Highly effective adsorption of heavy metal ions from aqueous solutions by macroporous xylan-rich hemicelluloses-based hydrogel

Xylan-rich hemicelluloses-based hydrogel was developed as a novel porous bioadsorbent by graft co-polymerization of acrylic acid (AA) and xylan-rich hemicelluloses for adsorption of heavy metal ions (Pd(2+), Cd(2+), and Zn(2+)) from aqueous solutions. The chemical structure, the interaction between the hydrogel and metal ions, and the porous structure of xylan-rich hemicelluloses-g-AA hydrogel were revealed by Fourier transform infrared spectroscopy and scanning electron microscopy. The effects of AA and cross-linker dosage, pH value, contacting time, and initial concentration of metal ion on the adsorption capacity were studied. The adsorption equilibrium time was about 60 min from the adsorption kinetics study. The maximum adsorption capacities of Pd(2+), Cd(2+), and Zn(2+) were 859, 495, and 274 mg/g, respectively. Furthermore, xylan-rich hemicelluloses-g-AA hydrogel also exhibited highly efficient regeneration and metal ion recovery efficiency and can be reused without noticeable loss of adsorption capacity for Pd(2+), Cd(2+), and Zn(2+) after quite a number of repeated adsorption/desorption cycles.

Hydrogel of ketoconazole and PAMAM dendrimers: formulation and antifungal activity

Ketoconazole (KET), an imidazole derivative with well-known antifungal properties, is lipophilic and practically insoluble in water, therefore its clinical use has some practical disadvantages. The aim of the present study was to investigate the influence of PAMAM-NH₂ and PAMAM-OH dendrimers generation 2 and generation 3 on the solubility and antifungal activity of KET and to design and evaluate KET hydrogel with PAMAM dendrimers. It was shown that the surface charge of PAMAM dendrimers strongly affects their influence on the improvement of solubility and antifungal activity of KET. The MIC and MFC values obtained by broth dilution method indicate that PAMAM-NH₂ dendrimers significantly (up to 16-fold) increased the antifungal activity of KET against Candida strains (e.g., in culture Candida albicans 1103059/11 MIC value was 0.008 μg/mL and 0.064 μg/mL, and MFC was 2 μg/mL and 32 μg/mL for KET in 10 mg/mL solution of PAMAM-NH₂ G2 and pure KET, respectively). Antifungal activity of designed KET hydrogel with PAMAM-NH₂ dendrimers measured by the plate diffusion method was definitely higher than pure KET hydrogel and than commercial available product. It was shown that the improvement of solubility and in the consequence the higher KET release from hydrogels seems to be a very significant factor affecting antifungal activity of KET in hydrogels containing PAMAM dendrimers.

Biopolymer system for cell recovery from microfluidic cell capture devices

Microfluidic systems for affinity-based cell isolation have emerged as a promising approach for the isolation of specific cells from complex matrices (i.e., circulating tumor cells in whole blood). However, these technologies remain limited by the lack of reliable methods for the innocuous recovery of surface captured cells. Here, we present a biofunctional sacrificial hydrogel coating for microfluidic chips that enables the highly efficient release of isolated cells (99% ± 1%) following gel dissolution. This covalently cross-linked alginate biopolymer system is stable in a wide variety of physiologic solutions (including EDTA treated whole blood) and may be rapidly degraded via backbone cleavage with alginate lyase. The capture and release of EpCAM expressing cancer cells using this approach was found to have no significant effect on cell viability or proliferative potential, and recovered cells were demonstrated to be compatible with downstream immunostaining and FISH analysis.

Graphene-supported hemin as a highly active biomimetic oxidation catalyst

Well supported: stable hemin-graphene conjugates formed by immobilization of monomeric hemin on graphene, showed excellent catalytic activity, more than 10 times better than that of the recently developed hemin-hydrogel system and 100 times better than that of unsupported hemin. The catalysts also showed excellent binding affinities and catalytic efficiencies approaching that of natural enzymes.

