Biomedical subjects

D G Castner

Publications and source records attributed to D G Castner.

16 recordsLinked to original sources

PubMed2004

Characterization of poly(L-lysine)-graft-poly(ethylene glycol) assembled monolayers on niobium pentoxide substrates using time-of-flight secondary ion mass spectrometry and multivariate analysis.

Control of protein adsorption onto solid surfaces is a critical area of biomaterials and biosensors research. Application of high performance surface analysis techniques to these problems can improve the rational design and understanding of coatings that control protein adsorption. We have used static time-of-flight secondary ion mass spectrometry (TOF-SIMS) to investigate several poly(L-lysine)-graft-poly(ethylene glycol) (PLL-g-PEG) adlayers adsorbed electrostatically onto negatively charged niobium pentoxide (Nb(2)O(5)) substrates. By varying the PEG graft ratio (i.e., the number of lysine monomers per grafted PEG chain) and the molecular weights of the PLL and PEG polymers, the amount of protein adsorption can be tailored between 1 and 300 ng/cm(2). Detailed multivariate analysis using principal component analysis (PCA) of the positive and negative ion TOF-SIMS spectra showed changes in the outermost surface of the polymer films that were related to the density and molecular weight of the PEG chains on the surface. However, no significant differences were noted due to PLL molecular weight, despite observed differences in the serum adsorption characteristics for adlayers of PLL-g-PEG polymers with different PLL molecular weights. From the PCA results, multivariate peak intensity ratios were developed that correlated with the thickness of the adlayer and the enrichment of the PEG chains and the methoxy terminus of the PEG chains at the outermost surface of the adlayer. Furthermore, partial least squares regression was used to correlate the TOF-SIMS spectra with the amount of protein adsorption, resulting in a predictive model for determining the amount of protein adsorption on the basis of the TOF-SIMS spectra. The accuracy of the prediction of the amount of serum adsorption depended on the molecular weight of the PLL and PEG polymers and the PEG graft ratio. The combination of multivariate analysis and static TOF-SIMS provides detailed information on the surface chemistry and insight into the mechanism for protein resistance of the coatings.

Adsorption↗

PubMed2003

Binding and orientation of fibronectin to silanated glass surfaces using immobilized bacterial adhesin-related peptides.

Previously, we have demonstrated the suitability of bacterial adhesin-related peptides, directly immobilized on polystyrene surfaces, to bind and orient fibronectin (FN). For these studies a method to bind the large protein FN in a desired orientation on a solid substratum was developed which utilizes a bacterial adhesin-related peptide (designated BRP-A), which is known to bind specifically to the NH3-terminus end of FN. Glass substrata was first coated with an amine-terminated silane, followed by streptavidin (SA), which was used as an intermediate tether to bind the biotinylated bacterial adhesin-related peptide. The BRP-A peptide, used for these studies was synthesized with a terminal biotin to assure irreversible coupling of the BRP-A to the streptavidin. The biotinylated BRP-A was next immobilized on the SA-silanated glass surfaces. 125I-FN was used to quantify the amount of FN binding to the (BRP-A):SA-silanated glass surface. Monoclonal antibodies, which react with specific epitopes at either the NH3- or -COOH-termini of FN, were used to quantify the binding and orientation of FN. The results of these studies indicated: (1) FN bound to the BRP-A:SA-silanated glass surface; and (2) the bound FN was oriented such that NH2-terminal region of FN was bound towards the glass surface and the COOH-terminus was oriented away from the glass surface. These studies demonstrate that small peptides can be used to specifically bind and orient large proteins such as FN on the surfaces.

Adhesins, Bacterial↗

PubMed2002

Variable linear polarization from an X-ray undulator.

A new X-ray undulator has been designed and constructed which produces linearly polarized X-rays in which the plane of polarization can be oriented to a user selectable angle, from horizontal to vertical. Based on the Apple-II elliptically polarizing undulator (EPU), the undulator rotates the angle of the linear polarization by a simple longitudinal motion of the undulator magnets. Combined with the circular and elliptical polarization capabilities of the EPU operating in the standard mode, this new undulator produces soft X-ray radiation with versatile polarization control. This paper describes the magnetic structure of the device and presents an analysis of the magnetic field with varying undulator parameters. The variable linear polarization capability is then exhibited by measuring the X-ray absorption spectrum of an oriented polytetrafluoroethylene thin film. This experiment, which measures the linear dichroism of the sample at two peaks near the C 1s absorption edge, demonstrates the continuous polarization rotation capabilities of the undulator.

