Development of macroporous poly(ethylene glycol) hydrogel arrays within microfluidic channels

Visualization of Multiphase Reactive Flow and Mass Transfer in Functionalized Microfluidic Porous Media

Multiphase reactive flow in porous media is an important research topic in many natural and industrial processes. In the present work, photolithography is adopted to fabricate multicomponent mineral porous media in a microchannel, microfluidics experiments are conducted to capture the multiphase reactive flow, methyl violet 2B is employed to visualize the real-time concentration field of the acid solution and a sophisticated image processing method is developed to obtain the quantitative results of the distribution of different phases. With the advanced methods, experiments are conducted with different acid concentration and inlet velocity in different porous structures with different phenomena captured. Under a low acid concentration, the reaction will be single phase. In the gaseous cases with higher acid concentration, preferential flow paths with faster flow and reaction are formed by the multiphase hydrodynamic instabilities. In the experiments with different inlet velocities, it is observed that a higher inlet velocity will lead to a faster reaction but less gas bubbles generated. In contrast, more gas bubbles would be generated and block the flow and reaction under a lower inlet velocity. Finally, in heterogeneous structures, fractures or cavities would significantly redirect the flow and promote the formation of preferential flow path nearby.

Tuning the water intrinsic permeability of PEGDA hydrogel membranes by adding free PEG chains of varying molar masses

We explore the effect of poly(ethylene glycol) (PEG) molar mass on the intrinsic permeability and structural characteristics of poly(ethylene glycol) diacrylate PEGDA/PEG composite hydrogel membranes. We observe that by varying the PEG content and molar mass, we can finely adjust the water intrinsic permeability by several orders of magnitude. Notably, we show the existence of maximum water intrinsic permeability, already identified in a previous study to be located at the critical overlap concentration C* of PEG chains, for the highest PEG molar mass studied. Furthermore, we note that the maximum intrinsic permeability follows a non-monotonic evolution with respect to the PEG molar mass and reaches its peak at 35 000 g mol-1. Besides, our results show that a significant fraction of PEG chains is irreversibly trapped within the PEGDA matrix even for the lowest molar masses down to 600 g mol-1. This observation suggests the possibility of covalent grafting of the PEG chains onto the PEGDA matrix. CryoSEM and AFM measurements demonstrate the presence of large micron-sized cavities separated by PEGDA-rich walls whose nanometric structures strongly depend on the PEG content. By combining our permeability and structural measurements, we suggest that the PEG chains trapped inside the PEGDA-rich walls induce nanoscale defects in the crosslinking density, resulting in increased permeability below C*. Conversely, above C*, we speculate that partially trapped PEG chains may form a brush-like arrangement on the surface of the PEGDA-rich walls, leading to a reduction in permeability. These two opposing effects are anticipated to exhibit molar-mass-dependent trends, contributing to the non-monotonic variation of the maximum intrinsic permeability at C*. Overall, our results demonstrate the potential to fine-tune the properties of hydrogel membranes, offering new opportunities for separation applications.

Construction of a PEGDA/chitosan hydrogel incorporating mineralized copper-doped mesoporous silica nanospheres for accelerated bone regeneration

Hydrogels, integrating diverse biocompatible materials, have emerged as promising candidates for bone repair applications. This study presents a double network hydrogel designed for bone tissue engineering, combining poly(ethylene glycol) diacrylate (PEGDA) and chitosan (CS) crosslinked through UV polymerization and ionic crosslinking. Concurrently, copper-doped mesoporous silica nanospheres (Cu-MSNs) were synthesized using a one-pot method. Cu-MSNs underwent additional modification through in-situ biomineralization, resulting in the formation of an apatite layer. Polydopamine was employed to facilitate the deposition of Calcium (Ca) and Phosphate (P) ions on the surface of Cu-MSNs (Cu-MSNs/PDA@CaP). Composite hydrogels were created by integrating varied concentrations of Cu-MSNs/PDA@CaP (25, 50, 100, 150, 200 μg/mL). Characterization unveiled distinctive interconnected porous structures within the composite hydrogel, showcasing a notable 169.6 % enhancement in compressive stress (elevating from 89.01 to 240.19 kPa) compared to pure PEGDA. In vitro biocompatibility experiments illustrated that the composite hydrogel maintained elevated cell viability (up to 106.6 %) and facilitated rapid cell proliferation over 7 days. The hydrogel demonstrated a substantial 57.58 % rise in ALP expression and a surprising 235.27 % increase in ARS staining. Moreover, it significantly enhanced the expression of crucial osteogenic genes, such as run-related transcription factors 2 (RUNX2), collagen 1a1 (Col1a1), and secreted phosphoprotein 1 (Spp1), establishing it as a promising scaffold for bone regeneration. This study shows how Cu-MSNs/PDA@CaP were successfully integrated into a double network hydrogel, resulting in a composite material with good biological responses. Due to its improved characteristics, this composite hydrogel holds the potential for advancing bone regeneration procedures.

Co-immobilization of AOA strains with anammox bacteria in three different synthetic bio-granules maintained under two substrate-level conditions

Hydrogel encapsulation of ammonium oxidizing archaea (AOA) along with anammox bacteria holds potential to enable mainstream partial nitritation (PN)-anammox process attributing to AOA's high affinity to ammonia and oxygen. This study explored the growth of AOA and anammox in hydrogel-based synthetic biogranules by testing two AOA strains, three types of hydrogel beads and two substrate levels, to identify the optimal combination favoring the concomitant growth of AOA and anammox. The AOA Nitrososphaera viennensis (AOA-NV) exhibited higher abundance (10-2.3±0.6 AOA/16S) than the AOA-DW (10-4.7±0.8 AOA/16S) during the entire experimental period. Amongst the three types of hydrogel beads, the PVA-SA-BaCl2 (140 days) and PVA-SA-H3BO3 beads (>180 days) exhibited better long-term structural stability than the PEGDMA-SA-CaCl2 beads. The PVA-SA-H3BO3 beads exhibited the best long-term stability and both the PVA/SA BaCl2 and PVA-SA-H3BO3 beads had comparable ability to retain AOA, anammox and the overall microbial community. Substrate conditions rather than the bead type primarily controlled the microbial community structure. Modest substrate concentrations (1 mM NH4+-N in the feed and 0.8 mg/L dissolved oxygen (DO) in the reactor during aeration phase) followed by low substrate conditions (0.1 mM NH4+-N and 0.2 mg DO/L) both supported the growth of AOA and anammox, while the low substrate condition also suppressed the growth of ammonia oxidizing bacteria (AOB) and nitrite oxidizing bacteria (NOB), with AOA /AOB and anammox/NOB ratio of 0.7 and 0.4 at moderate substrate condition and 16.5 and 2.6 at low substrate condition.

