Surfaces For Biomedical Applications Research Articles

Polymer Brushes: Novel Surfaces for Biomedical Applications

Polymer brushes played an important role in surface modification techniques to improve the biocompatibility of modified surfaces inside the human body for different biological and biomedical applications. This modification give the ability to control biointerfacial interactions such as cell attachment, protein adsorption and bacterial biofilm formation. Surface modification with polymer layers can be utilized to alter the surface properties, including biocompatibility, antifouling ability, corrosion resistance and wettability, and it can be achieved by immobilisation or spraying of polymers from solution. Also, it is easy to graft polymers with reactive end groups onto surfaces leading to the formation of polymer brushes at high density, which have specific features, such as chemical robustness, tunable mechanical properties and the flexibility to use polymers of different chemistry or introduction of bifunctional polymers for specific immobilisation of other molecules, especially proteins and enzymes. The specific properties of polymer brushes make them ideal candidates to be used in the biomedical field. For example,

Al2O3 and Pt Atomic Layer Deposition for Surface Modification of NiTi Shape Memory Films

Pt coatings on NiTi film micro-actuators and/or sensors can add some useful properties, e.g., they may improve the NiTi anticorrosion and thermomechanical characteristics or activate surface properties beneficial for a specific application (e.g., functionalized surfaces for biomedical applications). Pt coatings prepared via atomic layer deposition (ALD) may help reduce cost due to the nanometric thickness. However, no authors have reported preparation of Pt ALD coatings on NiTi films, perhaps due to the challenge of the concurrent NiTi film oxidation during the Pt ALD process. In the present study, Al2O3 and Pt ALD coatings were applied to NiTi thin films. The ALD coating properties were studied using electron and atomic force microscopies and X-ray photoelectron spectroscopy (XPS). Potential structural changes of NiTi due to the ALD process were evaluated using electron microscopy and X-ray diffraction. The presented ALD process resulted in well-controllable preparation of Pt nanoparticles on ultrathin Al2O3 seed layer and a change of the transformation temperatures of the NiTi films.

Water-Based Scalable Methods for Self-Cleaning Antibacterial ZnO-Nanostructured Surfaces.

Bacterial colonization poses significant health risks, such as infestation of surfaces in biomedical applications and clean water unavailability. If maintaining the surrounding water clean is a target, developing surfaces with strong bactericidal action, which is facilitated by bacterial access to the surface and mixing, can be a solution. On the other hand, if sustenance of a surface free of bacteria is the goal, developing surfaces with ultralow bacterial adhesion often suffices. Here we report a facile, scalable, and environmentally benign strategy that delivers customized surfaces for these challenges. For bactericidal action, nanostructures of inherently antibacterial ZnO, through simple immersion of zinc in hot water, are fabricated. The resulting nanostructured surface exhibits extreme bactericidal effectiveness (9250 cells cm–2 h–1) that eliminates bacteria in direct contact and also remotely through the action of reactive oxygen species. Remarkably, the remote bactericidal action is achieved without the need for any illumination, otherwise required in conventional approaches. As a result, ZnO nanostructures yield outstanding water disinfection of >99.98%, in the dark, by inactivating the bacteria within 3 h. Moreover, Zn2+ released to the aqueous medium from the nanostructured ZnO surface have a concentration of 0.73 ± 0.15 ppm, markedly below the legal limit for safe drinking water (5–6 ppm). The same nanostructures, when hydrophobized (through a water-based or fluorine-free spray process), exhibit strong bacterial repulsion, thus substantially reducing bacterial adhesion. Such environmentally benign and scalable methods showcase pathways toward inhibiting surface bacterial colonization.

