We gratefully acknowledge the financial support of this work by the Korean Carbon Capture and Sequestration R&amp;D Center (KCRC).

1. Preparation of the Prepolymer Solutions
<ol>
	<li>Preparation using water as a solvent
	<ol>
		<li>Add 10.00 g of deionized (DI) water to a glass bottle with a magnetic stir bar.</li>
		<li>Measure 2.00 g of SBMA and transfer it to the glass bottle containing the water. Stir the solution for 30 min, until the SBMA is completely dissolved.</li>
		<li>In a separate bottle, add 20.00 g of PEGDA (Mn = 700 g/mol).</li>
		<li>Add 20.0 mg of 1-hydroxycyclohexyl phenyl ketone (HCPK), a photo-initiator, to the PEGDA solution. Let the solution stir for at least 30 min.</li>
		<li>Using a disposable pipette, transfer 8.00 g of the PEGDA-HCPK solution to the SBMA aqueous solution. Continuously stir the mixture until the solution is homogenous.</li>
	</ol>
	</li>
	<li>Preparation using water/ethanol mixtures as solvents
	<ol>
		<li>Add 6.00 g of DI water and 4.00 g of ethanol to an amber glass bottle with a magnetic stir bar. Stir the solution to allow thorough mixing.</li>
		<li>Add 2.00 g of SBMA to the water/ethanol mixture. Stir the solution and allow the SBMA to completely dissolve.</li>
		<li>Use a pipette to transfer 8.00 g of the PEGDA-HCPK solution to the SBMA mixture. Stir to mix the solution thoroughly.</li>
	</ol>
	</li>
</ol>
2. Preparation of the Freestanding Films
<ol>
	<li>Place two spacers with known thicknesses on a clean quartz disc; the thickness of the spacers controls the thickness of the obtained polymer films19.</li>
	<li>Transfer a small amount (~1.0 mL) of the prepolymer solution to the quartz disc using a disposable pipette.</li>
	<li>Place another quartz disc on top of the liquid and ensure that there are no bubbles in the liquid film.</li>
	<li>Place the sample in an ultraviolet (UV) crosslinker and irradiate for 5 min using UV light with a wavelength of 254 nm19. 
	NOTE: Alternative irradiation times and wavelengths can be used depending on the type of photoinitiator.</li>
	<li>Separate the polymer film from the quartz discs using a sharp blade. Use tweezers to transfer the film to a DI water bath. Change the water twice during the first 24 h to remove the solvent, unreacted monomer/crosslinker, and sol from the film. 
	NOTE: The polymer film should be kept in the DI water to preserve the pore structure, if there is any.</li>
	<li>Prepare dried films for ATR-FTIR and DSC analysis.
	<ol>
		<li>Remove the film from the water bath and allow it to air dry for 24 h.</li>
		<li>Place the film in a vacuum oven at 80 &#176;C to dry overnight under vacuum.</li>
	</ol>
	</li>
</ol>
3. Preparation of the Impregnated Membranes
<ol>
	<li>Place a sheet of porous support onto a quartz disc.</li>
	<li>Using a foam brush, coat each side of the support twice with the prepolymer solution based on the water/ethanol mixture4. 
	NOTE: Since the support is hydrophobic, the prepolymer solution containing ethanol can easily wet the support.</li>
	<li>Place another quartz disc on top of the support.</li>
	<li>Place the sample in a UV crosslinker and irradiate for 5 min using UV light with a wavelength of 254 nm.</li>
	<li>To remove the impregnated membrane from the quartz discs, immerse the whole assembly in a DI water bath for 5 min and carefully remove the membrane using a sharp blade and tweezers.</li>
	<li>Keep the membrane in DI water. Change the water twice to remove the solvent, the unreacted monomer/crosslinker, and the sol from the membrane.</li>
	<li>Prepare dried, impregnated membranes for ATR-FTIR and DSC analyses.
	<ol>
		<li>Remove the membrane from the water bath. Allow the membrane to dry at ambient conditions for 24 h.</li>
		<li>Dry the membrane in a vacuum oven overnight at 80 &#176;C under vacuum.</li>
	</ol>
	</li>
</ol>
4. Characterization of the Freestanding Films and Impregnated Membranes
<ol>
	<li>ATR-FTIR analysis
	<ol>
		<li>Prepare a sample of the prepolymer solution, as stated in step 1.1, for FTIR analysis.</li>
		<li>Perform a background scan before scanning the sample. Set the wavenumber range from 600 cm-1 to 4,500 cm-1 at a 4-cm-1 resolution of measurement.</li>
		<li>Place the sample in the FTIR machine for analysis.</li>
		<li>Remove the sample. Clean the crystal and the tip with an appropriate solvent.</li>