Journal Article↗

PubMed2001

Characterization of adsorbed protein films by time of flight secondary ion mass spectrometry.

Time of flight secondary ion mass spectrometry (ToF-SIMS) is a useful technique in the study of adsorbed protein films because of its high surface sensitivity and chemical selectivity. However, the protein mass spectra generated by ToF-SIMS are complex fragmentation patterns of a polymer consisting of 20 different monomers (i.e., amino acids). Principal component analysis (PCA) was implemented to classify several reference positive ion protein spectra according to protein and substrate type. Furthermore, the positive ion 74/102 and 120/130 SIMS intensity ratios, radiolabeled experiments, and PCA were used to track the relative surface concentrations of bovine serum albumin and bovine fibronectin in a binary adsorption experiment. In all cases, the combination of ToF-SIMS and PCA proved capable in classifying proteins by their type (in the case of pure protein spectra) and relative surface concentration (in the case of the binary protein spectra).

Adsorption↗

PubMed2001

A system to impose prescribed homogenous strains on cultured cells.

There is presently significant interest in cellular responses to physical forces, and numerous devices have been developed to apply stretch to cultured cells. Many of the early devices were limited by the heterogeneity of deformation of cells in different locations and by the high degree of anisotropy at a particular location. We have therefore developed a system to impose cyclic, large-strain, homogeneous stretch on a multiwell surface-treated silicone elastomer substrate plated with pulmonary epithelial cells. The pneumatically driven mechanism consists of four plates each with a clamp to fix one edge of the cruciform elastomer substrate. Four linear bearings set at predetermined angles between the plates ensure a constant ratio of principal strains throughout the stretch cycle. We present the design of the device and membrane shape, the surface modifications of the membrane to promote cell adhesion, predicted and experimental measurements of the strain field, and new data using cultured airway epithelial cells. We present for the first time the relationship between the magnitude of cyclic mechanical strain and the extent of wound closure and cell spreading.

Algorithms↗

PubMed2001

Inhibition of monocyte adhesion and fibrinogen adsorption on glow discharge plasma deposited tetraethylene glycol dimethyl ether.

Monocytes and macrophages play important roles in host responses to implanted biomedical devices. Monocyte and macrophage interactions with biomaterial surfaces are thought to be mediated by adsorbed adhesive proteins such as fibrinogen and fibronectin. Non-fouling surfaces that minimize protein adsorption may therefore minimize monocyte adhesion, activation, and the foreign body response. Radio-frequency glow discharge plasma deposition (RF-GDPD) of tetraethylene glycol dimethyl ether (tetraglyme) was used to produce polyethylene oxide (PEO)-like coatings on a fluorinated ethylene-propylene (FEP) surface. Electron spectroscopy for chemical analysis (ESCA) and static time of flight secondary ion mass spectrometry (ToF-SIMS) were used to characterize the surface chemistry of tetraglyme coating. Fibrinogen adsorption to the tetraglyme surface was measured with 125I-labeled fibrinogen and ToF-SIMS. Adsorption of fibrinogen to plasma deposited tetraglyme was less than 10 ng cm(-2), a 20-fold decrease compared to untreated FEP or tissue culture polystyrene (TCPS). Monocyte adhesion to plasma deposited tetraglyme was significantly lower than adhesion to FEP or TCPS. In addition, when the surfaces were preadsorbed with fibrinogen, fibronectin, or blood plasma, monocyte adhesion to plasma deposited tetraglyme after 2 h or 1 day was much lower than adhesion to FEP. RF-GDPD tetraglyme coating provides a promising approach to make non-fouling biomaterials that can inhibit non-specific material-host interactions and reduce the foreign body response.

Blood↗

PubMed2000

Platelet adhesion and procoagulant activity induced by contact with radiofrequency glow discharge polymers: roles of adsorbed fibrinogen and vWF.