Microstructure and mechanical properties of titanium subjected to direct laser interference lithography

This study concerns a detailed cross-section microstructural analysis conducted by combining complementary methods such as FIB, SEM, EDS and STEM on different scales in order to elucidate the impact of direct laser interference lithography on the microstructure and surface chemistry of a Ti substrate after laser patterning. Special attention was paid to correlate the mechanical properties determined by the nanoindentation tests with the microstructure and phase composition analysed using GI-XRD. Direct laser interference lithography surface texturing results in the formation of a thin (1–1.5 μm), continuous layer with lath-like grains. The GI-XRD analysis showed no changes in phase composition, which is in agreement with our previous results. Furthermore, laser patterning led to an increase in the nano-hardness of the surface (from 2.8 GPa to 6.6 GPa) that is mainly related to the changes that took place in the microstructure. The results presented are important to an evaluation of laser-patterned surfaces in biomedical applications, as their ultimate use depends not only on topographical changes but also mechanical properties variations as well as microstructure evolution which affects its electrochemical properties.

Surface Deposition on Titania in a Physiological Solution with Ultraviolet Irradiation In Situ and Effect of Heat Treatment

Photocatalysis-enhanced surface deposition on titanium surfaces for biomedical applications is investigated in this work. Immersion tests of commercially pure titanium (CP-Ti) pieces in a simulated body fluid adding bovine serum albumin (BSA) under ultraviolet (UV) irradiation in situ are carried out. The morphologies of deposition are characterized by SEM and stereo imaging microscopy, and the quantity and composition of the deposition is examined by SEM, energy dispersive spectroscopy (EDS) and X-ray photoelectron spectroscopy. The results show a deposition layer with thickness 89 μm is produced on 600 °C heat-treated specimens. An irradiation pattern of lighting/dark repeated results in more deposition on heat-treated CP-Ti. It is confirmed that a mixture of anatase and rutile phases generated on 600 °C heat-treated specimens has enhanced photocatalysis. The decomposition of BSA by photocatalysis, a possible product of nitrite also results in enhanced deposition on Ti. EDS analysis shows large reduction of carbon in the deposition on UV-light exposed surfaces compared to no UV-light-exposed surfaces. Furthermore, C–H bond decreases and C–C, Ca–O, and P–O bond increases are found on photoactivated surfaces. The deposition produced by this method is expected to be useful for applications to biomaterials with high bioactivity.

Effect of plasma pretreatment on durability of sol-gel superhydrophobic coatings on laser modified stainless steel substrates

Superhydrophobic surfaces were generated on stainless steel SS 304 substrates, using a combination of physical as well as chemical modification of the surface and tested for use in biomedical applications. Nanosecond pulsed laser was used for physical modification, i.e. creating nanoscaled roughness on the substrates. An additional chemical modification was performed using fluorosilane-based sol-gel nanocomposite coatings to further improve the hydrophobicity. Presently, the key challenge that such surfaces face, is to possess a substantial durability. In this study, a surface activation technique such as plasma pre-treatment was adopted to improve the adhesion of coatings on the laser treated substrates. The coatings deposited using dip coating technique were cured at 150 °C. The surface morphology and the roughness of the processed substrates and the coated samples were characterized using Atomic Force Microscope and Scanning Electron Microscope. The wettability of the surface was monitored and evaluated throughout the study using water contact angle measurements. Weathering tests and scratch resistance measurements using a crockmeter were carried out to evaluate the durability, which revealed that the adhesion could be improved with plasma treatment of the laser textured substrates, prior to coating deposition. Maximum anti-bacterial activity of up to 90% towards the bacterial species Escherichia coli was found on the substrates coated with the fluorosilane-based superhydrophobic coatings for an exposure time of 30 min, without any addition of external anti-bacterial agents. Thus, the preliminary results obtained from the present investigation were found to be promising and were indicative of use of these surfaces for biomedical applications.

Nanostructure-Enabled and Macromolecule-Grafted Surfaces for Biomedical Applications.

