Adsorption of chondroitin-4-sulphate and heparin onto titanium: effect of bovine serum albumin

Selective Electrochemical Capture and Release of Heparin Based on Amine-Functionalized Carbon/Titanium Dioxide Nanotube Arrays

Heparin (HEP) is a sulfated glycosaminoglycan that is a clinical anticoagulant agent. Commercially derived from porcine intestinal mucosa, HEP is challenging to separate from this complex biological mixture for additional purification. This study aimed to raise the purity of isolated HEP using electrochemical potential to increase its selective capture and release. We demonstrate an electrochemical platform featuring an anode composed of amine-functionalized carbon/titanium dioxide nanotube arrays on titanium foil (Ti/C-TNTAs-NH₂) and a cathode made of expanded graphite. Our results show that Ti and Ti/C-TNTAs control plates do not adsorb HEP, even while applying an external potential to the cell. However, when the Ti/C-TNTAs electrode is modified by 3 aminopropyltriethoxysilane, the terminal NH₂ groups provide a high density of positive charges that serve as binding sites, enabling the adsorption of HEP. This attraction is further strengthened by applying an external potential to the anode. Subsequent release of the HEP molecules and regeneration of the Ti/C-TNTAs-NH₂ electrode are easily accomplished by applying an anodic potential to the plate, as well as by increasing the concentration of NaCl in solution. This electrochemical system demonstrates the good selectivity of HEP, even within a mixture of other probable interfering species (e.g., bovine serum albumin and chondroitin sulfate). Additionally, it maintains 90.11% of its initial electrosorption efficiency after ten repeated HEP adsorption/desorption cycles, indicating this system's promising stability and reusability for HEP purification.

The use of electrochemical techniques to evaluate the corrosion performance of metallic biomedical materials and devices

The corrosion performance of metallic biomedical materials and devices is commonly evaluated using electrochemical techniques. Although test standards involving such techniques have been released to address some forms of corrosion, a key issue is application of the results with regard to use of an implantable device in vivo. This review focuses on nitinol, 316L/LVM stainless steel, and Co-Cr alloys and is intended to provide some perspective on the significance of results from tests concerning general corrosion, localized corrosion, galvanic corrosion, and fretting corrosion of these alloys in simulated physiological solutions. It also examines the factors that could cause differences in the corrosion performance between in vitro and in vivo exposure, with the goal of providing some rationale for applying electrochemical characteristics obtained from the tests to predict the corrosion performance in vivo. © 2018 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater 107B: 1189-1198, 2019.

Roughness induced dynamic changes of wettability of acid etched titanium implant modifications

Dynamic contact angle analysis (DCA) was used to investigate time-dependent wettability changes of sandblasted and acid-etched commercially pure (cp) titanium (Ti) implant modifications during their initial contact with aqueous systems compared to a macrostructured reference surface. Surface topography was analyzed by scanning electron microscopy and by contact stylus profilometry. The microstructured Ti surfaces were found to be initially extremely hydrophobic. This hydrophobic configuration can shift to a completely wettable surface behavior with water contact angles of 0 degrees after the first emersion loop during DCA experiments. It is suggested that a hierarchically structured surface topography could be responsible for this unexpected wetting phenomenon. Roughness spatial and hybrid parameters could describe topographical features interfering with dynamic wettability significantly better than roughness height parameters. The Ti modifications which shift very sudden from a hydrophobic to a hydrophilic state adsorbed the highest amount of immunologically assayed fibronectin. The results suggest that microstructuring greatly influences both the dynamic wettability of Ti implant surfaces during the initial host contact and the initial biological response of plasma protein adsorption. The microstructured surfaces, once in the totally wettable configuration, may improve the initial contact with host tissue after implantation, due to the drastically increased hydrophilicity.