Preparation of a hyaluronic acid hydrogel through polyion complex formation using cationic polylactide-based microspheres as a biodegradable cross-linking agent

A novel hyaluronic acid (HA)-based hydrogel was prepared through polyion complex (PIC) formation between cationic polylactide (PLA)-based microspheres (MS+) and hyaluronic acid (HA-) as an anionic polyelectrolyte. The MS+ and HA formed a biodegradable PIC hydrogel (HA-/MS+) when mixed in aqueous media. The swelling behavior and mechanical properties of the PIC hydrogel could be controlled by changing the charge ratio between HA- and MS+. In addition, the HA-/MS+ PIC hydrogel resulted in a lower inflammatory response compared with a collagen hydrogel in vivo.

A hydrogel system for stimulus-responsive, oxygen-sensitive in situ gelation

A hydrogel system that is designed to gel due to oxidation by molecular oxygen is described. This is achieved by the use of a branched poly(ethylene glycol) modified with thiol end groups. A stable precursor molecule, starPEG thioacetate, was synthesized by radical addition of thioacetic acid to an intermediate starPEG allyl ether. Rapid deprotection of the thiol can be achieved using a base, e.g. sodium hydroxide, quantitatively liberating a thiol group and a non-toxic acetate ion. This step can be carried out under anaerobic conditions, yielding a solution with known thiol content that can be stored. The reaction with oxygen is accelerated by the use of a catalyst based on Fenton chemistry, which makes the material useful for biomedical applications where in situ polymerization of an injectable material is beneficial. This gelation takes place under near physiological conditions without the need for a cross-linking agent.

Effects of bFGF incorporated into a gelatin sheet on wound healing

Basic fibroblast growth factor (bFGF) is well known to promote the proliferation of almost all cells associated with wound healing. However, as the activation duration of bFGF is very short in vivo, we incorporated bFGF into an acidic gelatin hydrogel and studied the sustained release of bFGF in vivo. In addition, we investigated the effects of the acidic gelatin sheet containing bFGF on wound healing. To distinguish wound contraction from neoepithelialization, we measured both the wound area and neoepithelium length. Other histological parameters such as thickness of granulation tissue and number of capillaries were also determined as indices of wound healing. Fibrous tissue was assessed using an Elastica van Gieson and Azan stain. A skin defect (1.5 x 1.5 cm) of full thickness was created on the back of each test mouse and the wound was covered with an acidic gelatin hydrogel, referred to as a gelatin sheet in this study (2 x 2 cm), with bFGF (100 microg/site) (A) or without bFGF (B). 1, 2, 3, 5, 7 and 14 days after covering, mice were killed and an enzyme-linked immunosorbent assay (ELISA) was performed to estimate the concentration of bFGF in the plasma. In another experiment, each wound was covered with (A), (B) or a hydrogel dressing (control group, C) and the wound area was measured 1 or 2 weeks postoperatively with a computer planimeter. The histological parameters, as mentioned above, were assessed using a light microscope. Sustained release of bFGF from the gelatin sheet was observed and the gelatin sheet containing bFGF promoted neoepithelialization, granulation, neovascularization and wound closure. This gelatin sheet containing bFGF was concluded to be effective for wound healing and promising for clinical use.

In vivo degradability of hydrogels prepared from different gelatins by various cross-linking methods

This study is an investigation to evaluate the in vivo degradation of gelatin hydrogels in terms of their number of cross-links. Various hydrogels were prepared from acidic gelatin, extracted from bovine bone, porcine skin or fish scale, and basic gelatin, extracted from porcine skin, through four types of cross-linking methods, i.e., glutaraldehyde (GA) or dehydrothermal treatment and ultraviolet (UV) or electron beam irradiation. The water content of hydrogels and their number of cross-links, calculated from the tensile modulus of hydrogels, were evaluated as the measure of hydrogel cross-linking extent. Following subcutaneous implantation of 125I-labeled gelatin hydrogels into mice, the radioactivity remaining was measured at different time intervals to assess the in vivo degradability of hydrogels. Irrespective of the gelatin type and cross-linking method, a good correlation was found between the in vivo degradability of hydrogels and their number of cross-links, which is different from the correlation to their water content. This finding indicates that the degradability of hydrogels is governed by their number of cross-links.