Advances in nanotechnology and nanomaterials have enabled the development of functional biomaterials with surface properties that reduce the rate of the device rejection in injectable and implantable biomaterials. In addition, the surface of biomaterials can be functionalized with macromolecules for stimuli-responsive purposes to improve the efficacy and effectiveness in drug release applications. Furthermore, macromolecule-grafted surfaces exhibit a hierarchical nanostructure that mimics nanotextured surfaces for the promotion of cellular responses in tissue engineering. Owing to these unique properties, this review focuses on the grafting of macromolecules on the surfaces of various biomaterials (e.g., films, fibers, hydrogels, and etc.) to create nanostructure-enabled and macromolecule-grafted surfaces for biomedical applications, such as thrombosis prevention and wound healing. The macromolecule-modified surfaces can be treated as a functional device that either passively inhibits adverse effects from injectable and implantable devices or actively delivers biological agents that are locally based on proper stimulation. In this review, several methods are discussed to enable the surface of biomaterials to be used for further grafting of macromolecules. In addition, we review surface-modified films (coatings) and fibers with respect to several biomedical applications. Our review provides a scientific update on the current achievements and future trends of nanostructure-enabled and macromolecule-grafted surfaces in biomedical applications.

Visible light controls cell adhesion on a photoswitchable biointerface.

Bioactive surfaces with specific interactions with cells have been greatly interested due to their potential applications in biosensors and tissue engineering. Herein, we fabricated a dopamine contained photoswitch molecule (compound 1) which could form self-assembled monolayer (SAM) on substrates. The SAM showed a good photoswitch ability and manifested excellent fatigue resistance, which displayed its potential application as a biologically friendly surface coating. Contact angle analysis and cell experiments exhibited that the SAM surface was hydrophobic before irradiation which favored cell adhesion, while, it turned hydrophilic and induced cell unfouling or detachment after light irradiation. The uses of visible light stimulation (λex = 530 nm) and the reversible regulation on cell adhesion and detachment should open up new avenues for bioacitve surfaces in biomedical applications.

Surface Modified with a Host Defense Peptide-Mimicking β-Peptide Polymer Kills Bacteria on Contact with High Efficacy

Methicillin-resistant Staphylococcus aureus (MRSA) has been one of the major nosocomial pathogens to cause frequent and serious infections that are associated with various biomedical surfaces. This study demonstrated that surface modified with host defense peptide-mimicking β-peptide polymer, has surprisingly high bactericidal activities against Escherichia coli ( E. coli) and MRSA. As surface-tethered β-peptide polymers cannot move freely to adopt the collaborative interactions with bacterial membrane and are too short to penetrate the cell envelop, we proposed a mode of action by diffusing away the cell membrane-stabilizing divalent ions, Ca2+ and Mg2+. This hypothesis was supported by our study that Ca2+ and Mg2+ supplementation in the assay medium causes up to 80% loss of bacterial killing efficacy and that the addition of divalent ion chelating ethylenediaminetetraacetic acid into the above assay medium leads to significant recovery of the bacterial killing efficacy. In addition to its potent bacterial killing efficacy, the surface-tethered β-peptide polymer also demonstrated excellent biocompatibility by displaying no hemolysis and supporting mammalian cell adhesion and growth. In conclusion, this study demonstrated the potential of β-peptide polymer-modified surface in addressing nosocomial infections that are associated with various surfaces in biomedical applications.

A facile route to develop hydrophilicity on the polyolefin surface for biomedical applications

In this study, the surface of low-density polyethylene (LDPE) was functionalized with maleic anhydride (MA) using solution grafting method in the presence of benzoyl peroxide (BPO), an initiator. The surface chemistry of the grafted LDPE was characterized using different characterization tools. The effect of MA grafting for analysis of bulk properties such as the change in mechanical strength and thermal properties was studied. Further, the nanoindentation study was performed to analyze the surface mechanical property after MA grafting. Biocompatibility studies were carried out using NIH-3T3 cells through MTT assay test. FTIR analysis revealed the presence of carboxylic groups on LDPE surface. The contact angle value was found to be 44 ± 3°, which confirms the development of hydrophilicity in LDPE. Cell viability was found >75% in MTT assay. These results suggested that the prepared hydrophilic LDPE is a potential candidate for biomedical applications and surface coatings with other polar polymer.