		<li>Repeat steps 4.1.1 - 4.1.4 for the following samples: porous support, prepolymer solution, dried freestanding films, and dried impregnated membranes.</li>
	</ol>
	</li>
	<li>Differential scan calorimetry (DSC)
	<ol>
		<li>Place a DSC pan and lid in a weighing balance and record their weight.</li>
		<li>Place a small amount of sample (5-10 mg) inside the pan and close it with the lid.</li>
		<li>Weigh the pan containing the sample. From the weight difference between the occupied pan and lid and the unoccupied pan and lid, calculate the weight of the sample.</li>
		<li>Using a press, hermetically seal the sample inside the pan.</li>
		<li>Place the sealed pan inside the DSC cell in which the inert reference is located.</li>
		<li>Enter the weight of the unoccupied pan and lid and the weight of the sample in the program.</li>
		<li>Scan with the DSC from -80 &#176;C to 160 &#176;C at a heating rate of 10 &#176;C/min.</li>
		<li>Perform the DSC analysis using the manufacturer&#39;s protocol.</li>
		<li>Repeat the DSC experiments for different samples following the aforementioned steps.</li>
	</ol>
	</li>
	<li>Measurement of contact angles using a pendant drop method
	<ol>
		<li>Cut a rectangular strip of the membrane sample (approximately 30 mm by 6 mm).</li>
		<li>Soak this strip in DI water for 10 min and then dry it for 5 min.</li>
		<li>Place the dried sample on the sample holder.</li>
		<li>Submerge the sample holder in a transparent environmental chamber containing the DI water20.</li>
		<li>Using a microliter syringe with a stainless steel needle, dispense drops of n-decane (approximately 1 &#181;L) onto the membrane sample.</li>
		<li>Leave the setup undisturbed for 2 min to ensure the stabilization of the droplets.</li>
		<li>Use an appropriate image analysis software to determine the contact angle of the samples by measuring the angles of the dispensed droplets on the membrane surface.</li>
		<li>Take the average of the contact angle values obtained for various droplets.</li>
	</ol>
	</li>
	<li>Characterization of water permeability using a dead-end filtration system
	<ol>
		<li>Use a hammer-driven hole punch with an appropriate diameter to cut coupons of freestanding films and impregnated membranes.</li>
		<li>Place a prepared coupon on the porous support inside a dead end filtration cell.</li>
		<li>Place the O-ring on top of the sample. Screw the two halves of the permeation cell together.</li>
		<li>Add approximately 50 mL of DI water to the permeation cell. Screw on the cap and place the permeation cell on a magnetic stirrer. Set the stirring rate between 300 and 900 rpm.</li>
		<li>Place a covered beaker on a balance to collect the permeate water. Tare the balance.</li>
		<li>Open the valve on the gas cylinder. Turn the pressure regulator valve clockwise until the desired pressure is reached (45 psig for freestanding films and 35 psig for impregnated membranes).</li>
		<li>Open the release valve to deliver the pressure to the permeation cell.</li>
		<li>Monitor and record the weight of the beaker with time.</li>
		<li>Calculate the water permeance (Aw) and permeability (Pw) with the solution-diffusion model shown below4,21 
		<img alt="Equation" src="/files/ftp_upload/55426/55426eq1.jpg" /> 
		where Aw is the water permeance (L/m2hbar or LMH/bar), Pw is the water permeability (LMH cm/bar), &#961;w is the water density (g/L), A is the effective area of the membrane (m2), &#916;m is the change in the mass of water permeate (g) over a time period &#916;t (h), &#916;p is the pressure difference across the membrane (bar), and l is the thickness of the swollen film (cm).</li>
		<li>Use a BSA solution containing 0.5 g/L BSA in a phosphate-buffered saline (PBS) solution with pH = 7.4 to evaluate the antifouling properties and rejection rates of the membranes.</li>
		<li>Repeat steps 4.4.5 - 4.4.10 to determine the water flux in the presence of BSA. Calculate the BSA rejection rate with the following equation22 
		<img alt="Equation" src="/files/ftp_upload/55426/55426eq2.jpg" /> 
		where RBSA is the BSA rejection rate of the membrane (%), CP is the concentration of BSA in the permeate (g/L), and CF is the concentration of BSA in the feed (g/L); the concentration of BSA can be determined via UV spectroscopy.</li>
	</ol>
	</li>
</ol>

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The authors declare that they have no competing financial interests.