Selective Adsorption of Ionic Species Using Macroporous Monodispersed Polyethylene Glycol Diacrylate/Acrylic Acid Microgels with Tunable Negative Charge

Monodispersed polyethylene glycol diacrylate (PEGDA)/acrylic acid (AA) microgels with a tuneable negative charge and macroporous internal structure have been produced using a Lego-inspired droplet microfluidic device. The surface charge of microgels was controlled by changing the content of AA in the monomer mixture from zero (for noncharged PEGDA beads) to 4 wt%. The macroporosity of the polymer matrix was introduced by adding 20 wt% of 600-MW polyethylene glycol (PEG) as a porogen material into the monomer mixture. The porogen was successfully leached out with acetone after UV-crosslinking, which resulted in micron-sized cylindrical pores with crater-like morphology, uniformly arranged on the microgel surface. Negatively charged PEGDA/AA beads showed improved adsorption capacity towards positively charged organic dyes (methylene blue and rhodamine B) compared to neutral PEGDA beads and high repulsion of negatively charged dye molecules (methyl orange and congo red). Macroporous microgels showed better adsorption properties than nonporous beads, with a maximum adsorption capacity towards methylene blue of 45 mg/g for macroporous PEGDA/AA microgels at pH 8.6, as compared to 23 mg/g for nonporous PEGDA/AA microgels at the same pH. More than 98% of Cu(II) ions were removed from 50 ppm solution at pH 6.7 using 2.7 mg/mL of macroporous PEGDA/AA microgel. The adsorption of cationic species was significantly improved when pH was increased from 3 to 9 due to a higher degree of ionization of AA monomeric units in the polymer network. The synthesized copolymer beads can be used in drug delivery to achieve improved loading capacity of positively charged therapeutic agents and in tissue engineering, where a negative charge of scaffolds coupled with porous structure can help to achieve improved permeability of high-molecular-weight metabolites and nutrients, and anti-fouling activity against negatively charged species.

Sieving and Clogging in PEG-PEGDA Hydrogel Membranes

Hydrogels are promising systems for separation applications due to their structural characteristics (i.e., hydrophilicity and porosity). In our study, we investigate the permeation of suspensions of rigid latex particles of different sizes through free-standing hydrogel membranes prepared by photopolymerization of a mixture of poly(ethylene glycol) diacrylate (PEGDA) and large poly(ethylene glycol) (PEG) chains of 300,000 g·mol-1 in the presence of a photoinitiator. Atomic force microscopy and cryoscanning electron microscopy (cryoSEM) were employed to characterize the structures of the hydrogel membranes. We find that the 20 nm particle permeation depends on both the PEGDA/PEG composition and the pressure applied during filtration. In contrast, we do not measure a significant permeation of the 100 nm and 1 μm particles, despite the presence of large cavities of 1 μm evidenced by the cryoSEM images. We suggest that the PEG chains induce local nanoscale defects in the cross-linking of PEGDA-rich walls separating the micrometer-sized cavities, which control the permeation of particles and water. Moreover, we discuss the decline of the permeation flux observed in the presence of latex particles compared to that of pure water. We suggest that a thin layer of particles forms on the surface of the hydrogels.

Single-Particle Tracking in Poly(Ethylene Glycol) Diacrylate: Probe Size Effect on the Diffusion Behaviors of Nanoparticles in Unentangled Polymer Solutions

A thorough understanding of the relevant factors governing the transport of nanoparticles in poly(ethylene glycol) diacrylate (PEGDA) is crucial for many applications utilizing this polymer. Here, single-particle tracking (SPT) was used to systematically investigate the role of the probe size (3-200 nm) on the diffusion behaviors of individual fluorescent nanoparticles in semidilute and unentangled PEGDA solutions. The quantitative assessment of the SPT data via the recorded single-particle trajectories and diffusion coefficients (D) not only showed that the observed probe dynamics in PEGDA were temporally and spatially heterogeneous, but more importantly that the measured D were observed to be significantly reduced (vs in solvent) and strongly size-dependent. We explained these results based on a modified multiscale model for particle diffusion, built upon well-established hydrodynamics and obstruction theories. We furthermore showed that the presence of steric interactions and probe confinement effects in highly crowded, unentangled PEGDA microstructures can lead to deviations in the single-particle displacements from the expected Gaussian behavior, as revealed by the van Hove displacement distributions and the associated non-Gaussian parameters. This study has demonstrated the power of SPT methods in offering an advanced characterization of the transport characteristics in complex polymer structures, overcoming challenges posed by traditional characterization techniques.

Plug-and-play fiber-optic sensors based on engineered cells for neurochemical monitoring at high specificity in freely moving animals

In vivo detection of neurochemicals, including neurotransmitters and neuromodulators, is critical for both understanding brain mechanisms and diagnosing brain diseases. However, few sensors are competent in monitoring neurochemical dynamics in vivo at high specificity. Here, we propose the fiber-optic probes based on engineered cells (FOPECs) for plug-and-play, real-time detection of neurochemicals in freely moving animals. Taking advantages of life-evolved neurochemical receptors as key components, the chemical specificity of FOPECs is unprecedented. We demonstrate the applications of FOPECs in real-time monitoring of neurochemical dynamics under various physiology and pathology conditions. With no requirement of viral infection in advance and no dependence on animal species, FOPECs can be widely adopted in vertebrates, such as mice, rats, rabbits, and chickens. Moreover, FOPECs can be used to monitor drug metabolisms in vivo. We demonstrated the neurochemical monitoring in blood circulation systems in vivo. We expect that FOPECs will benefit not only neuroscience study but also drug discovery.

