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PubMedDate not supplied

Enhanced neointima formation and attachment on the high-porosity inner surface of modified PTFE vascular grafts.

Highly porous PTFE arterial prostheses form endothelium more extensively than the low-porosity grafts in clinical use, but are subject to seroma formation. PTFE vascular grafts were modified to produce a highly porous inner layer (inner layer 60 or 90 microns, outer layer 20 microns). The effect of this modified, composite design on the histology of graft healing was investigated. Twenty-five modified and 25 control grafts, each 4 mm in diameter by 5 cm in length, were implanted into carotid and femoral arteries of dogs. No late seroma formation was observed. After 12 and 18 weeks, the neointima of the grafts was examined by light microscopy and scanning electron microscopy. At 2- and 4-mm distances from the proximal and distal anastomoses, intimal thickness of the control grafts was 238.7 and 96.1 microns, respectively; for the modified grafts it was 236.2 and 202.8 microns at 18 weeks. Thus, the neotinima of modified grafts was thicker than that of control grafts when measured at 4 mm from the anastomoses. Neointimal coverage was less extensive in the control grafts than in modified grafts (26.8 +/- 6.1% vs. 58.8 +/- 13.2%; p < .05). Smooth muscle cells were seen on light-microscopy to penetrate the highly porous inner layer; on scanning electron microscopy, the PTFE fibrils appeared to anchor the neointima of the modified graft. The results suggest that modified PTFE grafts with an inner surface of 60 or 90 microns internodal distance have enhanced formation and anchoring of neointima while remaining impervious to blood.

Animals↗
PubMed1999

The relationship between porosity, collagen fiber orientation and strength of plated bone after rigid plate fixation and removal.

OBJECTIVE: To understand the relationship between porosity, collagen fiber orientation and strength of the plated bone after rigid plate fixation and removal. METHODS: Seventy-two New Zealand white rabbits were used in this experiment. Eight animals served as control and the other sixty-four were plated on their intact left tibiae with stainless steel (316L) 4-hole plates to induce early osteoporosis. The plates were removed 2 months after internal fixation in 40 plated animals, 8 of which were sacrificed immediately following plate removal and the other 32 were killed in successive groups with 8 in each group 1, 2, 3 and 4 months after plate removal. The remaining 24 plated animals were killed at 3, 4 and 6 months after plate fixation. After sacrifice, the samples of plated bone were prepared for light microscope, quantitative histological analysis, polarized light microscope and biomechanical test. RESULTS: The internal fixation with a rigid plate could induce the regional osteoporosis which manifested both bone loss and disorganized bone structure (loss of the orientation of the collagen fibers) leading to decreased strength of the plated bone. Although the regional osteoporosis could recover gradually after plate removal, the bone structure remained disorderly even when the bone mass returned to normal. Delayed restoration of bone structure was related to delayed restoration of bone strength. CONCLUSIONS: Besides the bone loss, the disorganized bone structure is the main cause of decrease of bone strength after rigid plate fixation and removal.

Journal Article↗
PubMed1975

Estimates of the porosity of Bacillus licheniformis and Bacillus subtilis cell walls.

The maximum porosity of Bacillus subtilis and Bacillus licheniformis cell walls was estimated by two independent and relatively simple methods. Peptidoglycan was isolated from Bacillus subtilis cell wall preparations and used as an insoluble support for exclusion chromatography of dextrans of known average molecular size. In an alternative approach the leakage of radioactively labelled proteins from Bacillus licheniformis cells incubated in butanol-saline mixtures was measured and their size estimated by exclusion chromatography on Sephadex G-100. Under these conditions the permeability barrier of the cytoplasmic membrane was destroyed with preservation of the structural integrity of the outer cell wall. The apparent exclusion threshold of the cell wall of either organism as determined by these means corresponded to molecules with a diffusional radius of not more than 2.5 nm.

Alanine↗
PubMed2004

[Repair of the rabbit ear cartilage defects with transforming growth factor-beta1 and allogenic chondrocyte/poly-DL-lactide higher porosity polymer].

OBJECTIVE: To study the repair of the rabbit ear cartilage defects with transforming growth factor-beta1 (TGF-beta1) and allogenic chondrocyte/poly-DL-lactide (PDLLA) higher porosity polymer. METHODS: A total of 18 rabbits were divided into the TGF-beta1 and chondrocytes/PDLLA graft group, the chondrocytes/PDLLA graft group, and the blank control group. Samples were taken out at 4, 12 and 18 weeks after implantation. The histological characteristics were investigated. RESULTS: After 18 weeks of the transplantation, the repaired effects of TGF-beta1 and allogenic chondrocytes/PDLLA graft group was better than the allogenic chondrocytes/PDLLA graft group not only on general sample but also histology, and the blank control group were repaired with fibrous tissue. CONCLUSIONS: The allogenic chondrocytes/PDLLA graft could repair the rabbit ear cartilage defects while TGF-beta1 could improve the quality of the rabbit ear cartilage defects.