A Review of Engineered Zirconia Surfaces in Biomedical Applications

Zirconia is widely used for load-bearing functional structures in medicine and dentistry. The quality of engineered zirconia surfaces determines not only the fracture and fatigue behaviour but also the low temperature degradation (ageing sensitivity), bacterial colonization and bonding strength of zirconia devices. This paper reviews the current manufacturing techniques for fabrication of zirconia surfaces in biomedical applications, particularly, in tooth and joint replacements, and influences of the zirconia surface quality on their functional behaviours. It discusses emerging manufacturing techniques and challenges for fabrication of zirconia surfaces in biomedical applications.

Investigation of human cell response to covalently attached RADA16-I peptide on silicon surfaces

We described a modification of the ionic (RADARADARADARADA)1 peptide or RADA16-I with 4-azidophenyl isothiocyanate via a specific and gentle reaction. The azidated peptide was covalently immobilized on an alkyne-terminated monolayer on Si(111) via the Cu(I)-catalyzed Huisgen 1,3-dipolar cycloaddition reaction. Detailed characterization using Impedance spectroscopy (IS), X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared (FTIR) spectroscopy demonstrated high coverage of the RADA 16-I peptide on silicon surfaces. Scanning electron microscopy (SEM) and methyl tetrazole sulfate (MTS) assay were used to characterize the morphology and proliferation ability of human fibroblast cells on surfaces. Cell adhesion assay was performed to examine cell-substrate interactions. Significant differences in fibroblast cell morphology, adhesion, and viability were observed on the RADA16-I peptide modified surfaces compared to the control surfaces. These results may suggest a potential application of RADA16-I peptide modified surfaces in biomedical applications.

Elevated temperature behaviour of Ti6Al4V sheets with thermo-electro-chemical modified surfaces for biomedical applications

Deformation at elevated temperature of Ti6Al4V sheets may represent a process route alternative to machining and Additive Manufacturing (AM) operations to produce biomedical implants characterized by a high surface-to-thickness-ratio. The paper investigates the mechanical and microstructural behaviour at elevated temperature of Ti6Al4V sheets whose surface was properly modified through thermo-electro-chemical processes to enhance the roughness, and therefore osseointegration, as well as bioactivity, to meet the requirements imposed by the specific biomedical application. After the surface characterization, tensile tests were carried out at different temperatures on samples modified on the surface in order to investigate the ductility, microstructure and micro-hardness after deformation and the effect of the surface treatments on them. The optimal surface treatment and deformation temperature were identified, which assured, at the same time, significant ductility increase compared to room temperature, and preservation of the roughness and bioactivity characteristics.

Structural and Viscoelastic Properties of Layer-by-Layer Extracellular Matrix (ECM) Nanofilms and Their Interactions with Living Cells.

Modulation of living cell surfaces by chemical and biological engineering and the control of cellular functions has enormous potential for immunotherapy, transplantation, and drug delivery. However, traditional detection techniques have limitations in the identification of physical properties of viscoelastic films and interaction with living cells in real time. Here, we present the structural analysis of extracellular matrix (ECM) based nanofilms and their interaction with living cells using a quartz crystal microbalance (QCM) with dissipation (QCM-D), multiple parameter surface plasmon resonance (SPR), and flow cytometry measurements. QCM-D measurements according to the Voigt-based viscoelastic model allowed for the evaluation of the kinetic adsorption of extracellular matrix (ECM) proteins and physical parameters of viscoelastic ECM-nanofilms in a swelled state. These results reflected the characteristics of viscoelastic films as compared to Sauerbrey's equation. Moreover, we found that gelatin molecules played a crucial role as a binder to build up layered films and control their properties. Using the multiple parameter SPR approach, we confirmed the interaction between FN-G nanofilms and living cells from signal response in real time which was different from the gold substrate-protein signal. Moreover, flow cytometry analysis supported the importance of the domain interaction between the RGD sequence in FN and integrin as a driving force to form the films on cell surfaces. The use of three different analyses supported clarification of the contribution of the protein-protein interaction and viscoelastic properties of ECM films and investigation of the interaction between films and living cells. The knowledge regarding protein-protein and protein-cell interaction in real time would make a contribution to biomaterial design by using protein interactions for modulating the living cell surfaces in biomedical applications.