We have demonstrated a facile method to prepare freestanding films and impregnated membranes based on zwitterionic hydrogels. The disappearance of three (meth)acrylate characteristic peaks (i.e., 810, 1,190, and 1,410 cm-1) in the IR spectra of the obtained polymer films and impregnated membrane (Figure 2) indicates the good conversion of the monomers and crosslinker4,19,21. Additionally, the...

There is a great need to develop low cost and energy efficient technologies to produce clean water in order to meet the increasing demand. Polymeric membranes have emerged as a leading technology for water purification due to their inherent advantages, such as their high energy efficiency, low cost, and simplicity in operation1. Membranes allow pure water to permeate through and reject the contaminants. However, membranes are often subjected to fouling by contaminants in the feed water, which can be adsorbed onto the membrane surface from their favorable interactions2,3. The fouling can dramatically decrease water flux through the membranes, increasing the membrane area required and the cost of water purification.
An effective approach to mitigate fouling is to modify the membrane surface to increase the hydrophilicity and thus decrease the favorable interactions between the membrane surface and foulants. One method is to use thin-film coating with superhydrophilic3 hydrogels. The hydrogels often have high water permeability; therefore, a thin-film coating can increase the long-term water permeance through the membrane due to the mitigated fouling, despite the slightly increased transport resistance across the whole membrane. The hydrogels can also be directly fabricated into impregnated membranes for water purification in osmotic applications4.
Zwitterionic materials contain both positively and negatively charged functional groups, with a net neutral charge, and have strong surface hydration through electrostatic-induced hydrogen bonding5,6,7,8,9. The tightly bound hydration layers act as physical and energy barriers, preventing foulants from attaching onto the surface, thus demonstrating excellent antifouling properties10. Zwitterionic polymers, such as poly(sulfobetaine methacrylate) (PSBMA) and poly(carboxybetaine methacrylate) (PCBMA), have been used to modify the membrane surface by coating11,12,13,14,15,16,17,18 to increase surface hydrophilicity and thus antifouling properties.
We demonstrate here a facile method to prepare zwitterionic hydrogels using sulfobetaine methacrylate (SBMA) via photopolymerization, which is crosslinked using poly(ethylene glycol) diacrylate (PEGDA, Mn = 700 g/mol) to improve the mechanical strength. We also present a procedure to construct robust membranes by impregnating the monomer and crosslinker in a highly porous hydrophobic support before the photopolymerization. The physical and water transport properties of the freestanding films and impregnated membranes are thoroughly characterized to elucidate the structure/property relationship for water purification. The prepared hydrogels can be used as a surface coating to enhance membrane separation properties. By adjusting the crosslinking density or by impregnating into hydrophobic porous supports, these materials can also form thin films with sufficient mechanical strength for osmotic processes, such as forward osmosis or pressure-retarded osmosis4.

<table><tbody><tr><td>Poly(ethylene glycol) diacrylate&amp;nbsp;&amp;nbsp;&amp;nbsp;&amp;nbsp;&amp;nbsp;&amp;nbsp;&amp;nbsp;&amp;nbsp;&amp;nbsp;&amp;nbsp;&amp;nbsp;&amp;nbsp;&amp;nbsp;&amp;nbsp;&amp;nbsp;&amp;nbsp;&amp;nbsp; M&lt;sub&gt;n&lt;/sub&gt; = 700 (PEGDA)</td><td>Sigma Aldrich</td><td>455008</td><td></td></tr><tr><td>1-Hydroxycyclohexyl phenyl ketone, 99% (HCPK)</td><td>Sigma Aldrich</td><td>405612</td><td></td></tr><tr><td>[2-(Methacrloyloxy)ethyl dimethyl-(3-sulfopropyl) ammonium hydroxide, 97%</td><td>Sigma Aldrich</td><td>537284</td><td>Acutely Toxic</td></tr><tr><td>Ethanol, 95%</td><td>Koptec, VWR International</td><td>V1101</td><td>Flamable</td></tr><tr><td>Decane, anhydrous, 99%</td><td>Sigma Aldrich</td><td>457116</td><td></td></tr><tr><td>Solupor Membrane</td><td>Lydall</td><td>7PO7D</td><td></td></tr><tr><td>Micrometer&amp;nbsp;</td><td>Starrett</td><td>2900-6</td><td></td></tr><tr><td>ATR-FTIR</td><td>Vertex 70</td><td></td><td></td></tr><tr><td>DSC: TA Q2000</td><td>TA Instruments</td><td></td><td></td></tr><tr><td>Rame&amp;rsquo;-hart Goniometer: Model 190</td><td>Rame&amp;rsquo;-hart Instruments</td><td></td><td></td></tr><tr><td>Ultraviolet Crosslinker: CX-2000</td><td>Ultra-Violet Products</td><td></td><td>UV radiation&amp;nbsp;</td></tr><tr><td>Permeation Cell: Model UHP-43</td><td>Advantec MFS</td><td></td><td></td></tr><tr><td>Deionized Water: Milli-Q Water</td><td>EMD Millipore</td><td></td><td></td></tr></tbody></table>

