Immobilization of DNA aptamers via plasma polymerized allylamine film to construct an endothelial progenitor cell-capture surface

Characterization of plasma polymerized acetonitrile film for fluorescence enhancement and its application to aptamer-based sandwich assay

Among biosensing systems for sensitive diagnoses fluorescence enhancement techniques have attracted considerable attention. This study constructed a simple multilayered structure comprising a plane metal mirror coated with a plasma-polymerized film (PPF) as an optical interference layer on a glass slide for fluorescence enhancement. Plasma polymerization enables the easy deposition of organic thin films containing functional groups, such as amino groups. This study prepared PPFs using acetonitrile as a monomer, and the influences of washing and the output powers of plasma polymerization on PPF thickness were examined by Fourier transform infrared spectroscopy. This is because controlling the PPF thickness is vital in fluorescence enhancement. Multilayered glass slides prepared using a silver layer with 84 nm-thick acetonitrile PPFs exhibited 11- and 281-fold fluorescence enhancements compared with those obtained from the substrates with a bare surface and only modified by the silver layer, respectively. Oligonucleotides labeled with a thiol group and cyanine5 were successfully immobilized on the multilayered substrates, and the fluorescence of the acetonitrile PPFs was superior to that of the allylamine and cyclopropylamine PPFs. Furthermore, an aptamer-based sandwich assay targeting thrombin was performed on the multilayered glass slides, resulting in an approximately 5.1-fold fluorescence enhancement compared with that obtained from the substrate with a bare surface. Calibration curves revealed the relationship between fluorescence intensity and thrombin concentration of 10-1000 nM. This study demonstrates that PPFs can function as materials for fluorescence enhancement, immobilization for biomaterials, and aptamer-based sandwich assays.

A small-diameter vascular graft immobilized peptides for capturing endothelial colony-forming cells

Combining synthetic polymers and biomacromolecules prevents the occurrence of thrombogenicity and intimal hyperplasia in small-diameter vascular grafts (SDVGs). In the present study, an electrospinning poly (L)-lactic acid (PLLA) bilayered scaffold is developed to prevent thrombosis after implantation by promoting the capture and differentiation of endothelial colony-forming cells (ECFCs). The scaffold consists of an outer PLLA scaffold and an inner porous PLLA biomimetic membrane combined with heparin (Hep), peptide Gly-Gly-Gly-Arg-Glu-Asp-Val (GGG-REDV), and vascular endothelial growth factor (VEGF). Attenuated total reflection Fourier transform infrared (ATR-FTIR) spectroscopy, X-ray photoelectron spectroscopy (XPS), and contact angle goniometry were performed to determine successful synthesis. The tensile strength of the outer layer was obtained using the recorded stress/strain curves, and hemocompatibility was evaluated using the blood clotting test. The proliferation, function, and differentiation properties of ECFCs were measured on various surfaces. Scanning electronic microscopy (SEM) was used to observe the morphology of ECFCs on the surface. The outer layer of scaffolds exhibited a similar strain and stress performance as the human saphenous vein via the tensile experiment. The contact angle decreased continuously until it reached 56° after REDV/VEGF modification, and SEM images of platelet adhesion showed a better hemocompatibility surface after modification. The ECFCs were captured using the REDV + VEGF + surface successfully under flow conditions. The expression of mature ECs was constantly increased with the culture of ECFCs on REDV + VEGF + surfaces. SEM images showed that the ECFCs captured by the REDV + VEGF + surface formed capillary-like structures after 4 weeks of culture. The SDVGs modified by REDV combined with VEGF promoted ECFC capture and rapid differentiation into ECs, forming capillary-like structures in vitro. The bilayered SDVGs could be used as vascular devices that achieved a high patency rate and rapid re-endothelialization.

Near-Infrared Light Regulation of Capture and Release of ctDNA Platforms Based on the DNA Assembly System

Despite recent progress, a challenge remains on how to gently release and recover viable ctDNA captured on DNA probe-based devices. Here, a reusable detector was successfully manufactured for the capture and release of ctDNA by means of an UCNPs@SiO2-Azo/CD-probe. Biocompatible NIR light is used to excite UCNPs and convert into local UV light. Continuous irradiation induces a rapid release of the entire ctDNA-probe–CD complex from the functionalized surface via the trans−cis isomerization of azo units without disrupting the ctDNA-structure receptor. Specifically, these composite chips allow reloading DNA probes for reusable ctDNA detection with no obvious influence on their efficiency. The results of our study demonstrated the potential application of this platform for the quantitative detection of ctDNA and the individualized analysis of cancer patients.

