Biomedical subjects

J L Ong

Publications and source records attributed to J L Ong.

At least 19 recordsLinked to original sources

PubMed2003

Effect of plasma-glow discharge as a sterilization of titanium surfaces.

In this study, in vitro osteoblast responses to glow-discharged, commercially pure titanium (Ti) surfaces were investigated. It was hypothesized that the glow-discharge treatment would be an effective sterilization procedure for Ti implantations before implantation. The Ti surfaces were prepared by grinding to 600 grits followed by cleaning. These were then divided into two groups, with one group being the control and the other group undergoing glow-discharge treatment using oxygen. Human embryonic palatal mesenchyme cells, an osteoblast precursor, were used to evaluate the cell responses to glow-discharged and control Ti surfaces. It was observed from this study that protein production and osteocalcin production on both surfaces exhibited no significant differences during the 10-day study. Similarly, no significant differences were observed for alkaline phosphatase (ALP) specific activity during the first 7 days of incubation. However, at day 10, the ALP specific activity for control Ti surfaces was significantly higher than the ALP activity for the glow-discharged surface. Overall, this study suggested that the use of glow discharge as an alternative sterilization procedure for medical and dental implants did not inhibit osteoblast phenotypic expression.

Alkaline Phosphatase↗

PubMed2003

Osteoblast precursor cell attachment on heat-treated calcium phosphate coatings.

The influence of properties of calcium phosphate (CaP) coatings on bone cell activity and bone-implant osseointegration is not well-established. This study investigated the effects of characterized CaP coatings of various heat treatments on osteoblast response. It was hypothesized that heat treatments of CaP coatings alter the initial osteoblast attachment. The 400 degrees C heat-treated coatings were observed to exhibit poor crystallinity and significantly greater phosphate or apatite species compared with as-sputtered and 600 degrees C heat-treated coatings. Similarly, human embryonic palatal mesenchyme (HEPM) cells, an osteoblast precursor cell line, seeded on 400 degrees C heat-treated coatings, exhibited significantly greater cell attachment compared with Ti surfaces, as-sputtered coatings, and 600 degrees C heat-treated coatings. The HEPM cells on Ti surfaces and heat-treated coatings were observed to attach through filopodia, and underwent cell division, whereas the cells on as-sputtered coatings displayed fewer filopodia extensions and cell damage. Analysis of the data suggested that heat treatment of CaP coatings affects cell attachment.

Apatites↗

PubMed2002

Experimental studies on bone induction using low-molecular-weight poly (DL-lactide-co-glycolide) as a carrier for recombinant human bone morphogenetic protein-2.

An appropriate carrier acting as a slow delivery vehicle for the BMPs is required for maximal clinical effectiveness of these bone-inductive proteins. The purpose of this study was to evaluate a low-molecular-weight PLGA copolymer as a synthetic, biodegradable carrier for rhBMP-2 implantation in vivo. Two, 10, or 50 microg of recombinant human BMP-2 were mixed with 10 mg of a poly (DL-lactide-co-glycolide) (PLGA) 50:50 copolymer and implanted into the calf muscles of Wistar rats. Soft X-ray analysis and histologic examination indicated that new bone formation occurred at all rhBMP-2-implanted sites within 3 weeks after implantation. Correlation of rhBMP-2 concentration with the amount of bone induction was confirmed by specific alkaline phosphatase activity and calcium content assay. In vitro analysis indicated that 78.5% of the PLGA copolymer was degraded to smaller molecular weight material after 14 days in PBS solution. It is suggested that rhBMP-2 was released in an active form at the implant site during the degradation of the copolymer, resulting in the induction of new bone formation. Thus this low-molecular-weight PLGA copolymer material represents a promising delivery vehicle for BMPs, and possibly other growth factors, around dental and orthopedic implants.

Absorption↗

PubMed2002

Bone response to radio frequency sputtered calcium phosphate implants and titanium implants in vivo.

