powered by FreeFind
Articles about Biomaterials
For the Biomaterials Industry - Hundreds of Biomaterials Articles! Polymers, Composites, Ceramics, Alloys... Biomaterials Articles
Biomaterials Articles
Biomaterials Articles
Biomaterials Articles

Record 3761 to 3780
First Page Previous Page Next Page Last Page
Stimulation of directed bone growth at oxidized titanium implants by macroscopic grooves: an in vivo study
Hall, J., P. Miranda-Burgos, et al. (2005), Clin Implant Dent Relat Res 7 Suppl 1: S76-82.
Abstract: BACKGROUND: The influence of thread design at the millimeter level and surface topography at the micrometer level on bone integration and the stability of dental implants have been studied extensively. However, less is known about the influence of implant structures in the range of 50 to 200 microm. PURPOSE: The present in vivo investigation was undertaken to study if bone formation and implant stability were influenced by 110 (S1) and 200 (S3) microm-wide and 70 microm-deep grooves positioned at a thread flank of oxidized titanium implants. MATERIALS AND METHODS: Eighteen rabbits and oxidized titanium implants (3.75 mm in diameter and 7 mm long) were used in the study. Nine rabbits received three control implants and three test implants with a 110 microm-wide groove added to one thread flank. The remaining nine rabbits received three control implants and three test implants with a 200 microm-wide groove. The animals were followed for 6 weeks. Removal torque (RTQ) tests were applied to two of the implants in each leg. The remaining implant per leg was retrieved for histology. The degree of bone fill within the grooves and corresponding bone formation at the opposing surfaces, the bone area within the threads, and the degree of bone-implant contact were calculated for each implant. RESULTS: The histologic analyses revealed an affinity for bone formation within the grooves. The RTQ tests showed that the peak RTQ was approximately 30% higher for the S1 implants compared with control implants without a groove. The difference was statistically significant (p <.05) for tibial and pooled implants. A similar but smaller and not statistically significant effect, approximately 8%, was measured for the S3 implants. The histomorphometric measurements confirmed the observed affinity of bone for the grooves. For S1 implants, 78.7 +/- 15.8% of the grooves were filled with bone, whereas only 46.2 +/- 27% of the corresponding flank surface showed the presence of bone (p <.05). The corresponding figures for S3 and control implants were 72.7 +/- 25.1% and 48.5 +/- 13.6%, respectively (p <.05). The degrees of bone-implant contact and bone area within the threads were similar for test and control implants. CONCLUSION: It is concluded that 110 and 200 microm-wide and 70 microm-deep grooves at oxidized implant surfaces stimulated bone to preferentially form within and along the groove in the rabbit model. The 110 microm-wide groove was shown to increase the resistance to shear forces significantly. It is suggested that implants with such a groove may be one way to optimize implant stability in suboptimal clinical conditions.

Stimulation of osteoblast responses to biomimetic nanocomposites of gelatin-hydroxyapatite for tissue engineering scaffolds
Kim, H. W., H. E. Kim, et al. (2005), Biomaterials 26(25): 5221-30.
Abstract: Collagen-derived gelatin/hydroxyapatite (HA) nanocomposites were biomimetically synthesized for hard tissue engineering scaffold. In vitro osteoblastic cellular responses to the nanocomposites were assessed in comparison with those conventionally mixed gelatin-HA composites. A three-dimensional culture method involving floating cells in a culture medium was introduced to assist in the initial attachment of the cells to the scaffolds, and the proliferation and differentiation behaviors of the cells were examined. The osteoblastic MG63 cells attached to the nanocomposites to a significantly higher degree and subsequently proliferated more. The alkaline phosphatase (ALP) activity and osteocalcin produced by the cells were significantly higher on the nanocomposite scaffolds than on the conventional composite scaffolds. These improved cellular responses on the nanocomposites are considered to result from the increased ionic release and serum protein adsorption on the nanocomposites, which was derived from the different structural and morphological characteristics, i.e., the nanocomposite scaffolds retained less-crystallized and smaller-sized apatite crystals and a more well-developed pore configuration than the conventional ones. Based on these findings, the biomimetically synthesized nanocomposite scaffolds are believed to be potentially useful in hard tissue regeneration and tissue engineering fields.