Facile DNA adsorption enabling ammonium-based hydrophilic affinity monolithic column for high-performance online selective microextraction of ochratoxin A

Herein, a facile protocol of simple DNA adsorption on UV-initiated polymerization supports was proposed for effectively fabricating aptamer-based affinity monolithic column. Hydrophilic cationic monolith with an excellent mechanical stability was achieved within 7 min and then massive aptamers were directly bound by DNA charge-dependent adsorption. Strong cationic quaternary ammonium-based monomer was employed to provide effective and stable positive charge surface for aptamer immobilization in a wide range of pH. An ultra-high aptamer coverage density of 6813 pmol/μL was achieved to gain a highly specific online recognition performance. Limitations such as low aptamer capacity, tedious modification and time-consuming reactions in the traditional biological or covalent modification strategies were avoided. By using ochratoxin A (OTA) as the given analyte, the selective recognition and high recoveries were successfully achieved, and little cross-reactivity towards OTB analogue was only 0.5% even if the content of OTB got up to 125 folds of OTA. Applied to sample analysis, the satisfactory discriminations of trace OTA were obtained at 93.9 ± 1.9% - 96.5 ± 1.7%（n = 3）in beer, wheat and chicken liver samples. It might light a cost-effective access to efficiently preparing high-performance affinity monoliths towards the selective in-tube microextraction of OTA.

Impact of REDV peptide density and its linker structure on the capture, movement, and adhesion of flowing endothelial progenitor cells in microfluidic devices

Ligand-immobilization to stents and vascular grafts is expected to promote endothelialization by capturing flowing endothelial progenitor cells (EPCs). However, the optimized ligand density and linker structure have not been fully elucidated. Here, we report that flowing EPCs were selectively captured by the REDV peptide conjugated with a short linker. The microchannel surface was modified with the REDV peptide via Gly-Gly-Gly (G3), (Gly-Gly-Gly)₃ (G9), and diethylene glycol (diEG) linkers, and the moving velocity and captured ratio were evaluated. On the unmodified microchannels, the moving velocity of the cells exhibited a unimodal distribution similar to the liquid flow. The velocity of the endothelial cells and EPCs on the peptide-immobilized surface indicated a bimodal distribution, and approximately 20 to 30% of cells moved slower than the liquid flow, suggesting that the cells were captured and rolled on the surface. When the immobilized ligand density was lower than 1 molecule/nm², selective cell capture was observed only in REDV with G3 and diEG linkers, but not in G9 linkers. An in silico study revealed that the G9 linker tends to form a bent structure, and the REDV peptide is oriented to the substrate side. These results indicated that REDV captured the flowing EPC in a sequence-specific manner, and that the short linker was more adequate.

A facile aptamer immobilization strategy to fabricate a robust affinity monolith for highly specific in-tube solid-phase microextraction

Developing a functional affinity monolithic column towards in-tube solid-phase microextraction (IT-SPME) for selective sample pretreatment is critical. Herein, a high-performance capillary affinity monolithic column with an ultra-high aptamer coverage density was rapidly fabricated via a simple adsorption strategy, in which aptamers with natural sequences were directly immobilized on an ammonium-based strongly cationic matrix. Limitations of the traditional biological or covalent methods such as time-consuming modification reactions, special requirement of active groups (e.g. -NH₂ and -SH) on the aptamer, and low aptamer coverage density levels were avoided. An ultra-high coverage density of 8616 pmol μL^-1 was achieved with excellent stability, and the highest aptamer-modification level among all the current methods was reached. Selective recognition and high recovery yields of the model mycotoxin ochratoxin A (OTA) were achieved in 95.9 ± 0.98%-97.9 ± 0.28% (n = 3). In particular, there was little cross-reactivity towards the OTB analogue of only 0.5% even in the case of 250 fold of the analogue OTB, which was not reported in previous affinity monoliths. Upon sample analysis, satisfactory discriminations of trace OTA were obtained at 93.7 ± 1.4%-95.5 ± 2.5% (n = 3) in beer and wheat. A facile and direct method for efficiently fabricating an aptamer-based affinity monolith towards online selective IT-SPME was proposed.

