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PubMed1999

The formation of hydroxyapatite-calcium polyacrylate composites.

Tetracalcium phosphate (TetCP, Ca4(PO4)2O) reacts rapidly with polyacrylic acid (PAA). Complete reaction results in the formation of hydroxyapatite (HAp) and calcium polyacrylate. Consequently, this combination of reactants can react to form a dental cement. However, reaction occurs so rapidly that it would be difficult to achieve a homogeneous mixture of reactants suitable for use in restorations. In order to explore extending the working time, the effects of prehydrating the TetCP to form surface layers of HAp on the TetCP particles was explored. Prehydration was found to be an effective means of allowing workability. Therefore, the effects of the proportions of TetCP and PAA, with and without HAp filler, on cement properties were investigated. The extents of the reactions were investigated by X-ray diffraction analysis; the extents of PAA neutralization were studied by Fourier transform infra-red spectroscopy (FTIR); pore structures were determined by mercury intrusion porosimetry; microstructures were observed by scanning microscopy, and compressive strengths were determined. After curing for 17 days at room temperature PAA neutralization was almost complete; however, residual TetCP could be detected by X-ray diffraction and PAA by FTIR. As expected, the compressive strengths of the cements showed a dependence on the liquid (water+polymer)-to-solid (TetCP+HAp filler) used. The presence of HAp filler caused a significant decrease in compressive strength and increasing the proportion of HAp filler resulted in a decrease in the compressive strength. The characteristics of the load-deflection curves showed a dependence on the presence of HAp filler. In the absence of filler, two slopes were observed in the curves whereas a linear curve, typical of a ceramic, was observed when HAp filler was present. Mercury intrusion porosimetry (MIP) indicated the majority of the porosity was present in pores larger than 0.1 microm. Porosity increased with increasing liquid-to-solids ratio and with an increasing proportion of HAp filler at a constant liquid-to-solids ratio. Microstructural observations indicated the effect of HAp filler on increasing porosity was the result of porosity present in the filler itself. Thus, poorly consolidated HAp filler contributed to increased porosity and reduced compressive strength.

Journal Article↗
PubMed1988

A new sealant for knitted Dacron prostheses: minimally cross-linked gelatin.

There has been a resurgence of interest in the concept of presealing high-porosity knitted Dacron prostheses with an absorbable biologic material. Such a material should provide reliable porosity control, preferably reducing water porosity from 2000 ml/cm2/min to less than 50 ml/cm2/min. It should not interfere with the fibrous and vascular ingrowth that securely anchors the developing pseudointima. In previous studies, we have examined fibrin glue and two forms of aldehyde cross-linked insoluble collagen used as Dacron sealants. We concluded that delayed resorption of the sealant as seen with glutaraldehyde cross-linked insoluble collagen results in undesirable healing characteristics, particularly lack of adhesion between pseudointima and the luminal surface of a prosthesis. This study examines a new sealant. Soluble collagen (gelatin) is treated to reduce the number of free amino groups available for aldehyde cross-linking. It is then weakly cross-linked with an aldehyde mixture and applied to a knitted Dacron prosthesis. Water porosity studies have confirmed satisfactory porosity control. Both rat subcutaneous and canine circulatory implants for 6 months reveal relatively rapid and complete sealant resorption without undesirable modification of the normal healing process of knitted Dacron.

Animals↗
PubMed2001

Influence of elastic deformation of particles on Heckel analysis.

The Heckel equation is one of the most useful equations for describing the compaction properties of pharmaceutical powders. Important material properties (e.g., yield strength) of powders can be derived using Heckel analysis. Two types of Heckel analysis are in common use. One is the "out-of-die," or "zero-pressure" method, the other is the "in-die" or "at-pressure" method. Because particles undergo elastic deformation under pressure, which tends to lower the porosity of the powder bed, the "out-of-die" method describes powder consolidation and compaction more accurately than the "in-die" method. However, "in-die" Heckel analysis has been widely used because of the speed and ease of data collection. Using L-lysine monohydrochloride dihydrate as a model compound, this work analyzes quantitatively the effects of elastic deformation on the calculation of porosity of a tablet, and therefore on the Heckel analysis. The effects of a small change in porosity, epsilon, on Heckel analysis are presented mathematically. It is found that a decrease in porosity of 0.001, when the porosity is lower than 0.05, causes a significant increase in the value of -ln epsilon. Therefore, data at epsilon < 0.05 should be interpreted with caution when using Heckel analysis. Elastic deformation causes positive deviations in the Heckel plot, and therefore leads to a yield strength that is lower than the true value. The lower the elastic modulus of the powder, the greater is the deviation from the true value. Therefore, the "in-die" method gives values of yield strength that are significantly lower than the true values for most pharmaceutical powders.