synthesis of hydrogels with antifouling properties as membranes for water purification

Hydrogels have been widely utilized to enhance the surface hydrophilicity of membranes for water purification, increasing the antifouling properties and thus achieving stable water permeability through membranes over time. Here, we report a facile method to prepare hydrogels based on zwitterions for membrane applications. Freestanding films can be prepared from sulfobetaine methacrylate (SBMA) with a crosslinker of poly(ethylene glycol) diacrylate (PEGDA) via photopolymerization. The hydrogels can also be prepared by impregnation into hydrophobic porous supports to enhance the mechanical strength. These films can be characterized by attenuated total reflection Fourier transform infrared spectroscopy (ATR-FTIR) to determine the degree of conversion of the (meth)acrylate groups, using goniometers for hydrophilicity and differential scanning calorimetry (DSC) for polymer chain dynamics. We also report protocols to determine the water permeability in dead-end filtration systems and the effect of foulants (bovine serum albumin, BSA) on membrane performance.

Freestanding films prepared with the prepolymer solutions specified in steps 1.1 and 1.2 are referred to as S50 and S30, respectively. Detailed information is shown in Table 1. The prepolymer solution specified in step 1.2 was also used to fabricate impregnated membranes, which are denoted as IMS30. Because the porous support is made of hydrophobic polyethylene, only the prepolymer solution containing ethanol can be impre...

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Synthesis of Hydrogels with Antifouling Properties As Membranes for Water Purification

This paper reports practical methods to prepare hydrogels in freestanding films and impregnated membranes and to characterize their physical properties, including water transport properties.

Hydrogels have been widely utilized to enhance the surface hydrophilicity of membranes for water purification, increasing the antifouling properties and ...

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9.3K Views.  The State University of New York at Buffalo. This paper reports practical methods to prepare hydrogels in freestanding films and impregnated membranes and to characterize their physical properties, including water transport properties. 

Video: Synthesis of Hydrogels with Antifouling Properties As Membranes for Water Purification

Preparation of Hydroxy-PAAm Hydrogels for Decoupling the Effects of Mechanotransduction Cues

It is now well established that many cellular functions are regulated by interactions of cells with physicochemical and mechanical cues of their extracellular matrix (ECM) environment. Eukaryotic cells constantly sense their local microenvironment through surface mechanosensors to transduce physical changes of ECM into biochemical signals, and integrate these signals to achieve specific changes in gene expression. Interestingly, physicochemical and mechanical parameters of the ECM can couple with each other to regulate cell fate. Therefore, a key to understanding mechanotransduction is to decouple the relative contribution of ECM cues on cellular functions.
Here we present a detailed experimental protocol to rapidly and easily generate biologically relevant hydrogels for the independent tuning of mechanotransduction cues in vitro. We chemically modified polyacrylamide hydrogels (PAAm) to surmount their intrinsically non-adhesive properties by incorporating hydroxyl-functionalized acrylamide monomers during the polymerization. We obtained a novel PAAm hydrogel, called hydroxy-PAAm, which permits immobilization of any desired nature of ECM proteins. The combination of hydroxy-PAAm hydrogels with microcontact printing allows to independently control the morphology of single-cells, the matrix stiffness, the nature and the density of ECM proteins. We provide a simple and rapid method that can be set up in every biology lab to study in vitro cell mechanotransduction processes. We validate this novel two-dimensional platform by conducting experiments on endothelial cells that demonstrate a mechanical coupling between ECM stiffness and the nucleus.