Strain-controlled enzymatic cleavage of collagen in loaded matrix
Ruberti, J. W. and N. J. Hallab (2005), Biochem Biophys Res Commun 336(2): 483-9.
Abstract: The purpose of this investigation is to support the novel hypothesis that collagenous matrices are intrinsically "smart" load-adapting biomaterials. This hypothesis is based fundamentally on the postulate that tensile strain directly modulates the susceptibility of collagen molecules to enzymatic degradation (i.e., protects molecules which are under load from cleavage). To test this postulate, collagenase (Clostridiopeptidase A) was applied to a uniaxially loaded, anisotropic, devitalized, collagenous matrix in which a subset of fibrils was loaded in tension while the remaining fibrils carried little or no load. The collagen degradation pattern (as assessed by polarization and transmission electron microscopy) was found to correspond inversely to the tensile stress field such that fibrils under lower tensile load were preferentially cleaved. These results have immediate implications for tissue engineering of load-bearing collagenous matrices in vitro and may contribute significantly to our understanding of synthesis, remodelling, and pathogenesis of collagen matrices in vivo.

Strategic leukofiltration in cardiac surgery
Gunaydin, S., K. McCusker, et al. (2005), Curr Med Chem Cardiovasc Hematol Agents 3(4): 323-31.
Abstract: Systemic inflammatory response syndrome (SIRS) with activation of molecular cascades, cell activation, accumulation of interstitial fluid, organ dysfunction and, occasionally, organ failure is still a commonly recognized consequence of cardiac surgery. SIRS leads to costly complications and several strategies intended to ameliorate the symptoms that have been studied, including leukocyte reduction, using filtration. Although, the body of work suggests that leukoreduction attenuates SIRS, discrepancies remain within the literature. The recent literature is reviewed highlighting the areas where concordance is lacking. In our study, on the basis of indirect indicators of SIRS, platelet function by thromboelastography biomaterial evaluation by light and scanning electron microscopy, we present our conclusions regarding clinical outcomes and the role of leukofiltration.

Strategies and results of atomic force microscopy in the study of cellular adhesion
Simon, A. and M. C. Durrieu (2006), Micron 37(1): 1-13.
Abstract: Atomic Force Microscopy (AFM) provides a range of strategies for investigating living cell adhesion to the extracellular matrix, other cells or biomaterials in their native environment. This review surveys the results obtained from major studies using AFM for mechanical force evaluation in the cell, morphological visualization of the cell and studies of the cell's response to chemical or mechanical stress. Recently, the use of AFM has been broadened to obtain experimental information about cell adhesion molecules. Quantitative measurements of binding forces between adhesion proteins and their ligands in the cell or on a surface are presented. These analyses provide data on individual molecules and their resulting collective behaviour at the cell level. They significantly contribute to the characterisation of cellular adhesion with physical principles relating to biochemistry.

Strategies for biological testing of biomaterials
Northup, S. J. (1987), J Biomater Appl 2(1): 132-48.
Abstract: Current perspectives on empirical, modeling, and mechanistic methods of medical device safety testing are reviewed. Empirical approaches, such as the U.S. Pharmacopeial biological tests for plastics, evaluate the total system to discover aberrations and abnormalities. Models consist of a single aspect of an integrated approach, whereas mechanistic methods are based on a thorough knowledge of the materials and the organism's biological response. Empirical studies develop data on general hazard potential, such as overt toxicity. Model approaches target the specific application and specific hazard potential. Mechanistic studies identify the cause of toxicity and can produce advances in the biocompatibility of medical devices.

Streaming potential and streaming current measurements to estimate surface conduction and electric double layer structure of biomaterials
Voigt, A., R. Becker, et al. (1984), J Biomed Mater Res 18(3): 317-20.