Musculoskeletal tissues-on-a-chip: role of natural polymers in reproducing tissue-specific microenvironments

Over the past years, 3D in vitro models have been widely employed in the regenerative medicine field. Among them, organ-on-a-chip technology has the potential to elucidate cellular mechanism exploiting multichannel microfluidic devices to establish 3D co-culture systems that offer control over the cellular, physico-chemical and biochemical microenvironments. To deliver the most relevant cues to cells, it is of paramount importance to select the most appropriate matrix for mimicking the extracellular matrix of the native tissue. Natural polymers-based hydrogels are the elected candidates for reproducing tissue-specific microenvironments in musculoskeletal tissue-on-a-chip models owning to their interesting and peculiar physico-chemical, mechanical and biological properties. Despite these advantages, there is still a gap between the biomaterials complexity in conventional tissue engineering and the application of these biomaterials in 3D in vitro microfluidic models. In this review, the aim is to suggest the adoption of more suitable biomaterials, alternative crosslinking strategies and tissue engineered-inspired approaches in organ-on-a-chip to better mimic the complexity of physiological musculoskeletal tissues. Accordingly, after giving an overview of the musculoskeletal tissue compositions, the properties of the main natural polymers employed in microfluidic systems are investigated, together with the main musculoskeletal tissues-on-a-chip devices.

Microfluidic osmotic compression of a charge-stabilized colloidal dispersion: Equation of state and collective diffusion coefficient

We show, using a model coupling mass transport and liquid theory calculations for a charge-stabilized colloidal dispersion, that diffusion significantly limits measurement times of its equation of state (EOS), osmotic pressure vs composition, using the osmotic compression technique. Following this result, we present a microfluidic chip allowing one to measure the entire EOS of a charged dispersion at the nanoliter scale in a few hours. We also show that time-resolved analyses of relaxation to equilibrium in this microfluidic experiment lead to direct estimates of the collective diffusion coefficient of the dispersion in Donnan equilibrium with a salt reservoir.

Interaction of epoxy-based hydrogels and water: A molecular dynamics simulation study

Biomaterials play a crucial role in tissue engineering as a functional replacement, regenerative medicines, supportive scaffold for guided tissue growth, and drug delivery devices. The term biomaterial refers to metals, ceramics, and polymers account for the vast majority. In the case of polymers, hydrogels have emerged as active materials for an immense variety of applications. Epoxy-based hydrogels possess a unique network structure that enables very high levels of hydrophilicity and biocompatibility. Hydrogel such as Medipacs Epoxy Polymers (MEPs) models were constructed to understand water's behavior at the water/hydrogel interface and hydrogel network. We computed the Gibbs dividing surface (GDS) to define the MEP/water interface, and all the physicochemical properties were computed based on GDS. We calculated the radial distribution function (RDF), the 2D surface roughness of the immersed MEPs. RDF analysis confirmed that the first hydration shell is at a distance of 1.86 Å, and most of the water molecules are near the hydroxyl group of the MEPs network. Hydrogen bonds (H-bonds) analysis was performed, and the observation suggested that the disruption of the H-bonds between MEP chains leads to an increase in the polymer matrix's void spaces. These void spaces are filled with diffused water molecules, leading to swelling of the MEP hydrogel. The swelling parameter was estimated from the fitted curve of the yz-lattice of the simulation cell. The MEP/water interface simulation results provide insightful information regarding the design strategy of epoxy-based hydrogel and other hydrogels vital for biomedical applications.

Remote near infrared identification of pathogens with multiplexed nanosensors

Infectious diseases are worldwide a major cause of morbidity and mortality. Fast and specific detection of pathogens such as bacteria is needed to combat these diseases. Optimal methods would be non-invasive and without extensive sample-taking/processing. Here, we developed a set of near infrared (NIR) fluorescent nanosensors and used them for remote fingerprinting of clinically important bacteria. The nanosensors are based on single-walled carbon nanotubes (SWCNTs) that fluoresce in the NIR optical tissue transparency window, which offers ultra-low background and high tissue penetration. They are chemically tailored to detect released metabolites as well as specific virulence factors (lipopolysaccharides, siderophores, DNases, proteases) and integrated into functional hydrogel arrays with 9 different sensors. These hydrogels are exposed to clinical isolates of 6 important bacteria (Staphylococcus aureus, Escherichia coli,…) and remote (≥25 cm) NIR imaging allows to identify and distinguish bacteria. Sensors are also spectrally encoded (900 nm, 1000 nm, 1250 nm) to differentiate the two major pathogens P. aeruginosa as well as S. aureus and penetrate tissue (>5 mm). This type of multiplexing with NIR fluorescent nanosensors enables remote detection and differentiation of important pathogens and the potential for smart surfaces.

Microfluidic dialysis using photo-patterned hydrogel membranes in PDMS chips

We report the fabrication of permeable membranes for microfluidic dialysis applications in poly(dimethylsiloxane) (PDMS) channels. A maskless UV projection device was used to photo-pattern long hydrogel membranes (mm-cm) with a spatial resolution of a few microns in PDMS chips integrating also micro-valves. We show in particular that multi-layer soft lithography allows one to deplete oxygen from the PDMS walls using a nitrogen gas flow and therefore makes possible in situ UV-induced polymerization of hydrogels. We also report a simple surface modification of the PDMS channels leading to strongly anchored hydrogel membranes that can withstand trans-membrane pressure drops up to 1 bar without leakages. We then measured the Darcy permeability of these membranes and estimated their cut-off by measuring the kinetics of diffusion of macromolecules of different sizes through the membrane. Finally, we illustrate the opportunities offered by such microfluidic chips for dialysis applications by observing in real time the crystallization of a model protein in a chamber of a few nanoliters.