Elasticity↗
PubMed1998

Quantitative assessment of bone injury and repair after reamed and unreamed locked intramedullary nailing.

BACKGROUND: Cortical reaming and intramedullary nail insertion injure the medullary vascular system. Little attention has been directed toward quantitative assessment of bone injury and repair after locked intramedullary nailing of long-bone fractures with and without reaming. The effects of reamed versus unreamed locked intramedullary nailing on cortical porosity and new bone formation were compared in a sheep fractured tibia model. METHODS: After creation of a standardized spiral fracture by three-point bending with torsion, each tibia was stabilized by insertion of a locked intramedullary nail. Ten sheep were randomized into two groups, one that had reaming before nail insertion and one that did not. Fluorochromes were given 2 weeks (xylenol orange), 6 weeks (calcein green), and 12 weeks (tetracycline) postoperatively. All animals were killed at 12 weeks postoperatively. Cortical porosity and new bone formation were determined for the proximal diaphysis, fracture site, and distal diaphysis. RESULTS: Overall cortical porosity was greater with reamed nails than with unreamed nails (p = 0.02). Porosity in the inner cortex (18.3% (reamed) vs. 14.3% (unreamed); p = 0.09) and outer cortex (16.8% (reamed) vs. 12.2% (unreamed); p = 0.04) was greater in the reamed group. With reamed nails only, there was less new bone formation at 2 (p = 0.04) and 12 (p = 0.05) weeks in the inner cortex compared with the central cortex and outer cortex. Overall, there was no difference between reamed and unreamed nails in the amount of new bone formation at 2, 6, or 12 weeks. CONCLUSIONS: This study demonstrates that greater injury or overall cortical porosity is associated with reamed nail insertion. There is no difference, however, between the amount of new bone formation after reamed and unreamed nail insertion. Nail insertion without reaming may be initially advantageous when tibial cortical vascularity is compromised, by limiting further injury to cortical bone. This may be important with open tibial fractures in which there is a significant risk of infection after injury. Between 2 and 12 weeks after injury, neither reamed nor unreamed nail insertion seems to have a significant advantage with respect to the amount of new bone formation that occurs.

Animals↗
PubMed2003

Chemometric evaluation of pharmaceutical properties of antipyrine granules by near-infrared spectroscopy.

The purpose of this research was to apply near-infrared (NIR) spectroscopy with chemometrics to predict the change of pharmaceutical properties of antipyrine granules during granulation by regulation of the amount of water added. The various kinds of granules (mean particle size, 70-750 microm) were obtained from the powder mixture (1 g of antipyrine, 6 g of hydroxypropylcellulose, 140 g of lactose, and 60 g of potato starch) by regulation of the added water amount (11-19 wt/wt%) in a high-speed mixer. The granules were characterized by mean particle size, angle of repose, compressibility, tablet porosity, and tablet hardness as parameters of pharmaceutical properties. To predict the pharmaceutical properties, NIR spectra of the granules were measured and analyzed by principal component regression (PCR) analysis. The mean particle size of the granules increased from 81 micro m to 650 micro m with an increase in the amount of water, and it was possible to make larger spherical granules with narrow particle size distribution using a high-speed mixer. Angle of repose, compressibility, and porosity of the tablets decreased with an increase of added water, but tablet hardness increased. The independent calibration models to evaluate particle size, angle of repose, and tablet porosity and hardness were established by using PCR based on NIR spectra of granules, respectively. The correlation coefficient constants of calibration curves for prediction of mean particle size, angle of repose, tablet porosity, and tablet hardness were 0.9109, 0.8912, 0.7437, and 0.8064, respectively. It is possible that the pharmaceutical properties of the granule, such as mean particle size, angle of repose, tablet porosity, and tablet hardness, could be predicted by an NIR-chemometric method.