Strength analysis of titanium and resorbable internal fixation in a mandibulotomy model
Ricalde, P., S. L. Engroff, et al. (2005), J Oral Maxillofac Surg 63(8): 1180-3.
Abstract: PURPOSE: Mandibulotomy is used to access various tumors of the tongue base, posterior oral cavity, pharynx, parapharyngeal space, and cranial base. Internal fixation using titanium plates and screws is the most common method of stabilization. These have the potential for interference with radiotherapy delivery. This in vitro study compares the strength of titanium and resorbable internal fixation in a mandibulotomy model by analyzing the force required for plate and screw breakage. MATERIALS AND METHODS: Red oak wood board was used to simulate the mandible. Titanium and resorbable plates and screws in various configurations were used to stabilize pieces of the wood. They were arranged in 6 different groups. The specimens were individually tested with a vertical load, while the test machine recorded the force-versus-displacement behavior automatically. RESULTS: Plate type and configuration affected the applied load required to induce displacement of the simulated mandibulotomy. Heating and cooling the resorbable plates prior to strength testing also affected the load-versus-displacement curve. CONCLUSIONS: Overall, the titanium system we studied exhibited greater resistance to deformation from a vertical load than did the resorbable plate groups.

Strengthening of calcium phosphate cement by compounding calcium carbonate whiskers
Kon, M., L. M. Hirakata, et al. (2005), Dent Mater J 24(1): 104-10.
Abstract: The purpose of this study was to investigate how aragonite (calcium carbonate) whiskers influenced the strengthening and carbonating of alpha-tricalcium phosphate (alpha-TCP) based calcium phosphate cement. Aragonite whiskers of 0.95 microm width with an aspect ratio of 6.6 were prepared. The cement powder, alpha-TCP containing 0-50 mass% aragonite whisker, was mixed with 0.6 mol/L NaH2PO4 solution and incubated at 37 degrees C and 100% relative humidity. Diametral tensile strength (DTS) value increased significantly when appropriate amount of aragonaite whiskers was added. For example, DTS value of set cement containing 20 mass% aragonite whisker was 5.8 +/- 0.5 MPa, whereas DTS value of set cement containing no whiskers was 1.3 +/- 0.2 MPa after 1-week incubation. SEM observation revealed that the shape of the whiskers and the densification of the structure could have contributed to the strengthening of the set cement. Moreover, FTIR spectra implied that a bone-like carbonated apatite was precipitated in the cement. The results obtained in the present study revealed that the shape as well as any slight dissolution of aragonite whiskers could contribute to improving the properties of a-TCP based calcium phosphate cement.

Structural and mechanical characteristics of silk fibroin and chitosan blend scaffolds for tissue regeneration
Gobin, A. S., V. E. Froude, et al. (2005), J Biomed Mater Res A 74(3): 465-73.
Abstract: The expanding field of tissue engineering has required the necessity of developing biomaterials that are tissue compatible, biodegradable, and comparable in mechanical properties to that of native tissue. We propose that the blending of two natural polymers, silk fibroin (SF) and chitosan (CS), into a 3D scaffold will provide unique chemical, structural, and mechanical properties that can be utilized for in vivo tissue regeneration. SF is an attractive material for biomedical applications because it is a fibrous protein that has high permeability to oxygen and water, relatively low thrombogenicity, low inflammatory response, protease susceptibility, supports cell adhesion and growth, and, foremost, high tensile strength with flexibility. CS is a crystalline polysaccharide, with structure similar to glycosaminoglycans, that has good wound healing properties, is nontoxic, and has minimal foreign body reactions. We hypothesized that increasing the SF-to-CS ratio would increase the ultimate tensile strength and elastic modulus and decrease the water capacity of the SFCS scaffolds. With increasing content of silk fibroin, it is observed that the ultimate tensile strength and elastic modulus increase significantly. The ultimate tensile strength and the elastic modulus were significantly higher in the short axis direction for 25:75 and 50:50 SFCS blends as compared to the long axis (p<0.05), while they were similar for the 75:25 SFCS blend. However, no differences were observed in the strain at failure among blends or due to directionality of applied strain. Increasing the chitosan content resulted in an increased water capacity of SFCS blends.