Formability Characteristics of Hot Stamped Ti6Al4V Sheets Electro-Chemically Modified on Surface for Biomedical Applications

Over these last decades Ti6Al4V has been largely employed for biomedical applications because of its biocompatibility and high strength-to-weight ratio. According to several studies, the implantation success is strongly dependent on the characteristics of its surface, since the roughness and the chemical composition of the surface play an important role in the osseointegration of the implant and in its bioactivity, respectively.In this paper different thermo-electro-chemical treatments were applied to Ti6Al4V sheets to increase their roughness for biomedical applications. The Ti6Al4V sheets underwent three different treatments, namely acid etching, acid etching followed by anodization and etching in a hydrothermal reactor, and finally furnace annealing.After the etching and annealing treatments, the surface morphology of the samples were analysed through Scanning Electron Microscopy, while its chemical composition was identified through the Energy Dispersive Spectroscopy. The surface roughness and topography were evaluated by using a 3D profilometer. Furthermore, the bioactivity of the treated samples was evaluated by diving them in Simulated Body Fluid and then analysed through SEM and EDS analyses.Based on these results, the treatment assuring the best performance in terms of roughness and bioactivity was identified and then applied to tensile samples tested at 700°C and strain rates of 0.1 and 1s-1 to evaluate the impact of the surface treatment on the material formability and, therefore, to prove the feasibility of applying the hot stamping process to surface modified sheets.

Effects of Surface Cathode Properties on Biopolymer Structuring via Electrochemical Deposition

Electrochemical deposition is a versatile bottom up-approach for the realization of advanced surfaces in biomedical applications. Deposition of chitosan via cathodic polarization has been recently proposed as a simple, fast, and effective technique also for the preparation of cellular solids [1], by their peeling-off from the deposition substrate. Chitosan ((1,4)-linked 2-amino-2- deoxy-d-glucan) is a natural cationic polymer that has been widely applied in drug delivery and tissue engineering for its proven biocompatibility, biodegradability, and antibacterial properties. Its electrodeposition, based on transport phenomena and reduction reactions at the diffusion layer, offers a control of the process parameters through simple adjustment of processing time and applied potential. The morphology of the obtained structures, being in the range of interest for tissue engineering scaffolds, can be easily tuned by an appropriate selection of anionic species and their concentration. Here we show the effects of the selection of anionic species and the surface cathode properties on the morphology of deposited coatings in order to modulate the obtained porosity. Electrocoagulation processes strongly depend on local reduction at the cathode, in turn affected by the acid/base equilibrium in solution: we hence examined (i) different water-based acidic bath and (ii) surfaces with different overvoltages for the hydrogen evolution reaction. Different coating morphologies, in terms of pore size and interconnection, were obtained by modifying electrochemical bath composition and controlling the overvoltage for hydrogen evolution by selecting the proper substrate material and surface preparation. Gas evolution at the cathode surface determined the growth of pores in the deposit coatings and, depending on the process parameters, close vs. open porosities were observed. A mass increase of deposited chitosan by increasing pH was generally observed, even if this trend is not monotone by increasing the pH. An increase of film porosity has been, in fact, noticed by increasing the mass rate deposition and hydrogen evolution and entrapment in the deposited gels. The overall deposition process seems affected by different electrolytes mainly as a consequence of their acid/base equilibria. Porosity can also be tuned according to the surface properties of selected metallic substrates, based on the characteristic exchange current for hydrogen evolution reaction. An accurate control of this process, hence allows to modulate open vs. closed pore structures. The possibility of tuning surface morphology of this class of films paves the way for the design of a novel class of 3D structures supporting tissue engineering approach and advanced drug delivery.[1] L. Altomare, L. Draghi, R. Chiesa, L. De Nardo, Materials Letters 78 (2012) 18.