Controlling modulus and morphology of hydrogel tubes through surface modification

Crosslinked, porous poly(2-hydroxyethyl methacrylate-co-methyl methacrylate) (PHEMA-MMA) tubes were prepared in cylindrical glass molds using a new centrifugal casting process developed in our group. The resulting hydrogel tubes have a bi-phasic wall structure, with a spongy inner layer and a gel-like outer layer, the latter of which provides mechanical strength to the tube. While many factors influence wall morphology and, thus, mechanical properties, we focused on the effect of the surface properties of the glass mold in which tubes are synthesized. Specifically, we investigated the impact of a diverse set of silane modifications of the glass mold on tube morphology, elastic modulus and mold release. We treated activated glass surfaces with one of three alkoxysilanes having either ethoxy, amine or fluorocarbon end-groups. Silane-modified glass surfaces were found to be more hydrophobic than the unmodified glass mold, with the most hydrophobic surface being that of the fluorocarbon-terminated silane. The presence of the silane layer on the mold was confirmed by X-ray photoelectron spectroscopy and the stability of this modification was confirmed by examining the surface chemistry of the hydrogel tubes. The biphasic hydrogel tube wall structure was observed for all tubes, yet those tubes synthesized in unmodified molds had a cracked outer morphology, whereas those synthesized in silane-modified molds had a smooth outer morphology. This influenced the mechanical properties of the tubes where tubes synthesized in silane-modified molds had a significantly greater elastic modulus than those tubes synthesized in unmodified molds. Release from the molds was easiest with ethoxy- and amine-functionalized silane mold modifications.

LF-NMR water self-diffusion and relaxation time measurements of hydrogel contact lenses interacting with artificial tears

The different swelling properties of ionic and non-ionic lenses, immersed in sodium chloride or artificial tears, were investigated by Low-Field Nuclear Magnetic Resonance (LF-NMR) through relaxation time and self-diffusion coefficient measurements. A new model was developed to estimate the water self-diffusion coefficient inside the lenses, the results of which revealed a different mechanism of interaction for ionic versus non-ionic materials with artificial tears. The consequence of this finding suggests clinical implications.

Hydrophilic interpenetrating polymer networks of poly(dimethyl siloxane) (PDMS) as biomaterial for cochlear implants

Poly(dimethyl siloxane) (PDMS) was bulk-modified to develop a new intra-cochlear electrode that can closely hug the inner wall of scala tympani (ST). The hydrophilicity of bulk and surface of PDMS was changed using a sequential method for preparation of interpenetrating polymer networks (IPNs). A series of IPNs, based on PDMS and poly(acrylic acid) (PAAc), was synthesized and characterized by means of attenuated total reflectance Fourier transform infrared spectroscopy, water contact-angle measurement, dynamic mechanical thermal analysis and peel strength tests. The performances of actual-sized fabricated electrodes were assessed inside a transparent model of ST, which was filled with saline. The cell behavior of L929 fibroblasts on materials was studied in vitro.

Synthesis and characterization of a novel hyaluronic acid hydrogel

Hyaluronic acid (hyaluronan, HA) has many medical applications as a biomaterial. To enhance its biostability, a novel hydrogel of cross-linked hyaluronic acid was prepared using a double cross-linking process, which involves building cross-linkages between hydroxyl group pairs and carboxyl group pairs. The present study explored a number of cross-linking processes in order to obtain different degrees of cross-linking, which were evaluated by the measurement of water absorption capacity as an index of the gel network density. To gain a better understanding of the stability of the gel, the chemical structure and particularly the rheological behaviour of the cross-linked HA, which included the influences of factors, such as degree of cross-linking, HA concentration and gel particle size, were investigated. The in vitro biostability against hyaluronidase and free radical degradation was tested to show that the cross-linked hydrogel had improved resistance to in vitro hyaluronidase and free radical degradation.

