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PubMed2006

Structural features of biomass in a hybrid MBBR reactor.

The structural features of biomass present in the hybrid MBBR (Moving Bed Biofilm Reactor) aeration tank were studied in two subsequent periods, which differed in hydraulic and substrate loads. The physical characteristics of attached-growth biomass, such as, biofilm thickness, density, porosity, inner and surface fractal dimensions, and those of suspended-growth biomass, such as, floc size distribution, density, porosity, inner and surface fractal dimensions, were investigated in each study period and then compared. The results indicated that biofilm always had a higher density, geometric porosity, and a larger boundary fractal dimension than flocs. Both types of biomass were found to exhibit at least two distinct Sierpinski fractal dimensions, indicating two major different pore space populations. With the increasing wastewater flow, both types of biomass were found to shift their structural properties to larger values, except porosity and surface roughness, which decreased. Floc density and biomass Sierpinski fractals were not affected much by the system loadings.

Biofilms↗

PubMed2001

The preparation of rapidly disintegrating tablets in the mouth.

Elderly people, children and patients sometimes have difficulties swallowing tablets. To solve this problem, a novel method of preparing tablets that disintegrate rapidly in the mouth was developed. A tablet with high porosity is required for rapid disintegration, but such a tablet is generally fragile. To make a tablet having both high porosity and practical strength, amorphous sucrose, which has good compactability, was used. Mannitol powder with freeze-dried amorphous sucrose was tableted at low compression and stored under certain conditions. The tablet disintegrated rapidly in the mouth, because of its high porosity. The tensile strength of the tablet increased remarkably during storage, while the porosity of the tablet seemed almost unchanged. The results of thermal analysis and powder x-ray diffraction measurement showed that the amorphous sucrose in tablet crystallized during storage. The increase in the tensile strength of the tablet was due to crystallization of the amorphous sucrose and formation of new internal contact points in the tablet. It was concluded that this crystalline transition method is a very useful method to prepare a rapidly disintegrating tablet.

Administration, Oral↗

PubMed2006

Porous poly(DL-lactic-co-glycolic acid)/calcium phosphate cement composite for reconstruction of bone defects.

Calcium phosphate (Ca-P) cements are injectable, self-setting ceramic pastes generally known for their favorable bone response. Ingrowth of bone and subsequent degradation rates can be enhanced by the inclusion of macropores. Initial porosity can be induced by CO(2) foaming during setting of the cement, whereas secondary porosity can develop after hydrolysis of incorporated poly(DL-lactic- co-glycolic acid) (PLGA) microparticles. In this study, we focused on the biological response to porous PLGA/Ca-P cement composites. Pre-set composite discs of four formulations (4 wt% or 15 wt% PLGA microparticles and low or high CO(2) induced porosity) were implanted subcutaneously and in cranial defects in rats for 12 weeks. Histological analysis of the explanted composites revealed that bone and fibrous tissue ingrowth was facilitated by addition of PLGA microparticles (number average diameter of 66 +/- 25 microm). No adverse tissue reaction was observed in any of the composites. Significant increases in composite density due to bone ingrowth in cranial implants were found in all formulations. The results suggest that the PLGA pores are suitable for bone ingrowth and may be sufficient to enable complete tissue ingrowth without initial CO(2) induced porosity. Finally, bone-like mineralization in subcutaneous implants suggests that, under appropriate conditions and architecture, porous PLGA/Ca-P cement composites can exhibit osteoinductive properties. These PLGA/Ca-P composites are a promising scaffolding material for bone regeneration and bone tissue engineering.

Absorbable Implants↗

PubMed1998

Determinations of strength of synthetic hydroxyapatite ceramic implants.

