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This method describes a novel approach to systematically investigate the effect of the fluid shear stress (FSS) on epithelial cells thanks to a single microfluidic device based on Hele-Shaw geometry. The method was validated with intestinal Caco-2 cell monolayers and lung A549 cells. We provide guidelines to adjust the experimental parameters to apply specific ranges of FSS and to specify more accurately the area where to image the cells within the device by the performance of a computational simulation of the fluid flow. Most importantly, this simulation enables to validate the equation. This approach was successfully applied to systematically investigate Caco-2 cell monolayers-based intestine-on-chip models as reported in a companion article published in Biomaterials. This study showed that exposure to microfluidic FSS induces significant phenotypical and functional changes. A detailed understanding of the effects of the FSS will enable the realization of in vitro organs-on-chip models with well-defined characteristics tailored to a specific purpose. The Hele-Shaw approach used in this study could be readily applied to other cell types and adapted for a wide range of physiologically relevant FSS.•Fluid shear stress is a key parameter in the differentiation of epithelial cells cultured in organ-on-chip models.•A simple approach can be used to assess the effect of fluid shear on cellular monolayer cultured in microfluidic devices.•Careful optimization of fluid shear stress environment is necessary for the development of better-defined organ-on-chip models.•Computational simulation of the fluid flow gives an accurate definition of the FSS in a microfluidic channel necessary to interpret the results., Graphical abstract Image, graphical abstract

Many highly effective chemotherapeutic agents can only be administered intravenously as their oral delivery is compromised by low gastro-intestinal solubility and permeability. SN-38 (7-ethyl-10-hydroxycamptothecin) is one such drug; however, recently synthesized lipophilic prodrugs offer a potential solution to the low oral bioavailability issue. Here we introduce a microfluidic-based intestine-on-A-chip (IOAC) model, which has the potential to provide new insight into the structure-permeability relationship for lipophilic prodrugs. More specifically, the IOAC model utilizes external mechanical cues that induce specific differentiation of an epithelial cell monolayer to provide a barrier function that exhibits an undulating morphology with microvilli expression on the cell surface; this is more biologically relevant than conventional Caco-2 Transwell models. IOAC permeability data for SN38 modified with fatty acid esters of different chain lengths and at different molecular positions correlate excellently with water-lipid partitioning data and have the potential to significantly advance their preclinical development. In addition to advancing mechanistic insight into the permeability of many challenging drug candidates, we envisage the IOAC model to also be applicable to nanoparticle and biological entities. Refereed/Peer-reviewed

Nanostructured field effect transistor (FET) based sensors have emerged as a powerful bioanalytical technology. However,performance variations across multiple devices and between fabrication batches inevitably exist and present a significant challenge holding back the translation of this cutting-edge technology. We reports an optimized and cost-effective fabrication process for high-performance indium oxide nanoribbon FET with a steep subthreshold swing of 80 mV/decade.Through systematic electrical characterizations of 57 indium oxide nanoribbon FETs from different batches, we demonstrate an optimal operation point within the subthrehold regime that mitigates the issue of device-to-device performance variation. A non-linear pH sensing of the fabricated indium oxide nanoribbon FETs is also presented. Refereed/Peer-reviewed

Bacteria in biofilms are more difficult to eradicate than planktonic bacteria and result in treatment challenges for many chronic infectious diseases. Nitric oxide (NO) is an endogenous molecule that offers potential as an alternative to conventional antibiotics; however its sustained topical delivery to biofilms is not readily achieved. With this in mind, we report the development of biodegradable poly(lactide-co-glycolide) (PLGA) based microparticles (MP) and nanoparticles (NP) for encapsulation of the NO precursor isosorbide mononitrate (ISMN) and the controlled delivery to Staphylococcus aureus (S. aureus) biofilms. Firstly, water-in-oil-in-water (w/o/w) emulsification/solvent evaporation methods for PLGA NP and MP syntheses were experimentally optimised with respect to particle size and ISMN loading/encapsulation efficiency. The influence of various experiment parameters, such as the volume of inner aqueous phase, concentration of surfactants, mixing time on the particle size, drug loading and encapsulation efficiency were investigated systematically. Both PLGA MP and NP formulations enabled sustained ISMN release in physiological media over 3 to 5 days. PLGA MP with diameters of ∼3 μm and ISMN loading of 2.2% (w/w) were identified as the optimum delivery system and demonstrated significant antibacterial activity in S. aureus biofilms. This behaviour is considered to be due to targeted biofilm delivery through a combination of effective penetration and sustained release of ISMN. Refereed/Peer-reviewed

Currently, it remains challenging to count protein-biomarker molecules present in a small droplet of biological samples. Herein, we propose a gold nanoparticle (GNP) probe-assisted sandwich-counting strategy that relies on a GNP probe, an antibody-functionalized chip to “count” antigen molecules using a scanning electron microscope. Both standard carcinoembryonic antigen (CEA) and two real CEA-related tumor samples (tumor tissues and serum) were assayed to demonstrate the proof-of-concept of the counting strategy. Results show that our method is excellently correlative with enzyme-linked immuno-sorbent assay (ELISA) that is widely used in clinics for antigen or antibody detection and the limit of detection of our enumeration strategy reaches down to 0.045 ng/mL, which is ∼40 times more sensitive than the conventional ELISA. Therefore, our GNP probe-assisted sandwich-counting strategy has the potential to be used for quantification of protein biomarkers at ultralow concentrations in early tumor specimens and detection of target proteins in much diluted concentrations. Refereed/Peer-reviewed

© 2019 by the authors. Licensee MDPI, Basel, Switzerland. Surface plasmon enhanced light scattering (SP-LS) is a powerful new sensing SPR modality that yields excellent sensitivity in sandwich immunoassay using spherical gold nanoparticle (AuNP) tags. Towards further improving the performance of SP-LS, we systematically investigated the AuNP size effect. Simulation results indicated an AuNP size-dependent scattered power, and predicted the optimized AuNPs sizes (i.e., 100 and 130 nm) that afford extremely high signal enhancement in SP-LS. The maximum scattered power from a 130 nm AuNP is about 1700-fold higher than that obtained from a 17 nm AuNP. Experimentally, a bio-conjugation protocol was developed by coating the AuNPs with mixture of low and high molecular weight PEG molecules. Optimal IgG antibody bioconjugation conditions were identified using physicochemical characterization and a model dot-blot assay. Aggregation prevented the use of the larger AuNPs in SP-LS experiments. As predicted by simulation, AuNPs with diameters of 50 and 64 nm yielded significantly higher SP-LS signal enhancement in comparison to the smaller particles. Finally, we demonstrated the feasibility of a two-step SP-LS protocol based on a gold enhancement step, aimed at enlarging 36 nm AuNPs tags. This study provides a blue-print for the further development of SP-LS biosensing and its translation in the bioanalytical field.