Cell viability of chitosan-containing semi-interpenetrated hydrogels based on PCL-PEG-PCL diacrylate macromer

Chitosan-modified biodegradable hydrogels were prepared by UV irradiation of solutions in mild aqueous acidic media of poly(caprolactone)-co-poly(ethylene glycol)-co-poly(caprolactone) diacrylate (PCL-PEG-PCL-DA) and chitosan. Hydrogels obtained were characterized using FT-IR, DSC, TGA and XPS. FT-IR, TGA and DSC revealed the semi-interpenetrating polymer network structure formed in the hydrogel. Though the water swelling degree of these chitosan-modified hydrogels was substantial in the range of 322-539%, it was found that fibroblasts could still attach, spread and grow on them; this is in contrast to the commonly investigated PEG-diacrylate hydrogel. The MTT assay demonstrated that cells could grow better on 3 or 6% chitosan-modified hydrogel than unmodified PCL-PEG-PCL-DA hydrogels or low-content (1%) chitosan-modified PCL-PEG-PCL-DA hydrogel. Increased chitosan content resulted in increased cell interaction and also decreased water swelling, both of which results in increased cell attachment and spread.

Aptamer-functionalized hydrogel microparticles for fast visual detection of mercury(II) and adenosine

With a low optical background, high loading capacity, and good biocompatibility, hydrogels are ideal materials for immobilization of biopolymers to develop optical biosensors. We recently immobilized mercury and lead binding DNAs within a monolithic gel and demonstrated ultrasensitive visual detection of these heavy metals. The high sensitivity was attributed to the enrichment of the analytes into the gels. The signaling kinetics was slow, however, taking about 1 h to obtain a stable optical signal because of a long diffusion distance. In this work, we aim to understand the analyte enrichment process and improve the signaling kinetics by preparing hydrogel microparticles. DNA-functionalized gel beads were synthesized using an emulsion polymerization technique and most of the beads were between 10 and 50 μm. Acrydite-modified DNA was incorporated by copolymerization. Visual detection of 10 nM Hg(2+) was still achieved and a stable signal was obtained in just 2 min. The gel beads could be spotted to form a microarray and dried for storage. A new visual sensor for adenosine was designed and immobilized within the gel beads. The adenosine aptamer binds its target about 1000-fold less tightly compared to the mercury binding DNA, allowing a comparison to be made on analyte enrichment by aptamer-functionalized hydrogels.

A randomized, controlled clinical evaluation of a synthetic gel membrane for guided bone regeneration around dental implants: clinical and radiologic 1- and 3-year results

PURPOSE

The objective of this study was to determine whether a synthetic bioresorbable polyethylene glycol (PEG) hydrogel membrane could provide similar clinical and radiographic outcomes as a standard collagen membrane, both in combination with a membrane-supporting material, during follow-up periods of 1 and 3 years.

MATERIALS AND METHODS

This study enrolled patients requiring implant treatment with an expected osseous defect in the posterior maxilla or mandible. Defects around the implants were grafted with deproteinized bovine bone mineral and covered with either a collagen membrane or a PEG hydrogel membrane, which is applied as a liquid and becomes a solid gel in situ. Surgical re-entry was performed after 6 months, and fixed partial dentures were inserted subsequently. Patients were examined clinically and radiographically 1 and 3 years after loading.

RESULTS

Thirty-six of the 37 included patients were reexamined in the third year. The implant survival rate at 3 years was 100%. The peri-implant tissues were healthy, with no differences between the two groups. Compared to the time of surgery, the mean changes in the distance between the first bone-to-implant contact to the transition point (ie, rough implant surface to polished neck portion) were 0.43 ± 0.56 mm (PEG) and 0.21 ± 0.36 mm (collagen) at 1 year and 0.61 ± 0.89 mm (PEG) and 0.33 ± 0.64 mm (collagen) at 3 years. The respective differences between groups were 0.13 mm (1 year) and 0.31 mm (3 years), which were not significant at either time point (analysis of covariance).

CONCLUSION

The tested PEG hydrogel was as successful as a standard collagen membrane for the treatment of bony dehiscence defects around dental implants after follow-up periods of 1 and 3 years.

Gelatin-based anionic hydrogel as biocompatible substrate for human keratinocyte growth

Ionic hydrogels are biocompatible candidates for skin tissue engineering. Two hydrogels synthesized by crosslinking gelatin with polylysine (positively charged HG1) or polyglutamic acid (negatively charged HG2) were tested using spontaneously immortalized human keratinocytes (HaCaT). HaCaT cells displayed higher adhesion and proliferation onto HG2, forming a continuous and stratified epithelium after 7 days. Moreover HaCaT cells grown onto HG2 showed a decreased Epilysin and Filaggrin expression, while transglutaminase-1 expression was increased. Those data indicate that human keratinocyte can form a stratified epithelium onto HG2 that could therefore be an useful tool for skin tissue engineering.