The potential hemocompatibility of radiofrequency glow discharge (RFGD) polymers made by copolymerization of mixtures of hexafluoropropene and ethylene (C(3)F(6)/C(2)H(4)) or acrylic acid and 1,7-octadiene was investigated using in vitro assays for platelet adhesion and platelet catalyzed thrombin generation. Thrombin generation rate normalized to platelet number was used as a measurement of platelet activation (procoagulant activity). RFGD polymers produced by copolymerization of acrylic acid and 1, 7-octadiene contained varying amounts of carboxylic acid species as determined by electron spectroscopy for chemical analysis (ESCA). These polymers induced little variation in platelet adhesion, thrombin generation, or platelet activation. RFGD polymerization of C(3)F(6) and C(2)H(4) resulted in polymers with varying proportions of fluorinated species, as determined by ESCA. Fibrinogen adsorption from plasma was maximal on a polymer made with 25% C(3)F(6) (75% C(2)H(4)) in the feed. However von Willebrand factor (vWF) adsorption was greater on polymers made with increased %C(3)F(6) in the feed. Platelet adhesion decreased with increasing %C(3)F(6) in the feed. Thrombin generation was lowest for platelets adherent to polymers made from both C(3)F(6) and C(2)H(4). Therefore, procoagulant activity of platelets increased for polymers made with increased %C(3)F(6) in the feed, similar to the trend in vWF adsorption. These findings suggest that increased incorporation of fluorinated species into RFGD polymers leads to decreased platelet adhesion and increased platelet activation (which is possibly due to increased vWF adsorption).

Adsorption↗

PubMed2000

Surface modification of poly(ethylene terephthalate) angioplasty balloons with a hydrophilic poly(acrylamide-co-ethylene glycol) interpenetrating polymer network coating.

An interpenetrating polymer network (IPN) of poly(acrylamide-co-ethylene glycol) (p(AAm-co-EG)) hydrogel was covalently grafted to polyethylene terephthalate (PET) angioplasty balloons to increase surface hydrophilicity and improve lubricity. A 2-step graft polymerization protocol was followed to first polymerize and cross-link acrylamide onto the substrate with a photosensitizer and/or oxygen plasma pretreatment. The effects of varying photo-initiation and plasma exposure times were investigated separately and conjunctively using water contact angles to obtain optimal coating deposition parameters. A poly(ethylene glycol) network was then grafted by swelling the preexisting polyacrylamide network to allow inter-diffusion of the monomer and cross-linker, which were then polymerized by photo-initiation. When the photo-initiation time was long enough to reach near gelation, pretreatment of PET with oxygen plasma did not offer significant benefit. X-ray photoelectron spectroscopy confirmed the presence of both polymer layers, and composition depth profiles supported the assessment that an interpenetrating network was formed. Tensile testing and application of Weibull statistics on unmodified and modified films indicated that the surface modification approach did not significantly alter the mechanical integrity of the material. These findings indicate that a p(AAm-co-EG) coating can be effectively deposited on PET surfaces without compromising the structural integrity of the substrate.

Acrylic Resins↗

PubMed1999

Surfaces designed to control the projected area and shape of individual cells.

Materials with spatially resolved surface chemistry were designed to isolate individual mammalian cells to determine the influence of projected area on specific cell functions (e.g., proliferation, cytoskeletal organization). Surfaces were fabricated using a photolithographic process resulting in islands of cell binding N-(2-aminoethyl)-3-aminopropyl-trimethoxysilane (EDS) separated by a nonadhesive interpenetrating polymer network [poly (acrylamide-co-ethylene glycol); P (AAm-co-EG)]. The surfaces contained over 3800 adhesive islands/cm2, allowing for isolation of single cells with projected areas ranging from 100 microns 2 to 10,000 microns 2. These surfaces provide a useful tool for researching how cell morphology and mechanical forces affect cell function.

Actins↗

PubMed1998

Biomolecular modification of p(AAm-co-EG/AA) IPNs supports osteoblast adhesion and phenotypic expression.