Identification by integrated computer modeling and light scattering studies of an electrostatic serum albumin-hyaluronic acid binding site

Dynamic light scattering and turbidimetry, carried out on solutions of hyaluronic acid (HA) and bovine or human serum albumin (SA) at fixed ionic strength (I), revealed a critical pH corresponding to the onset of HA-SA soluble complex formation. Subsequent reduction of pH below pH(c), corresponding to an increase in protein net positive charge, results in phase separation of the complex. The sensitivity of pH(c) to I indicated the primacy of electrostatic interactions in this process. Since pH(c) was always above the pK(a) of HA, these effects could be attributed to the influence of protein charge. The electrostatic potential around HSA was modeled using DelPhi (MSI) under pH, I conditions corresponding to incipient binding, phase separation, and noninteraction. At all incipient binding conditions (i.e., pH(c), at varying I), an identical region of positive potential 5 A from the protein van der Waals surface appeared. This unique domain intensified with a decrease in pH or I (corresponding to stronger binding), and diminished with an increase in pH or I (i.e., at noninteracting conditions). The size and low curvature of this domain could readily accommodate a 12 nm (decamer) sequence of HA. Simple electrostatic considerations indicate an electrostatic binding energy for the formation of this complex of ca. 1 kT, consistent with the condition of incipient complex formation. We suggest that such weak electrostatic binding may characterize nonspecific interactions for other protein-gylcosaminoglycan pairs.

Inhibition of polarizing activity in the anterior limb bud is regulated by extracellular factors

Anterior-posterior patterning of the developing limb is largely viewed as a function of polarizing activity. Recent evidence in polydactylous mutants, however, indicates that development of proper pattern also requires the involvement of inhibitory pathways in the anterior limb that prevent secondary polarizing zone formation, thus limiting the number of digits produced. We report the novel finding that grafts of extracellular matrix from the Mouse Posterior Limb Bud-4 cell line can induce supernumerary digits, including digits with posterior phenotype, from anterior chick limb mesenchyme. Unlike previously described mechanisms of pattern specification during limb development, it is shown that the extracellular matrix effect is not associated with release of an active signal. Rather, evidence is presented suggesting that heparan sulfate moieties in extracellular matrix grafts bind an endogenous, extracellular factor involved in inhibition of anterior polarizing activity, leading to derepression of the anterior limb and induction of polarizing zone marker genes including Sonic hedgehog and Bone morphogenetic protein-2.

Effect of surface roughness of the titanium alloy Ti-6Al-4V on human bone marrow cell response and on protein adsorption

The effect of surface roughness of the titanium alloy Ti-6Al-4V (Ti alloy) on the short- and long-term response of human bone marrow cells in vitro and on protein adsorption was investigated. Three different values in a narrow range of surface roughness were used for the substrata (R(alpha): 0.320, 0.490 and 0.874 microm). Cell attachment, cell proliferation and differentiation (alkaline phosphatase specific activity) were determined past various incubation periods. The protein adsorption of bovine serum albumin and fibronectin, from single protein solutions, on rough and smooth Ti alloy surfaces was examined with two methods, X-ray photoelectron spectroscopy (XPS) and radiolabeling. Cell attachment and proliferation were surface roughness sensitive and increased as the roughness of Ti alloy increased. No statistically significant difference was observed in the expression of ALP activity on all three Ti alloy surfaces and culture plastic. Both methods, XPS and protein radiolabeling, showed that human serum albumin was adsorbed preferentially onto the smooth substratum. XPS technique showed that the rough substratum bound a higher amount of total protein (from culture medium supplied with 10% serum) and fibronectin (10-fold) than did the smooth one. The cell attachment may be explained by the differential adsorption of the two proteins onto smooth and rough Ti alloy surfaces.

Adsorption of drugs onto a poly(acrylic acid) grafted cation-exchange membrane

The influence of pH, ionic strength and the concentration of albumin in the adsorption medium as well as the charge and lipophilicity of a model drug on their adsorption onto poly(acrylic acid) grafted poly(vinylidene fluoride) (PAA-PVDF) membranes was evaluated. The PAA-PVDF membrane is a responsive porous polymer membrane that we have studied for controlled drug delivery. Sodium salicylate (anionic), flunitrazepam (neutral), primidone (neutral), desipramine (cationic) and thioridazine (cationic) were used as model drugs. The extent of drug adsorption was dependent on pH. Drug adsorption was enhanced by the dissociation of the grafted PAA chains and by a positive charge and a high lipophilicity of the drug. Increasing the ionic strength of the medium retarded the adsorption of the cationic drugs. Interestingly, the present results showing that drugs are adsorbed onto the membrane while albumin is not adsorbed onto the membrane suggest that the PAA-PVDF membrane may be suitable for separating drugs from proteinaceous substances for subsequent monitoring and evaluation.