The therapeutic ratio of radiotherapy is limited by acute or chronic side effects with often severe consequences to patients. The microvasculature is a central player involved in both tumor responses and healthy tissue/organ radiological injuries. However, current preclinical vascular models based on 2D culture offer only limited radiobiological insight due to their failure in recapitulating the 3D nature experienced by endothelial cells within the human microvasculature. To address this issue, the use of a3D microvasculature-on-a-chip microfluidic technology is demonstrated in radiobiological studies. Within this vasculogenesis model a perfusable network that structurally mimics the human microvasculature is formed and the biological response to ionizing radiation including cellular apoptosis,vessel tight adherens junction breakage, DNA double strand break,and repair is systematically investigated. In comparison to cells grownin a 2D environment, human umbilical vein endothelial cells in the 3Dmicrovasculature-on-a-chip displays significant differences in biological responses, especially at high X-ray dose. This data confirms the feasibility of using microvascular-on-a-chip models for radiobiological studies.Such vasculogenesis models have strong potential to yield more accurate prediction of healthy tissue responses to ionizing radiation as well as to guide the development of risk-reducing strategies to prevent radiation-induced acute and long-term side-effects. Refereed/Peer-reviewed

Accuracy of sentinel lymph node identification using radioactive tracers in non-superficial cancers can be limited by radiation shine through and low spatial resolution of detection systems such as intraoperative gamma probes. By utilising a dual radioactive/magnetic tracer, sensitive lymphoscintigraphy can be paired with high spatial resolution intraoperative magnetometer probes to improve the accuracy of sentinel node detection in cancers with complex multidirectional lymphatic drainage. Dextran-coated magnetite nanoparticles (33 nm mean hydrodynamic diameter) were labelled with 99mTc and applied as a lymphotropic tracer in small and large animal models. The dual tracer could be radiolabelled with 98 ± 2% efficiency after 10 min of incubation at room temperature. Biodistribution studies of the tracer were conducted in normal rats (subdermal and intravenous tail delivery, n = 3) and swine (subdermal hind limb delivery, n = 5). In rats the dual tracer migrated through four tiers of lymph node, 20 min after subdermal injection. Results from intravenous biodistribution test for radiocolloids demonstrated no aggregation in vivo, however indicated the presence of some lower-molecular weight radioactive impurities (99mTc-dextran). In swine, the dual tracer could be effectively used to map lymphatic drainage from hind hoof to popliteal and inguinal basins using intraoperative gamma and magnetometer probes. Of the eight primary nodes excised, eight were positively identified by gamma probe and seven by magnetometer probe. The high-purity dual tracer shows early promise for sentinel node identification in complex lymphatic environments by combining sensitive preoperative lymphoscintigraphy with a high-resolution intraoperative magnetometer probe.

While noninvasive prenatal testing based on cell‐free fetal DNA has recently revolutionized the field of aneuploidy screening in pregnancy, it remains limited to aneuploidy and microdeletion screening, and is unable to reliably detect single gene disorders. A number of recent studies have demonstrated the potential of circulating trophoblastic cells in providing cell‐based noninvasive diagnosis with sequencing or array‐based assays. However, considering the extreme rarity of these cells in blood, efficient, high‐throughput, and clinically applicable enrichment technologies are yet to be developed. This study demonstrates for the first time the utility of inertial microfluidics for efficient isolation of trophoblastic cells from maternal peripheral blood. Under optimal operating conditions, high‐recovery yields (79%) are obtained using a trophoblastic cell‐line, which is subsequently confirmed with analysis of maternal blood. Feasibility of obtaining a diagnosis from cells isolated from a maternal sample is demonstrated in a case of confirmed fetal trisomy 21 in which six fetal cells are found in a 7 mL blood sample using fluorescence in situ hybridization. Finally, it is demonstrated that trophoblastic cells isolated using inertial microfluidics could be picked and subjected to a clinically validated sequencing assay, paving the way for further validation of this technology and larger clinical studies. Refereed/Peer-reviewed

Owing to their two-dimensional confinements, silicon nanowires display remarkable optical, magnetic, and electronic properties. Of special interest has been the development of advanced biosensing approaches based on the field effect associated with silicon nanowires (SiNWs). Recent advancements in top-down fabrication technologies have paved the way to large scale production of high density and quality arrays of SiNW field effect transistor (FETs), a critical step towards their integration in real-life biosensing applications. A key requirement toward the fulfilment of SiNW FETs' promises in the bioanalytical field is their efficient integration within functional devices. Aiming to provide a comprehensive roadmap for the development of SiNW FET based sensing platforms, we critically review and discuss the key design and fabrication aspects relevant to their development and integration within complementary metal-oxide-semiconductor (CMOS) technology. Refereed/Peer-reviewed

A robust and flexible approach is described for the straightforward preparation of multicellular tumor spheroids of controllable dimensions. The approach is based on a one-step plasma polymerization of the monomer allylamine carried out through conformal micropatterning physical masks that is used to deposit amine-rich (PolyAA) micrometer-scale features that promote cellular attachment and initiate the formation of multicellular spheroids. A simple backfilling step of the nonpolymerized poly- (dimethylsiloxane) background with Pluronic F127 significantly reduced background cellular adhesion on the untreated substrate and, in turn, improved the quality of the spheroid formed. Tumor cells grown on the PolyAA/F127 patterned surfaces reliably formed multicellular spheroids within 24−48 h depending on the cell type. The dimension of the spheroids could be readily controlled by the dimension of the amine-rich micropatterns. This simple approach is compatible with the long-term culture of multicellular spheroids and their characterization with high-resolution optical microscopy. These features facilitate the development of on-chip assays, as demonstrated here for the study of the binding of transferrin-functionalized gold nanoparticles to multicellular tumor spheroids. Refereed/Peer-reviewed

Optical coherence tomography (OCT) is a non-invasive interferometry imaging technique with micrometre scale resolution at millimetre scale penetration depths in highly scattering tissues. This study describes a new evolution of OCT, termed molecular optical coherence phase microscopy (molecular OCPM), which is capable of imaging the expression of molecular markers at the cellular level using gold nanorods as photothermal imaging agents. Gold nanorods were selected as the imaging agents due to their excellent photothermal energy conversion efficiency and tuneable plasmon bands. The gold nanorods were surface functionalized to achieve efficient and specific targeting of the tyrosine kinase human epidermal growth factor receptor HER2 molecular markers used as a model tumor biomarker. Phase modulation retrieval was used to generate photothermal maps which were overlayed on intensity images. Phase modulation within the filter corresponding to the laser excitation modulation frequency was clearly observed for cells targeted with the molecular photothermal imaging agents. These results confirm the ability of photothermal optical coherence phase microscopy to image accurately at the cellular level gold nanorods molecularly targeted to a biomarker expressed on cancer cell membranes, paving the way for its application to novel bioimaging procedures. Refereed/Peer-reviewed