We present a new polyacrylamide hydrogel, called hydroxy-PAAm, that allows a direct binding of ECM proteins with minimal cost or expertise. The combination of hydroxy-PAAm hydrogels with microcontact printing facilitates independent control of many cues of the natural cell microenvironment for studying cellular mechanostransduction.

It is now well established that many cellular functions are regulated by interactions of cells with physicochemical and mechanical cues of their ...

Electrophoretic Crystallization of Ultrathin High-performance Metal-organic Framework Membranes

We report the synthesis of thin, highly intergrown, polycrystalline metal-organic framework (MOF) membranes on a wide range of unmodified porous and non-porous supports (polymer, ceramic, metal, carbon, and graphene). We developed a novel crystallization technique, which is termed the ENACT approach: the electrophoretic nuclei assembly for the crystallization of highly intergrown thin films (ENACT). This approach allows for a high density of heterogeneous nucleation of MOFs on a chosen substrate via the electrophoretic deposition (EPD) directly from the precursor sol. The growth of well-packed MOF nuclei leads to a highly intergrown polycrystalline MOF film. We show that this simple approach can be used for the synthesis of thin, intergrown zeolite imidazole framework (ZIF)-7 and ZIF-8 films. The resulting 500 nm-thick ZIF-8 membranes show a considerably high H2 permeance (8.3 x 10-6 mol m-2 s-1 Pa-1) and ideal gas selectivities (7.3 for H2/CO2, 15.5 for H2/N2, 16.2 for H2/CH4, and 2655 for H2/C3H8). An attractive performance for C3H6/C3H8 separation is also achieved (a C3H6 permeance of 9.9 x 10-8 mol m-2 s-1 Pa-1 and a C3H6/C3H8 ideal selectivity of 31.6 at 25 &#176;C). Overall, the ENACT process, owing to its simplicity, can be extended to synthesize intergrown thin films of a wide range of nanoporous crystalline materials.

A simple, reproducible, and versatile approach for the synthesis of intergrown, polycrystalline metal-organic framework membranes on a wide range of unmodified porous and non-porous supports is presented.

We report the synthesis of thin, highly intergrown, polycrystalline metal-organic framework (MOF) membranes on a wide range of unmodified porous and ...

Chemistry

Fabricating Superhydrophobic Polymeric Materials for Biomedical Applications

Superhydrophobic materials, with surfaces possessing permanent or metastable non-wetted states, are of interest for a number of biomedical and industrial applications. Here we describe how electrospinning or electrospraying a polymer mixture containing a biodegradable, biocompatible aliphatic polyester (e.g., polycaprolactone and poly(lactide-co-glycolide)), as the major component, doped with a hydrophobic copolymer composed of the polyester and a stearate-modified poly(glycerol carbonate) affords a superhydrophobic biomaterial. The fabrication techniques of electrospinning or electrospraying provide the enhanced surface roughness and porosity on and within the fibers or the particles, respectively. The use of a low surface energy copolymer dopant that blends with the polyester and can be stably electrospun or electrosprayed affords these superhydrophobic materials. Important parameters such as fiber size, copolymer dopant composition and/or concentration, and their effects on wettability are discussed. This combination of polymer chemistry and process engineering affords a versatile approach to develop application-specific materials using scalable techniques, which are likely generalizable to a wider class of polymers for a variety of applications.

Two- and three-dimensional superhydrophobic polymeric materials are prepared by electrospinning or electrospraying biodegradable polymers blended with a lower surface energy polymer of similar composition.

Superhydrophobic materials, with surfaces possessing permanent or metastable non-wetted states, are of interest for a number of biomedical and industrial ...

Three-Dimensionally Printed Microfluidic Cross-flow System for Ultrafiltration/Nanofiltration Membrane Performance Testing

Minimization and management of membrane fouling is a formidable challenge in diverse industrial processes and other practices that utilize membrane technology. Understanding the fouling process could lead to optimization and higher efficiency of membrane based filtration. Here we show the design and fabrication of an automated three-dimensionally (3-D) printed microfluidic cross-flow filtration system that can test up to 4 membranes in parallel. The microfluidic cells were printed using multi-material photopolymer 3-D printing technology, which used a transparent hard polymer for the microfluidic cell body and incorporated a thin rubber-like polymer layer, which prevents leakages during operation. The performance of ultrafiltration (UF), and nanofiltration (NF) membranes were tested and membrane fouling could be observed with a model foulant bovine serum albumin (BSA). Feed solutions containing BSA showed flux decline of the membrane. This protocol may be extended to measure fouling or biofouling with many other organic, inorganic or microbial containing solutions. The microfluidic design is especially advantageous for testing materials that are costly or only available in small quantities, for example polysaccharides, proteins, or lipids due to the small surface area of the membrane being tested. This modular system may also be easily expanded for high throughput testing of membranes.&#160;

Design and fabrication of a three-dimensionally (3-D) printed microfluidic cross-flow filtration system is demonstrated. The system is used to test performance and observe fouling of ultrafiltration and nanofiltration (thin film composite) membranes.