The objective of this study was to evaluate the effect of radio frequency sputtered calcium phosphate (CaP) coatings of titanium (Ti) implants on the bond strength at the bone-implant interface and percent bone contact length. Cylindrical coated or noncoated implants (4.0-mm diameter by 8-mm long) were implanted for 3 and 12 weeks. At 3 weeks after implant placement, the ultimate interfacial strengths for as-deposited CaP-coated and heat-treated CaP-coated implants were 2.29 +/- 0.14 MPa and 1.28 +/- 0.04 MPa, respectively. These ultimate interfacial strength values at 3 weeks were statistically greater than the mean ultimate interfacial strength for control Ti implants (0.67 +/- 0.13 MPa). At 12 weeks after implant placement, no statistical differences in the mean ultimate interfacial strengths were observed between the as-deposited CaP-coated, heat-treated CaP-coated, and control Ti implants. Histomorphometric evaluation indicated greater percent bone contact lengths for the as-deposited CaP-coated implants compared with the heat-treated CaP-coated and control Ti implants 3 and 12 weeks after implant placement.

Animals↗

PubMed2001

Directed evolution of polymerase function by compartmentalized self-replication.

We describe compartmentalized self-replication (CSR), a strategy for the directed evolution of enzymes, especially polymerases. CSR is based on a simple feedback loop consisting of a polymerase that replicates only its own encoding gene. Compartmentalization serves to isolate individual self-replication reactions from each other. In such a system, adaptive gains directly (and proportionally) translate into genetic amplification of the encoding gene. CSR has applications in the evolution of polymerases with novel and useful properties. By using three cycles of CSR, we obtained variants of Taq DNA polymerase with 11-fold higher thermostability than the wild-type enzyme or with a >130-fold increased resistance to the potent inhibitor heparin. Insertion of an extra stage into the CSR cycle before the polymerase reaction allows its application to enzymes other than polymerases. We show that nucleoside diphosphate kinase and Taq polymerase can form such a cooperative CSR cycle based on reciprocal catalysis, whereby nucleoside diphosphate kinase produces the substrates required for the replication of its own gene. We also find that in CSR the polymerase genes themselves evolve toward more efficient replication. Thus, polymerase genes and their encoded polypeptides cooperate to maximize postselection copy number. CSR should prove useful for the directed evolution of enzymes, particularly DNA or RNA polymerases, as well as for the design and study of in vitro self-replicating systems mimicking prebiotic evolution and viral replication.

DNA-Directed DNA Polymerase↗

PubMed2001

Effect of biofluid environment on the dissolution and flexural strength of calcium phosphate bone cements.

This study investigates the dissolution of calcium (Ca2+), phosphorus (P5+), and the transverse strength of commercially available calcium phosphate (CaP) bone cements after immersion in fetal bovine serum and a tissue fluid substitute. It was observed that although a continual increase in Ca2+ and P5+ dissolution was detected in all three test media throughout the 21-day period, no statistical difference existed in the overall Ca2+ release after incubating the cements in the three different media. However, P5+ release after immersion in Tris solution (0.37 +/- 0.02 microgram/mm2) and fetal bovine serum solution (0.347 +/- 0.06 microgram/mm2) was significantly higher when compared with P5+ released (0.03 +/- 0.002 microgram/mm2) in tissue fluid substitute. In addition, no significant difference in transverse strength was observed for samples immersed in the three solutions during the 21-day period. However, the transverse strength for immersed CaP cement bars at 37 degrees C was statistically greater than non-immersed bars set aside at room temperature for the 21-day period (7.78 +/- 1.82 N and 3.19 +/- 0.93 N, respectively). It was concluded from this study that the transverse strength of the CaP bone cements was not significantly affected by the dissolution process but by the temperature at which the bone cement was exposed.

Animals↗

PubMed2000

Particulate retrieval of hydrolytically degraded poly(lactide-co-glycolide) polymers.