Antipyrine↗
PubMed2003

Influence of the temperature of salt brine on salt uptake by Ragusano cheese.

The influence of temperature (12, 15, 18, 21, and 24 degrees C) of saturated brine on salt uptake by 3.8-kg experimental blocks of Ragusano cheese during 24 d of brining was determined. Twenty-six 3.8-kg blocks were made on each of three different days. All blocks were labeled and weighed prior to brining. One block was sampled and analyzed prior to brine salting. Five blocks were placed into each of five different brine tanks at different temperatures. One block was removed from each brine tank after 1, 4, 8, 16, and 24 d of brining, weighed, sampled, and analyzed for salt and moisture content. The weight loss by blocks of cheese after 24 d of brining was higher, with increasing brine temperature, and represented the net effect of moisture loss and salt uptake. The total salt uptake and moisture loss increased with increasing brine temperature. Salt penetrates into cheese through the moisture phase within the pore structure of the cheese. Porosity of the cheese structure and viscosity of the water phase within the pores influenced the rate and extent of salt penetration during 24 d of brining. In a previous study, it was determined that salt uptake at 18 degrees C was faster in 18% brine than in saturated brine due to higher moisture and porosity of the exterior portion of the cheese. In the present study, moisture loss occurred from all cheeses at all temperatures and most of the loss was from the exterior portion of the block during the first 4 d of brining. This loss in moisture would be expected to decrease porosity of the exterior portion and act as a barrier to salt penetration. The moisture loss increased with increasing brine temperature. If this decrease in porosity was the only factor influencing salt uptake, then it would be expected that the cheeses at higher brine temperature would have had lower salt content. However, the opposite was true. Brine temperature must have also impacted the viscosity of the aqueous phase of the cheese. Cheese in lower temperature brine would be expected to have higher viscosity of the aqueous phase and slower salt uptake, even though the cheese at lower brine temperature should have had a more porous structure (favoring faster uptake) than cheese at higher brine temperature. Therefore, changing brine concentration has a greater impact on cheese porosity, while changing brine temperature has a larger impact on viscosity of the aqueous phase of the cheese within the pores in the cheese.

Cheese↗
PubMed2005

Composition, microstructure, and surface barrier layer development during brine salting.

The goal of this study was to characterize the changes in chemical composition, porosity, and structure that occur at the surface of a block of brine-salted cheese and their relationship to the rate at which salt is taken up from the brine. To create a difference in composition, salt uptake, and barrier layer properties, identical blocks of Ragusano cheese were placed in saturated and 18% salt brine at 18 degrees C for 12 d. The overall moisture content and porosity decreased, whereas salt and salt in moisture content increased near the surface of blocks of brine-salted Ragusano cheese for all treatments. The general appearance of the microstructure of the surface of the blocks of brine-salted cheese was much more compact than the microstructure 1 mm inside the block at both brine concentrations. Large differences in porosity of the barrier layer were produced by brine-salting cheese in 18% vs. saturated brine, with cheese in saturated brine having much lower porosity at the surface and taking up much less salt during brining. The macro network of water channels within the microstructure of the cheese was less open near the surface of the block for cheese in both saturated and 18% brine after 4 d. However, no large differences in the size of the macro channels in the cheese structure due to the difference in brine concentration were observed by scanning electron microscopy. It is possible that the shrinkage of the much smaller pore structure within the casein matrix of the cheese is more important and will become more limiting to the rate of salt diffusion. Further microstructure work at higher resolution is needed to answer this question. The calculated decrease in porosity at the exterior 1-mm portion of the block was 50.8 and 29.2% for cheeses that had been in saturated vs. 18% brine for 12 d, respectively. The difference in brine concentration had a very large impact on the salt in moisture content of the cheese. The exterior of the cheese in 18% brine reached a salt in moisture content almost identical to that of the brine very quickly (17.3% at 4 d), whereas the salt in moisture content at the surface of the cheese block in saturated brine was only 11.9% at 4 d. There appears to be some critical concentration of salt in brine above which there is a large negative impact on salt uptake due to the creation of a barrier layer at the surface of the block of cheese.

Cheese↗
PubMedDate not supplied

Pseudointima formation in woven and knitted dacron grafts. A comparative ultrastructural analysis.

