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PubMed1995

Skeletal repair by in situ formation of the mineral phase of bone.

A process has been developed for the in situ formation of the mineral phase of bone. Inorganic calcium and phosphate sources are combined to form a paste that is surgically implanted by injection. Under physiological conditions, the material hardens in minutes concurrent with the formation of dahllite. After 12 hours, dahllite formation was nearly complete, and an ultimate compressive strength of 55 megapascals was achieved. The composition and crystal morphology of the dahllite formed are similar to those of bone. Animal studies provide evidence that the material is remodeled in vivo. A novel approach to skeletal repair is being tested in human trials for various applications; in one of the trials the new biomaterial is being percutaneously placed into acute fractures. After hardening, it serves as internal fixation to maintain proper alignment while healing occurs.

Animals↗
PubMed2001

Structured drug-loaded bioresorbable films for support structures.

Bioresorbable films can serve simultaneously as anatomic support structures and as drug delivery platforms. In the present study, bioresorbable PLLA films containing dexamethasone were developed through solution processing. The effect of processing parameters on the film morphology and the resulting mechanical properties was studied. A model describing the structuring of these films is suggested. Generally, the solvent evaporation rate determines the kinetics of drug and polymer crystallization and thus, both the mode of drug dispersion in the polymer and the resulting mechanical properties. Two types of structured films were studied: (1) a polymer film with drug located on its surface, obtained due to drug skin formation accompanied by a later polymer core formation; and (2) a polymer film with small drug particles and crystals distributed within the bulk, obtained by parallel solidification of the two components. A prototypical application of these films is an expandable biodegradable support structure (stent). which we have developed. This stent demonstrated good initial mechanical properties. The film structure has only a minor effect on the stent radial compression strength, but more significantly affects the tensile mechanical properties.

Biocompatible Materials↗
PubMed2001

Characterization of bone cements prepared with functionalized methacrylates and hydroxyapatite.

Bone cements prepared with methyl methacrylate and either methacrylic acid or diethyl amino ethyl methacrylate as comonomers were characterized by infrared spectroscopy, nuclear magnetic resonance, gel permeation chromatography, dynamic mechanical thermal analysis, and mechanical testing. Selected formulations containing these functionalized methacrylates were filled with hydroxyapatite and studied in terms of their properties in tension, compression and bending, and X-ray diffraction. It was found that residual monomer was not greatly affected by the presence of either acid or basic comonomers in the unfilled bone cements. In contrast, molecular weight, curing times, and glass transition temperature were composition dependent. For samples with acidic comonomer, a faster curing time, higher molecular weight, and higher glass transition temperatures were observed with respect to those with the basic comonomer. X-ray diffraction revealed that the crystalline structure was not affected by the nature of comonomer in the bone cement while scanning electron microscopy showed that hydroxyapatite remained as clusters in the bone cement. The mechanical properties of filled bone cements depended mainly on composition and type of testing. Hydroxyapatite-filled bone cements fullfilled the minimum compressive strength (70 MPa) required for bone cement use. However, the minimum tensile strength (30 MPa) was only fullfilled by cements prepared without comonomer and those containing methacrylic acid. The minimum bending strength requirement (50 MPa) was not satisfied by any of the formulations studied.

Biocompatible Materials↗
PubMed2004

Polymer composition and acidification effects on the swelling and mechanical properties of poly(acrylamide-co-acrylic acid) superporous hydrogels.

Poly(acrylamide-co-acrylic acid) (poly(AM-co-AA)) superporous hydrogels (SPHs) were synthesized and the acidification effects on the swelling and mechanical properties were studied. Gelation exotherms were measured to determine the optimum introduction time for adding a blowing agent. The gelation kinetics decreased with increasing the AA concentration. The maximum equilibrium swelling was observed around an AA weight fraction of 0.4, but the compressive strength decreased monotonically with increasing the AA concentration. Poly(AM-co-AA) SPHs were much less swollen in acidic solution than in distilled water of pH 6.7. The swelling ratio decreased with increasing acidity (decreasing pH). Reduction of water absorption content by acidification led to considerable increase in the mechanical strength.

