Water-Based Route for Dopamine and Reduced Graphene Oxide Aerogel Production.

Water pollution caused by domestic waste oil and accidents with oil/organic spill needs immediate remediation, as such a pollution causes serious threats to health and the environment. Development of absorbent materials for the treatment of oil-polluted waters in a green and energy-efficient manner is highly desired. In this study, a green and simple strategy is proposed to prepare aerogels by hydrothermal reaction of graphene oxide (GO) dispersions using dopamine (DOPA) as the cross-linker. Concentrations of GO and DOPA were changed to determine their effects on absorption capacities. Aerogels produced had low densities ranging from 2.90 to 4.34 mg/cm3. Various organics, diesel oil, and sunflower oil were used to evaluate the absorption capacity of aerogels. It was observed that even with a mild thermal reduction at 150 °C, aerogels exhibited very high absorption capacities of up to 445 mg/mg. The produced aerogels showed high reusability (80%) and structural stability even after 10 absorption/desorption cycles. They possess great potential in oil/organic removal and water treatment based on their high absorption capacities and performances in separating organics/liquids from water.

Strain-enhanced sensitivity of polymeric sensors templated from cholesteric liquid crystals.

Detection of volatile organic compounds (VOCs) is an important issue due to their harmful impact on human health. In this study, we aimed at enhancing the sensitivity of the anisotropic polymeric films templated from cholesteric liquid crystals (CLCs) in the identification of VOCs at concentrations on the order of 100 ppm. To increase sensitivity, we introduced negative strain to the films in the direction parallel to the helical axis and evaluated its effect on the sensitivity. Specifically, we used LC mixtures of reactive [4-(3-acryloyoxypropyloxy)benzoic acid 2-methyl-1,4-phenylene ester (RM257)], nonreactive E7 mesogen and chiral dopant [4-((1-methylheptyloxycarbonyl)phenyl-4-hexyloxybenzoate) (S-811)] to synthesize CLC-templated polymeric films with programmed strain profiles using a curved wedge cell, and measured their response against a range of toluene vapor concentrations. Based on the obtained results, we demonstrated a relationship between the negative strain in the cholesteric pitch and the sensitivity of the sensor based on spacial responses evaluated from the change in coloring of the film. Our results showed that negative strain helps to increase the sensitivity of the sensors up to 15 times compared to their unstrained counterparts. Moreover, 90% of the equilibrium response is achieved in less than one minute of exposure which offers rapid diagnosis of VOCs. Our tests for the reversibility of the sensors showed that the CLC-templated polymeric films can be used multiple times without a significant loss of sensitivity.

A comparative study on EpCAM antibody immobilization on gold surfaces and microfluidic channels for the detection of circulating tumor cells.

Detection of circulating tumor cells (CTCs) from the bloodstream holds great importance to diagnose cancer at early stages. However, CTCs being extremely rare in blood makes them difficult to reach. In this paper, we introduced different surface modification techniques for the enrichment and detection of MCF-7 in microfluidic biosensor applications using gold surface and EpCAM antibody. Mainly, two different mechanisms were employed to immobilize the antibodies; covalent bonding and bioaffinity interaction. Self-assembled monolayers (SAMs) formed on the gold surfaces were treated further for the immobilization of the antibody. The bioaffinity-based studies were performed with streptavidin and biotinylated EpCAM over the SAM coated surfaces. The cell attachment events were monitored using fluorescent microscope. Comparisons were made considering the length and functional end of alkanethiols and the positioning of the antibody. Then, these methods were integrated into a microfluidic channel system. Surface characterizations were performed with X-ray Photoelectron Spectroscopy, Atomic Force Microscopy, and contact angle measurements. The selectivity studies were carried out with EpCAM negative K562 leukaemia cell lines and the experiments were repeated for different types of surfaces, such as glass and polymer. Studies showed that long (n>10) and aromatic ring containing alkanethiols lead to better cell capture events compared to shorter ones. Results obtained from the comparisons are of importance for the gold surface-based microfluidic biosensor designs aimed for CTC detection.

Dual growth factor delivery using PLGA nanoparticles in silk fibroin/PEGDMA hydrogels for articular cartilage tissue engineering.