Identification of circulating cells interacted with integrin α4β1 ligand peptides REDV or HGGVRLY

Recently, artificial blood vessels modified by integrin α4β1 ligand, such as REDV, showed endothelialization improvement and antithrombotic properties have been reported. Early endothelialization was affected by the type of circulating cells captured by the peptide in the initial transplantation state, however, it is still not clarified. In this study, we identified in vitro circulating cells bound with the peptides arginine-glutamic acid-aspartic acid-valine (REDV) or histidine-glycine-glycine-valine-arginine-leucine-tyrosine (HGGVRLY). The effect of free C- or N-terminal of HGGVRLY on the type of peptide-binding cells was also studied. The rat circulating cells were isolated from blood and incubated with 5(6)-carboxyfluorescein (5/6-FAM, F) labeled F-REDV (C-terminal free), F-HGGVRLY (C-terminal free), or HGGVRLY-F (N-terminal free). Furthermore, peptide-binding cells were identified by co-staining with various antibodies labeled with PE, PerCP/Cy5.5, or APC. N-terminal free HGGVRLY-F was found to bind to more circulating cells than C-terminal free F-REDV and F-HGGVRLY. The ratio of integrin α4β1 positive cell bound with F-REDV, F-HGGVRLY, or HGGVRLY-F reached over 90 %, demonstrating that HGGVRLY is also a ligand of integrin α4β1. Among identified cell types, we found that F-REDV mainly bounds with EPC and BMSC, while F-HGGVRLY with BMSC. HGGVRLY-F bounds with EPC and BMSC, exhibiting a higher EPC binding ratio than F-REDV and F-HGGVRLY.

Electrochemical sensor based on Prussian blue/multi-walled carbon nanotubes functionalized polypyrrole nanowire arrays for hydrogen peroxide and microRNA detection

A dual-sensing platform is proposed based on multi-walled carbon nanotubes/Prussian blue-functionalized polypyrrole nanowire array (PPY/MWCNTs/PB). Highly aligned PPY nanowire arrays were electrochemically prepared on the surface of glassy carbon electrodes, which were doped with MWCNTs/PB nanocomposites. The nanomaterial combines the characteristics of the PPY nanowires (high conductivity and large specific surface area) and MWCNTs/PB (excellent catalytic performance and intrinsic redox activity). Owing to the nanowire microstructure and outstanding electrical properties, the PPY/MWCNTs/PB nanowire arrays show excellent electrocatalysis of the reduction of hydrogen peroxide and facilitate the construction of a high-performance biosensing platform for microRNA (miRNA). A linear relationship between analytical signal and concentration of hydrogen peroxide and miRNA was obtained in the range 5 to 503 µM (1.4-5.1 mM) and 0.1 pM to 1 nM, and detection limits of 1.7 μM and 33.4 fM, respectively. This new supersensitive sensing platform has broad application prospects of biomolecule and other analyte determination in drug, biomedical, plant protection, and environmental analysis. Prussian blue/multi-walled carbon nanotubes functionalized polypyrrole nanowire arrays (PPY/MWCNTs/PB) were prepared by a facile one-step electrochemical method. PPY/MWCNTs/PB nanowire arrays show excellent electrocatalysis of the reduction of H₂O₂ and facilitate the construction of a high-performance biosensing platform for microRNA.

Poly-dopamine, poly-levodopa, and poly-norepinephrine coatings: Comparison of physico-chemical and biological properties with focus on the application for blood-contacting devices

Thanks to its simplicity, versatility, and secondary reactivity, dopamine self-polymerized coatings (pDA) have been widely used in surface modification of biomaterials, but the limitation in secondary molecular grafting and the high roughness restrain their application in some special scenarios. Therefore, some other catecholamine coatings analog to pDA have attracted more and more attention, including the smoother poly-norepinephrine coating (pNE), and the poly-levodopa coating (pLD) containing additional carboxyl groups. However, the lack of a systematic comparison of the properties, especially the biological properties of the above three catecholamine coatings, makes it difficult to give a guiding opinion on the application scenarios of different coatings. Herein, we systematically studied the physical, chemical, and biological properties of the three catecholamine coatings, and explored the feasibility of their application for the modification of biomaterials, especially cardiovascular materials. Among them, the pDA coating was the roughest, with the largest amount of amino and phenolic hydroxyl groups for molecule grafting, and induced the strongest platelet adhesion and activation. The pLD coating was the thinnest and most hydrophilic but triggered the strongest inflammatory response. The pNE coating was the smoothest, with the best hemocompatibility and histocompatibility, and with the strongest cell selectivity of promoting the proliferation of endothelial cells while inhibiting the proliferation of smooth muscle cells. To sum up, the pNE coating may be a better choice for the surface modification of cardiovascular materials, especially those for vascular stents and grafts, but it is still not widely recognized.

