Biomedical subjects

M C Davies

Publications and source records attributed to M C Davies.

At least 55 records · Page 3Linked to original sources

PubMed1999

Competitive protein adsorption as observed by surface plasmon resonance.

The competitive nature of protein adsorption has been investigated in situ by surface plasmon resonance (SPR) analysis. The adsorption from blood plasma solutions of albumin, fibrinogen and immunoglobulin-G (IgG), to a polystyrene surface was investigated as part of concentration- and time-dependent studies, to observe the sequential adsorption of the three proteins at the surface. Adsorption of plasma solutions at a range of concentrations or incubation times was performed and the resulting surfaces were probed by the addition of an appropriate antibody to the protein surface. The process was repeated for each antigen leading to a surface concentration profile of each protein with respect to plasma concentration and plasma incubation time. The SPR was able to detect changes in the relative surface concentration of each component demonstrating that the protein's residence time at the interface was dependent upon its molecular weight, bulk concentration and surface affinity. All ri,hts reserved

Adsorption↗

PubMed1999

Bone density in a population of long term oral contraceptive pill users does not differ from that in menstruating women.

Prevention of osteoporosis is a major public health issue. Amenorrhoeic women have lower bone density than normally menstruating women, which is related to the duration of amenorrhoea and the severity of oestrogen deficiency. Bone mineral density (BMD) in amenorrhoeic women can be improved by oestrogen replacement in the form of the combined oral contraceptive pill (COCP), so increased BMD might be an important non-contraceptive benefit of the COCP in menstruating women. Previous studies have been variably reported, but have used different methodologies for measurement of BMD. We measured BMD using the DEXA technique in long term COCP users and compared this with menstruating women who had never used the COCP. No differences in bone density were found, suggesting that the COCP does not improve bone mass in menstruating women who are adequately oestrogenised by their own ovaries.

Absorptiometry, Photon↗

PubMed1998

A novel biotinylated degradable polymer for cell-interactive applications.

We describe the development of a novel biodegradable polymer designed to present bioactive motifs at the surfaces of materials of any architecture. The polymer is a block copolymer of biotinylated poly(ethylene glycol) (PEG) with poly(lactic acid) (PLA); it utilizes the high-affinity coupling of the biotin-avidin system to undergo postfabrication surface engineering. We show, using surface plasmon resonance analysis (SPR) and confocal microscopy that surface engineering can be achieved under aqueous conditions in short time periods. These surfaces interact with cell surface molecules and generate beneficial responses as demonstrated by the model study of integrin-mediated spreading of endothelial cells on polymer surfaces presenting RGD peptide adhesion sequences.

Animals↗

PubMed1998

A surface plasmon resonance study of albumin adsorption to PEO-PPO-PEO triblock copolymers.

Pluronic surfactants, PEO-PPO-PEO triblock copolymers, have been investigated widely due to their protein-resistant properties in applications as coatings for implants and in controlled drug release systems. We have studied a wide range of these copolymers, varying in both PEO and PPO block size, by adsorbing them to a polystyrene surface and investigating their subsequent resistance to human serum albumin adsorption. This investigation has been carried out in real time, using surface plasmon resonance, with the surfaces subsequently visualized by atomic force microscopy. This approach has allowed determination of the effect of the lengths of the PEO and PPO polymer chains on protein resistivity. For low-molecular-weight Pluronics a significant, yet not complete, reduction in albumin adsorption has been observed whereas higher molecular weight Pluronics appear to completely inhibit adsorption within the time frame of this experiment. An increase in the PPO block size of the copolymer also appears to increase its protein resistance. This work further confirms that the binding strength of the anchoring block to the hydrophobic surface, rather than the length of the protruding hydrophilic PEO chains, determines a copolymer's protein resistance capability.

Albumins↗

PubMed1998

The use of SIMS, XPS and in situ AFM to probe the acid catalysed hydrolysis of poly(orthoesters).