Acrylamide↗
PubMed2005

Poly(N-isopropylacrylamide) (PNIPAM)-grafted gelatin as thermoresponsive three-dimensional artificial extracellular matrix: molecular and formulation parameters vs. cell proliferation potential.

A series of poly(N-isopropylacrylamide)-grafted gelatins (PNIPAM gelatins) of three different graft densities (approx. 11, 22 and 34 graft chains per gelatin molecule) and three different molecular weights of their graft chains (molecular weight approximately 1.2 x 10(4), 5.0 x 10(4) and 1.3 x 10(5) g/mol) were prepared by multiple derivatization of dithiocarbamyl (DC) group in a gelatin molecule and subsequent iniferter (acts as an initiator, transfer-agent and terminator)-based photopolymerization of NIPAM. The weight ratio of PNIPAM graft chains to gelatin (P/G) varied from 1.4 to 49. Aqueous solutions of PNIPAM-gelatins showed thermo-responsiveness, depended on the graft density and the molecular weight of PNIPAM graft chain or P/G. Aqueous solutions (10 or 20%, w/v) of PNIPAM-gelatins with P/G of more than 5.8 were converted to gels at 37 degrees C. Focal plane images of PNIPAM-gelatin gels by confocal laser scanning microscopy revealed that the size of hydrophobically clustered aggregates increased with P/G, whereas the space of microvoids decreased with concentration. Compressive strain-stress measurements revealed that compressive strength of PNIPAM-gelatin increased with P/G. Bovine smooth muscle cells (SMCs)-entrapped gels were produced from PNIPAM-gelatin-containing cell-suspended medium solutions at 37 degrees C. The entrapped cells proliferated in the gel with P/G of more than 12. A higher cell proliferativity was obtained at low concentration (5%, w/v) and higher P/G (>18). Tissue formation composed of proliferative SMCs and cell-secreted extracellular matrices (collagen) was obtained at 14 days incubation. The inter-relationship between the molecular parameters of PNIPAM-gelatin, internal structural features and cell proliferation potential was discussed.

Acrylic Resins↗
PubMed2005

Fabrication and characterization of porous alginate/polyvinyl alcohol hybrid scaffolds for 3D cell culture.

Porous alginate/polyvinyl alcohol (PVA) hybrid scaffolds as bioartificial cell scaffolds were fabricated to improve cell compatibility as well as flexibility of the scaffolds. The alginate/PVA hybrid scaffolds with different PVA compositions up to 50 wt% were fabricated by a modified freeze-drying method including the physical cross-linking of PVA and the following chemical cross-linking of alginate. The prepared alginate/PVA hybrid scaffolds were characterized by morphology observations using scanning electron microscopy (SEM), the measurements of porosity and average pore sizes and the measurements of compressive strength and modulus. The scaffolds exhibited highly porous, open-cellular pore structures with almost the same surface and cross-sectional porosities (total porosities about 85%, regardless of PVA composition) and the pore sizes from about 290 microm to about 190 microm with increasing PVA composition. The alginate/PVA hybrid scaffolds were more soft and elastic than the control alginate scaffold without significant changes of mechanical strength. The scaffolds were examined for their in vitro cell compatibility by the culture of chondrocytes (human chondrocyte cell line) in the scaffolds and the following analyses by MTT assay and SEM observation. It was observed that the alginate/PVA scaffolds had better cell adhesion and faster growth than the control alginate scaffold. It seems that 30 wt% addition of PVA to alginate in the fabrication of the hybrid scaffolds is desirable for improving their flexibility and cell compatibility.

Alginates↗
PubMed2006

Preparation, formulation and evaluation of novel photo-cured glass ionomers based on co-polymers of (meth)acrylated amino acids.