Degeneration of articular cartilage due to damages, diseases, or age-related factors can significantly decrease the mobility of the patients. Various tissue engineering approaches which take advantage of stem cells and growth factors in a three-dimensional constructs have been used for reconstructing articular tissue. Proliferative impact of basic fibroblast growth factor (bFGF) and chondrogenic differentiation effect of transforming growth factor-beta 1 (TGF-ß1) over mesenchymal stem cells have previously been verified. In this study, silk fibroin (SF) and of poly(ethylene glycol) dimethacrylate (PEGDMA) were used to provide a versatile platform for preparing hydrogels with tunable mechanical, swelling and degradation properties through physical and chemical crosslinking as a microenvironment for chondrogenic differentiation in the presence of bFGF and TGF-ß1 releasing nanoparticles (NPs) for the first time. Scaffolds with compressive moduli ranging from 95.70 ± 17.82 to 338.05 ± 38.24 kPa were obtained by changing both concentration PEGDMA and volume ratio of PEGDMA with 8% SF. Highest cell viability was observed in PEGDMA 10%-SF 8% (1:1) [PEG10-SF8(1:1)] hydrogel group. Release of bFGF and TGF-ß1 within PEG10-SF8(1:1) hydrogels resulted in higher DNA and glycosaminoglycans amounts indicating synergistic effect of dual release over proliferation and chondrogenic differentiation of dental pulp stem cells in hydrogels, respectively. Our results suggested that simultaneous delivery of bFGF and TGF-ß1 through utilization of PLGA NPs within PEG10-SF8(1:1) hydrogel provided a novel and versatile means for articular cartilage regeneration as they allow for dosage- and site-specific multiple growth factor delivery.

Use of Nanoparticles in Tissue Engineering and Regenerative Medicine.

Advances in nanoparticle (NP) production and demand for control over nanoscale systems have had significant impact on tissue engineering and regenerative medicine (TERM). NPs with low toxicity, contrasting agent properties, tailorable characteristics, targeted/stimuli-response delivery potential, and precise control over behavior (via external stimuli such as magnetic fields) have made it possible their use for improving engineered tissues and overcoming obstacles in TERM. Functional tissue and organ replacements require a high degree of spatial and temporal control over the biological events and also their real-time monitoring. Presentation and local delivery of bioactive (growth factors, chemokines, inhibitors, cytokines, genes etc.) and contrast agents in a controlled manner are important implements to exert control over and monitor the engineered tissues. This need resulted in utilization of NP based systems in tissue engineering scaffolds for delivery of multiple growth factors, for providing contrast for imaging and also for controlling properties of the scaffolds. Depending on the application, materials, as polymers, metals, ceramics and their different composites can be utilized for production of NPs. In this review, we will cover the use of NP systems in TERM and also provide an outlook for future potential use of such systems.

Examination of 2-methacryloyloxyethyl phosphorylcholine polymer coated acrylic resin denture base material: surface characteristics and Candida albicans adhesion.

The aim of this study is to evaluate the effects of 2-methacryloyloxyethyl phosphorylcholine (MPC) polymer coating with various concentrations onto acrylic resin denture base material on surface characteristics such as contact angle and surface roughness and on Candida albicans adhesion which is the major factor of denture stomatitis. Specimens, prepared from heat-polymerized acrylic denture base material, were divided into control and three test groups, randomly. Surfaces of the specimens in test groups were coated with poly(MPC) (PMPC) by graft polymerization of MPC in different concentrations (0.25 mol/L; 0.50 mol/L and 0.75 mol/L), while no surface treatment was applied to the control group. Contact angles and surface roughness were examined, and chemical composition of the surfaces was analyzed by Attenuated Total Reflectance-Fourier Transform Infrared Spectroscopy (FTIR) to verify the presence of PMPC coatings. Then, specimens were incubated with C. albicans for 18 h and the number of adhered cells was determined. Upon PMPC coating, the contact angle values statistically decreased, but no difference was found in surface roughness values. A statistically significant decrease was observed in C. albicans adhesion in parallel with the increase in the MPC polymer concentration. There was no significant difference between 0.50 mol/L and 0.75 mol/L groups in terms of adhesion. These findings indicated that graft polymerization of MPC on acrylic denture base material reduces the adhesion of C. albicans, and may be evaluated as a coating for prevention of denture stomatitis.