We report a new and controlled top-down fabrication process to prepare locally thinned down silicon nanowire field-effect devices at wafer-scale. In this process, a low temperature size reduction method based on optimized tetramethylammonium hydroxide wet-etching has been developed on silicon (100) to yield slow (~0.5 nm s-1) and controllable etching speed as well as an ultra-smooth silicon surface morphology (rms ~0.15 nm). Combined with electron beam lithography, arrays of monocrystalline silicon nanowires with locally confined thicknesses down to sub-20 nm, lateral dimensions of 150 nm, and lengths of 10 um were reliably prepared and used. This novel fabrication process provides an alternative route for the fast and reliable preparation of ultrathin silicon nanostructures that can be easily integrated into nanodevices. Refereed/Peer-reviewed

A robust analysis script was developed in MATLAB for cross-correlative quantification of internalised gold nanoparticle (AuNP) uptake in a large number of individual cells with the corresponding number of DNA double-strand breaks (DSBs) in the same cells. The correlation of inorganic NP content with a biological marker at the single-cell level will aid in the elucidation of mechanisms of NP radiosensitisation. PC-3 cells were co-cultured with AuNPs and irradiated using an iridium-192 source. AuNP uptake was measured using synchrotron X-ray fluorescence (XRF) and DSBs imaged via confocal microscopy. MATLAB 2016a was used to develop a script to cross-correlate the two imaging modalities and quantify both DSBs and internalised AuNP content in the same cell. Various user-defined options written into the script give a high degree of versatility, which can account for a large number of variables in experimental parameters and data acquisition. The analysis procedure is flexible and robust, which gives consistent consideration to the wide spectrum of potential input image/data sets. Quantitative correlative microscopy was achieved with a custom MATLAB script used to correlate γH2AX foci (a marker of DNA DSBs) from confocal microscopy with AuNP content acquired using synchrotron XRF at the single-cell level. The script can be extended to a broad range of multi-modality imaging spectroscopies. Refereed/Peer-reviewed

The development of simple yet ultrasensitive biosensing approaches for the detection of cancer prognostic microRNA is an important step toward their successful clinical PEG implementation. We demonstrate the relevance for the detection of circulating miRNA of a novel signal amplification scheme based on surface plasmon resonance enhanced light scattering (SP-LS). In addition to experimental optimization carried out using gold nanoparticle (AuNP) tags conjugated with a monoclonal antibody with high affinity for RNA*DNA hybrid duplexes, simulation modeling was conducted to obtain insights about SP-LS biosensing. SP-LS enabled the detection of miRNA-122 at subpicomolar concentrations within 30 min, and a limit of detection of 2 attomoles (60 fM, 50 mu L) was determined. MiRNA-122 could also be reliably detected in a high concentration background of nontarget miRNA. The proposed SP-LS miRNA detection approach could be readily applied to other miRNA targets of diagnostic importance and further developed to allow for multiplex measurements of miRNA panels. The promising results obtained in this study and advantageous features of SP-LS warrant further development and its application to clinical samples. Refereed/Peer-reviewed

Polysaccharides form an important class of natural polymers with critical structural functions and biological activities in plants and all living organisms. It comes as no surprise that polysaccharides are key players in the area of biomaterials, where they have found applications in fi elds as diverse as drug delivery, tissue engineering and regenerative medicine, biosensing and biodiagnostics. Nonetheless, in the early phase of polyelectrolyte multilayers development, up to ~2002, there were only a few studies of layer-by-layer (LbL) assemblies containing polysaccharides. These natural polymers, intrinsically, are more difficult to handle than synthetic polymers or proteins that can be defined precisely in terms of structure, architecture, and molecular weight. Polysaccharides consist of carbohydrate units linked by glycosidic bonds and occur naturally with a range of molecular weights. Specific substituents, such as hydroxyls, sulfates, carboxylates, and amines linked to the glycoside rings, directly control the physicochemical and biological properties of polysaccharides. They also affect the multilayer assembly process, often in unpredictable ways. In addition, polysaccharides undergo facile degradation in strong acidic or alkaline environments. Hence, the multilayer construction conditions need to be selected carefully in order to avoid undesired side-reactions.

In this investigation, for the first time we report the effects of pH on the molecular orientation, packing density, structural properties, adsorption characteristics and viscoelastic behaviour of resilin-mimetic protein rec1 - resilin at the solid–liquid interface using quartz crystal microbalance with dissipation monitoring (QCM-D) and surface plasmon resonance (SPR) spectroscopy. QCM-D and SPR data confirm that the binding ability of rec1 - resilin on a substrate is strongly pH-dependent the protein packing density on a gold surface is calculated to be 4.45 × 10 13 per cm 2 at the isoelectric point (IEP ∼ 4.9), 8.79 × 10 11 per cm 2 at pH 2 and 9.90 × 10 11 per cm 2 at pH 12, respectively. Our findings based on the thickness, dissipation and viscoelasticity of the rec1 - resilin adlayer also indicate that it is adsorbed onto the gold substrate with different orientation depending on pH, such as back-on adsorption at acidic pH of 2, compact end-on bilayer adsorption at the IEP and side-on at high alkaline pH of 12. When rec1 - resilin is ‘pinned’ to the substrate at IEP and subsequently exposed to an electrolyte solution adjusted to different pH, it switches from a compact globular conformation of the bio-macromolecule at the IEP to a coil conformation at pH between IEP to IED (IED = pKa value of tyrosine amino acid residue) and an extended coil conformation at pH > IED. This transformation from globule to coil to extended coil conformation is kinetically fast, robust and completely reversible. Such responsive surfaces created using ‘smart’ biomimetic rec1 - resilin have the potential to find applications in many areas including biotechnology, medicine, sensors, controlled drug delivery systems and engineering.

Conjugation of PEGylated superparamagnetic nanoparticles with the 3B9 mAb was reported and the specificity of reactions of these novel molecular hybrid medical resonance imaging (MRI) nanoprobes with apoptotic cells was examined. The PEGylated nanoparticles were activated with EDC/NHS and conjugated either with 3B9 or Sal5, an isotype-matched mAb of irrelevant specificity, to achieve immunotargeting. It is found that solvent-free PRGylation process produces nanoparticle aggregates that average 67 mm in diameter with a narrow polydispersity. Antibody immobilization is confirmed by the observation of frequency and dissipation shifts, which are observed after injection of a 100μg/mL 3B9 mAb solution into the flow cell. The concentration of 3B9-nnaoparticles required to reach half saturation is found to be equivalent to 0.65mM of Fe, which corresponds to 7.8nM 3B9 mAb.