Local mechanical stimulation of Mardin-Darby canine kidney cell sheets on temperature-responsive hydrogel

Collective motion of cell sheets plays a role not only in development and repair, but also in devastating diseases such as cancer. However, unlike single-cell motility, collective motion of cell sheets involves complex cell-cell communication during migration; therefore, its mechanism is largely unknown. To elucidate propagation of signaling transduced by cell-cell interaction, we designed a hydrogel substrate that can cause local mechanical stretching of cell sheets. Poly (N-isopropyl acrylamide) (PNIPAAm) hydrogel is a temperature-responsive polymer gel whose volume changes isotropically in response to temperature changes below 37 °C. We designed a combined hydrogel substrate consisting of collagen-immobilized PNIPAAm as the local stimulation side and polyacrylamide (PAAm) as the non-stimulation side to assess propagation of mechanical transduction. Mardin-Darby canine kidney (MDCK) cells adhered to the collagen-immobilized PNIPAAm gel increased it area and were flattened as the gel swelled with temperature decrease. E-cadherin in these cells became undetectable in some domains, and actin stress fibers were more clearly observed at the cell base. In contrast, E-cadherin in cells adhered to the collagen-immobilized PAAm side was equally stained as that in cells adhered to the collagen-immobilized PAAm side even after temperature decrease. ERK1/2 MAPK activation of cells on the non-stimulated substrate occurred after partial stretching of the cell sheet suggesting the propagation of signaling. These results indicate that a change in the balance of mechanical tension induced by partial stretching of cell sheets leads to activation and propagation of the cell signaling.

Multi-material bio-fabrication of hydrogel cantilevers and actuators with stereolithography

Cell-based biohybrid actuators are integrated systems that use biological components including proteins and cells to power material components by converting chemical energy to mechanical energy. The latest progress in cell-based biohybrid actuators has been limited to rigid materials, such as silicon and PDMS, ranging in elastic moduli on the order of mega (10(6)) to giga (10(9)) Pascals. Recent reports in the literature have established a correlation between substrate rigidity and its influence on the contractile behavior of cardiomyocytes (A. J. Engler, C. Carag-Krieger, C. P. Johnson, M. Raab, H. Y. Tang and D. W. Speicher, et al., J. Cell Sci., 2008, 121(Pt 22), 3794-3802, P. Bajaj, X. Tang, T. A. Saif and R. Bashir, J. Biomed. Mater. Res., Part A, 2010, 95(4), 1261-1269). This study explores the fabrication of a more compliant cantilever, similar to that of the native myocardium, with elasticity on the order of kilo (10(3)) Pascals. 3D stereolithographic technology, a layer-by-layer UV polymerizable rapid prototyping system, was used to rapidly fabricate multi-material cantilevers composed of poly(ethylene glycol) diacrylate (PEGDA) and acrylic-PEG-collagen (PC) mixtures. The incorporation of acrylic-PEG-collagen into PEGDA-based materials enhanced cell adhesion, spreading, and organization without altering the ability to vary the elastic modulus through the molecular weight of PEGDA. Cardiomyocytes derived from neonatal rats were seeded on the cantilevers, and the resulting stresses and contractile forces were calculated using finite element simulations validated with classical beam equations. These cantilevers can be used as a mechanical sensor to measure the contractile forces of cardiomyocyte cell sheets, and as an early prototype for the design of optimal cell-based biohybrid actuators.

Maleimide cross-linked bioactive PEG hydrogel exhibits improved reaction kinetics and cross-linking for cell encapsulation and in situ delivery

Engineered polyethylene glycol-maleimide matrices for regenerative medicine exhibit improved reaction efficiency and wider range of Young’s moduli by utilizing maleimide cross-linking chemistry. This hydrogel chemistry is advantageous for cell delivery due to the mild reaction that occurs rapidly enough for in situ delivery, while easily lending itself to “plug-and-play” design variations such as incorporation of enzyme-cleavable cross-links and cell-adhesion peptides.