Phenolic-amine chemistry mediated synergistic modification with polyphenols and thrombin inhibitor for combating the thrombosis and inflammation of cardiovascular stents

Antithrombogenicity, anti-inflammation, and rapid re-endothelialization are central requirements for the long-term success of cardiovascular stents. In this work, a plant-inspired phenolic-amine chemistry strategy was developed to combine the biological functions of a plant polyphenol, tannic acid (TA), and the thrombin inhibitor bivalirudin (BVLD) for tailoring the desired multiple surface functionalities of cardiovascular stents. To realize the synergistic modification of TA and BVLD on a stent surface, an amine-bearing coating of plasma polymerized allylamine was firstly prepared on the stent surface, followed by the sequential conjugation of TA and BVLD in alkaline solution based on phenolic-amine chemistry (i.e., Michael addition reaction). TA and BVLD were successfully immobilized onto the stent surface with considerable amounts of 330 ± 12 and 930 ± 80 ng/cm², respectively. The abundant phenolic hydroxyl groups of TA imparted the stent with ability to suppress inflammation. Meanwhile, BVLD provided an antithrombogenic and endothelial-friendly microenvironment. As a result, the combined functions of the TA and BVLD facilitate the rapid stent re-endothelialization for reduced intimal hyperplasia in vivo, and may be a promising strategy to address the clinical complications associated with restenosis and late stent thrombosis.

Biointerface Materials for Cellular Adhesion: Recent Progress and Future Prospects

While many natural instances of adhesion between cells and biological macromolecules have been elucidated, understanding how to mimic these adhesion events remains to be a challenge. Discovering new biointerface materials that can provide an appropriate environment, and in some cases, also providing function similar to the body’s own extracellular matrix, would be highly beneficial to multiple existing applications in biomedical and biological engineering, and provide the necessary insight for the advancement of new technology. Such examples of current applications that would benefit include biosensors, high-throughput screening and tissue engineering. From a mechanical perspective, these biointerfaces would function as bioactuators that apply focal adhesion points onto cells, allowing them to move and migrate along a surface, making biointerfaces a very relevant application in the field of actuators. While it is evident that great strides in progress have been made in the area of synthetic biointerfaces, we must also acknowledge their current limitations as described in the literature, leading to an inability to completely function and dynamically respond like natural biointerfaces. In this review, we discuss the methods, materials and, possible applications of biointerface materials used in the current literature, and the trends for future research in this area.

Endothelial progenitor cells as the target for cardiovascular disease prediction, personalized prevention, and treatments: progressing beyond the state-of-the-art

Stimulated by the leading mortalities of cardiovascular diseases (CVDs), various types of cardiovascular biomaterials have been widely investigated in the past few decades. Although great therapeutic effects can be achieved by bare metal stents (BMS) and drug-eluting stents (DES) within months or years, the long-term complications such as late thrombosis and restenosis have limited their further applications. It is well accepted that rapid endothelialization is a promising approach to eliminate these complications. Convincing evidence has shown that endothelial progenitor cells (EPCs) could be mobilized into the damaged vascular sites systemically and achieve endothelial repair in situ, which significantly contributes to the re-endothelialization process. Therefore, how to effectively capture EPCs via specific molecules immobilized on biomaterials is an important point to achieve rapid endothelialization. Further, in the context of predictive, preventive, personalized medicine (PPPM), the abnormal number alteration of EPCs in circulating blood and certain inflammation responses can also serve as important indicators for predicting and preventing early cardiovascular disease. In this contribution, we mainly focused on the following sections: the definition and classification of EPCs, the mechanisms of EPCs in treating CVDs, the potential diagnostic role of EPCs in predicting CVDs, as well as the main strategies for cardiovascular biomaterials to capture EPCs.