Gold nanoparticle (AuNP) molecular tags yield a significant signal enhancement in SPR-based immunoassays. While the structure functions of the AuNP tags have been exhaustively investigated, the roles of the evanescent field intensity and distribution remains to be elucidated. Long range surface plasmon resonance (LRSPR) possesses significantly larger fields and longer penetration depth than conventional SPR (cSPR). We report here on the optimization of AuNP tag LRSPR signal enhancement immunoassays using both theoretical simulations built using the finite element method and experimental measurements. A model sandwich immunoassay for the carcinoembryonic antigen (CEA) was then used to demonstrate the feasibility of AuNP tag enhanced LRSPR. The experimental measurements were in excellent agreement with the theoretical model and up to 50-fold improvement in sensitivity was obtained when using 50 nm AuNP tags in comparison to label-free LRSPR. However, the benefit of AuNP tag signal amplification approaches was found to be greater for cSPR than for LRSPR. Refereed/Peer-reviewed

Within an hour, as little as one disseminated tumor cell (DTC) per lymph node can be quantitatively detected using an intraoperative biosensing platform based on silicon nanowire field-effect transistors (SiNW FET). It is also demonstrated that the integrated biosensing platform is able to detect the presence of circulating tumor cells (CTCs) in the blood of colorectal cancer patients. The presence of DTCs in lymph nodes and CTCs in peripheral blood is highly significant as it is strongly associated with poor patient prognosis. The SiNW FET sensing platform out-performed in both sensitivity and rapidity not only the current standard method based on pathological examination of tissue sections but also the emerging clinical gold standard based on molecular assays. The possibility to achieve accurate and highly sensitive analysis of the presence of DTCs in the lymphatics within the surgery time frame has the potential to spare cancer patients from an unnecessary secondary surgery, leading to reduced patient morbidity, improving their psychological wellbeing and reducing time spent in hospital. This study demonstrates the potential of nanoscale field-effect technology in clinical cancer diagnostics. Refereed/Peer-reviewed

Membrane-covered devices could help treat disease of the vasculature such as aneurysm, rupture, and fistulas. They are also investigated to reduce embolic complication associated with revascularization of saphenous vein graft. The aim of this study is to design a clinically applicable biodegradable membrane-covered stent based on the natural polysaccharide chitosan, which has been developed. The mechanical properties of the membrane is optimized through blending with polyethylene oxide (70:30% Wt CH:PEO). The membrane was able to sustain the mechanical deformation of the supporting self-expandable metallic stents during its deployment. The membrane was demonstrated to resist physiological transmural pressure (burst pressure resistance >500 mm Hg) and presented a high-water permeation resistance (1 mL/cm(2) min(-1) at 120 mmHg). The CH-PEO membrane showed a good hemocompatibility in an ex vivo assay. Heparin and hyaluronan surface complexation with the membrane further reduced platelet adhesion by 50.1 and 63% (p = 0.05). The ability of the membrane-covered devices to be used as a drug reservoir was investigated using the nitric oxide donor sodium nitroprusside (SNP). SNP-loaded membranes displayed significantly reduced platelet adhesion.

Layer-by-layer self-assembly of two polysaccharides, hyaluronan (HA) and chitosan (CH), was employed to engineer bioactive coatings for endovascular stents. A polyethyleneimine (PEI) primer layer was adsorbed on the metallic surface to initiate the sequential adsorption of the weak polyelectrolytes. The multilayer growth was monitored using a radiolabeled HA and shown to be linear as a function of the number of layers. The chemical structure, interfacial properties, and morphology of the self-assembled multilayer were investigated by time-of-flight secondary ions mass spectrometry (ToF-SIMS), contact angle measurements, and atomic force microscopy (AFM), respectively. Multilayer-coated NiTi disks presented enhanced antifouling properties, compared to unmodified NiTi disks, as demonstrated by a decrease of platelet adhesion in an in vitro assay (38% reduction; p = 0.036). An ex vivo assay on a porcine model indicated that the coating did not prevent fouling by neutrophils. To assess whether the multilayers may be exploited as in situ drug delivery systems, the nitric-oxide-donor sodium nitroprusside (SNP) was incorporated within the multilayer. SNP-doped multilayers were shown to further reduce platelet adhesion, compared to standard multilayers (40% reduction). When NiTi wires coated with a multilayer containing a fluorescently labeled HA were placed in intimate contact with the vascular wall, the polysaccharide translocated on the porcine aortic samples, as shown by confocal microscopy observation of a treated artery. The enhanced thromboresistance of the self-assembled multilayer together with the antiinflammatory and wound healing properties of hyaluronan and chitosan are expected to reduce the neointimal hyperplasia associated with stent implantation.

Current 'gold standard' staging of breast cancer and melanoma relies on accurate in vivo identification of the sentinel lymph node. By replacing conventional tracers (dyes and radiocolloids) with magnetic nanoparticles and using a handheld magnetometer probe for in vivo identification, it is believed the accuracy of sentinel node identification in non-superficial cancers can be improved due to increased spatial resolution of magnetometer probes and additional anatomical information afforded by MRI road-mapping. By using novel iron core/iron oxide shell nanoparticles, the sensitivity of sentinel node mapping via MRI can be increased due to an increased magnetic saturation compared to traditional iron oxide nanoparticles. A series of in vitro magnetic phantoms (iron core vs. iron oxide nanoparticles) were prepared to simulate magnetic particle accumulation in the sentinel lymph node. A novel handheld magnetometer probe was used to measure the relative signals of each phantom, and determine if clinical application of iron core particles can improve in vivo detection of the sentinel node compared to traditional iron oxide nanoparticles. The findings indicate that novel iron core nanoparticles above a certain size possess high magnetic saturation, but can also be produced with low coercivity and high susceptibility. While some modification to the design of handheld magnetometer probes may be required for particles with large coercivity, use of iron core particles could improve MRI and magnetometer probe detection sensitivity by up to 330 %. Refereed/Peer-reviewed