Hemocompatibility and anti-biofouling property improvement of poly(ethylene terephthalate) via self-polymerization of dopamine and covalent graft of lysine

Inspired by the composition of adhesive proteins in mussels, we used self-polymerized dopamine to form a thin and surface-adherent polydopamine layer onto poly(ethylene terephthalate) (PET) sheet, followed by covalently grafting lysine (Lys) to improve hemocompatibility and anti-biofouling property. The obtained surfaces were characterized by water contact angle measurements, attenuated total reflectance Fourier transform infrared spectroscopy, and X-ray photoelectron spectroscopy analysis. The results of platelet adhesion and protein adsorption tests showed that Lys-immobilized PET was endowed with improved resistance to nonspecific protein adsorption and platelet adhesion. Cell assay results showed that PET-g-Lys surface could greatly inhibit NIH 3T3 cell adhesion. These works provide a facile hemocompatible and anti-fouling surface for biomedical applications.

表面設計による付着制御とバイオマテリアルへの応用

表面設計による付着制御とバイオマテリアルへの応用

Surface modification of PDMS by surface-initiated atom transfer radical polymerization of water-soluble dendronized PEG methacrylate

The current paper reports the synthesis of a highly hydrophilic, antifouling dendronized poly(3,4,5-tris(2-(2-(2-hydroxylethoxy)ethoxy)ethoxy)benzyl methacrylate) (PolyPEG) brush using surface initiated atom transfer radical polymerization (SI-ATRP) on PDMS substrates. The PDMS substrates were first oxidized in H(2)SO(4)/H(2)O(2) solution to transform the Si-CH(3) groups on their surfaces into Si-OH groups. Subsequently, a surface initiator for ATRP was immobilized onto the PDMS surface, and PolyPEG was finally grafted onto the PDMS surface via copper-mediated ATRP. Various characterization techniques, including contact angle measurements, attenuated total reflection infrared spectroscopy, and X-ray photoelectron spectroscopy, were used to ascertain the successful grafting of the PolyPEG brush onto the PDMS surface. Furthermore, the wettability and stability of the PDMS-PolyPEG surface were examined by contact angle measurements. Anti-adhesion properties were investigated via protein adsorption, as well as bacterial and cell adhesion studies. The results suggest that the PDMS-PolyPEG surface exhibited durable wettability and stability, as well as significantly anti-adhesion properties, compared with native PDMS surfaces. Additionally, our results present possible uses for the PDMS-PolyPEG surface as adhesion barriers and anti-fouling or functional surfaces in biomedical applications.

Surface‐modified nanoparticles as a new, versatile, and mechanically robust nonadhesive coating: Suppression of protein adsorption and bacterial adhesion

The synthesis of surface-modified silica nanoparticles, chemically grafted with acrylate and poly(ethylene glycol) (PEG) groups, and the ability of the resulting crosslinked coatings to inhibit protein adsorption and bacterial adhesion are explored. Water contact angles, nanoindentation, and atomic force microscopy were used to characterize the cross-linked coatings. Coatings showed a high degree of hydrophilicity combined with a remarkable hardness and stiffness in the dry state. Adsorption of the small protein lysozyme from buffer solution on coated silica wafers decreased significantly with increasing grafting density of the PEG groups on the nanoparticles and was completely inhibited at 0.6 chains nm(-2). Coatings significantly reduced adhesion of Staphylococcus epidermidis HBH 276 in a parallel plate flow chamber with respect to bare glass (>90%), whereas adhesion of Pseudomonas aeruginosa AK1 was only marginally affected by the presence of the coating (<15%). Passage of an air-bubble resulted in almost complete detachment (>93%) of both strains from coated glass, indicating that the adhesion strength between both bacterial strains and the coated surface was significantly reduced by the grafted PEG groups. These coatings thus provide a new method to prepare mechanically robust films with nonadhesive properties that will be extremely useful for the design of biocompatible surfaces in biomedical applications.