Imaging enzyme-triggered self-assembly of small molecules inside live cells

Self-assembly of small molecules in water to form nanofibres, besides generating sophisticated biomaterials, promises a simple system inside cells for regulating cellular processes. But lack of a convenient approach for studying the self-assembly of small molecules inside cells hinders the development of such systems. Here we report a method to image enzyme-triggered self-assembly of small molecules inside live cells. After linking a fluorophore to a self-assembly motif to make a precursor, we confirmed by (31)P NMR and rheology that enzyme-triggered conversion of the precursor to a hydrogelator results in the formation of a hydrogel via self-assembly. The imaging contrast conferred by the nanofibres of the hydrogelators allowed the evaluation of intracellular self-assembly, the dynamics and the localization of the nanofibres of the hydrogelators in live cells. This approach explores supramolecular chemistry inside cells and may lead to new insights, processes or materials at the interface of chemistry and biology.

Investigation of the free volume changes in one day hydrogel and one day silicone-hydrogel contact lenses by means of positron annihilation lifetime spectroscopy

PURPOSE OF JOB: The evolution of materials used to manufacture contact lenses, there is a need to increase comfort and visual acuity man while improving biocompatibility and minimizing the impact of the material on the physiology of the cornea. There is still a problem with limiting the level of oxygen available to the cornea, resulting in various diseases. Therefore, the aim of this work is to investigate the physical and structural properties of hydrogel and silicone-hydrogel contact lenses.

MATERIALS AND METHODS

To achieve the main objective, the project involves the complete, systematic and comprehensive research methodology, techniques of positron lifetime spectroscopy PAL associated with polymerization, nanovoid natural structure of modern polymeric materials used in ophthalmology. This method is particularly sensitive to detect the structure of disordered materials with structural defects. Therefore it is reasonable to use PAL spectroscopy in studies of polymer nanostructures change contact lenses used in ophthalmology.

RESULTS

As a result of the measurements obtained curve describing the dependence of the number of counts of acts of annihilation as a function of time. Distribution of positron lifetime spectra into three components, allows to extract the longest third component which gives information about the geometrical parameters of free volume. Clear changes were observed long-living component lifetimes of ortho-positronium and their intensities between the lenses tested.

CONCLUSIONS

The measurements allowed us to isolate and calculate the value of long-living tau3 and its intensity I3, which values are component of positron lifetime associated with the formation of ortho-positronium (o-Ps) and is a measure of the density distribution of free volume creation. The results of these measurements indicate that the formation of free volume holes takes place both in the hydrogel lens and silicone-hydrogel. However, the size of free volume and the amount of free volume occurring for silicone-hydrogel lenses are greater than for hydrogel lenses. The study nanovoid structure of polymeric materials, their size and number suggest a relationship with the oxygen permeability of contact lenses, which implies a continuation and extension of the initial research.

[Regeneration of corneal epithelium using keratin modified chitosan membranes]

The cornea is a transparent front layer of the eye. It functions like a window that controls and focuses the light entering into the eye. The cornea contributes to 65-75% of the eye's total focusing power and it acts as a physical barrier against pathogenic microorganisms, dirt and other noxious physical factors. The corneal tissue is arranged in five basic layers. The outermost layer (epithelium) is made up of highly regenerative cells that allow for quick healing of superficial injuries. Eye infections, diseases, or mechanical injury can harm corneal epithelium and cause blindness. Under certain circumstances, to prevent that, it is recommended to perform complete corneal transplantation. However, due to lack of sufficient number of donors, researchers are searching for alternative solutions.. Regeneration of epidermal tissue can restore and ensure normal functioning of cornea. For that purpose proper grafts are needed. The goal of current research was to develop the material for scaffold preparation providing optimal conditions for the epithelium cornea cell culturing and to determine its chemical, physical, and biological properties. The scaffolds, which could be applied in ophthalmology should fulfill a lot of requirements, among them such as biocompatibility, biodegradability, restorability, non-toxicity. They should also have adequate mechanical strength, flexibility and porosity. The aim of this work was to synthesize and to determine the properties of polymeric material for ophthalmic surgery applications. A hydrogel scaffold in the form of membrane was obtained from chitosan - natural, biocompatible, biologically inert, stable in the natural environmental and antibacterial polysaccharide derived from chitin. Biodegradable chitosan films containing keratin were crosslinked with genipin - a naturally occurring and nontoxic agent. In this study we present physicochemical characterization of the scaffolds. Porosity, contact angle and swelling ratio (at different pH) were determined. The optical microscope technique was used to visualize the microstructure of the scaffolds. Atomic force microscopy (AFM) measurements revealed the topography of the surfaces of membranes. The biological tests have shown that epithelial cells seeded on the membranes proliferated efficiently.