The integration of microfluidics with living biological systems has paved the way to the exciting concept of 'organson-a-chip', which aims at the development of advanced in vitro models that replicate the key features of human organs. Glass based devices have long been utilised in the field of microfluidics but the integration of alternative functional elements within multi-layered glass microdevices, such as polymeric membranes, remains a challenge. To this end, we have extended a previously reported approach for the low-temperature bonding of glass devices that enables the integration of a functional polycarbonate porous membrane. The process was initially developed and optimised on specialty low-temperature bonding equipment (μTAS2001, Bondtech, Japan) and subsequently adapted to more widely accessible hot embosser units (EVG520HE Hot Embosser, EVG, Austria). The key aspect of this method is the use of low temperatures compatible with polymeric membranes. Compared to borosilicate glass bonding (650 °C) and quartz/fused silica bonding (1050 °C) processes, this method maintains the integrity and functionality of the membrane (Tg 150 °C for polycarbonate). Leak tests performed showed no damage or loss of integrity of the membrane for up to 150 hours, indicating sufficient bond strength for long term cell culture. A feasibility study confirmed the growth of dense and functional monolayers of Caco-2 cells within 5 days. Refereed/Peer-reviewed

Acute and subacute stents thrombosis along with thrombus mediating neointimal proliferation within the stent struts remain major concerns in coronary stenting. Up to date, there is an obvious lack of data on the thrombogenicity of stent materials in physiological conditions. This study was performed to compare the relative thrombogenicity of nitinol versus stainless steel stents. Nitinol stents were laser cut to reproduce the exact geometry of the stainless steel Palmaz stents and tested in an ex vivo AV shunt porcine model under controlled conditions. Nitinol stents presented only small amounts of white and/or red thrombus principally located at the strut intersections while Palmaz stents clearly exhibited more thrombus. As a result, 125I-fibrin(ogen) adsorption and (111)I-platelets adhesion were significantly lower on nitinol than on stainless steel devices (36%, p = 0.03 for fibrin(ogen) and 63%, p = 0.01 for platelet). These results were confirmed by scanning electron observations showing different thrombus morphologies for nitinol and stainless steel. Along with the unique mechanical properties of nitinol, its promising haemocompatibility demonstrated in our study may promote their increasing use for both peripheral and coronary revascularization procedures.

Aim: To evaluate the potential of newly-developed, biocompatible iron oxide magnetic nanoparticles (MNPs) conjugated with J591, an antibody to an extracellular epitope of PSMA, to enhance MRI of prostate cancer. Materials & methods: Specific binding to PSMA by J591-MNP was investigated in vitro. MRI studies were performed on orthotopic tumor-bearing NOD.SCID mice 2 h and 24 h after intravenous injection of J591-MNPs, or non-targeting MNPs. Results & conclusion: In vitro, MNPs did not affect prostate cancer cell viability, and conjugation to J591 did not compromise antibody specificity and enhanced cellular iron uptake. Magnetic resonance contrast of tumors was increased in vivo using PSMA-targeting MNPs, but not by non-targeting MNPs. This provides proof-of-concept that PSMA-targeting MNPs have potential to enhance magnetic resonance detection/localization of prostate cancer.

A novel approach based on advanced micromachining is demonstrated to fabricate concave microwell arrays for the formation of high quality multicellular tumor spheroids. Microfabricated molds were prepared using a state-of-the-art CNCmachining center, containing arrays of 3D convex micropillars withsize ranging from 150 μm to 600 μm. Microscopic imaging of themicropillars machined on the mold showed smooth, curved microfeatures of a dramatic 3D shape. Agarose microwells could be easily replicated from the metallic molds. EMT-6 tumor cells seeded in the primary macrowell sedimented efficiently to the bottom of the concave microwells and formed multicellular spheroidswithin 48 h. Dense and homogeneous multicellular spheroids were obtained after 10 days of culture, confirming the suitability ofthe proposed approach. To facilitate long term spheroid culture and reliable on-chip drug assay, polydimethylsiloxane microwells were also replicated from the metallic molds. A solvent swelling method was adapted and optimized to Pluronic F127 towardsphysically entrapping the block copolymer molecules within the polydimethylsiloxane network and in turn to improve long termcell-binding resistance. Homogeneous multicellular spheroids were efficiently formed in the concave microwells and on-chip drug assays could be reliably carried out using curcumin as a model anti-cancer drug. Advanced micromachining provides an excellent technological solution to the fabrication of high quality concave microwells. Refereed/Peer-reviewed

Large area mapping of inorganic material in biological samples has suffered severely from prohibitively long acquisition times. With the advent of new detector technology we can now generate statistically relevant information for studying cell populations, inter-variability and bioinorganic chemistry in large specimen. We have been implementing ultrafast synchrotron-based XRF mapping afforded by the MAIA detector for large area mapping of biological material. For example, a 2.5 million pixel map can be acquired in 3 hours, compared to a typical synchrotron XRF set-up needing over 1 month of uninterrupted beamtime. Of particular focus to us is the fate of metals and nanoparticles in cells, 3D tissue models and animal tissues. The large area scanning has for the first time provided statistically significant information on sufficiently large numbers of cells to provide data on intercellular variability in uptake of nanoparticles. Techniques such as flow cytometry generally require analysis of thousands of cells for statistically meaningful comparison, due to the large degree of variability. Large area XRF now gives comparable information in a quantifiable manner. Furthermore, we can now image localised deposition of nanoparticles in tissues that would be highly improbable to `find' by typical XRF imaging. In addition, the ultra fast nature also makes it viable to conduct 3D XRF tomography over large dimensions. This technology avails new opportunities in biomonitoring and understanding metal and nanoparticle fate ex-vivo. Following from this is extension to molecular imaging through specific anti-body targeted nanoparticles to label specific tissues and monitor cellular process or biological consequence.

Lipid-based liquid crystalline systems are showing potential as stimuli-responsive nanomaterials, and NIR-responsive gold nanoparticles have been demonstrated to provide control of transitions in nonlamellar phases. In this study, we focus on a deeper understanding of the photothermal response of both lamellar and non-lamellar phases, and new systems formed by alternative lipid systems not previously reported, by linking the photothermal heating to the bulk thermal properties of the materials. Dynamic photothermal studies were performed using NIR laser irradiation and monitoring the structural response using time resolved small angle X-ray scattering for the bulk phases and hexosomes. In addition, cryoFESEM and cryoTEM were used to visualise and assess the effect of GNR incorporation into hexagonal phase nanostructures. The ability of the systems to respond to photothermal heating was correlated with the thermal phase behaviour and heat capacities of the different structures. Access to alternative phase transitions in these systems and understanding the likely photothermal response will facilitate different modes of application of these hybrid nanomaterials for on-demand drug delivery applications. Refereed/Peer-reviewed