Animals↗
PubMed1990

The double porosity model for mass transfer between capillaries and tissues in lung microcirculation.

This paper proposes a double porosity model to deal with the mass transfer between capillaries and tissues in the lung microcirculation on the basis of. Utilizing the analytic method of small parameter expansion and the numerical method, the nonlinear governing equations are solved. Comparison shows that the small parameter solution is accurate enough to illustrate the mass exchange between the lung capillary and tissues. Finally the results are used to discuss the mechanism of formation of lung edema.

Capillaries↗
PubMed1990

Optimization and comparison of three vacuum mixing systems for porosity reduction of Simplex P cement.

Simplex P bone cement was prepared in three commercially available vacuum mixing systems, the Enhancement Mixer, the Mixevac II High Vacuum System, and the Mitab Vacuum System, to determine the improvement in fatigue strength associated with porosity reduction of the cement in all three systems. The results of the fatigue tests of vacuum-mixed Simplex P were also compared to the fatigue strength of Simplex P prepared by centrifugation of the cement immediately after mixing. Vacuum mixing one pack of Simplex P per syringe in all three systems was not effective in complete removal of all the large voids from the cement. Fatigue failure occurred very early in those specimens containing the large voids. There was no significant difference in fatigue life between one pack of cement per syringe mixed under vacuum in the three systems and the control cement (no vacuum, uncentrifuged). Vacuum mixing two packs of cement per syringe was more effective than one pack per syringe, and all three systems significantly increased the cycles to failure of Simplex P over the control cement. However, the Enhancement and Mitab vacuum mixing systems still produced some very weak specimens in fatigue. Two packs of cement per syringe prepared in the Mixevac II vacuum mixing system were significantly stronger in fatigue than two packs mixed in either the Enhancement or Mitab vacuum system. The Mixevac II vacuum mixing system was the most effective technique of the three vacuum mixing systems tested. Centrifugation of one or two packs of Simplex P per syringe produced a more uniform cement that was free of large voids and thus eliminated the very weak specimens.(ABSTRACT TRUNCATED AT 250 WORDS)

Bone Cements↗
PubMed1989

[Comparative study of the seal and porosity of provisional coronal filling materials in endodontics].

The porosity and the leakage properties of 13 temporary fillings used between each appointment during endodontic treatment were investigated by means of thermocycling and dye staining of the interface between the teeth and the filling material. A scanning electron microscope was also used for these observations. The 8 commercially produced temporary fillings seal adequately the cavity whereas the 5 materials prepared and mixed by the practitioner allowed wide staining diffusion and therefore were leaky.

Calcium Hydroxide↗
PubMed1989

[Results of using high porosity aortofemoral bifurcation prostheses].

The authors report on their four-year experience with the use of extremely highly porous vascular polyester prostheses of Czechoslovak proveniencè, whose wall was sealed with fibrin. Aortofemoral bifurcated prostheses with a permeability of 6 100 ml/cm2/min were implanted in 102 patients. The method of fibrination appears to be simple and safe. No hemorrhage through the prosthetic wall was observed. The authors expect the high porosity of the prostheses to result in longer lasting patency of the grafts and thus in improvement of long-term results.

Adult↗
PubMed1980

[Composite porosity depending on the powder-fluid quotient, the mixing process and the methods of application].

Porosity (number of pores, pore size distribution, relative area of pores) of powder/liquid composite depended on processing conditions (powder/liquid ratio, manual or mechanical mixing, method of application). The minimum number of pores and the least relative area of all pores in a cross-section of the sample was found in the mechanically mixed composite. Injection-capsule composites are recommended. Application in small portions should be avoided. The higher the powder/liquid ratio the higher the number of pores and relative area of pores. The ratio of components and the method of application have a different effect on the pore size distribution.

Chemical Phenomena↗
PubMed1977

The role of implant porosity on the development of infection.

The role of implant porosity as a determinant of infection was studied. Standardized porous and nonporous polymethyl methacrylate implants were fabricated for this investigation. In rabbits, the premolded polymethyl methacrylate implants were placed under the paravertebral fascia, just superficial to the paravertebral muscle fascia, before inoculation with a measured number of staphylococci. The polymethyl methacrylate implants did not enhance the infection rate of the contaminated wounds. The presence of pores within the implants did not damage tissue defenses. Polymethyl methacrylate implants did not alter the success of antibiotic treatment. Antibiotics prevented the development of infection in wounds containing 10(6) organisms, even in the presence of an implant. When higher levels of organisms were delivered to the wound, antibiotic treatment had a negligible benefit in the implant and control wounds.