Interpenetrating polymer networks (IPNs) were designed to resist materials fouling caused by non-specific protein adsorption, and indiscriminate cell or bacterial adhesion. These IPNs were thin adherent films (approximately 20 nm) comprised of acrylamide (AAm), ethylene glycol (EG), and acrylic acid (AA) grafted to either silicon waters or quartz substrates via photoinitiated free radical polymerization. These networks were further modified to promote specific cell adhesion by tethering bioactive groups such as peptides that mimic cell-binding domains found on extracellular matrix molecules. As a specific example of biomolecular surface engineering, peptides from the cell-binding domain of bone sialoprotein were tethered to a p(AAm-co-EG/AA) IPN to control cell behavior at the surface. The networks were characterized by contact angle measurements, spectroscopic ellipsometry, and X-ray photoelectron spectroscopy to convey information on IPN wettability, thickness, and chemistry. The surface characterization data supported the theory that the PEG/AA layer formed an IPN with the underlying p(AAm) network, and after graft modification of this IPN with diamino PEG (PEG(NH2)2), the PEG(NH2)2 chains were enriched at the surface. Rat calvarial osteoblasts attached to Arg-Gly-Asp (RGD) modified IPNs at levels significantly greater than on clean quartz, Arg-Gly-Glu (RGE) modified, or the PEG(NH2)2 modified IPN, with or without serum in the media. Cells maintained in media containing 15% fetal bovine serum (FBS) proliferated, exhibited nodule formation, and generated sheets of mineralized extracellular matrix (ECM) with the addition on beta-glycerophosphate to the media. Cell adhesion and mineralized ECM formation were specifically dependent on the peptide sequence present at the surface.

Acrylic Resins↗

PubMed1993

ESCA surface characterization of four IUPAC reference polymers.

Four reference polymers studied by the International Union of Pure and Applied Chemistry working party on interactions of polymers with living systems were characterized by electron spectroscopy for chemical analysis. The surface of a polyethylene specimen was found to consist of only hydrocarbon (-CH2-) groups, as expected. Similarly, the surface of a poly(dimethyl siloxane) was found to be in close agreement with the expected stoichiometry of this polymer. The surface of the PVC sample showed a high surface concentration of hydrocarbon-rich plasticizer. Also, Si, O and Zn were detected. Cellulose coil specimens were heavily silicone contaminated. A 24 h rinse of this material in water reduced the Si level to 5%, and produced a surface spectrum closer to that expected for cellulose.

Cellulose↗

PubMed1992

Variations between Biomer lots. I. Significant differences in the surface chemistry of two lots of a commercial poly(ether urethane).

We have studied the surface chemistry of two lots of Biomer (BSP067 and BSUA001), a widely used commercial poly(ether urethane) (PEU). Although transmission infrared adsorption studies revealed no differences in the bulk chemistry of the two lots, the surface chemistry, as seen by x-ray photoelectron spectroscopy (XPS) and static secondary ion mass spectrometry (SIMS), was different. Lot BSP067 showed soft-segment enrichment at the surface, which is typical of PEU. Lot BSUA001 showed no evidence of either hard- or soft-segment PEU components at the surface. The surface of this lot was completely covered with a nonextractable additive identified as poly(diisopropyl amino ethyl methacrylate). Small amounts of a low-molecular-weight antioxidant were observed at the surface of both samples. Because the biological response to polymers is dependent on surface structure, these results are of considerable importance to biomaterials research.

Antioxidants↗

PubMed1992

Surface characterization of 2-hydroxyethyl methacrylate/styrene copolymers by angle-dependent X-ray photoelectron spectroscopy and static secondary ion mass spectrometry.

The surface composition and structure of three structurally distinct amphiphilic copolymers of 2-hydroxyethyl methacrylate (HEMA) and styrene have been examined with angle-dependent X-ray photoelectron spectroscopy (XPS) and static secondary ion mass spectrometry (SIMS). The phase-separated block copolymer made by anionic living polymerization, HSH-A50, showed significant surface enrichment of styrene. The outermost 2-3 A appeared to be approximately 100% styrene, with the styrene concentration decreasing to its bulk value at a depth of approximately 50 A from the surface. However, HEMA was detected in the outer 20 A of this copolymer. The presence of HEMA in the surface region implies this copolymer may undergo significant restructuring when hydrated in a hydrophilic environment (as opposed to the hydrophobic environment in which the sample was prepared and analyzed). The phase-separated block copolymer made by telechelic coupling of free radical polymerized functionalized oligomers, HSH-B60, showed only slight styrene enrichment at the surface. Both HEMA and styrene were detected at all sampling depths, including the outermost surface layer, consistent with the presence of discrete HEMA and styrene domains at the copolymer surface. Since both components are already present at the surface under hydrophobic conditions, the degree of restructuring this copolymer may undergo upon hydration should be minor. The random HEMA--styrene copolymer made by conventional free radical initiation techniques, HS-RAN50, had a surface composition that was similar to the bulk composition and independent of depth, as expected for a homogeneously mixed copolymer film.