Biomimetic engineering endothelium-like coating on cardiovascular stent through heparin and nitric oxide-generating compound synergistic modification strategy

Co-immobilization of two or more molecules with different and complementary functions to prevent thrombosis, suppress smooth muscle cell (SMC) proliferation, and support endothelial cell (EC) growth is generally considered to be promising for the re-endothelialization on cardiovascular stents. However, integration of molecules with distinct therapeutic effects does not necessarily result in synergistic physiological functions due to the lack of interactions among them, limiting their practical efficacy. Herein, we apply heparin and nitric oxide (NO), two key molecules of the physiological functions of endothelium, to develop an endothelium-mimetic coating. Such coating is achieved by sequential conjugation of heparin and the NO-generating compound selenocystamine (SeCA) on an amine-bearing film of plasma polymerized allylamine. The resulting surface combines the anti-coagulant (anti-FXa) function provided by the heparin and the anti-platelet activity of the catalytically produced NO. It also endows the stents with the ability to simultaneously up-regulate α-smooth muscle actin (α-SMA) expression and to increase cyclic guanylate monophosphate (cGMP) synthesis of SMC, thereby significantly promoting their contractile phenotype and suppressing their proliferation. Importantly, this endothelium-biomimetic coating creates a favorable microenvironment for EC over SMC. These features impressively improve the antithrombogenicity, re-endothelialization and anti-restenosis of vascular stents in vivo.

Surface plasmon resonance aptasensor for detection of human activated protein C

The aim of this study is a highly sensitive and selective label-free surface plasmon resonance (SPR) aptasensor preparation for the specific detection of human activated protein C (APC). In the first step, DNA aptamer was complexed with N-methacryloyl-L-cysteine (MAC) monomer. Then, cyanamide and 2-hydroxyethyl methacrylate solution was mixed with the DNA-Apt/MAC complex. Two different SPR sensors (Random-DNA and HEMA-MAC polymeric films) were also prepared by following the same experimental procedure. The characterization of SPR aptasensors was done by contact angle, atomic force microscopy, and ellipsometer analysis. Selectivity studies of SPR aptasensors were performed in the presence of bovine serum albumin, hemoglobin and myoglobin. Desorption studies were performed by using 0.025 M NaCl solution. The limit of detection (LOD) and limit of quantification (LOQ) values of DNA-Apt SPR aptasensor was determined as 1.5 ng/mL and 5.2 ng/mL.

Surface modification of stainless steel for biomedical applications: Revisiting a century-old material

Stainless steel (SS) has been widely used as a material for fabricating cardiovascular stents/valves, orthopedic prosthesis, and other devices and implants used in biomedicine due to its malleability and resistance to corrosion and fatigue. Despite its good mechanical properties, SS (as other metals) lacks biofunctionality. To be successfully used as a biomaterial, SS must be made resistant to the biological environment by increasing its anti-fouling properties, preventing biofilm formation (passive surface modification), and imparting functionality for eluting a specific drug or capturing selected cells (active surface modification); these features depend on the final application. Various physico-chemical techniques, including plasma vapor deposition, electrochemical treatment, and attachment of different linkers that add functional groups, are used to obtain SS with increased corrosion resistance, improved osseointegration capabilities, added hemocompatibility, and enhanced antibacterial properties. Existing literature on this topic is extensive and has not been covered in an integrated way in previous reviews. This review aims to fill this gap, by surveying the literature on SS surface modification methods, as well as modification routes tailored for specific biomedical applications.

STATEMENT OF SIGNIFICANCE

Stainless steel (SS) is widely used in many biomedical applications including bone implants and cardiovascular stents due to its good mechanical properties, biocompatibility and low price. Surface modification allows improving its characteristics without compromising its important bulk properties. SS with improved blood compatibility (blood contacting implants), enhanced ability to resist bacterial infection (long-term devices), better integration with a tissue (bone implants) are examples of successful SS surface modifications. Existing literature on this topic is extensive and has not been covered in an integrated way in previous reviews. This review paper aims to fill this gap, by surveying the literature on SS surface modification methods, as well as to provide guidance for selecting appropriate modification routes tailored for specific biomedical applications.

