abdominal abscess. The other 22 animals (22/24, 91.7%) did well, gaining weight. Early endoscopic studies (5-14 d) showed an intact patch. Upper GI studies showed varying degrees of stenosis at the repair site at 3-4 months. Sacrifice after 2-5 months showed complete healing of the defect and a dissolved patch. Our new elastin patch material provides a reliable barrier for repair of duodenal injury, and the biodegradable glue provides quick and easy watertight tissue fusion for our patch.

Adhesives↗