Rapid, reliable and unbiased circulating tumor cell (CTC) isolation and molecular characterization methods are urgently required for implementation in routine clinical diagnostic and prognostic procedures. We report on the development of a novel unbiased CTC detection approach that combines high-throughput automated microscopy with a simple yet efficient approach for achieving a high level of tumor cell binding in standard tissue culture polystyrene (PS) well plates. A single 5 min high-power oxygen plasma treatment was used to create homogeneous nanoscale roughness on standard PS tissue culture plates and, in turn, drastically enhance the binding of a range of tumor cells. After physical adsorption of an adlayer of poly-l-lysine, binding yields above 97% were obtained at 2 h for all tumor cell lines used in the study. Morphological analysis of the cells confirmed strong adherence to the nanorough PS substrates. Clinically relevant concentrations of a highly metastatic breast cancer cell line, used as model for CTCs, could be reliably detected among blood cells on the nanorough polystyrene plates using an automated microscopy system. The approach was then successfully used to detect CTCs in the blood of a stage IIIc colorectal cancer patient. By combining the high binding abilities of nanorough PS well plates with the high-throughput nature of high-content analysis systems, this methodology has great potential toward enabling unbiased routine clinical analysis of CTCs. It could be applied, once clinically validated, in any clinical center equipped with an automated microscopy facility at a fraction of the cost of current CTC isolation technologies. Refereed/Peer-reviewed

The next generation of therapeutic nanoparticles in the treatment of cancer incorporate specific targeting.There is implicit importance in understanding penetration of targeted nanomedicines within tumour tissues via accurate and quantitative temporospatial measurements. In this study we demonstrate the potential of state-of-the-art synchrotron X-ray fluorescence microscopy (XFM) to provide such insights. To this end,quantitative mapping of the distribution of transferrin-conjugated gold nanoparticles inside multicellular tumour spheroids was achieved using XFM and compared with qualitative data obtained using reflectance confocal microscopy. Gold nanoparticles conjugated with human transferrin with a narrow size-distribution and high binding affinity to tumour cells were prepared as confirmed by cellular uptake studies performed on 2D monolayers. Although the prepared 100 nm transferrin-conjugated goldnanoparticles had high targeting capability to cancer cells, penetration inside multicellular spheroids was limited even after 48 hours as shown by the quantitative XFM measurements. The rapid, quantitative and label-free nature of state-of-the-art synchrotron XFM make it an ideal technology to provide the structure-activity relationship understanding urgently required for developing the next generation of immuno-targeted nanomedicines. Refereed/Peer-reviewed

We present a robust wafer-scale top-down process for the fabrication of locally thinned-downed silicon nanowire (SiNW) devices. The fabrication is based on electron-beam lithography in combination with a two-step tetramethylammonium hydroxide (TMAH) wet etch. We optimized the etching profile of the TMAH process on siliconon- insulator using isopropanol additive and temperature regulation, yielding very low and controllable etching rates and enabling the formation of ultra-smooth silicon morphology. The optimized TMAH etching process was confined using photolithography to the middle sections of silicon nanowire channels to achieve localized step-etching of the nanowires. The thinned silicon nanowires were addressed via metal contact lines in the final step of the fabrication. Preliminary currentvoltage characterization in liquid demonstrated a p-channel field effect transistor behavior in depletion mode with a very high output current and negligible contact resistance. The proposed process provides an alternative route for reliable and reproducible fabrication of ultra-thin silicon nanowire devices. Refereed/Peer-reviewed

A multilayered biosensing architecture based on long range surface plasmons (LRSPs) is reported. LRSPs originate from the coupling of surface plasmons on the opposite sides of a thin metal film embedded in a symmetrical refractive index environment. With respect to regular SPs, LRSPs are characterized by extended electromagnetic field profiles and lower losses, making them of high interest in biosensing, especially for large biological entities. LRSPs-supporting layer structures are typically prepared by using fluoropolymers with refractive indices close to that of water. Unfortunately, fluoropolymers have low surface energies which can translate into poor adhesion to substrates and sub-optimal properties of coatings with surface plasmon resonance-active metal layers such as gold. In this work, a multilayered fluoropolymer structure with tuneable average refractive index is described and used to adjust the penetration depth of LRSP from the sensor surface. The proposed methodology also provides a simple solution to increase the adhesion of LRSP-supporting structures to glass substrates. Towards taking full advantage of long range surface plasmon resonance sensors, a novel approach based on the plasma-polymerization of allylamine is also described to improve the quality of gold layers on fluoropolymers such as Teflon AF. Through these advancements, long range surface plasmon resonance sensors were fabricated with figures of merit as high as 466 RIU −1 . The remarkable performance of these sensors combined with their high stability is expected to foster applications of LRSPR in biosensing.

The integration of microfluidics with living biological systems has paved the way to the exciting concept of "organs-on-a-chip," which aims at the development of advanced in vitro models that replicate the key features of human organs. Glass-based devices have long been utilized in the field of microfluidics but the integration of alternative functional elements within multilayered glass microdevices, such as polymeric membranes, remains a challenge. To this end, we have extended a previously reported approach for the low-temperature bonding of glass devices that enables the integration of a functional polycarbonate porous membrane. The process was initially developed and optimized on specialty low-temperature bonding equipment (μTAS2001, Bondtech, Japan) and subsequently adapted to more widely accessible hot embosser units (EVG520HE Hot Embosser, EVG, Austria). The key aspect of this method is the use of low temperatures compatible with polymeric membranes. Compared to borosilicate glass bonding (650°C) and quartz/fused silica bonding (1050°C) processes, this method maintains the integrity and functionality of the membrane (Tg 150°C for polycarbonate). Leak tests performed showed no damage or loss of integrity of the membrane for up to 150 h, indicating sufficient bond strength for long-term cell culture. A feasibility study confirmed the growth of dense and functional monolayers of Caco-2 cells within 5 days. Refereed/Peer-reviewed

Gold nanoparticles are of high interest in the and bioimaging field owing to their unique optical biodiagnostic properties such as localized surface plasmon resonance (LSPR) and high Rayleigh scattering efficiency in the visible range. Although biofunctionalization is a prerequirement prior to their integration in diagnostic procedures, aggregation-free conjugation of biomacromole- cules to large gold nanoparticle is not trivial. Here, a robust and simple method based on commercially available reactants is reported for the efficient biofunctionalization of gold nanoparticles with sizes ranging from 15 to 175 nm. It is demonstrated that mixed poly(ethylene glycol) (PEG) layers, prepared using specific ratios of low- and high-molecular-weight PEG chains, can be conjugated to proteins and monoclonal antibodies using standard carbodiimide chemistry without detectable aggregation. The properties of the mixed PEG interlayer modified gold nanoparticles were investigated using UV−vis spectrometer, dynamic light scattering, and X-ray photoelectron spectroscopy, which demonstrated the importance of controlling biointerfacial properties. Using the epithelial cell adhesion molecule (EpCAM) as a model target antigen, the benefit of the mixed PEG layers over coatings prepared using high-molecular-weight PEG chains only is demonstrated in vitro using bright field microscopy and reflectance confocal microscopy. Very high binding affinity to breast cancer cells was obtained for the mixed PEG layers. This robust procedure demonstrates that, under optimal conditions, a compromise can be achieved between the excellent steric protection provided by thick PEG adlayers and the high bioconjugation yields afforded by adlayers from low-molecular-weight tethers. Refereed/Peer-reviewed