Rapid purification of cell encapsulated hydrogel beads from oil phase to aqueous phase in a microfluidic device

In this paper, we demonstrate a new type of microfluidic chip that can realize continuous-flow purification of hydrogel beads from a carrier oil into aqueous solution by using a laminar-like oil/water interface. The microfluidic chip is composed by two functional components: (1) a flow-focusing bead generation module that can control size and shape of beads, (2) a bead extraction module capable of purifying hydrogel beads from oil into aqueous solution. This module is featured with large branch channels on one side and small ones on the opposite side. Water is continuously infused into the bead extraction module through the large branch channels, resulting in a laminar-like oil/water interface between the branch junctions. Simulation and experimental data show that the efficiency of oil depletion is determined by the relative flow rates between infused water and carrier oil. By using such a microfluidic device, viable cells (HCT116, colon cancer cell line) can be encapsulated in the hydrogel beads and purified into a cell culture media. Significantly improved cell viability was achieved compared to that observed by conventional bead purification approaches. This facile microfluidic chip could be a promising candidate for sample treatment in lab-on-a-chip applications.

Multifunctional core-shell nanoparticles: discovery of previously invisible biomarkers

Many low-abundance biomarkers for early detection of cancer and other diseases are invisible to mass spectrometry because they exist in body fluids in very low concentrations, are masked by high-abundance proteins such as albumin and immunoglobulins, and are very labile. To overcome these barriers, we created porous, buoyant, core-shell hydrogel nanoparticles containing novel high affinity reactive chemical baits for protein and peptide harvesting, concentration, and preservation in body fluids. Poly(N-isopropylacrylamide-co-acrylic acid) nanoparticles were functionalized with amino-containing dyes via zero-length cross-linking amidation reactions. Nanoparticles functionalized in the core with 17 different (12 chemically novel) molecular baits showed preferential high affinities (K(D) < 10(-11) M) for specific low-abundance protein analytes. A poly(N-isopropylacrylamide-co-vinylsulfonic acid) shell was added to the core particles. This shell chemistry selectively prevented unwanted entry of all size peptides derived from albumin without hindering the penetration of non-albumin small proteins and peptides. Proteins and peptides entered the core to be captured with high affinity by baits immobilized in the core. Nanoparticles effectively protected interleukin-6 from enzymatic degradation in sweat and increased the effective detection sensitivity of human growth hormone in human urine using multiple reaction monitoring analysis. Used in whole blood as a one-step, in-solution preprocessing step, the nanoparticles greatly enriched the concentration of low-molecular weight proteins and peptides while excluding albumin and other proteins above 30 kDa; this achieved a 10,000-fold effective amplification of the analyte concentration, enabling mass spectrometry (MS) discovery of candidate biomarkers that were previously undetectable.

Enzyme-directed assembly and manipulation of organic nanomaterials

Enzymes are the prime protagonists in the chemistry of living organisms. As such, chemists and biologists have long been fascinated by the array of highly selective transformations possible under biological conditions that are facilitated by enzyme-catalyzed reactions. Moreover, enzymes are involved in replicating, repairing and transmitting information in a highly selective and organized fashion through detection and signal amplification cascades. Indeed, because of their selectivity and potential for use outside of biological systems, enzymes have found immense utility in various biochemical assays and are increasingly finding applications in the preparation of small molecules. By contrast, the use of enzymatic reactions to prepare and build supramolecular and nanoscale materials is relatively rare. In this article, we seek to highlight efforts over the past 10 years at taking advantage of enzymatic reactions to assemble and manipulate complex soft, organic materials on the nanoscale. It is tantalizing to think of these processes as mimics of natural systems where enzymes are used in the assembly and transformation of the most complex nanomaterials known, for example, virus capsid assemblies and the myriad array of nanoscale biomolecular machinery.