Twelve specially designed crimped aortobifurcated grafts (aorta, woven 200 porosity; right limb, woven 500 porosity; left limb, knitted 1200 porosity) were implanted into mongrel dogs that were sacrificed at two, six, eight and twelve-month intervals. Pseudointima from the mid portion of each type of graft was studied with light (LM) and transmission electron microscopy (TEM). An ocular micrometer was used to determine the thickness of the pseudointima. A trilaminar cytoarchitecture resembling the wall of a medium-sized artery existed in the pseudointima. This was characterized by an inner cellular layer, outer fibrocollagenous layer, and multi-interlamination of cells and glycosaminoglycan in the middle layer. The cellular inner layer was thickest in the knitted and thinnest in the woven 200 porosity. A zone of acellularity separated the luminal cells from the underlying myoblasts and myofibroblasts. Specificity of varying types of cell distribution occurred in the pseudointima. Myoblasts and myofibroblasts were located near the lumen while fibroblasts and mesenchymoid cells were situated near the graft. The luminal cells had the combined features of endothelial cells and myofibroblasts. Collagen and glycosaminoglycans were the dominant extracellular matrix. Despite the difference of fluid permeability in high porosity woven and knitted dacron grafts, the pseudointima was well formed and revealed no striking general cytoarchitectural difference between these two types of grafts.

Animals↗
PubMed1986

Heat-denatured albumin-coated Dacron vascular grafts: physical characteristics and in vivo performance.

Dacron fabrics with a wide range of porosities were autoclaved for 3 minutes after being soaked in serum, 5% albumin, or 25% albumin. Porosity of compound Dacron grafts made with 25% albumin was less than 1 ml/min/cm2 regardless of the fabric base, whereas porosity of grafts made with serum or 5% albumin was proportional to the porosity of the base fabric. Porosity of the compound grafts remained stable for more than 48 hours and to pressure greater than 450 mm Hg, if the grafts were kept moist. Tubes of Marlex mesh coated with heat-denatured albumin, implanted as infrarenal aortic replacements in dogs, showed complete albumin absorption by 3 weeks. However, perigraft tissue reaction and graft incorporation were minimal and extensive false aneurysm formation resulted. Knitted filamentous Dacron 6 mm tubes coated with heat-denatured albumin were implanted as iliofemoral bypass grafts in 12 dogs, with blood-preclotted knitted filamentous Dacron grafts implanted as contralateral control grafts. Comparison of the albumin-coated grafts with the blood-preclotted control grafts showed no differences in healing or patency at 4 to 6 months. Heat-denatured 25% albumin forms a strong and hemostatic coating regardless of fabric base. Albumin-Dacron compound grafts are easily and rapidly made in the operating room, handle well, and are suitable for large and medium-sized arterial replacements without changes in healing or patency. Because of slow tissue incorporation, however, albumin-coated knitted Dacron grafts should be avoided in patients who require long-term anticoagulation therapy.

Albumins↗
PubMed1986

Biomaterial aspects of Interpore-200 porous hydroxyapatite.

Interpore-200 is the product of over 11 years of continuous research and development. It has been investigated at over 25 research centers in a wide variety of animal and human implant settings, including alveolar ridge augmentation, periodontics, and orthognathic reconstructions. The biomaterial aspects of Interpore-200 show the following: Interpore-200 has a highly interconnected, three-dimensional porosity that is uniform and consistent. The hydroxyapatite manufactured from marine corals is biocompatible and nontoxic. Interpore-200 is essentially pure hydroxyapatite, with the balance consisting of tricalcium phosphate. Interpore-200 is approximately 55 to 65 per cent porous with nominal pore diameters of 200 micron. Unlike nonporous materials, Interpore-200 is osteoconductive and results, when placed next to a viable bone, in an advancing front of bone into the implant. From 50 to 88 per cent of the porosity within the implant is filled with woven and lamellar bone within 3 months. Moreover, the surfaces of Interpore-200 are intimately bonded with the bone tissue. The biomechanical properties of Interpore-200 blocks are similar to those of a cancellous bone graft. Once ingrown with vascularized bone tissue, the defect site is, in effect, restored. Interpore-200 adequately matches the elastic properties of bone so that stresses necessary to maintain healthy bone are transmitted throughout the regenerated region. Extensive animal and clinical studies have shown that nonporous implants or implants without interconnected porosity can result in aberrant mineralization, stress shielding, low fatigue strength, and bulk displacement. Hydroxyapatite with interconnected porosity like Interpore-200 reacts differently than materials with limited or no porosity. In animals, Interpore-200 exhibits 0 to 5 per cent biodegradation per year. Moreover, this minimal biodegradation is compensated by regeneration of bone. These studies have now been extended for 4 years. Interpore-200 and its ingrown bone are remodeled in response to the same chemical and biomechanical forces that remodel normal bone. Therefore, Interpore-200 responds in accordance to Wolff's law. Having achieved an optimal combination of biomaterial (hydroxyapatite) in an ideal porous structure (replamineform), Interpore-200 fulfills the expectation of early researchers in the basic sciences who demonstrated that an interconnected porous material is better tolerated by the body than the same material in solid form.(ABSTRACT TRUNCATED AT 400 WORDS)