Lipid-based liquid-crystalline matrixes provide a unique prospect for stimuli-responsive nanomaterials, attributed to the ability to effect self-assembly of the lipids at the molecular level. Differences in liquid crystal nanostructure have previously been shown to change drug diffusion and hence release, with research progressing toward the use of in situ changes to nanostructure to control drug release. Toward this goal, we have previously communicated the ability to switch between nonlamellar structures using gold nanorod (GNR)−phytantriol-based liquid-crystalline hybrid nanomaterials as near-infrared light responsive systems (Fong et al. Langmuir 2010, 26, 6136− 6139). In this study, the effect of laser activation on matrix nanostructure with changes in a number of system variables including lipid composition, GNR aspect ratio, GNR concentration, and laser pulse time were investigated. The nanostructure of the matrix was followed using small-angle X-ray scattering, while both cryoFESEM and cryoTEM were used to visualize the effect of GNR incorporation into the liquid crystal nanostructure. The system response was found to be dependent on all variables, thus demonstrating the potential of these nanocomposite materials as reversible "on-demand" drug delivery applications. Refereed/Peer-reviewed

Synchrotron FTIR microscopy has been used to probe the structure of model boundary lubricant layers confined at the solid−solid interface. The combination of high brightness of the IR source and a novel contact geometry that uses a hemispherical internal reflection element as the means for light delivery has enabled the detection of

The nanostructure of mesophase liquid crystals prepared from amphiphilic lipids controls the rate of release of incorporated agents from the material, such as drug molecules, and reversible transition between different nanostructures essentially provides an "on-off" switch for release (Fong, W.-K.; Hanley, T.; Boyd, B. J. J. Controlled Release 2009, 135, 218-226). In this study, the incorporation of plasmonic hydrophobized gold nanorods (GNRs) permits reversible manipulation of nanostructure on-demand, by irradiation of the matrix using a near-infrared laser. Synchrotron small-angle X-ray scattering was used to probe the kinetics of the response of nanostructure to laser irradiation, and the specificity of the approach is shown by the lack of response in the absence of nanorods, or for GNR whose dimensions are not matched to the specific wavelength of the incident light.

Towards an integrated multifunctional nanocarrier, core–shell nanostructures have been developed using the electrostatic self-assembly of an organic shell onto magnetic nanoparticles. Refereed/Peer-reviewed

Towards a robust and universal functionalization procedure with alkanethiols for gold nanorods and plasmonic nanoparticles, a straightforward two-step approach is described. Refereed/Peer-reviewed

Nanotechnology has generated tremendous hopes in recent years toward the design of advanced functional materials, especially in the bio-medical field. Nano-sized-materials such as magnetite nanoparticles display indeed fascinating physico-chemical properties that, if tuned properly, can be exploited to design new bio-diagnostic and therapeutic strategies as well as innovative biotechnology methodologies. Owing to their biocompatibility and excellent magnetic properties, magnetite nanocrystals have been the object of a tremendous amount of research in the last decade and numerous (bio)applications have been reported. Importantly, advances in the synthesis of magnetite nanoparticles enable excellent control over their size, shape, and composition. Despite these remarkable progresses, many issues remain to be overcome for these nanotechnology products to revolution the medical practice. The fine control and application of colloidal nanostructures such as magnetite nanoparticles in complex biological systems ...

Catheter-based brachytherapy is one of the most effective modalities to inhibit hyperplasia following revascularization procedures. Radioactive stents have failed, however, to prevent clinical hyperplasia due to excessive late lumen loss on the edge of the devices. Numerous strategies have been proposed to circumvent the drawbacks of irradiation therapies, such as the use of more appropriate radionuclides or the "hot-end" stents approach. This paper describes versatile radioactive devices obtained by coating plasma functionalized surfaces-stents or catheters-with a hyaluronan (HA)-diethylenetriamine pentaacetic acid (DTPA) conjugate (HA-DTPA) complexed with a gamma or beta radionuclide. Yttrium and indium were used as radionuclide models, due to their suitability for endovascular radiotherapy. X-ray photoelectron microscopy and time-of-flight secondary ions mass spectrometry analyses confirmed the successful immobilization of the HA-DTPA conjugate on both the metallic (NiTi) and polymeric (Teflon) plasma functionalized surfaces. HA-DTPA-coated surfaces were significantly more hydrophilic than bare surfaces (39.5 degrees vs. 67 degrees on NiTi substrate and 29 degrees vs. 128 degrees on Teflon substrate). Therapeutic doses of yttrium and indium were easily loaded onto the surfaces and remained stable over 2 weeks with a radionuclide loss of about 6%. The HA-DTPA-coated Teflon surfaces presented significantly less fibrinogen adsorption than uncoated materials in an in vitro flow model. This approach, which combines the hemocompatibility of HA-coated surfaces and the anti-proliferative effects of an appropriate radiotherapy, constitutes a promising methodology to alleviate the restenosis induced by existing devices.

Functional silicon nanowires (SiNWs) are promising building blocks in the design of highly sensitive photodetectors and bio-chemical sensors. We systematically investigate the photoresponse properties of ultrathin SiNWs (20 nm) fabricated using a size-reduction method based on e-beam lithography and tetramethylammonium hydroxide wet-etching. The high-quality SiNWs were able to detect light from the UV to the visible range with excellent sensitivity (∼1 pW/array), good time response, and high photoresponsivity (R ∼ 2.5 x 10⁴A/W). Improvement of the ultrathin SiNWs' photoresponse has been observed in comparison to 40 nm counter-part nanowires. These properties are attributable to the predominance surface-effect due to the high surface-to-volume ratio of ultrathin SiNWs. Long-term measurements at different temperatures in both the forward and reverse bias directions demonstrated the stability and reliability of the fabricated device. By sensitizing the fabricated SiNW arrays with cadmium telluride quantum dots (QDs), hybrid QD SiNW devices displayed an improvement in photocurrent response under UV light, while preserving their performance in the visible light range. The fast, stable, and high photoresponse of these hybrid nanostructures is promising towards the development of optoelectronic and photovoltaic devices. Refereed/Peer-reviewed

The objectives of this study were to establish an in-depth understanding of the signals induced by mammalian cells in surface plasmon resonance (SPR) sensing. To this end, two plasmonic structures with different propagation and penetration distances were used: conventional surface plasmon resonance and long-range surface plasmon resonance. Long-range SPR showed a lesser sensitivity to the absolute number of round cells but a greater resolution due to its very narrow spectral dip. The effect of cell spreading was also investigated and the resonance angle of long-range SPR was mostly insensitive unlike in the conventional SPR counterpart. Experimental data was compared with suitable models used in the SPR literature. Although these simple averaging models could be used to describe some of the experimental data, important deviations were observed which could be related to the fact that they do not take into consideration critical parameters such as plasmon scattering losses, which is particularly crucial in the case of long-range SPR structures. The comparison between conventional and long-range SPR for cellular schemes revealed important fundamental differences in their responses to the presence of cells, opening new horizons for SPR-based cell assays. From this study, long-range SPR is expected to be more sensitive towards both the detection of intracellular events resulting from biological stimulation and the detection of microorganisms captured from complex biological samples.