Structural and photocatalytic properties of TiO2 films fabricated on silicon substrates by MOCVD method
Yang, J. L., Y. Li, et al. (2005), J Environ Sci (China) 17(1): 146-51.
Abstract: Silicon (111) and Silicon(100) were employed for fabrication of TiO2 films by metal organic chemical vapor deposition(MOCVD). Titanium(IV) isopropoxide(Ti[O(C3H7)4]) was used as a precursor. The as-deposited TiO2 films were characterized with FE-SEM, XRD and AFM. The photocatalytic properties were investigated by decomposition of aqueous Orange II. And UV-VIS photospectrometer was used for checking the absorption characteristics and photocatalytic degradation activity. The crystalline and structural properties of TiO2 film had crucial influences on the photodegradation efficiency. For MOCVD in-situ deposited films on Si substrates, the photoactivities varied following a shape of "M": at lower(350 degrees C), middle(500 degrees C) and higher(800 degrees C) temperature of deposition, relative lower photodegradation activities were observed. At 400 degrees C and 700 degrees C of deposition, relative higher efficiencies of degradation were obtained, because one predominant crystallite orientation could be obtained as deposition at the temperature of two levels, especially a single anatase crystalline TiO2 film could be obtained at 700 degrees C.

Structural changes in pericardium tissue modified with tannic acid
Cwalina, B., A. Turek, et al. (2005), Int J Artif Organs 28(6): 648-53.
Abstract: INTRODUCTION: Structural modification of proteins, mainly collagen in connective tissues, is important in the manufacture of tissue-derived biomaterials. Natural compounds like genipin or tannic acid (TA) have been proposed instead of glutaraldehyde which shows cytotoxic effects on the processed tissue. Furthermore, calcification of glutaraldehyde-treated tissue limits the functional lifetime of bioprostheses. TA is known to form numerous hydrogen bonds with proteins. The purpose of our study was to investigate structural changes in porcine pericardium upon chemical modification with tannic acid. METHODS: Porcine pericardium tissue (PP) was soaked in 2% TA for 4, 24 or 48 hours. Changes in tissue structure were studied using electrophoresis (SDS-PAGE) and histological examination. Structural stability of PP tissue was evaluated by SDS/NaCl extraction method and enzymatic digestion with pancreatin. RESULTS: TA-modification of PP caused a time-dependent decrease in the number of peptides extracted from tissue. Microscopic studies revealed no significant morphological differences between native and TA-modified tissues, except for the native pancreatin-digested tissue where lack of both cells and low molecular peptides was observed. CONCLUSION: Modification of PP with TA causes the structural changes leading to an increase in the tissue resistance to SDS/NaCl extraction and enzymatic digestion, providing experimental evidence for the higher structural stability of TA-treated tissue.

Structural characteristics of impaction allografting for revision total hip arthroplasty
Robinson, M. C., G. Fernlund, et al. (2005), Clin Biomech (Bristol, Avon) 20(8): 853-5.
Abstract: BACKGROUND: The impaction allografting procedure for treatment of failed hip reconstructions has shown promising but variable results. The objective of this study was to compare the structural characteristics of revision total hip arthroplasty constructs with impaction allografting (cement+morsellized bone) with all-cement and all-morsellized bone constructs. METHODS: Uniaxial cyclic compression was applied to a simplified uniaxial, parallel, aluminum tube model to simulate normal gait. Applied force and axial stem displacement were recorded to determine stem subsidence and construct stiffness. FINDINGS: Introduction of a small amount of cement into the bone graft, as suggested in an impaction allografting procedure previously reported, makes the construct behave structurally more similar to an all-cemented construct than to an all-bone graft construct. INTERPRETATION: The results suggest that the structural properties achieved in an impaction allografting construct are sensitive to the amount of cement in the graft and that care should be taken clinically to achieve consistent constructs.