Glucose-Responsive Trehalose Hydrogel for Insulin Stabilization and Delivery.

Effective delivery of therapeutic proteins is important for many biomedical applications. Yet, the stabilization of proteins during delivery and long-term storage remains a significant challenge. Herein, a trehalose-based hydrogel is reported that stabilizes insulin to elevated temperatures prior to glucose-triggered release. The hydrogel is synthesized using a polymer with trehalose side chains and a phenylboronic acid end-functionalized 8-arm poly(ethylene glycol) (PEG). The hydroxyls of the trehalose side chains form boronate ester linkages with the PEG boronic acid cross-linker to yield hydrogels without any further modification of the original trehalose polymer. Dissolution of the hydrogel is triggered upon addition of glucose as a stronger binder to boronic acid (Kb = 2.57 vs 0.48 m-1 for trehalose), allowing the insulin that is entrapped during gelation to be released in a glucose-responsive manner. Moreover, the trehalose hydrogel stabilizes the insulin as determined by immunobinding after heating up to 90 °C. After 30 min heating, 74% of insulin is detected by enzyme-linked immunosorbent assay in the presence of the trehalose hydrogel, whereas only 2% is detected without any additives.

Encapsulated Hydrogels by E-beam Lithography and Their Use in Enzyme Cascade Reactions.

Electron beam (e-beam) lithography was employed to prepare one protein immobilized hydrogel encapsulated inside another by first fabricating protein-reactive hydrogels of orthogonal reactivity and subsequently conjugating the biomolecules. Exposure of thin films of eight arm star poly(ethylene glycol) (PEG) functionalized with biotin (Biotin-PEG), alkyne (Alkyne-PEG) or aminooxy (AO-PEG) end-groups to e-beam radiation resulted in cross-linked hydrogels with the respective functionality. It was determined via confocal microscopy that a nominal size exclusion effect exists for streptavidin immobilized on Biotin-PEG hydrogels of feature sizes ranging from 5 to 40 µm. AO-PEG was subsequently patterned as an encapsulated core inside a contiguous outer shell of Biotin-PEG. Similarly, Alkyne-PEG was patterned as a core inside an AO-PEG shell. The hydrogel reactive end-groups were conjugated to dyes or proteins of complementary reactivity, and the three-dimensional (3-D) spatial orientation was determined for both configurations using confocal microscopy. The enzyme glucose oxidase (GOX) was immobilized in the core of the encapsulated Alkyne-PEG core/ AO-PEG shell architecture, and horseradish peroxidase (HRP) was conjugated to the shell periphery. Bioactivity for the HRP-GOX enzyme pair was observed in this encapsulated configuration by demonstrating that the enzyme pair was capable of enzyme cascade reactions.

Direct Write Protein Patterns for Multiplexed Cytokine Detection from Live Cells Using Electron Beam Lithography.

Simultaneous detection of multiple biomarkers, such as extracellular signaling molecules, is a critical aspect in disease profiling and diagnostics. Precise positioning of antibodies on surfaces, especially at the micro- and nanoscale, is important for the improvement of assays, biosensors, and diagnostics on the molecular level, and therefore, the pursuit of device miniaturization for parallel, fast, low-volume assays is a continuing challenge. Here, we describe a multiplexed cytokine immunoassay utilizing electron beam lithography and a trehalose glycopolymer as a resist for the direct writing of antibodies on silicon substrates, allowing for micro- and nanoscale precision of protein immobilization. Specifically, anti-interleukin 6 (IL-6) and antitumor necrosis factor alpha (TNFα) antibodies were directly patterned. Retention of the specific binding properties of the patterned antibodies was shown by the capture of secreted cytokines from stimulated RAW 264.7 macrophages. A sandwich immunoassay was employed using gold nanoparticles and enhancement with silver for the detection and visualization of bound cytokines to the patterns by localized surface plasmon resonance detected with dark-field microscopy. Multiplexing with both IL-6 and TNFα on a single chip was also successfully demonstrated with high specificity and in relevant cell culture conditions and at different times after cell stimulation. The direct fabrication of capture antibody patterns for cytokine detection described here could be useful for biosensing applications.