Alveolar Ridge Augmentation↗
PubMed1981

[Studies on Au-Ag-Pd-Cu alloys. (Part 3) Effects of additional elements to Au-Ag-Pd-Cu alloys (author's transl)].

In the previous papers, the author pointed out that alloys containing 30 wt% Au, 15-25 wt% Pd and Cu were more favourable for Au-Ag-Pd-Cu quarternary dental alloys. In this paper, the experiments were carried out to find the effects of additional elements and so, Pt, Ir, Os, W, Mo, Cr, Mn, Co, Zn, In, Sn and Si were added to 30 wt% Au-30 wt% Ag-20 wt% Pd-20 wt% Cu alloys ranging 0.1 wt% to 2.0 wt% respectively. Then, tensile strength, elongation, hardness, corrosion resistivity and porosity ratio were tested on these specimen. Results were as follows. 1) The addition of 0.2 wt% Ir, 0.2 wt% Os and 1.0 wt% Co were comparatively effective for the fineness of grain sizes, elongation and tensile strength. 2) The addition of 0.2 wt% W, 1.0 wt% Mo and 0.2 wt% Si showed respectively bad effect for porosities or mechanical properties. 3) The addition of 1.0 wt% Cr, 2.0 wt% Mn, 1.0 wt% Co, 2.0 wt% Zn and 2.0 wt% In were good for the decrease of porosities respectively and showed that the porosity ratio was lower than 0.2%. 4) The additions of 2.0 wt% Zn-1.0 wt% Pt-0.5 wt% Co to Au-Ag-Pd-Cu alloy was especially good and showed 80 kg/mm2 of tensile strength, 5.1% of elongation, 249 of Vicker's hardness number and 0.4% of porosity ratio.

Copper↗
PubMed1994

Ultrastructure and mineral composition of urinary calculi from horses.

Urinary calculi from 17 horses with urolithiasis were examined to study their mineral content and ultrastructure. Among the analytic methods used were X-ray diffractometry, scanning electron microscopy, and electron microprobe analysis. The calculi initially were observed by use of a stereoscopic dissecting microscope and generally were found to have nodular surfaces surrounding a banded or granular-to-chalky interior. Observation by scanning electron microscopy revealed an intricate pattern of irregularly concentric, fine bands and spherules. These had a round, finely banded, globular texture formed by precipitation of ultrafine-grained radiating crystals. The original pore spaces (ie, between spherules, between bands and spherules, or between crystal generations) could be observed as primary porosity. Precipitation and dissolution of these urinary calculi were observed to be spontaneous processes, which can occur simultaneously within an individual calculus. Another prominent feature of the ultrastructure was secondary porosity (spontaneous dissolution) which, in its incipient stages, appeared to be site-selective (ie, some bands appeared to be more susceptible to development of pinpoint porosity). Textures indicative of dissolution were observed not only on the calculus surface, but within the calculus interior as well. Areas that had more advanced stages of dissolution, resulting in increased secondary porosity, also were observed. All 17 samples of the study were found to be composed of calcium carbonate in the form of the mineral calcite, although minor quantities of 2 other polymorphs of calcium carbonate, minerals vaterite and aragonite, also were encountered. Vaterite was observed in 5 of the samples, whereas aragonite was found in 1 sample. Strontium and sulfur were observed as trace elements in 3 of the calculi, whereas magnesium was present in all calculi. Magnesium was observed to substitute for calcium within the calcite crystal lattice in larger quantities than those of strontium or sulfur. Magnesium K alpha X-ray dot maps generated by use of an electron microprobe analyzer indicated that the distribution pattern of magnesium appeared to closely follow layer-by-layer growth of the calculus. Magnesium distribution also appeared to be related to porosity development. In samples where preferential dissolution was observed, the more porous areas had higher magnesium content. Quantitative chemical analyses, using the electron microprobe analyzer, confirmed these observations. Association of the magnesium distribution pattern to the primary growth texture of the calculus indicated that magnesium content of the calculus varied during the formation process. This also indicated that changes in urine chemical analytes may be reflected in composition of the calculi formed.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed2006