Biocompatible Materials↗

PubMed1990

Poly(dimethylsiloxane)-poly(ethylene oxide)-heparin block copolymers. III: Surface and bulk compositional differences.

Previously observed bioactivity of poly(dimethylsiloxane)-poly(ethylene oxide)-heparin (PDMS-PEO-Hep) triblock copolymers has prompted studies of the surface and bulk character of this copolymer using angular-dependent electron spectroscopy for chemical analysis (ADESCA), static secondary mass spectroscopy (SIMS), differential scanning calorimetry (DSC), and thermogravimetric analysis (TGA). Because the low-energy PDMS phase dominates surfaces of this copolymer when solvent cast under air or vacuum conditions, attempts were made to explain surface restructuring and rearrangements induced in hydrated or aqueous environments that permit surface accessibility and bioactivity of heparin moieties. Based on comparisons with PDMS, PEO, and heparin homopolymers, PEO/heparin blends, and an unheparinized PDMS-PEO diblock copolymer, PDMS-PEO-heparin demonstrates both phase-mixed and phase-separated regions in DSC analysis. During annealing cycles above the Tg values of the copolymer constituents, phase-mixed regions become increasingly phase separated and PEO enriched. TGA analysis confirmed the presence block copolymer constituents and presented evidence of intermolecular segmental interactions, hence phase-mixing in the copolymers. ADESCA analysis indicates that the outer 5 A of both the PDMS-PEO and PDMS-PEO-Hep copolymers is essentially pure PDMS. However, significant amounts of PEO are detected 5 to 20 A below the surface. Static SIMS also detects the presence of PDMS at the surfaces of the PDMS-PEO and PDMS-PEO-Hep copolymers. Compositional models based on ADESCA, SIMS, and DSC data are presented for desiccated and hydrated copolymer surfaces.

Biocompatible Materials↗

PubMed1990

Characterization of alkyl grafted polyurethane block copolymers by variable takeoff angle x-ray photoelectron spectroscopy.

Variable takeoff angle x-ray photoelectron spectroscopy was used to determine the surface composition of five polyurethane block copolymers. The high-resolution C1s spectra from all five polyurethane samples had peaks at binding energies of 285.0, 286.5, and 289.5 eV, which are consistent with the presence of hydrocarbon, ether, and urethane carbon species. Both the measured elemental compositions at the low takeoff angles (deepest sampling depths) and the calculated elemental compositions for depths greater than 15 A generally showed good agreement with the expected bulk compositions. The outer 15 A of the surface of all five samples was depleted in the nitrogen-containing hard segment. For the base polyurethane sample in this series, an enrichment of the poly(tetramethylene oxide) soft segment and the presence of an organic silicone impurity were detected. Doubling the chain length of both the hard and soft segments resulted in a further decrease of the hard segment concentration in the outer surface of the sample. The grafting of C2 and C18 alkyl groups onto 10 or 20% of the urethane linkages resulted in an increase in the percentage of aliphatic carbon species present on the surface. In the case of the C18-alkylated material, the presence of alkyl chains at the surface was inferred using contact angle measurements.

Biocompatible Materials↗

PubMed1990

Surface characterization of a series of polyurethanes by X-ray photoelectron spectroscopy and contact angle methods.

X-ray photoelectron spectroscopy (XPS) and contact angle methods were used to examine the surfaces of an homologous series of poly(ether urethane) (PEU) samples before and after cleaning treatments. Four PEU films with Shore hardnesses varying from 45 to 75 D were studied as well as two commercially available intravenous catheters of related PEUs. The four as received PEU films have similar surface compositions (approximately 79% C, approximately 17% O, approximately 2% N, and approximately 2% Si) although they differ in bulk composition. Critical surface tension (gamma c) values are all similar and high (45-46 dynes/cm). The similarity in the surfaces of the four PEUs, despite the differences in their mechanical properties, demonstrates that surface properties do not necessarily reflect bulk properties. Soap washing and methanol-acetone extraction of the PEU films resulted in surfaces more representative of the bulk compositions of the PEUs. Analysis of the intravenous catheters confirmed that they are lubricated with PDMS, a common practice in the medical device industry. This study documents the value of detailed surface analysis for an enhanced understanding of the surface zone of PEUs. It also illustrates how cleaning protocols can remove labile surface species.

Biocompatible Materials↗