Imine Hydrogels with Tunable Degradability for Tissue Engineering.

A shortage of available organ donors has created a need for engineered tissues. In this context, polymer-based hydrogels that break down inside the body are often used as constructs for growth factors and cells. Herein, we report imine cross-linked gels where degradation is controllable by the introduction of mixed imine cross-links. Specifically, hydrazide-functionalized poly(ethylene glycol) (PEG) reacts with aldehyde-functionalized PEG (PEG-CHO) to form hydrazone linked hydrogels that degrade quickly in media. The time to degradation can be controlled by changing the structure of the hydrazide group or by introducing hydroxylamines to form nonreversible oxime linkages. Hydrogels containing adipohydrazide-functionalized PEG (PEG-ADH) and PEG-CHO were found to degrade more rapidly than gels formed from carbodihydrazide-functionalized PEG (PEG-CDH). Incorporating oxime linkages via aminooxy-functionalized PEG (PEG-AO) into the hydrazone cross-linked gels further stabilized the hydrogels. This imine cross-linking approach should be useful for modulating the degradation characteristics of 3D cell culture supports for controlled cell release.

Trehalose glycopolymer resists allow direct writing of protein patterns by electron-beam lithography.

Direct-write patterning of multiple proteins on surfaces is of tremendous interest for a myriad of applications. Precise arrangement of different proteins at increasingly smaller dimensions is a fundamental challenge to apply the materials in tissue engineering, diagnostics, proteomics and biosensors. Herein, we present a new resist that protects proteins during electron-beam exposure and its application in direct-write patterning of multiple proteins. Polymers with pendant trehalose units are shown to effectively crosslink to surfaces as negative resists, while at the same time providing stabilization to proteins during the vacuum and electron-beam irradiation steps. In this manner, arbitrary patterns of several different classes of proteins such as enzymes, growth factors and immunoglobulins are realized. Utilizing the high-precision alignment capability of electron-beam lithography, surfaces with complex patterns of multiple proteins are successfully generated at the micrometre and nanometre scale without requiring cleanroom conditions.

Biodegradable elastomers for biomedical applications and regenerative medicine.

Synthetic biodegradable polymers are of great value for the preparation of implants that are required to reside only temporarily in the body. The use of biodegradable polymers obviates the need for a second surgery to remove the implant, which is the case when a nondegradable implant is used. After implantation in the body, biomedical devices may be subjected to degradation and erosion. Understanding the mechanisms of these processes is essential for the development of biomedical devices or implants with a specific function, for example, scaffolds for tissue-engineering applications. For the engineering and regeneration of soft tissues (e.g., blood vessels, cardiac muscle and peripheral nerves), biodegradable polymers are needed that are flexible and elastic. The scaffolds prepared from these polymers should have tuneable degradation properties and should perform well under long-term cyclic deformation conditions. The required polymers, which are either physically or chemically crosslinked biodegradable elastomers, are reviewed in this article.

Morphing hydrogel patterns by thermo-reversible fluorescence switching.

Stimuli responsive surfaces that show reversible fluorescence switching behavior in response to temperature changes were fabricated. Oligo(ethylene glycol) methacrylate thermoresponsive polymers with amine end-groups were prepared by atom transfer radical polymerization (ATRP). The polymers were patterned on silicon surfaces by electron beam (e-beam) lithography, followed by conjugation of self-quenching fluorophores. Fluorophore conjugated hydrogel thin films were bright when the gels were swollen; upon temperature-induced collapse of the gels, self-quenching of the fluorophores led to significant attenuation of fluorescence. Importantly, the fluorescence was regained when the temperature was cooled. The fluorescence switching behavior of the hydrogels for up to ten cycles was investigated and the swelling-collapse was verified by atomic force microscopy. Morphing surfaces that change shape several times upon increase in temperature were obtained by patterning multiple stimuli responsive polymers.

Chemoselective immobilization of proteins by microcontact printing and bio-orthogonal click reactions.