To study the physical strengths of various types of synthetic high porosity hydroxyapatite plates, we constructed samples of a fixed shape, 8 X 25 mm in size, with varying degrees of thickness (3 to 10 mm) and porosity (40, 50, and 60 percent), as well as samples with varying degrees of curvature and samples constructed with computer-aided design-computer-aided manufacturing (CAD-CAM) technology based on a real-size model made with laser lithography from computed tomography data. The strength of the samples was studied with the three-point bending test and crush tests. Studies showed that strength decreases with increasing porosity and increases with increasing thickness. In addition, results of testing plates of varying shapes and degrees of curvature revealed that the effects of these variations were small and that when the width and thickness were held constant, changing the curvature of the entire unit (from a height of 20 to 30 mm) or altering both sides had no remarkable effect on strength. On the other hand, strength testing of plates of various shapes and thicknesses constructed from clinical computed tomography data revealed that minimum optimization of the parameters was achieved when plates had a porosity of about 40 percent and a thickness of about 8 mm.

Biomechanical Phenomena↗

PubMed1995

Evaluation of porous biphasic calcium phosphate ceramics for anterior cervical interbody fusion in a caprine model.

STUDY DESIGN: This study compared the efficacy of characterized 50/50 hydroxyapatite/beta-tricalcium phosphate ceramics of 30%, 50%, and 70% porosity and autograft to promote interbody spinal fusion at C2-C3 and C5-C6 in 24 goats: 12 at 3 months and 12 at 6 months. OBJECTIVES: Radiographs, histology, dual energy x-ray absorptiometry analysis, and biomechanical testing were used to evaluate the ability of the 30%, 50%, and 70% porous 50/50 hydroxyapatite/beta-tricalcium phosphate ceramics and autograft to promote cervical interbody fusion. SUMMARY OF BACKGROUND DATA: The conundrum in the use of calcium phosphates for interbody fusion is what porosity is most effective to promote ingrowth yet strong enough to resist compressive stresses found in the spine? It is known that the ability for bone ingrowth increases and the compressive strength decreases as porosity of the ceramic is increased. Dense ceramics remain intact but may be surrounded by fibrous tissue. Porous ceramics have good ingrowth but may fracture. METHODS: Radiographs were evaluated for fusion and fracture or collapse of the ceramics or autograft. Dual energy x-ray absorptiometry was used to evaluate the fusion mass. Treated motion segments underwent biomechanical testing to quantify the flexibility of the segment. Undecalcified and decalcified histologic analysis were performed to evaluate the presence or absence of a bony union. RESULTS: Thirty percent, 50%, and 70% porous ceramics had better radiographic fusion scores than the autograft at 3 and 6 months. Incidence of ceramic fracture did not increase with porosity and was equivalent to the collapse of autograft, although ceramics maintained disc height when fracture occurred. No statistically significant differences were found between autograft and the porous ceramics with biomechanical testing and peri-implant bone mineral density values as measured by dual energy x-ray absorptiometry. At 3 months, histologic analysis showed a union rate of 0% for autograft and 30% porous ceramic, 67% for 50% porous ceramic, and 83% for 70% porous ceramic. At 6 months, the union rate was 67% for the 30%, 50%, and 70% porous ceramics and 50% for autograft. CONCLUSIONS: Thirty percent, 50%, and 70% porous ceramics performed equal to or better than autogenous bone after 3 and 6 months. There may be promise for the use of 50/50 hydroxyapatite/beta-tricalcium phosphate in spine surgery as the need to harvest autograft from the iliac crest is obviated, and complications and cost associated with the harvest are avoided.

Animals↗

PubMed2005

Comparison of measurements of phase velocity in human calcaneus to Biot theory.

Biot's theory for elastic propagation in porous media has previously been shown to be useful for modeling the dependence of phase velocity on porosity in bovine cancellous bone in vitro. In the present study, Biot's theory is applied to measurements of porosity-dependent phase velocity in 53 human calcanea in vitro. Porosity was measured using microcomputed tomography for some samples (n = 23) and estimated based on bone mineral densitometry for the remaining samples (n = 30). The phase velocity at 500 kHz was measured in a water tank using a through-transmission technique. Biot's theory performed well for the prediction of the dependence of sound speed on porosity. The trend was quasilinear, but both the theory and experiment show similar slight curvature. The root mean square error (RMSE) of predicted versus measured sound speed was 15.8 m/s.