Fabrication and evaluation of porous 2,3-dialdehydecellulose membrane as a potential biodegradable tissue-engineering scaffold.

A simple, novel method to produce porous 2,3-dialdehydecellulose (DAC) membranes as a potential tissue-engineering scaffold has been developed from methylolcellulose by the simultaneous water-induced phase separation and sodium chloride salt leaching techniques, followed by oxidation with sodium periodate in water. Membrane pores increased in size with increasing weight or particle size of the sodium chloride salt. The porosity of the membrane was not affected by the salt particle size, but it increased with an increase in the salt weight to 60%. At higher salt weight percentages, no significant change in the membrane porosity was observed. The oxidation step had no effect on the membrane porosity or pore size. All membranes with a porosity value ranging between 87 and 93% showed interconnected porous structures. The use of these membranes as a potential tissue-engineering scaffold was evaluated with the use of human neonatal skin fibroblast cells. Confocal microscopy showed cell attachment and spreading on these membranes. Immunohistochemical tests revealed the presence of collagen type III and fibronectin, indicating that the cells were viable and formed the extracellular matrix. In conclusion, the DAC membrane supports cell adhesion and proliferation and hence shows potential to be used as a tissue-engineering scaffold.

Absorbable Implants↗
PubMed2006

The structure of the bond between bone and porous silicon-substituted hydroxyapatite bioceramic implants.

The significance of micrometer-sized strut porosity in promoting bone ingrowth into porous hydroxyapatite (HA) scaffolds has only recently been noted. In this study, silicon-substituted HA (0.8 wt % Si-HA) with approximately 8.5% of the total porosity present as microporosity within the struts of the implant was prepared for high-resolution transmission electron microscopy (HR-TEM) via both ultramicrotomy and focused ion beam milling. Between the struts of the porous Si-HA, pores with varying shapes and sizes (1-10 microm in diameter) were characterized. Within the struts, the Si-HA contained features such as grain boundaries and triple-junction grain boundaries. Bone ingrowth and dissolution from a Si-HA implant were studied using HR-TEM after 6 weeks in vivo. Minor local dissolution occurred within several pores within the struts. Organized, mineralized collagen fibrils had grown into the strut porosity at the interface between the porous Si-HA implant and the surface of the surrounding bone. In comparison, deeper within the implant, disorganized and poorly mineralized fibers were observed within the strut porosity. These findings provide valuable insight into the development of bone around porous Si-HA implants.

Animals↗
PubMed2003

Preparation of interconnected highly porous polymeric structures by a replication and freeze-drying process.

Three-dimensional degradable porous polymeric structures with high porosities (93-98%) and well-interconnected pore networks have been prepared by freeze-drying polymer solutions in the presence of a leachable template followed by leaching of the template. Templates of the pore network were prepared by fusing sugar or salt particles to form a well-connected structure. The interstices of the template were then filled with a polymer solution (5-15% w/v) in 1,4-dioxane, followed by freeze-drying of the solvent. Subsequent leaching of the sugar template ensures the connectivity of the pore network. The scaffold architecture consists of relatively large interconnected pores modeled after the template and smaller pores resulting from the freeze-drying process. The total porosity of the resultant porous structures is determined by the interstitial space of the leachable template and by the polymer concentration in the freeze-drying solution. The freezing temperature also has an effect on the final morphology of the porous structures. Compared with freeze-drying and combination of freeze-drying /particulate leaching techniques, this method facilitates higher interconnectivity of the scaffolds. Porous structures have been prepared from several relevant polymers in the biomedical and tissue-engineering field: poly(D,L-lactide) (PDLLA), 1000PEOT70PBT30, a segmented poly(ether ester) based on polyethylene oxide and polybutylene terephthalate, and poly(epsilon-caprolactone) (PCL). The mechanical properties of the porous structures prepared by this technique depend on the nature of the polymer, porosity, and the freezing temperature. With porosities in the range of 95-97%, the compression moduli of scaffolds prepared from the different polymers could be varied between 13.0 and 301.5 kPa.