Microfluidic In-Situ Measurement of Poisson's Ratio of Hydrogels

Being able to precisely characterize the mechanical properties of soft microparticles is essential for numerous situations, from the understanding of the flow of biological fluids to the development of soft micro-robots. Here, we present a simple measurement technique for determining Poisson's ratio of soft micron-sized hydrogels in the presence of a surrounding liquid. This method relies on the measurement of the deformation, in two orthogonal directions, of a rectangular hydrogel slab compressed uni-axially inside a microfluidic channel. Due to the in situ character of the method, the sample does not need to be dried, allowing for the measurement of the mechanical properties of swollen hydrogels. Using this method, we determined Poisson's ratio of hydrogel particles composed of polyethylene glycol (PEG) and varying solvents fabricated using a lithography technique. The results demonstrate, with high precision, the dependence of the hydrogel compressibility on the solvent fraction and character. The method is easy to implement and can be adapted for the measurement of a variety of soft and biological materials.

Laterally Aggregated Polyacrylamide Gels for Immunoprobed Isoelectric Focusing

Immunoprobed isoelectric focusing (IEF) resolves proteins based on differences in isoelectric point (pI) and then identifies protein targets through immunoprobing of IEF-separated proteins that have been immobilized onto a gel scaffold. During the IEF stage, the gel functions as an anti-convective medium and not as a molecular sieving matrix. During the immunoprobing stage, the gel acts as an immobilization scaffold for IEF-focused proteins via photoactive moieties. Here, we characterized the effect of gel pore size on IEF separation and in-gel immunoassay performance. We modulated polyacrylamide (PA) gel pore size via lateral chain aggregation initiated by PEG monomers. During IEF, the 2% PEG highly porous PA gel formulation offered higher resolution (minimum pI difference ∼0.07 ± 0.02) than unmodified 6%T, 3.3%C (benchmark) and 6%T, 8%C (negative control) PA gels. The highly porous gels supported a pH gradient with slope and linearity comparable to benchmark gels. The partition coefficient for antibodies into the highly porous gels (K = 0.35 ± 0.02) was greater than the benchmark (3×) and negative control (1.75×) gels. The highly porous gels also had lower immunoassay background signal than the benchmark (2×) and negative control (3×) gels. Taken together, lateral aggregation creates PA gels that are suitable for both IEF and subsequent in-gel immunoprobing by mitigating immunoprobe exclusion from the gels while facilitating removal of unbound immunoprobe.

Affinity-Enhanced CTC-Capturing Hydrogel Microparticles Fabricated by Degassed Mold Lithography

Technologies for the detection and isolation of circulating tumor cells (CTCs) are essential in liquid biopsy, a minimally invasive technique for early diagnosis and medical intervention in cancer patients. A promising method for CTC capture, using an affinity-based approach, is the use of functionalized hydrogel microparticles (MP), which have the advantages of water-like reactivity, biologically compatible materials, and synergy with various analysis platforms. In this paper, we demonstrate the feasibility of CTC capture by hydrogel particles synthesized using a novel method called degassed mold lithography (DML). This technique increases the porosity and functionality of the MPs for effective conjugation with antibodies. Qualitative fluorescence analysis demonstrates that DML produces superior uniformity, integrity, and functionality of the MPs, as compared to conventional stop flow lithography (SFL). Analysis of the fluorescence intensity from porosity-controlled MPs by each reaction step of antibody conjugation elucidates that more antibodies are loaded when the particles are more porous. The feasibility of selective cell capture is demonstrated using breast cancer cell lines. In conclusion, using DML for the synthesis of porous MPs offers a powerful method for improving the cell affinity of the antibody-conjugated MPs.

Lossless immunocytochemistry using photo-polymerized hydrogel thin-films

Encapsulating cell samples in porous hydrogel thin-films eliminates cell loss and reduces processing time in standard immunocytochemistry workflows.

Controlling Macroscopic Phase Separation of Aqueous Two-Phase Polymer Systems in Porous Media

In previous work, our group discovered a phenomenon in which a mixed polymer-salt or mixed micellar aqueous two-phase system (ATPS) separates into its two constituent phases as it flows within paper. While these ATPSs worked well in their respective studies to concentrate the target biomarker and improve the sensitivity of the lateral-flow immunoassay, different ATPSs can be advantageous for new applications based on factors such as biomarker partitioning or biochemical compatibility between ATPS and sample components. However, since the mechanism of phase separation in porous media is not completely understood, introducing other ATPSs to paper is an unpredictable process that relies on trial and error experiments. This is especially true for polymer-polymer ATPSs in which the characteristics of the two phases appear quite similar. Therefore, our group aimed to develop semiquantitative guidelines for choosing ATPSs that can phase separate in paper. In this work, we evaluated the Washburn equation and its parameters as a potential mathematical framework to describe the flow behavior of polymer-salt and micellar ATPSs in fiberglass paper. We compared bulk phase fluid characteristics and identified the viscosity difference between the phases as a key determinant of the potential for phase separation in paper. We then used this parameter to predict the phase separation capabilities of polyethylene glycol (PEG)-dextran ATPSs in paper and control the composition of the leading and lagging phases. We also, for the first time, successfully demonstrated the phase separation phenomenon in hydrogels, thereby extending its application and potential benefits to an alternative porous medium.

Macroporous Hydrogels for Stable Sequestration and Sustained Release of Vascular Endothelial Growth Factor and Basic Fibroblast Growth Factor Using Nucleic Acid Aptamers

Macroporous hydrogels have been widely studied for biological and biomedical applications such as drug delivery and tissue engineering. However, these hydrogels cannot stably sequester molecules of interest due to their high permeability. The purpose of this work was to study the feasibility of using two aptamers to sequester two protein drugs, quantify the apparent diffusivity of protein drugs in aptamer-functionalized macroporous hydrogels, and evaluate the function of aptamer-functionalized macroporous hydrogels in controlling protein release for angiogenesis. Vascular endothelial growth factor (VEGF) and basic fibroblast growth factor (bFGF) were used as model proteins. The data show that anti-VEGF and anti-bFGF aptamers could be uniformly incorporated into macroporous hydrogels for stable and specific sequestration of VEGF and bFGF. The aptamers could reduce the apparent diffusivity of VEGF and bFGF in the macroporous hydrogels by approximately three orders of magnitude. Moreover, as the aptamers could prolong the release of these growth factors, dual aptamer-functionalized macroporous hydrogels could stimulate synergistic angiogenesis. Therefore, this work has successfully demonstrated that aptamer-functionalized macroporous hydrogels hold great potential of stably sequestering multiple molecules of interest for various biological and biomedical applications.