Strategies to develop endogenous stem cell-recruiting bioactive materials for tissue repair and regeneration

A leading strategy in tissue engineering is the design of biomimetic scaffolds that stimulate the body's repair mechanisms through the recruitment of endogenous stem cells to sites of injury. Approaches that employ the use of chemoattractant gradients to guide tissue regeneration without external cell sources are favored over traditional cell-based therapies that have limited potential for clinical translation. Following this concept, bioactive scaffolds can be engineered to provide a temporally and spatially controlled release of biological cues, with the possibility to mimic the complex signaling patterns of endogenous tissue regeneration. Another effective way to regulate stem cell activity is to leverage the inherent chemotactic properties of extracellular matrix (ECM)-based materials to build versatile cell-instructive platforms. This review introduces the concept of endogenous stem cell recruitment, and provides a comprehensive overview of the strategies available to achieve effective cardiovascular and bone tissue regeneration.

Nanomaterial coatings applied on stent surfaces

The advent of percutaneous coronary intervention and intravascular stents has revolutionized the field of interventional cardiology. Nonetheless, in-stent restenosis, inflammation and late-stent thrombosis are the major obstacles with currently available stents. In order to enhance the hemocompatibility of stents, advances in the field of nanotechnology allow novel designs of nanoparticles and biomaterials toward localized drug/gene carriers or stent scaffolds. The current review focuses on promising polymers used in the fabrication of newer generations of stents with a short synopsis on atherosclerosis and current commercialized stents, nanotechnology's impact on stent development and recent advancements in stent biomaterials is discussed in context.

MiR-497∼195 cluster regulates angiogenesis during coupling with osteogenesis by maintaining endothelial Notch and HIF-1α activity

A specific bone vessel subtype, strongly positive for CD31 and endomucin (CD31^hiEmcn^hi), is identified as coupling angiogenesis and osteogenesis. The abundance of type CD31^hiEmcn^hi vessels decrease during ageing. Here we show that expression of the miR-497∼195 cluster is high in CD31^hiEmcn^hi endothelium but gradually decreases during ageing. Mice with depletion of miR-497∼195 in endothelial cells show fewer CD31^hiEmcn^hi vessels and lower bone mass. Conversely, transgenic overexpression of miR-497∼195 in murine endothelium alleviates age-related reduction of type CD31^hiEmcn^hi vessels and bone loss. miR-497∼195 cluster maintains the endothelial Notch activity and HIF-1α stability via targeting F-box and WD-40 domain protein (Fbxw7) and Prolyl 4-hydroxylase possessing a transmembrane domain (P4HTM) respectively. Notably, endothelialium-specific activation of miR-195 by intravenous injection of aptamer-agomiR-195 stimulates CD31^hiEmcn^hi vessel and bone formation in aged mice. Together, our study indicates that miR-497∼195 regulates angiogenesis coupled with osteogenesis and may represent a potential therapeutic target for age-related osteoporosis.

H-type endothelium, defined by the high expression of CD31 and endomucin, is found in the bone where it promotes angiogenesis and osteogensis. Here Yang et al. show that the miR-497∼195 cluster regulates the generation and maintenance of the H-type endothelium by controlling the levels of Notch regulator Fbxw7 and the HIF regulator P4HTM.

Heparin/DNA aptamer co-assembled multifunctional catecholamine coating for EPC capture and improved hemocompatibility of vascular devices

Good hemocompatibility and rapid endothelialization are two key factors in the success of stent interventional therapy. In this study, aptamers with the ability to capture endothelial progenitors and anticoagulant molecular heparin were successfully immobilized on the surface of dopamine/polyethylenimine (PDA/PEI) copolymer coating via electrostatic interaction. The results of X-ray spectroscopy (XPS), water contact angle (WCA), and immunofluorescence staining tests confirmed the successful introduction of heparin and aptamers. Platelet adhesion and whole blood experiments demonstrated that the hemocompatibility of the co-modified surface was improved. Dynamic endothelial progenitor cell (EPC) capture experiments showed that the modified surfaces could effectively capture the endothelial progenitor in dynamic conditions. More importantly, ex vivo experiments revealed that the modified surfaces could regulate the distribution of CD34/vWF-positive cells on stent surfaces, and this was beneficial for the endothelialization of vascular stents. These results suggested that heparin and aptamer co-modified stents could capture EPCs and promote endothelialization. This surface co-modification strategy has great potential for enhancing stent development.

Anti-thrombotic technologies for medical devices

Thrombosis associated with medical devices may lead to dramatic increases in morbidity, mortality and increased health care costs. Innovative strategies are being developed to reduce this complication and provide a safe biocompatible interface between device and blood. This article aims to describe the biological phenomena underlying device-associated thrombosis, and surveys the literature describing current and developing technologies designed to overcome this challenge. To reduce thrombosis, biomaterials with varying topographical properties and incorporating anti-thrombogenic substances on their surface have demonstrated potential. Overall, there is extensive literature describing technical solutions to reduce thrombosis associated with medical devices, but clinical results are required to demonstrate significant long-term benefits.