Structural characterization of a serendipitously discovered bioactive macromolecule, lignin sulfate
Raghuraman, A., V. Tiwari, et al. (2005), Biomacromolecules 6(5): 2822-32.
Abstract: The herpes simplex virus-1 (HSV-1) utilizes cell-surface glycosaminoglycan, heparan sulfate, to gain entry into cells and cause infection. In a search for synthetic mimics of heparan sulfate to prevent HSV infection, we discovered potent inhibitory activity arising from sulfation of a monomeric flavonoid. Yet, detailed screening indicated that the sulfated flavonoid was completely inactive and the potent inhibitory activity arose from a macromolecular substance present in the parent flavonoid. The active principle was identified through a battery of biophysical and chemical analyses as a sulfated form of lignin, a three-dimensional network polymer composed of substituted phenylpropanoid monomers. Mass spectral analysis of the parent lignin and its sulfated derivative indicates the presence of p-coumaryl monomers interconnected through uncondensed beta-O-4-linkages. Elemental analysis of lignin sulfate correlates primarily with a polymer of p-coumaryl alcohol containing one sulfate group. High-performance size exclusion chromatography shows a wide molecular weight distribution from 1.5 to 40 kDa suggesting significant polydispersity. Polyacrylamide gel electrophoresis (PAGE) analysis indicates a highly networked polymer that differs significantly from linear charged polymers with respect to its electrophoretic mobility. Overall, macromolecular lignin sulfate presents a multitude of substructures that can interact with biomolecules, including viral glycoproteins, using hydrophobic, hydrogen-bonding, and ionic forces. Thus, lignin sulfate represents a large number of interesting structures with potential medicinal benefits.

Structural characterization of self-assembled polypeptide films on titanium and glass surfaces by atomic force microscopy
Pelsoczi, I., K. Turzo, et al. (2005), Biomacromolecules 6(6): 3345-50.
Abstract: Chemically modified biomaterial surfaces (titanium and glass) covered with polyelectrolyte self-assembled films formed by the alternating adsorption of cationic poly-L-lysine (PLL) and anionic poly-L-glutamic acid (PGA) were structurally characterized by atomic force microscopy. Complementary information concerning the thickness and layer-by-layer growth of the films was provided by optical waveguide light-mode spectroscopy. The frequently used ex situ and the rarely used in situ build-up methods were compared. Important aspects of the industrial applicability of these films, their stability in time, and possible differences in their morphology were investigated. The films revealed a granular pattern, with grain diameters of 270 +/- 87 nm for glass (up to 8 bilayers) and 303 +/- 89 nm for titanium (up to 10 bilayers), independently of the build-up procedure. Both surfaces displayed a rehydration capability, the titanium surface exhibiting a better stability in time. The high roughness values observed at acidic or basic pH are related to the degree of ionization of PGA and PLL.

Structural dynamics and resonance in plants with nonlinear stiffness
Miller, L. A. (2005), J Theor Biol 234(4): 511-24.
Abstract: Although most biomaterials are characterized by strong stiffness nonlinearities, the majority of studies of plant biomechanics and structural dynamics focus on the linear elastic range of their behavior. In this paper, the effects of hardening (elastic modulus increases with strain) and softening (elastic modulus decreases with strain) nonlinearities on the structural dynamics of plant stems are investigated. A number of recent studies suggest that trees, crops, and other plants often uproot or snap when they are forced by gusting winds or waves at their natural frequency. This can be attributed to the fact that the deflections of the plant, and hence mechanical stresses along the stem and root system, are greatest during resonance. To better understand the effect of nonlinear stiffness on the resonant behavior of plants, plant stems have been modeled here as forced Duffing oscillators with softening or hardening nonlinearities. The results of this study suggest that the resonant behavior of plants with nonlinear stiffness is substantially different from that predicted by linear models of plant structural dynamics. Parameter values were considered over a range relevant to most plants. The maximum amplitudes of deflection of the plant stem were calculated numerically for forcing frequencies ranging from zero to twice the natural frequency. For hardening nonlinearities, the resonant behavior was 'pushed' to higher frequencies, and the maximum deflection amplitudes were lower than for the linear case. For softening nonlinearities, the resonant behavior was pushed to lower frequencies, and the maximum deflection amplitudes were higher than for the linear case. These nonlinearities could be beneficial or detrimental to the stability of the plant, depending on the environment. Damping had the effect of drastically decreasing deflection amplitudes and reducing the effect of the nonlinearities.