Due to poly(orthoesters) being susceptible to acid catalysed hydrolysis, these polymers have attracted considerable interest for the controlled delivery of therapeutic agents within biodegradable matrices. The pH-sensitivity of the poly (orthoesters) has lead to several drug delivery systems being developed, whose rate of drug release is predominantly controlled by the rate of polymer hydrolysis. This study reports on the use of X-ray photoelectron spectroscopy (XPS), secondary ion mass spectrometry (SIMS), and atomic force microscopy (AFM) in a multitechnique approach to probe the effect of acid catalysed hydrolysis at the interface of poly(orthoesters). The molecular specificity of SIMS was successfully employed, suggesting that the preferred mechanism for hydrolysis was via the cleavage of an exocyclic alkoxy bond in the 3,9,-diethylidene-2,4,8,10-tetraoxaspiro [5,5] undecane(DETOSU) unit. The resulting change in the surface chemical structure of the partially hydrolysed poly(orthoester) is such that it was not detectable by XPS analysis. Images acquired from an in situ AFM study of the hydrolysis ofa poly(orthoester), showed changes in the surface morphology, seen as the formation of pits, and an overall thinning of the polymer film. The use of SIMS, XPS and AFM has enabled changes in surface chemistry to be compared with changes in surface morphology. These complementary data, on the behaviour of the polymer during degradation have important implications for the further design of novel biodegradable materials.

Biocompatible Materials↗

PubMed1998

Interactions of chondrocytes with methacrylate copolymers.

Copolymers of poly(ethylmethacrylate) (PEMA) and tetrahydrofurfurylmethacrylate (THFMA) have been shown to exhibit potential as a biomaterial for use in cartilage repair. However, the interactions of chondrocytes with the polymer surface is not well understood. A series of novel methacrylate copolymers containing PEMA, THFMA and hydroxyethylmethacrylate (HEMA) were prepared and the ability of these various copolymers to support chondrocytes attachment in vitro has been assessed by the Alamar blue assay for cell number and environmental scanning electron microscopy (ESEM). As the mole fraction of HEMA in PEMA/THFMA/HEMA copolymers increased, chondrocyte attachment to the polymer surface in 24 h decreased. Chondrocytes maintained a rounded morphology and were strongly attached on the THFMA/PEMA polymer surface, but as the mole fraction of HEMA increased the cells present became much smaller with fewer cell to cell interactions. The effect of pre-adsorbing fibronectin on to the polymer surface on cell attachment was assessed both in the presence and absence of serum. Chondrocyte attachment was significantly reduced in serum-free medium. Pre-adsorption of fibronectin on to the copolymer surface substantially increased cell attachment in all cases. In conclusion, chondrocyte attachment and proliferation on these copolymers may be controlled by changes in the polymer surface chemistry and is highly sensitive to the presence of proteins either in the culture media or pre-adsorbed on to the copolymer surface.

Journal Article↗

PubMed1998

Spatially controlled cell engineering on biodegradable polymer surfaces.

Controlling receptor-mediated interactions between cells and template surfaces is a central principle in many tissue engineering procedures (1-3). Biomaterial surfaces engineered to present cell adhesion ligands undergo integrin-mediated molecular interactions with cells (1, 4, 5), stimulating cell spreading, and differentiation (6-8). This provides a mechanism for mimicking natural cell-to-matrix interactions. Further sophistication in the control of cell interactions can be achieved by fabricating surfaces on which the spatial distribution of ligands is restricted to micron-scale pattern features (9-14). Patterning technology promises to facilitate spatially controlled tissue engineering with applications in the regeneration of highly organized tissues. These new applications require the formation of ligand patterns on biocompatible and biodegradable templates, which control tissue regeneration processes, before removal by metabolism. We have developed a method of generating micron-scale patterns of any biotinylated ligand on the surface of a biodegradable block copolymer, polylactide-poly(ethylene glycol). The technique achieves control of biomolecule deposition with nanometer precision. Spatial control over cell development has been observed when using these templates to culture bovine aortic endothelial cells and PC12 nerve cells. Furthermore, neurite extension on the biodegradable polymer surface is directed by pattern features composed of peptides containing the IKVAV sequence (15, 16), suggesting that directional control over nerve regeneration on biodegradable biomaterials can be achieved.