Biomechanical Phenomena↗

PubMed1999

Bone hyperemia precedes disuse-induced intracortical bone resorption.

An in vivo model was used to determine whether bone hyperemia precedes increased intracortical porosity induced by disuse. Twenty-four adult male roosters (age 1 yr) were randomly assigned to intact-control, 7-days-sham-surgery, 7-days-disuse, and 14-days-disuse groups. Disuse was achieved by isolating the left ulna diaphysis from physical loading via parallel metaphyseal osteotomies. The right ulna served as an intact contralateral control. Colored microspheres were used to assess middiaphyseal bone blood flow. Bone blood flow was symmetric between the left and right ulnae of the intact-control and sham-surgery groups. After 7 days of disuse, median (+/-95% confidence interval) standardized blood flow was significantly elevated compared with the contralateral bone (6.5 +/- 5.2 vs. 1.0 +/- 0.8 ml x min-1 x 100 g-1; P = 0.03). After 14 days of disuse, blood flow was also elevated but to a lesser extent. Intracortical porosity in the sham-surgery and 7-days-disuse bones was not elevated compared with intact-control bones. At 14 days of disuse, the area of intracortical porosity was significantly elevated compared with intact control bones (0.015 +/- 0.02 vs. 0. 002 +/- 0.002 mm2; P = 0.03). We conclude that disuse induces bone hyperemia before an increase in intracortical porosity. The potential interaction between bone vasoregulation and bone cell dynamics remains to be studied.

Animals↗

PubMed1995

Fabrication of biodegradable polymer scaffolds to engineer trabecular bone.

We present a novel method for manufacturing three-dimensional, biodegradable poly(DL-lactic-co-glycolic acid) (PLGA) foam scaffolds for use in bone regeneration. The technique involves the formation of a composite material consisting of gelatin microspheres surrounded by a PLGA matrix. The gelatin microspheres are leached out leaving an open-cell foam with a pore size and morphology defined by the gelatin microspheres. The foam porosity can be controlled by altering the volume fraction of gelatin used to make the composite material. PLGA 50:50 was used as a model degradable polymer to establish the effect of porosity, pore size, and degradation on foam mechanical properties. The yield strengths and moduli in compression of PLGA 50:50 foams were found to decrease with increasing porosity according to power law relationships. These mechanical properties were however, largely unaffected by pore size. Foams with yield strengths up to 3.2 MPa were manufactured. From in vitro degradation studies we established that for PLGA 50:50 foams the mechanical properties declined in parallel with the decrease in molecular weight. Below a weight average molecular weight of 10,000 the foam had very little mechanical strength (0.02 MPa). These results indicate that PLGA 50:50 foams are not suitable for replacement of trabecular bone. However, the dependence of mechanical properties on porosity, pore size, and degree of degradation which we have determined will aid us in designing a biodegradable scaffold suitable for bone regeneration.

Analysis of Variance↗

PubMed2001

Fabrication of porous polymeric matrix drug delivery devices using the selective laser sintering technique.