Structural studies of biomaterials using double-quantum solid-state NMR spectroscopy
Drobny, G. P., J. R. Long, et al. (2003), Annu Rev Phys Chem 54: 531-71.
Abstract: Proteins directly control the nucleation and growth of biominerals, but the details of molecular recognition at the protein-biomineral interface remain poorly understood. The elucidation of recognition mechanisms at this interface may provide design principles for advanced materials development in medical and ceramic composites technologies. Here, we describe both the theory and practice of double-quantum solid-state NMR (ssNMR) structure-determination techniques, as they are used to determine the secondary structures of surface-adsorbed peptides and proteins. In particular, we have used ssNMR dipolar techniques to provide the first high-resolution structural and dynamic characterization of a hydrated biomineralization protein, salivary statherin, adsorbed to its biologically relevant hydroxyapatite (HAP) surface. Here, we also review NMR data on peptides designed to adsorb from aqueous solutions onto highly porous hydrophobic surfaces with specific helical secondary structures. The adsorption or covalent attachment of biological macromolecules onto polymer materials to improve their biocompatibility has been pursued using a variety of approaches, but key to understanding their efficacy is the verification of the structure and dynamics of the immobilized biomolecules using double-quantum ssNMR spectroscopy.

Structural study of very thin anodic alumina films on silicon by anodization in citric acid aqueous solution
Kokonou, M., A. G. Nassiopoulou, et al. (2005), J Nanosci Nanotechnol 5(3): 454-8.
Abstract: The formation of thin alumina films on a silicon substrate by anodization in a mild acid, specifically in 1% wt citric acid aqueous solution, is investigated by transmission electron microscopy (TEM). We present a comparative study between two cases of starting material: pure aluminum and an alloy of aluminum with 1% silicon. In both cases the thickness of the Al layer was less than 50 nm. It was observed that under exactly the same conditions, in the first case the anodization was stopping before anodizing the whole film and a remaining non-anodized Al layer was always present, while in the second case, the Al layer was fully anodized, resulting in an alumina matrix with a very high density of silicon nanocrystals of uniform sizes embedded in it. In both cases the alumina film was compact and amorphous.

Structural, mechanical and in vitro characterization of individually structured Ti-6Al-4V produced by direct laser forming
Hollander, D. A., M. von Walter, et al. (2006), Biomaterials 27(7): 955-63.
Abstract: Direct laser forming (DLF) is a rapid prototyping technique which enables prompt modelling of metal parts with high bulk density on the base of individual three-dimensional data, including computer tomography models of anatomical structures. In our project, we tested DLF-produced material on the basis of the titanium alloy Ti-6Al-4V for its applicability as hard tissue biomaterial. To this end, we investigated mechanical and structural properties of DLF-Ti-6Al-4V. While the tensile and yield strengths of untreated DLF alloy ranged beyond 1000MPa, a breaking elongation of 6.5+/-0.6% was determined for this material. After an additional post-DLF annealing treatment, this parameter was increased two-fold to 13.0+/-0.6%, while tensile and yield strengths were reduced by approx. 8%. A Young's modulus of 118.000+/-2.300MPa was determined for post-DLF annealed Ti-6Al-4V. All data gained from tensile testing of post-DLF annealed Ti-6Al-4V matched American Society of Testing and Materials (ASTM) specifications for the usage of this alloy as medical material. Rotating bending tests revealed that the fatigue profile of post-DLF annealed Ti-6Al-4V was comparable to casted/hot isostatic pressed alloy. We characterized the structure of non-finished DLF-Ti-6Al-4V by scanning electron microscopy and observed a surface-associated layer of particles, which was removable by sandblasting as a finishing step. We manufactured porous specimens with nominal pore diameters of 500, 700 and 1000mum. The diameters were reduced by the used DLF processing by approx. 300mum. In an in vitro investigation, we cultured human osteoblasts on non-porous and porous blasted DLF-Ti-6Al-4V specimens to study morphology, vitality, proliferation and differentiation of the cells. The cells spreaded and proliferated on DLF-Ti-6Al-4V over a culture time of 14 days. On porous specimens, osteoblasts grew along the rims of the pores and formed circle-shaped structures, as visualized by live/dead staining as well as scanning electron microscopy. Overall, the DLF-Ti-6Al-4V approach proved to be efficient and could be further advanced in the field of hard tissue biomaterials.