Herein, a combination of microcontact printing of functionalized alkanethiols and site-specific modification of proteins is utilized to chemoselectively immobilize proteins onto gold surfaces, either by oxime- or copper-catalyzed alkyne-azide click chemistry. Two molecules capable of click reactions were synthesized, an aminooxy-functionalized alkanethiol and an azide-functionalized alkanethiol, and self-assembled monolayer (SAM) formation on gold was confirmed by IR spectroscopy. The alkanethiols were then individually patterned onto gold surfaces by microcontact printing. Site-specifically modified proteins-horse heart myoglobin (HHMb) containing an N-terminal α-oxoamide and a red fluorescent protein (mCherry-CVIA) with a C-terminal alkyne-were immobilized by incubation onto respective stamped functionalized alkanethiol patterns. Pattern formation was confirmed by fluorescence microscopy.

Trehalose glycopolymers as excipients for protein stabilization.

Herein, the synthesis of four different trehalose glycopolymers and investigation of their ability to stabilize proteins to heat and lyophilization stress are described. The disaccharide, α,α-trehalose, was modified with a styrenyl acetal, methacrylate acetal, styrenyl ether, or methacrylate moiety resulting in four different monomers. These monomers were then separately polymerized using free radical polymerization with azobisisobutyronitrile (AIBN) as an initiator to synthesize the glycopolymers. Horseradish peroxidase and glucose oxidase were incubated at 70 and 50 °C, respectively, and ß-galactosidase was lyophilized multiple times in the presence of various ratios of the polymers or trehalose. The protein activities were subsequently tested and found to be significantly higher when the polymers were present during the stress compared to no additive and to equivalent amounts of trehalose. Different molecular weights (10 kDa, 20 kDa, and 40 kDa) were tested, and all were equivalent in their stabilization ability. However, some subtle differences were observed regarding stabilization ability between the different polymer samples, depending on the stress. Small molecules such as benzyl ether trehalose were not better stabilizers than trehalose, and the trehalose monomer decreased protein activity, suggesting that hydrophobized trehalose was not sufficient and that the polymeric structure was required. In addition, cytotoxicity studies with NIH 3T3 mouse embryonic fibroblast cells, RAW 264.7 murine macrophages, human dermal fibroblasts (HDFs), and human umbilical vein endothelial cells (HUVECs) were conducted with polymer concentrations up to 8 mg/mL. The data showed that all four polymers were noncytotoxic for all tested concentrations. The results together suggest that trehalose glycopolymers are promising as additives to protect proteins from a variety of stressors.

Physical properties and erosion behavior of poly(trimethylene carbonate-co-ε-caprolactone) networks.

Form-stable resorbable networks are prepared by gamma irradiating trimethylene carbonate (TMC)- and ε-caprolactone (CL)-based (co)polymer films. To evaluate their suitability for biomedical applications, their physical properties and erosion behavior are investigated. Homopolymer and copolymer networks that are amorphous at room temperature are flexible and rubbery with elastic moduli ranging from 1.8 ± 0.3 to 5.2 ± 0.4 MPa and permanent set values as low as 0.9% strain. The elastic moduli of the semicrystalline networks are higher and range from 61 ± 3 to 484 ± 34 MPa. The erosion behavior of (co)polymer networks is investigated in vitro using macrophage cultures, and in vivo by subcutaneous implantation in rats. In macrophage cultures, as well as upon implantation, a surface erosion process is observed for the amorphous (co)polymer networks, while an abrupt decrease in the rate and a change in the nature of the erosion process are observed with increasing crystallinity. These resorbable and form-stable networks with tuneable properties may find application in a broad range of biomedical applications.

Crosslinking of trimethylene carbonate and D, L-lactide (co-) polymers by gamma irradiation in the presence of pentaerythritol triacrylate.

High-molecular-weight (co)polymers of trimethylene carbonate and D,L-lactide are efficiently crosslinked using PETA during gamma irradiation. Form-stable networks with gel contents of 86 ± 5 to 96 ± 1 are obtained from non-crystalline (co)polymers. Glass transition temperatures and elastic moduli of the networks can be varied by adjusting the copolymer composition. The PETA-containing (co)polymer networks are not cytotoxic. Upon incubation in macrophage cultures for 14 d, all (co)polymer films and PETA-containing network films erode to varying extents, showing that these materials can be degraded by cell-mediated erosion processes. This method is very useful for the facile preparation of TMC- and DLLA-containing form-stable networks from high-molecular-weight polymers.