New techniques in solid freeform fabrication (SFF) have prompted research into methods of manufacturing and controlling porosity. The strategy of this research is to integrate computer aided design (CAD) and the SFF technique of selective laser sintering (SLS) to fabricate porous polymeric matrix drug delivery devices (DDDs). This study focuses on the control of the porosity of a matrix by manipulating the SLS process parameters of laser beam power and scan speed. Methylene blue dye is used as a drug model to infiltrate the matrices via a degassing method; visual inspection of dye penetration into the matrices is carried out. Most notably, the laser power matrices show a two-stage penetration process. The matrices are sectioned along the XZ planes and viewed under scanning electron microscope (SEM). The morphologies of the samples reveal a general increase in channel widths as laser power decreases and scan speed increases. The fractional release profiles of the matrices are determined by allowing the dye to diffuse out in vitro within a controlled environment. The results show that laser power and scan speed matrices deliver the dye for 8-9 days and have an evenly distributed profile. Mercury porosimetry is used to analyse the porosity of the matrices. Laser power matrices show a linear relationship between porosity and variation in parameter values. However, the same relationship for scan speed matrices turns out to be rather inconsistent. Relationships between the SLS parameters and the experimental results are developed using the fractional release rate equation for the infinite slab porous matrix DDD as a basis for correlation.

Computer-Aided Design↗

PubMed2004

Pre-heating of components in cemented total hip arthroplasty.

Fatigue fractures which originate at stress-concentrating voids located at the implant-cement interface are a potential cause of septic loosening of cemented femoral components. Heating of the component to 44 degrees C is known to reduce the porosity of the cement-prosthesis interface. The temperature of the cement-bone interface was recorded intra-operatively as 32.3 degrees C. A simulated femoral model was devised to study the effect of heating of the component on the implant-cement interface. Heating of the implant and vacuum mixing have a synergistic effect on the porosity of the implant-cement interface, and heating also reverses the gradients of microhardness in the mantle. Heating of the implant also reduces porosity at the interface depending on the temperature. A minimum difference in temperature between the implant and the bone of 3 degrees C was required to produce this effect. The optimal difference was 7 degrees C, representing a balance between maximal reduction of porosity and an increased risk of thermal injury. Using contemporary cementing techniques, heating the implant to 40 degrees C is recommended to produce an optimum effect.

Arthroplasty, Replacement, Hip↗

PubMed2004

Polymerization time for a microwave-cured acrylic resin with multiple flasks.

This study aimed at establishing the polymerization time of a microwave-cured acrylic resin (AcronTM MC), simultaneously processing 2, 4, and 6 flasks. Required time was measured according to the parameters: monomer release in water, Knoop hardness, and porosity. Samples were made with AcronTM MC in different shapes: rectangular (32 x 10 x 2.5 mm) for monomer release and porosity; and half-disc (30 mm in diameter x 4 mm in height) for Knoop hardness. There were four experimental groups (n = 24 per group): G1) one flask (control); G2) two flasks; G3) four flasks, and G4) six flasks. At first, polymerization protocol was similar for all groups (3 min/450 W). Time was then adjusted for G2, G3, and G4, based on monomer release evaluation in the control group, obtained by spectrophotometer Beckman DU-70, with emitting wave of 206 nm. Knoop hardness test was performed using a Shimadzu HMV 2000 hardness tester, and 10 indentations were performed on each specimen's surface. Porosity was assessed after specimens were immersed in black ink and the pores counted in a microscope. Results showed that the complete polymerization of the resin occurred in 4.5 min for two flasks (G2); 8.5 min for four flasks (G3); and 13 min for six flasks (G4), all with 450 W. Statistical analysis revealed that the number of flasks does not interfere with polymerization, Knoop hardness, and porosity of the resin. Results showed that polymerization of microwave-curing resin with more than one flask is a viable procedure, as long as polymerization time is adjusted.

Acrylic Resins↗

PubMed2003

Effects of preheating of hip prostheses on the stem-cement interface.