This article describes a technique for the retrieval of polymeric particulate debris following advanced hydrolytic in vitro degradation of a biodegradable polymer and presents the results of the subsequent particle analysis. Granular 80/20 poly(L-lactide-co-glycolide) (PLG) was degraded in distilled, deionized water in Pyrextrade mark test tubes at 80 degrees C for 6 weeks. Subsequently, a density gradient was created by layering isopropanol over the water, followed by a 48-h incubation. Two opaque layers formed in the PLG tubes, which were removed and filtered through 0.2-micrometer polycarbonate membrane filters. In addition, Fourier transform IR spectroscopy (FTIR) was performed to confirm the presence of polymer in the removed layers. The filters were gold sputter coated, and scanning electron microscopy (SEM) images were made. FTIR analysis confirmed that the removed material was PLG. SEM images of the extracts from the upper (lowest density) opaque layer showed a fine, powderlike substance and globular structures of 500-750 nm. The SEM images of the lower (highest density) opaque layer showed particles with a crystalline-like morphology ranging in size from 4 to 30 micrometer. Particulate PLG debris generated with the described technique can be useful for further studies of its biological role in complications associated with poly(alpha-hydroxy)ester implants. This study shows the presence of very persistent nano- and microparticles in the degradation pathway of PLG.

2-Propanol↗

PubMed2000

Quantification of leucite concentration using X-ray diffraction.

OBJECTIVES: This study sought to evaluate the efficacy of using an X-ray diffractometer for the determination of leucite in Finesse, Ceramco II, and IPS Empress porcelains. METHODS: An internal standard, copper, was used. Two quantification methods are presented: (1) the generation of a calibration curve using peak height ratios; and (2) the generation of a calibration curve using peak area ratio. RESULTS: The leucite concentration obtained from the peak height versus concentration calibration curve was observed to be statistically different from leucite concentration obtained from the peak area versus concentration calibration curve. Other information obtained from X-ray powder diffraction include the lattice parameters and volume of the unit leucite cell. SIGNIFICANCE: The leucite contained in the dental porcelains (Finesse, Ceramco II, and Empress) has expanded a-lattice spacings and contracted c-lattice spacings relative to standard leucite. These changes in the lattice parameters resulted in a net expansion of the leucite cell volume.

Aluminum Silicates↗

PubMed2000

Effect of protein on the dissolution of HA coatings.

The dissolution behavior of hydroxyapatite (HA) in the presence and absence of protein needs to be investigated in order to fully understand the initial cellular response to HA surfaces. In this study, HA coatings were characterized using X-ray diffraction, X-ray photoelectron spectroscopy, and Fourier transform infrared spectroscopy (FTIR) prior to protein study. Fibronectin and albumin adsorption study were also performed. Calcium and phosphorus released in the presence and absence of albumin were measured. pH of the solution was measured daily. From the materials characterization, it was observed that the coatings exhibit a HA-type structure, with traces of sodium on the surface. FTIR indicated the possible presence of carbonates on the coatings. From the adsorption study, the amount of albumin adsorbed (0.052+/-0.005 microg/mm2) was statistically higher than the amount of fibronectin adsorbed on HA surfaces (0.035+/-0.002 microg/mm2). Flame atomic absorption indicated a significantly higher calcium ions released initially for HA coatings incubated with proteins as compared to coatings in the absence of proteins. However, after 7 days incubation, no significant difference in calcium ions release was observed between the HA coatings in the presence and absence of proteins. Phosphorus dissolution on HA coatings was not significantly affected by the presence of proteins. Thus, it was suggested from this study that the initial dissolution properties of calcium ions from HA coatings was dependent on the media.

Albumins↗

PubMed2000

Hydroxyapatite and their use as coatings in dental implants: a review.