Structure and reactivity of water at biomaterial surfaces
Vogler, E. A. (1998), Adv Colloid Interface Sci 74: 69-117.
Abstract: Molecular self association in liquids is a physical process that can dominate cohesion (interfacial tension) and miscibility. In water, self association is a powerful organizational force leading to a three-dimensional hydrogen-bonded network (water structure). Localized perturbations in the chemical potential of water as by, for example, contact with a solid surface, induces compensating changes in water structure that can be sensed tens of nanometers from the point of origin using the surface force apparatus (SFA) and ancillary techniques. These instruments reveal attractive or repulsive forces between opposing surfaces immersed in water, over and above that anticipated by continuum theory (DLVO), that are attributed to a variable density (partial molar volume) of a more-or-less ordered water structure, depending on the water wettability (surface energy) of the water-contacting surfaces. Water structure at surfaces is thus found to be a manifestation of hydrophobicity and, while mechanistic/theoretical interpretation of experimental results remain the subject of some debate in the literature, convergence of experimental observations permit, for the first time, quantitative definition of the relative terms 'hydrophobic' and 'hydrophilic'. In particular, long-range attractive forces are detected only between surfaces exhibiting a water contact angle theta > 65 degrees (herein defined as hydrophobic surfaces with pure water adhesion tension tau O = gamma O cos theta < 30 dyn/cm where gamma O is water interfacial tension = 72.8 dyn/cm). Repulsive forces are detected between surfaces exhibiting theta < 65 degrees (hydrophilic surfaces, tau O > 30 dyn/cm). These findings suggest at least two distinct kinds of water structure and reactivity: a relatively less-dense water region against hydrophobic surfaces with an open hydrogen-bonded network and a relatively more-dense water region against hydrophilic surfaces with a collapsed hydrogen-bonded network. Importantly, membrane and SFA studies reveal a discrimination between biologically-important ions that preferentially solubilizes divalent ions in more-dense water regions relative to less-dense water regions in which monovalent ions are enriched. Thus, the compelling conclusion to be drawn from the collective scientific evidence gleaned from over a century of experimental and theoretical investigation is that solvent properties of water within the interphase separating a solid surface from bulk water solution vary with contacting surface chemistry. This interphase can extend tens of nanometers from a water-contacting surface due to a propagation of differences in self association between vicinal water and bulk-phase water. Physicochemical properties of interfacial water profoundly influence the biological response to materials in a surprisingly straightforward manner when key measures of biological activity sensitive to interfacial phenomena are scaled against water adhesion tension tau O of contacting surfaces. As examples, hydrophobic surfaces (tau O < 30 dyn/cm) support adsorption of various surfactants and proteins from water because expulsion of solute from solution into the interphase between bulk solid and solution phases is energetically favorable. Adsorption to hydrophobic surfaces is driven by the reduction of interfacial energetics concomitant with replacement of water molecules at the surface by adsorbed solute (surface dehydration). Hydrophilic surfaces (tau O > 30 dyn/cm) do not support adsorption because this mechanism is energetically unfavorable. Protein-adsorbing hydrophobic surfaces are inefficient contact activators of the blood coagulation cascade whereas protein-repellent hydrophilic surfaces are efficient activators of blood coagulation. Mammalian cell attachment is a process distinct from protein adsorption that occurs efficiently to hydrophilic surfaces but inefficiently to hydrophobic surfaces. (ABSTRACT TRUNCATED)

First Page Previous Page Next Page Last Page

Last Modified: 8 February 2006