BACKGROUND: Debonding of the cement from metal implants has been implicated in the loosening of cemented total hip prostheses. Strengthening of the stem-cement interface has been suggested as a way to prevent loosening of the component. Previously, it was reported that preheating the stem to 44 degrees C reduced the porosity of the cement at the stem-cement interface. The purpose of this study was to determine the effect of stem preheating on the characteristics of the stem-cement interface. METHODS: The effects of stem preheating, at temperatures of 37 degrees C, 44 degrees C, and 50 degrees C, on the stem-cement interface were studied in a test model and a preparation that closely simulated the clinical situation. Static interface strength was determined initially and after the stems had been kept in isotonic saline solution at 37 degrees C for two weeks. Fatigue lifetimes were measured, and the nature and extent of porosity at the interface were quantified. RESULTS: Stem preheating had significant effects on the stem-cement interface. Stems preheated to 37 degrees C had greater interface shear strength than stems at room temperature both initially (53% greater strength) and after simulated aging (155% greater strength). Fatigue lifetimes were also improved, and there was a >99% decrease in interface porosity. The setting time of the cement decreased 12%, and the maximum temperature at the cement-bone interface increased 6 degrees C. Similar effects were found after preheating to 44 degrees C and 50 degrees C. CONCLUSIONS: Stem preheating had significant effects on the stem-cement interface, with significant improvements in the shear strength and cement porosity of the interface. Also, polymerization temperatures at the cement-bone interface increased. The possible biological effects of these increased interface temperatures at the cement-bone interface require further study.

Arthroplasty, Replacement, Hip↗

PubMed2001

[Manufacture and study of porous poly(l-lactic acid) (PLLA)/beta-tricalcium phosphate (beta-TCP) composite].

A promising alternative to supply bone substitutes is to develop living tissue substitutes based on biodegradable materials, which is called bone tissue engineering. One of the research high-lights of bone tissue engineering is to design and manufacture scaffolds for cell attaching, migrating, and proliferating. A process which consists of a solvent casting stage, a compression molding stage and a leaching stage has been used to fabricate macroporous composites of poly(l-lactic acid) (PLLA) and beta-tricalcium phosphate (beta-TCP). The effects of the weight fraction of porogen--NaCl, of the weight ratio of PLLA to beta-TCP and of the diameters of beta-TCP on the porosities, the average pore diameters and the compressive yield strength and compressive modulus have been studied. The results showed that the porosities and the average pore diameters increased and the compressive yield strength and modulus decreased when the weight fraction went from 50% to 90%. The compressive yield strength and compressive modulus could be improved by changing the weight ratio of PLLA to beta-TCP and the diameters of beta-TCP in low-porosity composites (lower than 70%). But high-porosity composites (90%) were not reinforced by changing the weight ratio.

Biocompatible Materials↗

PubMedDate not supplied

Variations of permeability and pore size distribution of porous media with pressure.

Porosity and permeability of porous and fractured geological media decrease with the exploitation of formation fluids such as petroleum, natural gas, or ground water. This may result in ground subsidence and a decrease of recovery of petroleum, natural gas, or ground water. Therefore, an evaluation of the behavior of permeability and porosity under formation fluid pressure changes is important to petroleum and ground water industries. This study for the first time establishes a method, which allows for the measurement of permeability, porosity, and pore size distribution of cores simultaneously. From the observation of the pore size distribution by low-field nuclear magnetic resonance (NMR) relaxation time spectrometry the mechanisms of pressure-dependent porosity and permeability change can be derived. This information cannot be obtained by traditional methods. As the large-size pores or fractures contribute significantly to the permeability, their change consequently leads to a large permeability change. The contribution of fractures to permeability is even larger than that of pores. Thus, the permeability of the cores with fractures decreased more than that of cores without fractures during formation pressure decrease. Furthermore, it did not recover during formation pressure increase. It can be concluded that in fractures, mainly plastic deformation takes place, while matrix pores mainly show elastic deformation. Therefore, it is very important to keep an appropriate formation fluid pressure during the exploitation of ground water and petroleum in a fractured formation.

Environmental Monitoring↗

PubMedDate not supplied

The effect of prolonged packing on the surface hardness of posterior composites.