Animals↗

PubMed1997

Detection of antigen-antibody binding events with the atomic force microscope.

An atomic force microscope (AFM) has been used to directly monitor specific interactions between antibodies and antigens employed in an immunoassay system. Results were achieved using AFM probes functionalized with ferritin, and monitoring the adhesive forces between the probe and anti-ferritin antibody-coated substrates. Analysis of the force distribution data suggests a quantization of the forces, with a period of 49 +/- 10 pN. This periodic force may be attributed to single unbinding events between individual antigen and antibody molecules. These results demonstrate that the AFM could be employed as an analytical tool to study the interactions between the molecules involved in biosensor systems. The potential of the technique to provide information relating to the manner in which the antibody molecule binds to its specific antigen is also discussed.

Animals↗

PubMed1997

The minimum single oral metronidazole dose for treating trichomoniasis: a randomized, blinded study.

OBJECTIVE: To identify the minimum effective single oral dose of metronidazole for trichomoniasis. METHODS: Women attending an inner-city sexually transmitted disease clinic who had Trichomonas vaginalis vaginitis diagnosed by microscopy were recruited for this randomized, double-blind study. Subjects were given a 0.5-, 1-, 1.5-, or 2-g single oral dose of metronidazole, taken under direct observation. Demographic information, symptoms, and clinical findings were collected from patient interviews, and physical examinations were conducted at the time of enrollment and at the follow-up visit. The primary outcome measure was treatment success at the follow-up visit, established by negative culture and microscopy. RESULTS: Three (1.8%) of the 167 women enrolled were excluded because of vomiting after taking metronidazole, and 66 (40%) of the 164 remaining subjects did not return for the follow-up visit. No associations were found between the proportion of subjects lost to follow-up and the characteristics of these subjects across assignment groups. The treatment success ratio was highest in subjects who received the 1.5-g dose (23, 85%), followed by the 2-g (16, 84%), 1-g (18, 62%), and the 0.5-g dose (8, 35%). CONCLUSION: A single 1.5-g dose of metronidazole has efficacy equivalent to a single 2-g dose for the treatment of T vaginalis vaginitis.

Administration, Oral↗

PubMed1997

Starch granule surface imaging using low-voltage scanning electron microscopy and atomic force microscopy.

High resolution imaging of wheat and potato starch granule surfaces has been performed using low-voltage scanning electron microscopy and atomic force microscopy. The complimentary images of uncoated granules demonstrate that the two starch types possess substantially different surface topologies; potato starch has many protrusions (100-300 nm in diameter), above a flatter surface containing 20-50 nm structures, whilst wheat starch possesses far fewer protrusions and generally has a smoother surface composed of approximately 20 nm structures. The protrusions are believed to be carbohydrate in nature and thus represent the ends of amylopectin side-chain clusters at the granule surface.

Microscopy, Atomic Force↗

PubMed1997

Investigation of the dissolution of the bioceramic hydroxyapatite in the presence of titanium ions using ToF-SIMS and XPS.

Time-of-flight secondary ion mass spectrometry (ToF-SIMS) and X-ray photoelectron spectroscopy (XPS) analyses have been used to investigate the dissolution of hydroxyapatite in the presence of titanium chloride suggesting the substitution of titanium ions for calcium in the hydroxyapatite structure. The surface analytical data suggest that titanium was incorporated within the solid phase as titanium phosphate. Comparison of relative ion intensities in the ToF-SIMS spectra reveals changes in the composition of the surface chemistry of hydroxyapatite. These relative ion intensities show that the maximum surface uptake of titanium occurred at a solution concentration of 500 ppm titanium chloride for a time of incubation of 30 min. These data correlate with that obtained using XPS highlighting the semi-quantitative information which ToF-SIMS can provide.