A novel photo-cured amino-acid-constructed glass-ionomer cement system has been developed. Glutamic acid- and beta-alanine-based methacrylate and acrylate derivatives were synthesized, characterized and used to construct the polyalkenoic acids and formulated with water and Fuji II glass filler to form self-cured cement. Compressive strength (CS) of the cement and viscosity of the liquid were used as tools for evaluation. The effects of molar ratio and molecular weight (MW) were studied. The optimized co-polymer was further modified with glycidyl methacrylate (GM) and formulated with water, acrylic acid and Fuji II LC filler to form photo-cured cement. The effects of MW, GM tethering ratio, polymer liquid ratio and glass filler powder/polymer liquid (P/L) ratio were investigated. CS, flexural strength (FS) and viscosity were used as screening tools to find the optimal formulation. All the specimens were conditioned in distilled water at 37 degrees C for either 24 h or 7 days prior to testing. The results show that amino-acid-constructed polyalkenoic acids can be formed only from amino acid methacrylate derivatives or by co-polymerization of methacrylate with acrylate derivatives. Among the numerous co-polymers synthesized, poly(methacryloyl glutamic acid-co-acryloyl beta-alanine) or poly(MGA-co-ABA) with the molar ratio of 8:2 and MW of 19.5 kg/mol contributed the highest mechanical strengths and lower working viscosity to the cement. For photo-cured system, the effects of GM tethering ratio, polymer content and P/L ratio were significant. It is found that an appropriate ratio balance between these parameters is very important. The effect of molecular weight was not significant. The self-cured experimental cement was 32% higher in FS than Fuji II and the same in CS and DTS as Fuji II. The photo-cured experimental cement was 19%, 47% and 176% higher in CS, DTS and FS than Fuji II LC.

Amino Acids↗
PubMed1978

Physical properties of zinc phosphate cement prepared on a frozen slab.

The physical properties of a zinc phosphate cement prepared on a room temperature slab were compared to those of the cement prepared on a frozen slab. Solubility, compressive strength, and setting time of cements prepared on both types of slabs were within the limits set by A.D.A. Specification No. 8.

Chemical Phenomena↗
PubMedDate not supplied

Clinical performance and physical properties of twelve amalgam alloys.

An assessment of the marginal failure rate of 1,041 restorations of twelve alloys was made at one year. In addition, physical property tests were conducted. A correlation was found between the clinical performance and creep (.79), flow (.62) and 24-hour compressive strength (.60).

Chemical Phenomena↗
PubMed1980

The role of zinc in dental amalgams.

Twenty-five AG-Sn alloys containing various additions of Zn were amalgamated and the amalgams tested for physical properties pertinent to dental restoration use. The mercury retained, dimensional change, compressive strength, and creep were all functions of the Zn content.

Corrosion↗
PubMed1981

Effect of moisture contamination on high-copper amalgam.

Moisture contamination caused delayed excessive expansion and deterioration of the physical properties only with the non-high-copper lathe-cut alloy amalgam containing zinc, but not with the new high-copper amalgam and the non-high-copper spherical alloy amalgam containing zinc. It affected the compressive strength and creep but not the hardness. The setting dimensional change of all amalgams containing zinc was slightly affected by it.

Chemical Phenomena↗
PubMed1987

Temperature-dependence of compressive properties of human dentin.

The effect of temperature on compressive stress/strain behavior of human dentin obtained from recently extracted permanent lower molar teeth has been determined over the range 0-80 degrees C. Dentin specimens were loaded uni-axially in a direction perpendicular to the tubule orientation. A statistically significant, linear regression relationship was found between modulus (E) and temperature (T): E (GPa) = 15.55-0.0734 . (T degrees C). The observed temperature coefficient of the modulus is in close agreement with that observed for cortical bone. Proportional limit, compressive strength, and resilience were also found to undergo a linear decrease with increasing temperature. Mechanical failure of specimens generally occurred along lines determined by maximum shear stresses, approximately 45 degrees to the axial load direction.