This study evaluated the effect of four different packing times on the Knoop Hardness Number of three composites (Surefil, Z100 and Spectrum TPH). Ten samples of each composite were prepared for each packing time and 10 readings were made on each sample to produce the KHN. Photomicrographs were made of 147 indentations to determine whether the indentations had routinely been made on porosity-free sites. Statistical analysis was made using two-way ANOVA and least square means. Generally, as the packing time increased, the KHN decreased,and although the indentations appeared to have been made in porosity-free composite, the potential effect of porosities was not discounted. Increasing the packing time for clinical composites may result in a lower KHN and increased clinical wear, which would further increase if also associated with porosities within the composite.

Analysis of Variance↗

PubMed1992

Do we need to vacuum mix or centrifuge cement?

In total hip surgery, the goal of porosity reduction techniques in the preparation of acrylic bone cement is to provide a stronger, more fatigue resistant material between the implant and bone. Conventional mixing of polymethylmethacrylate bone cement produces porosity of 5% to 16%, whereas vacuum mixing or centrifugation reduces the porosity to a range of 0.1% to 3.4%. Multiple studies have demonstrated that this results in a cement that has a significant increase in static and dynamic testing to failure. Fracture of the cement mantle has been found as a part of the failure pattern in many total hip prostheses requiring revision for loosening. Vacuum mixing or centrifugation produces a stronger cement to resist the component of loosening caused by fracture of the cement mantle. Where failure occurs at the bone-cement interface, as in cemented acetabular migration, no improvements from porosity reduction would be expected. Along with enhanced femoral designs, improvements in cement technique with modern methods of bone preparation and administration of the cement have resulted in a marked improvement in clinical and roentgenographic loosening rates in cemented femoral components at medium-term follow-up periods of five to ten years. Intact total hip prostheses, retrieved for reasons other than loosening, at longer-term follow-up periods, have shown intact bone-cement interfaces. However, these specimens have also shown incipient cracks in the acrylic cement that emanate from and connect defects in the cement mantle and at the metal-cement interface. The use of a void-free, structurally stronger material is expected to improve the stability and longevity of the cement supporting femoral implants.

Bone Cements↗

PubMed2004

HAp physical investigation--the effect of sintering temperature.

The paper presents the effect of sintering temperature on the physical properties of porous hydroxyapatite (HAp In this study, the HAp was prepared using polymeric sponge techniques with different binder concentrations. The sintering process was carried out in air for temperature ranging from 1200 degrees C to 1600 degrees C. Different physical properties namely density and porosity were observed at different sintering temperatures. The HAp prepared with higher PVP binder showed a slightly decreased in apparent density with increasing sintering temperature, while those HAp prepared with lower PVP showed a slightly increase in apparent density with increasing sintering temperature. The total porosity was found to be approximately constant in the whole sintering temperature range. However, closed porosity decreases with increasing sintering temperature for HAp prepared by lower binder concentration. On the other hand, the HAp prepared by higher binder concentrations showed increasing closed porosity with increasing sintering temperature. Other features such as the influence of sintering temperatures on grain and strut would also be presented in this paper.

Bone Substitutes↗

PubMed2004

Coral--polyhydroxybutrate composite scaffold for tissue engineering: prefabrication properties.

In this study the surface properties of two particulate coral and polyhydroxybutrate (PHB) were studied in order to characterize them prior to use in composite production. Coral powder and PHB particle were evaluated using scanning electron microscopy and confocal laser scanning microscopy, to measure surface porosity and pores size. The results showed that coral powder has multiple pleomorphic micropores cross each others give appearance of micro-interconnectivity. Some pore reached to 18 microm with an average porosity of 70%. PHB revealed multiple different size pores extended to the depth, with an average some times reach 25 microm and porosity 45%. These findings demonstrate that both coral and PHB have excellent pores size and porosity that facilitate bone in growth, vascular invasion and bone development. We believe that incorporation of coral powder into PHB will make an excellent composite scaffold for tissue engineering.

Animals↗