Engineering functional hydrogel microparticle interfaces by controlled oxygen-inhibited photopolymerization

Functional poly(ethylene glycol) diacrylate (PEGDA) hydrogel microparticles for the detection of bioactive macromolecules were fabricated via oxygen-inhibited photopolymerization in a droplet microfluidic device. Hydrogel network functionalization and architecture were characterized using a biotin-avidin binding assay, which revealed radial network inhomogeneities dependent on exposure conditions. Empirical results were corroborated using a reaction-diffusion model, describing the effects of exposure intensity on the spatial photopolymerization kinetics and resulting polymeric mesh network. The combination of finely controlled exposure conditions and predictive simulations enables the generation of tailored particles with microengineered interfaces and gradients in crosslinking density, which dictate solute diffusivity and elasticity, augmenting the utility of this approach in engineering multifunctional, size-excluding hydrogel particles for multiplexed biomolecular sensing.

A soft 3D polyacrylate hydrogel recapitulates the cartilage niche and allows growth-factor free tissue engineering of human articular cartilage

Cartilage degeneration or damage treatment is still a challenge, but, tissue engineering strategies, which combine cell therapy strategies, which combine cell therapy and scaffolds, and have emerged as a promising new approach. In this regard, polyurethanes and polyacrylates polymers have been shown to have clinical potential to treat osteochondral injuries. Here, we have used polymer microarrays technology to screen 380 different polyurethanes and polyacrylates polymers. The top polymers with potential to maintain chondrocyte viability were selected, with scale-up studies performed to evaluate their ability to support chondrocyte proliferation during long-term culture, while maintaining their characteristic phenotype. Among the selected polymers, poly (methylmethacrylate-co-methacrylic acid), showed the highest level of chondrogenic potential and was used to create a 3D hydrogel. Ultrastructural morphology, microstructure and mechanical testing of this novel hydrogel revealed robust characteristics to support chondrocyte growth. Furthermore, in vitro and in vivo biological assays demonstrated that chondrocytes cultured on the hydrogel had the capacity to produce extracellular matrix similar to hyaline cartilage, as shown by increased expression of collagen type II, aggrecan and Sox9, and the reduced expression of the fibrotic marker's collagen type I. In conclusion, hydrogels generated from poly (methylmethacrylate-co-methacrylic acid) created the appropriate niche for chondrocyte growth and phenotype maintenance and might be an optimal candidate for cartilage tissue-engineering applications. SIGNIFICANCE STATEMENT: Articular cartilage has limited self-repair ability due to its avascular nature, therefore tissue engineering strategies have emerged as a promising new approach. Synthetic polymers displaygreat potential and are widely used in the clinical setting. In our study, using the polymer microarray technique a novel type of synthetic polyacrylate was identified, that was converted into hydrogels for articular cartilage regeneration studies. The hydrogel based on poly (methylmethacrylate-co-methacrylic acid-co-PEG-diacrylate) had a controlable ultrastructural morphology, microstructure (porosity) and mechanical properties (stiffness) appropriate for cartilage engineering. Our hydrogel created the optimal niche for chondrocyte growth and phenotype maintenance for long-term culture, producing a hyaline-like cartilage extracellular matrix. We propose that this novel polyacrylate hydrogel could be an appropriate support to help in the treatment efficient cartilage regeneration.

Preparation of Xylan-g-/P(AA-co-AM)/GO Nanocomposite Hydrogel and its Adsorption for Heavy Metal Ions

Xylan-g-/P(AA-co-AM)/Graphene oxide (GO) hydrogels were prepared and used in the removal of heavy mental ions. Acrylamide (AM), acrylic acid (AA), and xylan were used as the raw materials to prepare the hydrogels with ammonium persulfate (APS) as the initiator. The prepared hydrogels were characterized by Fourier transform infrared (FTIR), thermogravimetric analysis (TGA), and energy dispersive X-ray (EDX). Some important properties of nanocomposite hydrogels such as swelling behavior, mechanical property, and adsorption capacity were also examined as well as the regeneration of the hydrogels. The results showed that the prepared hydrogels reached the equilibrium state of swelling after 12 h, and the compressive strength of the hydrogel with 30 mg of GO could reach up to 203 kPa. Compared with traditional hydrogel, the mechanical properties of the hydrogels with GO were obviously improved. The maximum adsorption capacity of hydrogels for Pb²⁺, Cd²⁺, and Zn²⁺ could reach up to 683 mg/g, 281 mg/g, and 135 mg/g, respectively. After five cycles of adsorption and desorption, the recovery rate of the hydrogels on Pb²⁺, Cd²⁺, and Zn²⁺ was still up to 87%, 80%, and 80%, respectively—all above 80%.

Nano-in-Micro Smart Hydrogel Composite for a Rapid Sensitive Immunoassay

Immunoassays are an important tool in various bioanalytical settings, such as clinical diagnostics, biopharmaceutical analysis, environmental monitoring, and food testing. An enzyme-linked immunosorbent assay (ELISA) is usually used to amplify immunoassay signals; however, it requires labor-intensive and time-consuming procedures, which hinders its application to rapid cytokine detection. In this study, a nano-in-micro composite system, where immunosensing polystyrene beads (≈320 nm) are incorporated within a stimuli-responsive microgel matrix (≈40 µm) via microfluidics, is investigated. The intrinsic volume phase-transition change properties of the smart microgels allows an enzyme-free enhanced immunoassay, enabling instant enhancement in signal-to-noise ratios of ≈5-fold. This nano-in-micro hydrogel composite offers a simple yet highly effective method for sensitive and multiplexed cytokine analysis without complex enzyme-based signal amplification steps, greatly benefitting advanced immune medicine.