At present, no standard manufacturing guideline exists for depositing hydroxyapatite (HA) on implant surfaces. Although animal and in vitro studies have reported on the benefits of using HA-coated implants as well as the risks of dissolution, these short-term studies did not demonstrate that the dissolution of the HA coating leads to a loss of implants. In addition, many in vivo and clinical studies did not include the chemical and structural characterization of the coatings, and thus comparisons between studies are difficult. In the clinics, the recommendation is that HA-coated screw implants be used for the anterior maxilla and posterior mandible where the bone depth exceeds 10 mm and when the cortical layer is thinner and spongiosia is less dense. In the posterior maxilla or when the cortical layer is very thin with low density, the use of HA-coated cylindrical implants is recommended. However, there are concerns for using HA-coated implants. The clinician needs to take into consideration the enhanced bacterial susceptibility of HA coatings compared with titanium implants. In addition, the clinician needs to consider the possible failure of HA coatings as a result of coating-substrate interfacial fracture. Finally, besides the surgical skills, it is also important that the clinical investigators be well versed with the materials characterization needed for HA-coated implants, the problems associated with the current HA coatings, and the indications for use. In addition, the correlation between well characterized coatings and their effect on bone formation rate and long-term implant success, coating-implant interfacial strength, and alternative superior coating process need to be investigated further.

Animals↗

PubMed1999

BMP stimulation of bone response adjacent to titanium implants in vivo.

The objective of this study was to evaluate the effect of bone morphogenetic protein (BMP) on the bond strength of titanium (Ti) implants at the bone-implant interface. Thirty-six Brånemark screw implants (3.75 mm diameter by 15 mm long) were implanted for 3 and 12 weeks. At 3 weeks after implantation, the mean reverse torque value for implants stimulated with BMP delivered using an atelopeptide type-I collagen carrier (74.2 +/- 5.2 N cm) was observed to be statistically greater (P < 0.000016) than the mean reverse torque value for control Ti implants (32.8 +/- 1.1 N cm). Similarly, at 12 weeks after implantation, the mean reverse torque value for implants stimulated with BMP (89.2 +/- 2.7 N cm) was statistically greater (P < 0.0042) than the mean reverse torque value for control Ti implants (75.8 +/- 2.4 N cm). In addition, histomorphometric evaluations indicated more bone contact with the BMP stimulated implant surfaces compared to the controls after 3 weeks implantation. It was concluded from this study that the use of BMP-atelopeptide type-I collagen mixture is an effective means of obtaining greater bond strength at the bone implant interface within a shorter time period than Ti implants without BMP.

Animals↗

PubMed1999

Osteoblast progenitor cell responses to characterized titanium surfaces in the presence of bone morphogenetic protein-atelopeptide type I collagen in vitro.

The goal of this study was to investigate the effect of bone cell response to titanium (Ti) surfaces in the presence of bone morphogenetic protein (BMP)-atelopeptide type I collagen mixture. The atelopeptide type I collagen was used as a potential carrier for the BMP. Sterilized 600-grit Ti samples were used as substrates for the cell culture study. X-ray photoelectron spectroscopy indicated the presence of TiO2 on the Ti surface. The in vitro cell culture study was performed using an osteoblast progenitor cell line derived from mice (2T9). At confluency, the cells cultured on Ti surfaces were divided into three groups: unstimulated culture, culture stimulated by BMP-atelopeptide type I collagen (40 ng/mL), and culture stimulated by atelopeptide type I collagen (40 ng/mL). The unstimulated and atelopeptide type I collagen cultures were controls in this study. After 4 days of incubation, protein production, alkaline phosphatase (ALP) activity, and hexosaminidase activity were observed to be the highest for cells exposed to the BMP-atelopeptide type I collagen mixture. Statistical differences in cellular protein production and ALP activity were observed between the controls and the surfaces exposed to the BMP-atelopeptide type I collagen mixture. Similarly, a statistical difference in hexosaminidase activity was observed between unstimulated Ti surfaces and surfaces exposed to BMP-atelopeptide type I collagen mixture. However, no statistical differences in protein production, ALP activity, and hexosaminidase activity were observed between cells exposed to atelopeptide type I collagen solution and the unstimulated surfaces.

Alkaline Phosphatase↗

PubMed1999

Protein adsorption and osteoblast responses to heat-treated titanium surfaces.