Biocompatible Materials↗

PubMed1997

Surface plasmon resonance for real time in situ analysis of protein adsorption to polymer surfaces.

The adsorption of a range of plasma proteins to metal and polymer surfaces has been examined using surface plasmon resonance (SPR). The adsorption of proteins was initially studied on the SPR silver sensor surface, and then on a model polystyrene film spun coated directly onto this substrate. In both cases, reproducible adsorption profiles for albumin were attained which compared well with corresponding atomic force microscopy (AFM) and ellipsometry data on protein monolayer packing and thickness respectively. The SPR data revealed the influence of concentration on both protein adsorption kinetics and the time for formation of a monolayer coating. SPR data also highlighted different adsorption kinetics and final monolayer SPR angle shift values for three plasma proteins which have been interpreted in terms of their molecular dimensions and orientation at the polymer interface. AFM data confirmed the presence of a closely packed protein layer for all three protein systems. These studies are discussed in terms of employing SPR in the study of protein interactions at surfaces which are important in the design and evaluation of novel biomedical polymeric materials.

Adsorption↗

PubMed1997

Preparation of surface-modified albumin nanospheres.

Surface-modified human serum albumin (HSA) nanospheres with a size of around 100 nm in diameter were prepared from poly(amidoamine)-poly(ethylene glycol) copolymer grafted human serum albumin (HSA-PAA-PEG) and poly(thioetheramido acid)-poly(ethylene glycol) copolymer grafted human serum albumin (HSA-PTAAC-PEG). The nanospheres were produced using a pH-coacervation method and cross-linked with glutaraldehyde. The cross-linking efficiency was affected by the type of albumin conjugate used. The zeta potential of the surface-modified nanospheres was significantly lower than that of unmodified particles. The existence of a hydrated steric barrier surrounding the nanospheres was confirmed by electrolyte- and pH-induced flocculation tests. The surface-modified nanospheres showed a reduced plasma protein adsorption on the particle surface compared with unmodified particles.

Adsorption↗

PubMed1997

Atomic force microscopic study of the surface morphology of apatite films deposited by pulsed laser ablation.

Atomic force microscopy (AFM) has been used to study the surface morphology of apatite films deposited on metallic and polyethylene substrates by laser ablation using KrF and transversely excited atmospheric CO2 lasers. The films are found to consist of a smooth apatite coating with macroparticles scattered on the surface. A wide variety of macroparticles, differing in size, shape and roughness, were found and analysed employing the high spatial resolution of AFM (< 1 nm). We have investigated the correlation between the apatite film morphology and the deposition conditions. Of particular importance are laser fluence, gas pressure, the nature of the target and the substrate temperature. We have explained these dependencies on the basis of a theoretical model which includes evaporation and a cluster-type laser ablation mechanism.

Apatites↗

PubMed1997

Biodegradable polymeric microparticles for drug delivery and vaccine formulation: the surface attachment of hydrophilic species using the concept of poly(ethylene glycol) anchoring segments.

Poly(ethylene glycol)-dextran (PEG-DEX) conjugates have been used as a combined stabilizer and surface modifier to produce resorbable poly(DL-lactide-co-glycolide) (PLG) microparticles by an emulsification/solvent evaporation technique. The use of PEG or dextran polymers alone was incapable of producing microparticles. Particle size measurements revealed smaller mean particle sizes (480 nm) and improved polydispersity when using a 1.2% PEG substituted conjugate relative to a 9% substituted material (680 nm). PLG microparticles modified by post-adsorbed PEG-DEX conjugates flocculated in 0.01 M salt solutions, whereas PLG microparticles prepared using PEG-DEX as a surfactant were stable in at least 0.5 M NaCl solutions. Surface modification of PLG microparticles was confirmed by zeta potential measurements and surface analysis using X-ray photoelectron spectroscopy. The presence of surface exposed dextran was confirmed by an immunological detection method using a dextran-specific antiserum in an enzyme-linked immunosorbent assay. The findings support a model in which the PEG component of the PEG-DEX conjugate provides an anchor to the microparticle surface while the dextran component extends from the particle surface to contribute a steric stabilization function. This approach offers opportunities for attaching hydrophilic species such as targeting moieties to biodegradable microparticles to improve the interaction of drug carriers and vaccines with specific tissue sites.