3D biosensors in advanced medical diagnostics of high mortality diseases

Cardiovascular diseases, cancer, and diabetes are high mortality diseases, which account for almost two thirds of all deaths worldwide. Their early detection and continuous evaluation are fundamental for an improved patient prognosis and reduced socioeconomic impact. Current biosensor technologies are typically based on the analysis of whole blood samples from patients for the detection of disease-specific biomarkers. However, these technologies display serious shortcomings, such as reduced sensitivity and dynamic range, limited in vivo applicability, and lack of continuous monitoring. There is the urgent need for new diagnostic and treatment follow-up tools, which allow for the early detection of the pathology as well as for the continuous monitoring of the physiological responses to specific therapies. During the last years, a new generation of biosensor technologies with improved performance has emerged in the biomedical sector. The combination of advanced biomaterial methods, biochemical tools, and micro/nanotechnology approaches has resulted in the development of innovative three-dimensional (3D) biosensor platforms for advanced medical diagnosis. In this review, we report the most recent advances in the field of 3D biosensors for clinical applications, focusing on the diagnosis and monitoring of cardiovascular diseases, cancer, and diabetes. We discuss about their clinical performance compared to standard biosensor technologies, their implantable capability, and their integration into microfluidic devices to develop clinically-relevant models. Overall, we anticipate that 3D biosensors will drive us toward a new paradigm in medical diagnosis, resulting in real-time in vivo biosensors capable to significantly improve patient prognosis.

A visually distinguishable light interfering bioresponsive silica nanoparticle hydrogel sensor fabricated through the molecular imprinting technique

Methods of the early detection of diseases are based on recognition of the smallest change in the levels of a disease-specific biomarker in body fluids.

One-step photostructuring of multiple hydrogel arrays for compartmentalized enzyme reactions in microfluidic devices

A moulding technique is presented for the simultaneous photostructuring on the μm scale of hydrogels with nanomaterials on one substrate, usable for the fabrication of microfluidic double-chamber reactors.

Xylan-Based Hydrogels as a Potential Carrier for Drug Delivery: Effect of Pore-Forming Agents

Pore-forming agents have a significant influence on the pore structure of hydrogels. In this study, a porogenic technique was employed to investigate the preparation of macroporous hydrogels which were synthesized by radical copolymerization of carboxymethyl xylan with acrylamide and N-isopropylacrylamide under the function of a cross-linking agent. Six kinds of pore-forming agents were used: polyvinylpyrrolidone K30, polyethylene glycol 2000, carbamide, NaCl, CaCO₃, and NaHCO₃. The application of these hydrogels is also discussed. The results show that pore-forming agents had an important impact on the pore structure of the hydrogels and consequently affected properties of the hydrogels such as swelling ratio and mechanical strength, while little effect was noted on the thermal property of the hydrogels. 5-Fluorouracil was used as a model drug to study the drug release of the as-prepared hydrogels, and it was found that the drug release was substantially improved after using the NaHCO₃ pore-forming agent: a cumulative release rate of up to 71.05% was achieved.

Smart Hydrogel Microfluidics for Single-Cell Multiplexed Secretomic Analysis with High Sensitivity

Secreted proteins determine a range of cellular functionalities correlated with human health and disease progression. Because of cell heterogeneity, it is essential to measure low abundant protein secretions from individual cells to determine single-cell activities. In this study, an integrated platform consisting of smart hydrogel immunosensors for the sensitive detection of single-cell secretions is developed. A single cell and smart hydrogel microparticles are encapsulated within a droplet. After incubation, target secreted proteins from the cell are captured in the smart hydrogel particle for immunoassay. The temperature-induced volume phase transition of the hydrogel biosensor allows the concentration of analytes within the gel matrix to increase, enabling high-sensitivity measurements. Distinct heterogeneity for live cell secretions is determined from 6000 cells within 1 h. This method is tested for low abundant essential secretions, such as interleukin-6, interleukin-8, and monocyte chemoattractant protein-1 secretions of both suspended cells (HL60) and adherent cells (MCF7 and MDA-MB-231). This platform is highly flexible and can be used to simultaneously measure a wide range of clinically relevant cellular secretions; it thus represents a novel tool for precise biological assays.

Quantum Dots-Doped Tapered Hydrogel Waveguide for Ratiometric Sensing of Metal Ions

Advances in fluorescent nanomaterials and photonics have led to a new generation of photonic devices for applications in biosensing, diagnostics, and therapy. However, for clinical utility, biocompatibility and limited light guiding in tissues pose significant challenges. Here, we report a new type of soft, biocompatible, and tapered optical waveguide with capability of delivering light in deep tissues and demonstrate it as a ratiometric probe for rapid point-of-care detection of metal ions. The waveguide was made from quantum dots (QDs)-incorporated biocompatible hydrogels and coated with a thin sensing film to ensure fast exchanges with the surrounding analytes. The tapered design of the waveguide allows more light extraction for efficient excitation of the coating film. To achieve ratiometric measurements, two types of QDs with well-resolved emission bands are synthesized and immobilized in the waveguide and the coating film, respectively. We show that the ratiometric readout of the waveguide sensor is free of environmental disturbances and exhibits negligible drifts when applied in various environments such as being immersed in water or embedded in tissues. The waveguide device provides a new photonic-sensing platform that may allow being engineered to sense a wide range of metal ions and analytes.

Application of Millifluidics to Encapsulate and Support Viable Human Mesenchymal Stem Cells in a Polysaccharide Hydrogel

Human adipose-derived stromal cells (hASCs) are widely known for their immunomodulatory and anti-inflammatory properties. This study proposes a method to protect cells during and after their injection by encapsulation in a hydrogel using a droplet millifluidics technique. A biocompatible, self-hardening biomaterial composed of silanized-hydroxypropylmethylcellulose (Si-HPMC) hydrogel was used and dispersed in an oil continuous phase. Spherical particles with a mean diameter of 200 μm could be obtained in a reproducible manner. The viability of the encapsulated hASCs in the Si-HPMC particles was 70% after 14 days in vitro, confirming that the Si-HPMC particles supported the diffusion of nutrients, vitamins, and glucose essential for survival of the encapsulated hASCs. The combination of droplet millifluidics and biomaterials is therefore a very promising method for the development of new cellular microenvironments, with the potential for applications in biomedical engineering.