The clinical success of dental implants is governed in part by surface properties of implants and their interactions with the surrounding tissues. The objective of this study was to investigate the effect of heat-treated titanium (Ti) surfaces on protein adsorption and osteoblast responses in vitro. The passivated Ti samples used in this study were either nonheat-treated or heat-treated at 750 degrees C for 90 minutes. Using x-ray diffraction analyses, no oxide peaks were observed on the nonheat-treated surfaces, suggesting an amorphous oxide. Crystalline rutile TiO2 peaks were observed on the heat-treated Ti surfaces. The contact angles of water on heat-treated Ti surfaces (32.0 +/- 2.5 degrees) were statistically lower compared with the nonheat-treated Ti surfaces (47.7 +/- 2.3 degrees). In addition, the mean albumin concentration on the nonheat-treated Ti surfaces (3.57 +/- 0.33 micrograms/mL) was observed to be significantly different from the mean albumin concentration on heat-treated Ti surfaces (2.25 +/- 0.26 micrograms/mL). In the presence of an osteoblast precursor cell line, significantly different hexosaminidase activity, protein production, and alkaline phosphatase activity were observed for cells grown on heat-treated Ti surfaces compared with nonheat-treated Ti surfaces.

Adsorption↗

PubMed1998

Osteoblast precursor cell activity on HA surfaces of different treatments.

The clinical success of dental implants is governed by implant surfaces and bone cell responses that promote rapid osseointegration and long-term stability. The specific objective of this study was to investigate osteoblast precursor cell responses to hydroxyapatite (HA) surfaces of different treatments. Since the nature of bone cell responses in vitro is influenced by the properties of HA ceramics, this study was divided into two components: a chemical and crystallographic characterization of the HA ceramics and an in vitro cell culture study. The sintered HA samples were observed to have the highest crystallite size as compared to the as-received HA and calcined HA samples. No differences in the surface roughness and chemical composition were observed among the sintered, calcined, and as-received HA surfaces. In concurrence with the X-ray diffraction, high resolution XPS resolution of Ca 2p also indicated a higher crystallinity on sintered HA samples as compared to the calcined and as-received HA samples. As indicated by increased alkaline phosphatase-specific activity, increased cell-surface and matrix-associated protein, and 1.25 (OH2) vitamin D3-stimulated osteocalcin production, a more differentiated osteoblast-like phenotype was observed on the sintered HA surfaces compared to the as-received HA and calcined HA surfaces. An increased osteoblast-like cell activity on the sintered HA surfaces suggested that the crystallite size of HA surfaces may play an important role in governing cellular response.

Alkaline Phosphatase↗

PubMed1998

Auger electron spectroscopy and its use for the characterization of titanium and hydroxyapatite surfaces.

This review paper provides the basic background and underlying theory behind Auger electron spectroscopy (AES). Among the many surface analytical tools, AES has been shown to be very effective for surface composition analysis. These analyses are critically needed to better understand the interactions between the host and implant. The use of AES for titanium (Ti) and hydroxyapatite (HA) biomaterials characterization is demonstrated in this paper. The relative peak heights of TiL(2,3)M(2,3)V can be used as 'fingerprints' for TiO2 surfaces which have undergone different degrees of reduction. Similarly, for HA coatings, a shift in the phosphorus Auger peaks to a higher kinetic energy indicates the presence of a phosphate group, with strong P-O bonds. Depth compositional profiling and thin-film analysis can be performed using AES. In our studies, oxide thicknesses on Ti surfaces range from 36.8 +/- 7.4 A to 436 +/- 49 A depending on the surface treatment. Depth profiling can also be used to determine the subsurface composition of biomaterials. For HA coatings, a phosphorus concentration at the oxide/metal interface has been observed to be higher than at the outermost oxide surface. The HA coatings have also been observed to coexist within the titanium oxide, suggesting the occurrence of chemical bonding between the coatings and the metallic substrates. However, like other analytical tools, AES has its limitations. The electron beam damage can severely limit useful analysis of organic and biological materials and occasionally ceramic materials. Carbide buildup during long beam exposure times has been shown to affect the relative peak-to-peak intensities of the oxygen and metal Auger signals. The determination of film thickness requires a standard of known thickness and depth profiling of overlapping peaks can be very problematic. Even with these limitation, AES can be a powerful analytical tool for the characterization of biomaterial surfaces.