Resorbable elastomeric networks prepared by photocrosslinking of high-molecular-weight poly(trimethylene carbonate) with photoinitiators and poly(trimethylene carbonate) macromers as crosslinking aids.

Resorbable and elastomeric poly(trimethylene carbonate) (PTMC) networks were efficiently prepared by photoinitiated crosslinking of linear high-molecular-weight PTMC. To crosslink PTMC films, low-molecular-weight PTMC macromers with methacrylate end groups were synthesized and used as crosslinking aids. By exposing PTMC films containing only photoinitiator (Irgacure(®) 2959) or both photoinitiator and PTMC macromers to ultraviolet light, PTMC networks with high gel contents (87-95%) could be obtained. The crosslink density could be readily varied by adjusting the irradiation time or the amount of crosslinking aid used. The formed networks were flexible, with low elastic modulus values ranging from 7.1 to 7.5MPa, and also showed excellent resistance to creep in cyclic tests. In vitro experiments showed that the photocrosslinked PTMC networks could be eroded by macrophages, and upon incubation in aqueous cholesterol esterase enzyme- or potassium dioxide solutions. The rate of surface erosion of photocrosslinked PTMC networks was significantly lower than that observed for films prepared from linear PTMC. These resorbable PTMC elastomeric networks are compatible with cells and may find application in tissue engineering and controlled release.

In vivo behavior of trimethylene carbonate and ε-caprolactone-based (co)polymer networks: degradation and tissue response.

The in vivo erosion behavior of crosslinked (co)polymers based on trimethylene carbonate (TMC) and ε-caprolactone (CL) was investigated. High molecular weight poly(trimethylene carbonate) (PTMC) homopolymer- and copolymer films were crosslinked by gamma irradiation. To adjust the in vivo erosion rate of the (co)polymer films, both the irradiation dose (25, 50, or 100 kGy) for PTMC and composition (100-70 mol % TMC) at a constant irradiation dose of 25 kGy were varied. After subcutaneous implantation of irradiated films in rats, their in vivo behavior was evaluated qualitatively and quantitatively. When the irradiation dose for PTMC was increased from 25 to 100 kGy, the erosion rate of nonextracted PTMC films (determined at day 5) decreased from 39.7 ± 16.0 µm day(-1) to 15.1 ± 2.5 µm day(-1), and the number of lymphocytes in the tissue surrounding the films decreased from 235 ± 114 cells mm(-2) to 64 ± 33 cells mm(-2). The number of macrophages and giant cells at the tissue-polymer interface also decreased with increasing irradiation dose. All (co)polymer films eroded completely within 28 days of implantation. Variation of the TMC content of gamma irradiated (co)polymer films did not affect the tissue response to the gamma irradiated (co)polymer films and their in vivo erosion behavior much.

Biodegradable elastomeric networks: highly efficient cross-linking of poly(trimethylene carbonate) by gamma irradiation in the presence of pentaerythritol triacrylate.

Biodegradable elastomeric poly(trimethylene carbonate) (PTMC) networks were efficiently formed by gamma irradiating the linear polymer in the presence of pentaerythritol triacrylate (PETA). The properties of networks formed upon irradiation of PTMC films containing (0, 1, 5 wt %) PETA as a cross-linking aid were evaluated. The gel contents and network densities increased with increasing PETA contents, irradiation dose, and initial polymer molecular weights. At a dose of 25 kGy, networks with gel fractions up to 0.96 could be obtained. The networks were noncytotoxic, had elastic moduli below 10.7 MPa and high tensile strengths of up to 37.7 MPa. The incorporation of PETA also improved the resistance to creep and to tear propagation significantly, resulting in permanent set values that were as low as 0.9% strain and tear strengths up to 9.3 ± 2.0 N/mm. Furthermore, the enzymatic erosion rates of the networks could be decreased from 12.0 ± 2.9 to 3.0 ± 1.6 µm/day. These biodegradable elastomeric PTMC networks may be utilized in a broad range of medical applications.