In situ photo-patterning of pressure-resistant hydrogel membranes with controlled permeabilities in PEGDA microfluidic channels

We report the fabrication of highly permeable membranes in poly(ethylene glycol) diacrylate (PEGDA) channels, for investigating ultra- or micro-filtration, at the microfluidic scale. More precisely, we used a maskless UV projection setup to photo-pattern PEG-based hydrogel membranes on a large scale (mm-cm), and with a spatial resolution of a few microns. We show that these membranes can withstand trans-membrane pressure drops of up to 7 bar without any leakage, thanks to the strong anchoring of the hydrogel to the channel walls. We also report in situ measurements of the Darcy permeability of these membranes, as a function of the deposited energy during photo-polymerization, and their formulation composition. We show that the use of PEG chains as porogens, as proposed in [Lee et al., Biomacromolecules, 2010, 11, 3316], significantly increases the porosity of the hydrogels, up to Darcy permeabilities of about 1.5 × 10-16 m2, while maintaining the strong mechanical stability of the membranes. We finally illustrate the opportunities offered by this technique, by investigating frontal filtration of colloidal dispersions in a straight microfluidic channel.

Digital Manufacturing of Selective Porous Barriers in Microchannels Using Multi-Material Stereolithography

We have developed a sequential stereolithographic co-printing process using two different resins for fabricating porous barriers in microfluidic devices. We 3D-printed microfluidic channels with a resin made of poly(ethylene glycol) diacrylate (MW = 258) (PEG-DA-258), a UV photoinitiator, and a UV sensitizer. The porous barriers were created within the microchannels in a different resin made of either PEG-DA (MW = 575) (PEG-DA-575) or 40% (w/w in water) PEG-DA (MW = 700) (40% PEG-DA-700). We showed selective hydrogen ion diffusion across a 3D-printed PEG-DA-575 porous barrier in a cross-channel diffusion chip by observing color changes in phenol red, a pH indicator. We also demonstrated the diffusion of fluorescein across a 3D-printed 40% PEG-DA-700 porous barrier in a symmetric-channel diffusion chip by measuring fluorescence intensity changes across the porous barrier. Creating microfluidic chips with integrated porous barriers using a semi-automated 3D printing process shortens the design and processing time, avoids assembly and bonding complications, and reduces manufacturing costs compared to micromolding processes. We believe that our digital manufacturing method for fabricating selective porous barriers provides an inexpensive, simple, convenient and reproducible route to molecule delivery in the fields of molecular filtration and cell-based microdevices.

Tissue and Organ 3D Bioprinting

Three-dimensional (3D) bioprinting enables the creation of tissue constructs with heterogeneous compositions and complex architectures. It was initially used for preparing scaffolds for bone tissue engineering. It has recently been adopted to create living tissues, such as cartilage, skin, and heart valve. To facilitate vascularization, hollow channels have been created in the hydrogels by 3D bioprinting. This review discusses the state of the art of the technology, along with a broad range of biomaterials used for 3D bioprinting. It provides an update on recent developments in bioprinting and its applications. 3D bioprinting has profound impacts on biomedical research and industry. It offers a new way to industrialize tissue biofabrication. It has great potential for regenerating tissues and organs to overcome the shortage of organ transplantation.

Integrated Methods to Manufacture Hydrogel Microparticles with High Protein Conjugation Capacity and Binding Kinetics via Viral Nanotemplate Display

Genetically modified tobacco mosaic virus (TMV) can serve as a potent nanotemplate for high capacity protein conjugation through covalent coupling to its coat proteins with precise nanoscale spacing. TMV's own genomic RNA can also be exploited for orientationally controlled assembly onto various platforms with sequence and spatial selectivity via nucleic acid hybridization. Here we describe detailed methods for fabrication of hydrogel microparticles with capture DNA sequences, chemical activation and programming of TMV templates, TMV assembly with the microparticles and protein conjugation via bio-orthogonal click reactions.

Polysaccharide Hydrogels Support the Long-Term Viability of Encapsulated Human Mesenchymal Stem Cells and Their Ability to Secrete Immunomodulatory Factors

While therapeutically interesting, the injection of MSCs suffers major limitations including cell death upon injection and a massive leakage outside the injection site. We proposed to entrap MSCs within spherical particles derived from alginate, as a control, or from silanized hydroxypropyl methylcellulose (Si-HPMC). We developed water in an oil dispersion method to produce small Si-HPMC particles with an average size of about 68 μm. We evidenced a faster diffusion of fluorescein isothiocyanate-dextran in Si-HPMC particles than in alginate ones. Human adipose-derived MSCs (hASC) were encapsulated either in alginate or in Si-HPMC, and the cellularized particles were cultured for up to 1 month. Both alginate and Si-HPMC particles supported cell survival, and the average number of encapsulated hASC per alginate and Si-HPMC particle (7102 and 5100, resp.) did not significantly change. The stimulation of encapsulated hASC with proinflammatory cytokines resulted in the production of IDO, PGE₂, and HGF whose concentration was always higher when cells were encapsulated in Si-HPMC particles than in alginate ones. We have demonstrated that Si-HPMC and alginate particles support hASC viability and the maintenance of their ability to secrete therapeutic factors.

Integration of a Genetically Encoded Calcium Molecular Sensor into Photopolymerizable Hydrogels for Micro-Optrode-Based Sensing

Genetically encoded molecular-protein sensors (GEMS) are engineered to sense and quantify a wide range of biological substances and events in cells, in vitro and even in vivo with high spatial and temporal resolution. Here, we aim to stably incorporate these proteins into a photopatternable matrix, while preserving their functionality, to extend the application of these proteins as spatially addressable optical biosensors. For this reason, we examined the fabrication of 3D hydrogel microtips doped with a genetically encoded fluorescent biosensor, GCaMP3, at the end of an optical fiber. Stable incorporation parameters of GCaMP3 into a photo-cross-linkable monomer matrix were investigated through a series of characterization and optimization experiments. Different precursor-solution formulations and irradiation parameters of in situ photopolymerization were tested to determine the factors affecting protein stability and sensor reproducibility during photoencapsulation. The microstructure and performance of hydrogel microtips were controlled by varying UV irradiation intensity as well as the molecular weight and concentration of the photocurable monomer, PEGDA (polyethylene glycol diacrylate), in precursor solution. Protein-doped hydrogel micro-optrodes (microtip sensors) were fabricated successfully and reproducibly at the distal end of optical fiber. Under optimized conditions, the bioactivity of GCaMP3 within a hydrogel matrix of micro-optrodes remained similar to that of the protein-free matrix in buffer. The limit of detection of protein optrodes for free calcium was also determined to be 4.3 nM. The hydrogel formulation and fabrication process demonstrated here using microtip optrodes can be easily adapted to other conformation-dependent protein biosensors and can be used in sensing applications.