Biocompatible Materials↗
PubMed2006

Dual hydroxyapatite composite with porous and solid parts: experimental study using canine lumbar interbody fusion model.

Hydroxyapatite (HA) has been evaluated for use in a variety of applications in bone reconstruction surgery because of its high affinity with host bone and biocompatibility. However, because of the difficulty in combining porosity (for bone ingrowth) and strength in HA, it is generally considered inappropriate to use HA for high-load applications such as spinal interbody fusion. In the present study, we constructed a HA implant for spinal interbody fusion, composed of a dual HA composite (DHC) that combines two HA materials with different porosities: HA with 75% porosity, for bone ingrowth; and HA with 0% porosity, for load bearing. We used a canine lumbar interbody fusion model to evaluate bone conduction of the implant and its efficacy for bony fusion. Six months after the operation, DHC exhibited almost the same efficacy for bony fusion as iliac bone grafts. Moreover, pores of the porous part of the DHC were completely filled with newly formed bone and bone marrow cells. The present findings indicate that DHC is suitable for use as an implant material for spinal interbody fusion as a substitute for iliac bone grafts, which could eliminate the disadvantages associated with autograft harvesting.

Animals↗
PubMed2007

Internal adaptation and some physical properties of methacrylate-based denture base resins polymerized by different techniques.

This study evaluated the internal adaptation, porosity, transverse and impact strength of three denture base polymers: (1) conventional heat-polymerized, (2) microwave-polymerized, and (3) injection-molded resins. Internal adaptation was measured by weighing a vinyl polysiloxane film reproducing the gap between the denture base and the metallic master model of an edentulous maxilla. The measurements were performed immediately after finishing and after 30-day storage in water. Porosity was evaluated by weighing each specimen in air and in water using an analytical scale balance. Transverse strength test (three-point bending test) was performed using a universal machine under axial load, at a crosshead speed of 5 mm/min. Impact strength test (Charpy's test) was performed with a 40 kJ/cm load. Data were analyzed by ANOVA and Tukey test (alpha = 0.05). Internal adaptation, porosity, transverse and impact strength varied according to the type of acrylic resin and the processing technique. The injection-molded resin showed better internal adaptation compared with the conventional heat-polymerized and the microwave-polymerized resins, particularly after 30 days, but there was no relevant improvement of porosity, transverse and impact strength.

Acrylic Resins↗
PubMed2002

Drop penetration into porous powder beds.

The kinetics of drop penetration were studied by filming single drops of several different fluids (water, PEG200, PEG600, and HPC solutions) as they penetrated into loosely packed beds of glass ballotini, lactose, zinc oxide, and titanium dioxide powders. Measured times ranged from 0.45 to 126 s and depended on the powder particle size, viscosity, surface tensions, and contact angle. The experimental drop penetration times were compared to existing theoretical predictions by M. Denesuk et al. (J. Colloid Interface Sci.158, 114, 1993) and S. Middleman ("Modeling Axisymmetric Flows: Dynamics of Films, Jets, and Drops," Academic Press, San Diego, 1995) but did not agree. Loosely packed powder beds tend to have a heterogeneous bed structure containing large macrovoids which do not participate in liquid flow but are included implicitly in the existing approach to estimating powder pore size. A new two-phase model was proposed where the total volume of the macrovoids was assumed to be the difference between the bed porosity and the tap porosity. A new parameter, the effective porosity epsilon(eff), was defined as the tap porosity multiplied by the fraction of pores that terminate at a macrovoid and are effectively blocked pores. The improved drop penetration model was much more successful at estimating the drop penetration time on all powders and the predicted times were generally within an order of magnitude of the experimental results.

Glass↗