Biocompatible Materials↗

PubMed1997

Long circulating biodegradable poly(phosphazene) nanoparticles surface modified with poly(phosphazene)-poly(ethylene oxide) copolymer.

The biodistribution of biodegradable poly(organo phosphazene) nanoparticles surface modified by adsorption of a novel poly(organo phosphazene)-poly(ethylene oxide) copolymer with a 5000 M(W) PEO chain (PF-PEO[5000]), following intravenous administration in rats and rabbits, is described. The data are compared to the biodistribution of poly(organo phosphazene) and poly(lactide-co-glycolide) nanoparticles coated with a tetrafunctional copolymer of poly(ethylene oxide)-poly(propylene oxide) ethylenediamine, commercially available as Poloxamine 908. This copolymer has a PEO chain of the same size as the poly(organo phosphazene)-PEO derivative used. The results in the rat model reveal that poly(organo phosphazene) nanoparticles with a Poloxamine 908 coating were mainly captured by the liver, although a retardation in clearance from the systemic circulation was seen. In contrast, the poly(organo phosphazene) nanoparticles coated with PF-PEO(5000) showed a prolonged blood circulating profile, with only a small amount of the nanoparticles sequestered by the liver. This indicates the importance of the nature of both the anchoring group and the particle surface on the biological performances of the system. Study of the biodistribution of the PF-PEO(5000)-coated poly(organo phosphazene) nanoparticles in the rabbit model also indicated a prolonged systemic circulation lifetime and reduced liver uptake, whereby a significant amount of the administered nanoparticles was targeted to the bone marrow.

Animals↗

PubMed1997

Data analysis using the Internet: the World Wide Web scanning probe microscopy data analysis system.

The first interactive world-wide web-based image analysis system is presented (http://pharm6.pharm.nottingham.ac.uk/processing/main. html). The system, currently tailored to scanning probe microscopy image data, has been developed to permit the use of software algorithms developed within our laboratory by researchers throughout the world. The implementation and functionality of the scanning probe microscopy server is described. Feedback from users of the facility has demonstrated its value within the research community, and highlighted key operational issues which are to be addressed. A future role of Internet-based data processing software is also discussed.

Algorithms↗

PubMed1997

Human serum albumin as a probe for protein adsorption to nanoparticles: relevance to biodistribution.

A range of poloxamers and poloxamines were adsorbed to biodegradable poly(lactide-co-glycolide) (PLGA) and non-biodegradable polystyrene (PS) particulate systems in order to alter their surface characteristics and produce potential drug targeting systems. Human serum albumin (HSA) was chosen as a model protein to investigate protein adsorption to the above systems and was quantified by two techniques. I125 radiolabelled HSA proved to be a useful probe for determining protein adsorption but was limited by a modification that occurred on storage. Also, HSA eluted from the particle surface was quantified by densitometry following it's development on an SDS-PAGE gel. Both techniques produced similar results. For cleaned coated PS particles it was found that the PEO chain length and the molecular structure of the block copolymer were important in preventing protein adsorption. The presence of excess block copolymer in the uncleaned preparations resulted in further suppression of HSA adsorption, which was thought to be due to their detergent properties. Due to the different results obtained with similarly coated PLGA particles, it was concluded that the block copolymers adsorb onto the surface of the PLGA particles in a different conformation to those adsorbed onto PS particles. Correlating in vivo biodistribution in terms of the prevention of protein (opsonin) adsorption was of only limited success and it was concluded that adsorption data for a single model protein can only be used with caution to predict the in vivo behaviour of colloidal targeting systems.

Adsorption↗