Background: Staphylococcus aureus in its biofilm form has been associated with recalcitrant chronic rhinosinusitis with significant resistance to conventional therapies. This study aims to determine if liposomal-encapsulation of a precursor ofthe naturally occurring antimicrobial nitric oxide (NO) enhances its desired anti-biofilm effects against S. aureus, in the hope that improving its efficacy can provide an effective topical agent for future clinical use. Methodology: S. aureus ATCC 25923 biofilms were grown in-vitro using the Minimum Biofilm Eradication Concentration(MBEC) device and exposed to 3 and 60 mg/mL of the NO donor isosorbide mononitrate (ISMN) encapsulated into different anionic liposomal formulations based on particle size (unilamellar ULV, multilamellar MLV) and lipid content (5 and 25 mM) at 24 h and 5 min exposure times. Biofilms were viewed using Live-Dead Baclight stain and confocal scanning laser microscopy and quantified using the software COMSTAT2. Results: At 3 and 60 mg/mL, ISMN-ULV liposomes had comparable and significant anti-biofilm effects compared to untreated control at 24 h exposure (p = 0.012 and 0.02 respectively). ULV blanks also had significant anti-biofilm effects at both 24 h and 5 min exposure (p = 0.02 and 0.047 respectively). At 5 min exposure, 60 mg/mL ISMN-MLV liposomes appeared to have greater anti-biofilm effects compared to pure ISMN or ULV particles. Increasing liposomal lipid content improved the anti-biofilm efficacy of both MLV and ULVs at 5 min exposure. Conclusion: Liposome-encapsulated ‘‘nitric oxide’’ is highly effective in eradicating S. aureus biofilms in-vitro, giving great promise for use in the clinical setting to treat this burdensome infection. Further studies however are needed to assess its safety and efficacy in-vivo before clinical translation is attempted. Refereed/Peer-reviewed

Nickel-titanium (NiTi) alloy derives its biocompatibility and good corrosion resistance from a homogeneous oxide layer mainly composed of TiO(2), with a very low concentration of nickel. In this article, we described the corrosion behavior of NiTi alloys after mechanical polishing, electropolishing, and sterilization processes using cyclic polarization and atomic absorption. As a preparative surface treatment, electropolishing decreased the amount of nickel on the surface and remarkably improved the corrosion behavior of the alloy by increasing the mean breakdown potential value and the reproducibility of the results (0.99 +/- 0.05 V/SCE vs. 0.53 +/- 0. 42). Ethylene oxide and Sterrad(R) sterilization techniques did not modify the corrosion resistance of electropolished NiTi, whereas a steam autoclave and, to a lesser extent, peracetic acid sterilization produced scattered breakdown potential. In comparing the corrosion resistance of common biomaterials, NiTi ranked between 316L stainless steel and Ti6A14V even after sterilization. Electropolished NiTi and 316L stainless-steel alloys released similar amounts of nickel after a few days of immersion in Hank's solution. Measurements by atomic absorption have shown that the amount of released nickel from passive dissolution was below the expected toxic level in the human body. Auger electron spectroscopy analyses indicated surface contamination by Ca and P on NiTi during immersion, but no significant modification in oxide thickness was observed.

Based on promising reports from international randomized trials such as BENESTENT, vascular stent implantation has been increasingly used - with more than 500,000 implantations per year worldwide - and has become a procedure of choice in the treatment of atherosclerotic vascular disease [1,2]. Since the first implantation in 1986, many devices, mostly balloon expandable stainless steel stents, have been approved by regulatory agencies, for both peripheral and coronary revascularization. In the early 90’s, many studies have reported experimental temporary or permanent use of NiTi stents [3,4]. Due to the thermoelastic properties of the alloy, optimal deployment of NiTi self expanding stents can be easily achieved with high expansion ratio and less longitudinal shortening than most common stainless steel devices. In addition, their flexibility and radiopacity along with their good biocompatibility and resistance to corrosion have contributed to their increasing use in cardiovascular applications [5-7]. Despite its good biocompatibility, like all metallic materials NiTi is prone to adsorption of plasma protein such as fibrinogen, which is a potent promoter of platelet adhesion [8]. In a recent study, Makkar et al. have shown that surface topography significantly affects the thrombogenicity of NiTi stents, which may in turn have an effect on complications observed much after implantation [9]. Indeed, platelets adhesion is the first step of thrombus formation which may lead to acute and sub-acute thrombosis. Stent thrombosis still represents a major complication after stent implantation, especially for small vessels, thrombus containing lesions and bifurcation stenoses [10]. Moreover, through the release of growth factor by activated platelets, thrombus formation is expected to participate to the restenosis process initiation [11]. Many strategies have been developed to reduce stents thrombogenicity such as improvement of surface characteristics or coating with pharmacological drugs and polymers [9,12,13].

Sterilization is required for using any device in contact with the human body. Numerous authors have studied device properties after sterilization and reported on bulk and surface modifications of many materials after processing. These surface modifications may in turn influence device biocompatibility. Still, data are missing on the effect of sterilization procedures on new biomaterials such as nickel-titanium (NiTi). Herein we report on the effect of dry heat, steam autoclaving, ethylene oxide, peracetic acid, and plasma-based sterilization techniques on the surface properties of NiTi. After processing electropolished NiTi disks with these techniques, surface analyses were performed by Auger electron spectroscopy (AES), atomic force microscopy (AFM), and contact angle measurements. AES analyses revealed a higher Ni concentration (6-7 vs. 1%) and a slightly thicker oxide layer on the surface for heat and ethylene oxide processed materials. Studies of surface topography by AFM showed up to a threefold increase of the surface roughness when disks were dry heat sterilized. An increase of the surface energy of up to 100% was calculated for plasma treated surfaces. Our results point out that some surface modifications are induced by sterilization procedures. Further work is required to assess the effect of these modifications on biocompatibility, and to determine the most appropriate methods to sterilize NiTi.