Animals↗
PubMed2005

Three-dimensional fiber-deposited PEOT/PBT copolymer scaffolds for tissue engineering: influence of porosity, molecular network mesh size, and swelling in aqueous media on dynamic mechanical properties.

Among novel scaffold fabrication techniques, 3D fiber deposition (3DF) has recently emerged as a means to fabricate well-defined and custom-made scaffolds for tissue regeneration, with 100% interconnected pores. The mechanical behavior of these constructs is dependent not only on different three-dimensional architectural and geometric features, but also on the intrinsic chemical properties of the material used. These affect the mechanics of the solid material and eventually of 3D porous constructs derived from them. For instance, poly(ethylene oxide terephthalate)-poly(butylene terephthalate) (PEOT/PBT) block copolymers are known to have mechanical properties, depending on the PEOT/PBT weight ratio in block form and on the molecular weight of the initial poly(ethylene glycol) (PEG) blocks. These differences are enhanced even more by their different swelling properties in aqueous media. Therefore, this article examines the influence of copolymer compositions in terms of their swelling on dynamic mechanical properties of solid material and porous 3DF scaffolds. The molecular weight of the starting PEG blocks used in the copolymer synthesis varied from 300 to 1000 g/mol. The PEOT/PBT weight ratio in the blocks used varied from 55/45 to 80/20. This corresponded to an increase of the swelling ratio Q from 1.06 to 2.46, and of the mesh size xi from approximately 9 Angstrom to approximately 47 Angstrom. With increased swelling, dynamic mechanical analysis (DMA) revealed a decrease in elastic response and an increase of viscoelasticity. Thus, by coupling structural and chemical characteristics, the viscoelastic properties of PEOT/PBT 3DF scaffolds may be fine tuned to achieve mechanical requirements for a variety of engineered tissues. Ultimately, the combination of 3DF and DMA may be useful to validate the hypothesis that mimicking the biomechanical behavior of a specific tissue for its optimal replacement is an important issue for at least some tissue-engineering applications.

Animals↗
PubMed2006

Effects of degradation and porosity on the load bearing properties of model hydroxyapatite bone scaffolds.

Degradation of three types of model hydroxyapatite (HA) scaffolds was studied after in vitro degradation in a sodium acetate buffer (pH 4). Degradation was evaluated using compression testing, scanning electron microscopy (SEM), inductively coupled plasma (ICP) analysis, and weight measurements. Scaffolds were fabricated with a solid freeform fabrication (SFF) technique based on the robotic deposition of colloidal pastes. Scaffolds had a macrostructure resembling a lattice of rods. Scaffolds contained either macropores (270 or 680 microm in the x-y direction and 280 microm in the z-direction) and micropores (1-30-microm pores and pores <1 microm) or only macropores pores (270 microm in the x-y direction and 280 microm in the z-direction). A computer-aided design (CAD) program controlled the size and distribution of macropores; micropores were created by polymethylmethacrylate (PMMA) microsphere porogens (1-30-microm pore diameter) and controlled sintering (pores <1 microm). Percent weight loss of the scaffolds and calcium and phosphorus ion concentrations in solution increased as the degradation period increased for all scaffold types. After degradation, compressive strength and compressive modulus decreased significantly for those scaffolds with microporosity. For scaffolds without microporosity, the changes in strength and modulus after degradation were not statistically significant. The compressive strength of scaffolds without microporosity was significantly greater than the scaffolds with microporosity.

Bone Substitutes↗
PubMed2005

Does early PTH treatment compromise bone strength? The balance between remodeling, porosity, bone mineral, and bone size.

The treatment of osteoporotic women with recombinant human parathyroid hormone (rhPTH) increases bone mineral density and reduces fracture risk. However, there has been concern that the initiation of therapy in women with low bone mass may cause an early and transient increased fracture risk because PTH stimulates bone remodeling, which in its first phase is associated with bone resorption. Animal and human studies suggest, however, that the stimulation of remodeling caused by rhPTH(1-34) does not lead to a deterioration of bone's mechanical properties or to an increased fracture risk even early in the treatment. There are several reasons for this. Bone biomarkers associated with formation rise earlier than those associated with resorption, suggesting that there is an initial period prior to the stimulation of remodeling during which bone formation occurs on surfaces without prior resorption. This initial period of formation may protect the patient from the later small and transient losses that occur through remodeling. Moreover, the increased remodeling occurs on cancellous surfaces or close to the endosteal surface of bone, where its mechanical effect is minimal. Additionally, these transient losses may be compensated by periosteal apposition that maintains the overall strength of the bone. Thus, the early stimulation of bone formation without prior resorption, and the redistribution of bone from cancellous and endocortical surfaces to the periosteal surface combine to prevent the mechanical deterioration that could otherwise occur with a transient acceleration of bone remodeling in a patient with low bone mass.

Animals↗