Fluorescent hydrogel waveguide for on-site detection of heavy metal ions

Hydrogels have great applications in tissue engineering and drug delivery. Recently, there have been intense interests in developments and applications of nanocomposite hydrogels by incorporating nanomaterials into polymer matrix, which endows the hydrogels with new functionalities. Here, we report on the first carbon dots (CDs) doped hydrogel waveguide for selective, on-site detection of heavy metal ions in aqueous solutions. The CDs-doped hydrogel waveguide exhibits efficient light confinement in water due to the refractive index contrast. The smooth waveguide surfaces lead to low light scattering loss. Real-time spectra measurement of the CDs-doped hydrogel waveguide with a compact interrogation setup demonstrates that the novel design can be used as a portable, robust sensing platform for on-site analysis and assessment of heavy metal ions.

Hydrogel-based three-dimensional cell culture for organ-on-a-chip applications

Recent studies have reported that three-dimensionally cultured cells have more physiologically relevant functions than two-dimensionally cultured cells. Cells are three-dimensionally surrounded by the extracellular matrix (ECM) in complex in vivo microenvironments and interact with the ECM and neighboring cells. Therefore, replicating the ECM environment is key to the successful cell culture models. Various natural and synthetic hydrogels have been used to mimic ECM environments based on their physical, chemical, and biological characteristics, such as biocompatibility, biodegradability, and biochemical functional groups. Because of these characteristics, hydrogels have been combined with microtechnologies and used in organ-on-a-chip applications to more closely recapitulate the in vivo microenvironment. Therefore, appropriate hydrogels should be selected depending on the cell types and applications. The porosity of the selected hydrogel should be controlled to facilitate the movement of nutrients and oxygen. In this review, we describe various types of hydrogels, external stimulation-based gelation of hydrogels, and control of their porosity. Then, we introduce applications of hydrogels for organ-on-a-chip. Last, we also discuss the challenges of hydrogel-based three-dimensional cell culture techniques and propose future directions. © 2017 American Institute of Chemical Engineers Biotechnol. Prog., 33:580-589, 2017.

Fabrication of Highly Porous Nonspherical Particles Using Stop-Flow Lithography and the Study of Their Optical Properties

A microfluidic flow lithography approach was investigated to synthesize highly porous nonspherical particles and Janus particles in a one-step and high-throughput fashion. In this study, using common solvents as porogens, we were able to synthesize highly porous particles with different shapes using ultraviolet (UV) polymerization-induced phase separation in a microfluidic channel. We also studied the pore-forming process using operating parameters such as porogen type, porogen concentration, and UV intensity to tune the pore size and increase the pore size to submicron levels. By simply coflowing multiple streams in the microfluidic channel, we were able to create porous Janus particles; we showed that their anisotropic swelling/deswelling exhibit a unique optical shifting. The distinctive optical properties and the enlarged surface area of the highly porous particles can improve their performance in various applications such as optical sensors and drug loading.

Macroporous materials: microfluidic fabrication, functionalization and applications

This article provides an up-to-date highly comprehensive overview (594 references) on the state of the art of the synthesis and design of macroporous materials using microfluidics and their applications in different fields.

Detecting cell-secreted growth factors in microfluidic devices using bead-based biosensors

Microfluidic systems provide an interesting alternative to standard macroscale cell cultures due to the decrease in the number of cells and reagents as well as the improved physiology of cells confined to small volumes. However, the tools available for cell-secreted molecules inside microfluidic devices remain limited. In this paper, we describe an integrated microsystem composed of a microfluidic device and a fluorescent microbead-based assay for the detection of the hepatocyte growth factor (HGF) and the transforming growth factor (TGF)-β1 secreted by primary hepatocytes. This microfluidic system is designed to separate a cell culture chamber from sensing chambers using a permeable hydrogel barrier. Cell-secreted HGF and TGF-β1 diffuse through the hydrogel barrier into adjacent sensing channels and are detected using fluorescent microbead-based sensors. The specificity of sensing microbeads is defined by the choice of antibodies; therefore, our microfluidic culture system and sensing microbeads may be applied to a variety of cells and cell-secreted factors.

Improved Protein Conjugation with Uniform, Macroporous Poly(acrylamide-co-acrylic acid) Hydrogel Microspheres via EDC/NHS Chemistry

We demonstrate a robust and tunable micromolding method to fabricate chemically functional poly(acrylamide-co-acrylic acid) (p(AAm-co-AA)) hydrogel microspheres with uniform dimensions and controlled porous network structures for rapid biomacromolecular conjugation. Specifically, p(AAm-co-AA) microspheres with abundant carboxylate functional groups are fabricated via surface-tension-induced droplet formation in patterned poly(dimethylsiloxane) molds and photoinduced radical polymerization. To demonstrate the chemical functionality, we enlisted rapid EDC/NHS (1-ethyl-3-(3-(dimethylamino)propyl)carbodiimide (EDC) and N-hydroxysuccinimide (NHS)) chemistry for fluorescent labeling of the microspheres with small-molecule dye fluorescein glycine amide. Epifluorescence imaging results illustrate the uniform incorporation of carboxylate groups within the microspheres and rapid conjugation kinetics. Furthermore, protein conjugation results using red fluorescent protein R-phycoerythrin demonstrate the highly porous nature of the microspheres as well as the utility of the microspheres and the EDC/NHS scheme for facile biomacromolecular conjugation. Combined, these results illustrate the significant potential for our fabrication-conjugation strategy in the development of biofunctionalized polymeric hydrogel microparticles toward rapid biosensing, bioprocess monitoring, and biodiagnostics.