Light-Triggered Specific Cancer Cell Release from Cyclodextrin/Azobenzene and Aptamer-Modified Substrate

Cell adhesion behaviors of stimuli-responsive surfaces have attracted significant attention for their potential biomedical applications. Distinct from temperature and pH stimuli, photoswitching avoids the extra input of thermal energy or chemicals. Herein, we designed a novel reusable cyclodextrin (CD)-modified surface to realize photoswitched specific cell release utilizing host-guest interactions between CD and azobenzene. The azobenzene-grafted specific cell capture agent was assembled onto the CD-modified surface to form a smart surface controlling cell adhesion by light radiation. After UV light irradiation, the azobenzene switched from trans- to cis-isomers, and the cis-azobenzene was not recognized by CD due to the unmatched host-guest pairs; thus, the captured MCF-7 cells could be released. Light-triggered specific cancer cell release with high efficiency may afford a smart surface with significant potential applications for the isolation and analysis of circulating tumor cells.

The effect of anti-CD34 antibody orientation control on endothelial progenitor cell capturing cardiovascular devices

Efficient immobilization of the antibody to the substrate is of crucial importance in the development of anti-CD34-based endothelial progenitor cells capturing cardiovascular devices. This should go along with precise control of the antibody orientation by appropriate immobilization technology for retaining antibody activity, like in immunosensors. Recently, great attention was paid to immobilization of anti-CD34 antibody onto substrates by covalent binding, but at random orientation. Here, to investigate the biological effect of antibody orientation, we have prepared two kinds of anti-CD34 antibody coated surfaces, with random immobilization and oriented immobilization. The immunological binding activity (IBA) of the antibody at oriented immobilization was 3.48 times higher than at random immobilization, indicating that the two different surfaces were successfully prepared. The endothelial progenitor cell-capturing capability of oriented antibody-immobilized surface was 1.35 and 1.64 times higher than for the random immobilized surface after seeding for 2 and 12 h under flow condition, respectively. The endothelial progenitor cell-capturing efficiency per antibody by oriented immobilization was 5.16 and 6.26 times higher than for the random after seeding for 2 and 12 h under flow condition, respectively. In addition, the oriented antibody-immobilized surface possessed better blood-compatibility. These results clearly revealed the significance of antibody orientation which could retain its biological effect and may revolutionize the antibody-immobilization protocols used in cardiovascular and other blood-contacting biomedical devices.

Cell-based strategies for vascular regeneration

Vascular regeneration is known to play an essential role in the repair of injured tissues mainly through accelerating the repair of vascular injury caused by vascular diseases, as well as the recovery of ischemic tissues. However, the clinical vascular regeneration is still challenging. Cell-based therapy is thought to be a promising strategy for vascular regeneration, since various cells have been identified to exert important influences on the process of vascular regeneration such as the enhanced endothelium formation on the surface of vascular grafts, and the induction of vessel-like network formation in the ischemic tissues. Here are a vast number of diverse cell-based strategies that have been extensively studied in vascular regeneration. These strategies can be further classified into three main categories, including cell transplantation, construction of tissue-engineered grafts, and surface modification of scaffolds. Cells used in these strategies mainly refer to terminally differentiated vascular cells, pluripotent stem cells, multipotent stem cells, and unipotent stem cells. The aim of this review is to summarize the reported research advances on the application of various cells for vascular regeneration, yielding insights into future clinical treatment for injured tissue/organ.

Facile immobilization of vascular endothelial growth factor on a tannic acid-functionalized plasma-polymerized allylamine coating rich in quinone groups

Biomolecules like VEGF with thiol or amine groups can easily be covalently immobilized onto a Tannic Acid functional plasma polymerized allylamine surface rich in quinone groups in a mild alkali buffer solution based on Schiff base or Michael addition reactions.