Biocompatible Materials↗

PubMed1998

Protein adsorption and osteoblast responses to different calcium phosphate surfaces.

The purpose of this study was to investigate the effect of sintering different calcium phosphate (CaP) surfaces on protein adsorption and osteoblast cell response. As-received and sintered hydroxyapatite (HA) and brushite were used in this study. X-ray diffraction revealed a poorly crystallized HA structure for the unsintered HA and a highly crystallized HA for the sintered HA surfaces. A brushite-type structure was indicated on the unsintered brushite surfaces, whereas sintered brushite surfaces contained mixtures of different CaP phases. Using 1 mg/mL albumin solution, protein was suggested to selectively adsorb on the CaP surfaces. A statistically higher albumin adsorption was observed on unsintered HA (9.5 micrograms/mL) and unsintered brushite (50.1 micrograms/mL) surfaces compared to sintered HA (3.2 micrograms/mL) and sintered brushite (3.4 micrograms/mL) surfaces. In the in vitro study using osteoblast cells, no statistical responses were observed between cells cultured on sintered HA and sintered brushite after 8 days of incubation. However, statistical differences in osteocalcin and protein production were observed between the unsintered HA and unsintered brushite. In addition, statistical differences in protein production, alkaline phosphatase activity, and osteocalcin production were observed between sintered CaP and unsintered CaP surfaces. From the protein adsorption and cell responses observed in this study, it was concluded that CaP surfaces need to be fully characterized prior to implantation.

Adsorption↗

PubMed1997

Properties of calcium phosphate coatings before and after exposure to simulated biological fluid.

The surface qualities of calcium phosphate (CaP) implants are important factors determining the nature and degree of cellular behaviour, especially cellular attachment, proliferation and differentiation. Thus, in this study, the chemical composition and crystallographic properties of radiofrequency sputter-deposited CaP coatings prior to and after in vitro immersion in a physiological solution were characterized. Significant differences in crystallite size were observed with different heat treatments, with coatings heat treated at 850 degrees C (CA8) having larger crystallites compared to coatings heat treated at 700 degrees C (CA7). However, no statistical difference in the Ca/P ratio, carbon concentration and surface energy were observed with different heat treatments. After immersion in a physiological solution, the crystallite size was significantly increased. The crystallite size for the CA8 and CA7 coatings remained statistically different after 1-week immersion in solution. An increase in carbon concentration was also observed for both samples after 1-week immersion in solution. However, no significant differences in the Ca/P ratio and surface energy were indicated between the two coatings after 1-week immersion in solution. In addition, no statistical difference in surface energy was observed for both samples initially and after 1 week.

Calcium Phosphates↗

PubMed1997

Surface roughness of titanium on bone morphogenetic protein-2 treated osteoblast cells in vitro.

Surface topography plays a critical role in the interaction of dental implants with adjacent tissues. No statistical differences in oxide composition and surface contamination were observed between 600 grit and polished titanium surfaces. The expression of osteoblast phenotype was enhanced when osteoblast progenitor cells (2T9) were stimulated with bone morphogenetic protein-2 on polished and 600 grit titanium surfaces. Bone morphogenetic protein-2 stimulated phenotypic expression on 600 grit titanium surfaces was marked by prolonged alkaline phosphatase specific activity and more rapid osteocalcin production as compared with the polished titanium surfaces. Because the surface area of the 600 grit titanium surface was shown to be 8 percent greater than that of the polished titanium surface, it is possible that increased surface area played a role in the enhanced expression of the osteoblast phenotype.

Alkaline Phosphatase↗