Cold Temperature↗
PubMed1990

Casting pure titanium into commercial phosphate-bonded SiO2 investment molds.

Pure titanium was cast into five different phosphate-bonded SiO2 investment mold materials (at 350 degrees C) with an argon-arc melting and pressure casting machine. The mesh castability, the fit of the MOD inlay castings, and the Knoop hardness and the micro-structure in cross-sections of castings were examined. The setting and thermal expansion, the compressive strength, and the X-ray diffraction analysis of the investments were also measured. The castability, the fit, and the thickness of the reacted layer differed in degree among these investments, in spite of the same phosphate-bonded SiO2-type investment. A significant correlation was obtained between the thermal expansion (at 350 degrees C) and the casting accuracy.

Analysis of Variance↗
PubMed1993

New aspects of the setting of glass-ionomer cements.

For many years, glass-ionomer cements have been described as setting by the formation of a poly(acrylate) matrix. Recent research has suggested that a second reaction may be involved, namely, the formation of a silica matrix. So that this hypothesis could be tested, non-polymer cements, based on an ionomer glass plus acetic acid, were prepared and stored for up to six months. They were insoluble in water, and their compressive strength was found to increase rapidly over the period of storage. By contrast, the product of the reaction between ZnO and acetic acid was soluble in water. These results support the idea that there is a secondary setting reaction in glass ionomers and suggest that it is responsible for the increase in strength observed.

Acetates↗
PubMed2001

A systematic study of cement/PFA chemical stabilisation/solidification process for the treatment of heavy metal waste.

The aim of this study is to systematically quantify the physical and chemical properties of the cement based solidified/stabilised heavy metal waste with increasing replacement of cement by PFA. Bulk density and unconfined compressive strength are measured as the physical parameters. The equilibrium extraction tests, sequential chemical tests and dynamic leaching tests are reported as chemical characteristics. The results showed PFA-blended cement-based waste forms have higher porosity and lower strength than the pure cement-based waste forms at experimental curing time. The lower alkalinities of the PFA-blended cement-based waste forms, however, lead to higher leach rates of heavy metals when the waste is exposed to an acidic medium.

Environmental Pollution↗
PubMed2002

The production of synthetic aggregate from a quarry waste using an innovative style rotary kiln.

The large volumes of wastes generated by industrialised society has led to efforts to find practical uses for these wastes, whilst also offsetting the consumption of natural resources. This paper describes the use of an innovative rotary kiln to produce synthetic aggregates from a variety of waste streams. The main waste used was a quarry fines which was blended with either paper sludge, clay, or a dredged harbour sediment. The different combinations were extruded and fired in the kiln to produce a material suitable for natural aggregate replacement. Two of the synthetic aggregates produced were tested by incorporation in to concrete as coarse aggregate replacement. The concrete 28-day compressive strengths achieved were above 40 N mm(-2) and compared favourably with control concretes made with natural aggregates and a commercially available lightweight aggregate (Lytag). Leaching tests have also been carried out to assess the potential environmental impact of utilisation. Although not finalised, these tests have also given favourable results.

Aluminum Silicates↗
PubMed2002

Adding crumb rubber into exterior wall materials.

In Arizona US, most houses are built with walls covered by stuccos/coatings/mortars. This paper presents an explorative investigation of adding crumb rubber into stuccos/coatings/mortars. A series of experiments are conducted to examine the thermal and mechanical performance of the crumb rubber mixes. The results show that, the mixes with crumb rubber do exhibit more desirable performances like being high in crack-resistance and thermal insulation, and low in thermal expansion/contraction. The drawback for the crumb rubber mixes is the reduction in compressive strength, but which can be compensated by other means. As a site experiment, an area of 100 square-feet of crumb rubber coatings for two mix designs is sprayed on a tire-adobe wall. After being sprayed more than 14 months, the coatings apparently are in good condition. Significance of this study is that this practice, if accepted, will yield improved products that consume large quantities of crumb rubber.

Arizona↗