REDV/Rapamycin-loaded polymer combinations as a coordinated strategy to enhance endothelial cells selectivity for a stent system

A major challenge in the development of drug eluting stent platform is the sustained inhibition of smooth muscle cell (SMC) proliferation while endothelial cell (EC) coverage is promoted. We demonstrated in this study that the combination of rapamycin-loaded polymer base layer and Arg-Glu-Asp-Val (REDV) peptide tethered top layer is a coordinated strategy to enhance EC-specific selectivity. A 2-methacryloyloxyethyl phosphorylcholine(MPC)-co-n-stearyl methacrylate (SMA) [PMS] film was prepared as a base coating to load rapamycin. MPC-co-SMA-co-p-nitrophenyloxycarbonyl polyethyleneglycol methacrylate (MEONP) [PMSN] was synthesized to form the top layer, which conjugated the EC-specific ligand REDV peptide that promotes EC attachment. The top layer functioned as a diffusion barrier, and the polymer film can sustain the rapamycin release of for over 120 days. The In vitro cell behavior of EC and SMC indicated that the rapamycin loaded polymer film inhibited cell growth in the first few days of drug release. After 8 days of drug release, the composite coating consistently resisted the nonspecific adsorption of SMC, whereas REDV enhanced EC attachment specifically. A rabbit iliac injury model was used to evaluate the in vivo of the application of this kind of surface-modified stainless steel stent. The composite polymer coating approach could significantly promote re-endothelialization without causing neointimal hyperplasia. The combination of an EC-specific ligand with rapamycin-loaded polymeric coating may potentially be an effective therapeutic alternative to improve currently available drug-eluting stents.

In-line coupling of an aptamer based miniaturized monolithic affinity preconcentration unit with capillary electrophoresis and Laser Induced Fluorescence detection

A composite 30-cm capillary was prepared. The head of the capillary was a 1.5-cm original and miniaturized aptamer-based monolithic affinity support that was in-line coupled to the end of the capillary used for capillary electrophoresis (CE) with laser induced fluorescence (LIF) detection. The device was used for the preconcentration, separation and quantification of ochratoxin A (OTA) as a test solute. The 1.5-cm preconcentration unit consists of a fritless affinity monolithic bonded with 5'-SH-modified oligonucleotide aptamers. A vinyl spacer was used for thiol-ene photoclick chemistry with a 5min irradiation at 365nm. Photografting allowed to confine the binding reaction to the desired silica monolithic segment, upstream the empty section of the CE capillary using an UV mask. The photografting procedure was optimized preparing 10-cm capillary monoliths for nano-LC. The retention factors of cationic solutes in ion-exchange nano-LC allowed to follow the aptamer binding on the monolith. The reproducibility of the photografting process was satisfactory with inter-capillary variation lower than 10%. The aptamer bonding density can be increased by successive graftings of 100μM aptamer concentration solution (5pmol/cm/grafting). The optimal conditions to successfully perform the in-line coupling (preconcentration, elution and separation of OTA) with the composite capillary were adjusted depending on individual requirements of each step but also insuring compatibility. Under optimized conditions, OTA was successfully preconcentrated and quantified down to 0.1pg (percolation of 2.65μL of a 40ng/L OTA solution). A quantitative recovery of OTA (93±2%) was achieved in a single elution of 30pg percolated OTA amount. The reproducibility of the overall process was satisfactory with a relative standard deviation lower than 10% with negligible non-specific adsorption. This device was applied for the preconcentration and analysis of OTA in beer and wine at the ppb level within a total analysis time of 30min.

Predicting the Uncertain Future of Aptamer-Based Diagnostics and Therapeutics

Despite the great promise of nucleic acid aptamers in the areas of diagnostics and therapeutics for their facile in vitro development, lack of immunogenicity and other desirable properties, few truly successful aptamer-based products exist in the clinical or other markets. Core reasons for these commercial deficiencies probably stem from industrial commitment to antibodies including a huge financial investment in humanized monoclonal antibodies and a general ignorance about aptamers and their performance among the research and development community. Given the early failures of some strong commercial efforts to gain government approval and bring aptamer-based products to market, it may seem that aptamers are doomed to take a backseat to antibodies forever. However, the key advantages of aptamers over antibodies coupled with niche market needs that only aptamers can fill and more recent published data still point to a bright commercial future for aptamers in areas such as infectious disease and cancer diagnostics and therapeutics. As more researchers and entrepreneurs become familiar with aptamers, it seems inevitable that aptamers will at least be considered for expanded roles in diagnostics and therapeutics. This review also examines new aptamer modifications and attempts to predict new aptamer applications that could revolutionize biomedical technology in the future and lead to marketed products.