Minimization and management of membrane fouling is a formidable challenge in diverse industrial processes and other practices that utilize membrane ...

Proof-of-Concept for Gas-Entrapping Membranes Derived from Water-Loving SiO2/Si/SiO2 Wafers for Green Desalination

Desalination through direct contact membrane distillation (DCMD) exploits water-repellent membranes to robustly separate counterflowing streams of hot and salty seawater from cold and pure water, thus allowing only pure water vapor to pass through. To achieve this feat, commercial DCMD membranes are derived from or coated with water-repellent perfluorocarbons such as polytetrafluoroethylene (PTFE) and polyvinylidene difluoride (PVDF). However, the use of perfluorocarbons is limiting due to their high cost, non-biodegradability, and vulnerability to harsh operational conditions. Unveiled here is a new class of membranes referred to as gas-entrapping membranes (GEMs) that can robustly entrap air upon immersion in water. GEMs achieve this function by their microstructure rather than their chemical make-up. This work demonstrates a proof-of-concept for GEMs using intrinsically wetting SiO2/Si/SiO2 wafers as the model system; the contact angle of water on SiO2 is &#952;o &#8776; 40&#176;. Silica-GEMs had 300 &#956;m-long cylindrical pores whose diameters at the (2 &#956;m-long) inlet and outlet regions were significantly smaller; this geometrically discontinuous structure, with 90&#176; turns at the inlets and outlets, is known as the &#34;reentrant microtexture&#34;. The microfabrication protocol for silica-GEMs entails designing, photolithography, chrome sputtering, and isotropic and anisotropic etching. Despite the water loving nature of silica, water does not intrude silica-GEMs on submersion. In fact, they robustly entrap air underwater and keep it intact even after six weeks (&#62;106 seconds). On the other hand, silica membranes with simple cylindrical pores spontaneously imbibe water (&#60; 1 s). These findings highlight the potential of the GEMs architecture for separation processes. While the choice of SiO2/Si/SiO2 wafers for GEMs is limited to demonstrating the proof-of-concept, it is expected that the protocols and concepts presented here will advance the rational design of scalable GEMs using inexpensive common materials for desalination and beyond.

Proof-of-Concept for Gas-Entrapping Membranes Derived from Water-Loving SiO2/Si/SiO2 Wafers for Green Desalination

Presented here is a stepwise protocol for realizing gas-entrapping membranes (GEMs) from SiO2/Si wafers using integrated circuit microfabrication technology. When silica-GEMs are immersed in water, the intrusion of water is prevented, despite the water-loving composition of silica.

Desalination through direct contact membrane distillation (DCMD) exploits water-repellent membranes to robustly separate counterflowing streams of hot and ...

Engineering

Fabricating Degradable Thermoresponsive Hydrogels on Multiple Length Scales via Reactive Extrusion, Microfluidics, Self-assembly, and Electrospinning

While various smart materials have been explored for a variety of biomedical applications (e.g., drug delivery, tissue engineering, bioimaging, etc.), their ultimate clinical use has been hampered by the lack of biologically-relevant degradation observed for most smart materials. This is particularly true for temperature-responsive hydrogels, which are almost uniformly based on polymers that are functionally non-degradable (e.g., poly(N-isopropylacrylamide) (PNIPAM) or poly(oligoethylene glycol methacrylate) (POEGMA)). As such, to effectively translate the potential of thermoresponsive hydrogels to the challenges of remote-controlled or metabolism-regulated drug delivery, cell scaffolds with tunable cell-material interactions, theranostic materials with the potential for both imaging and drug delivery, and other such applications, a method is required to render the hydrogels (if not fully degradable) at least capable of renal clearance following the required lifetime of the material. To that end, this protocol describes the preparation of hydrolytically-degradable hydrazone-crosslinked hydrogels on multiple length scales based on the reaction between hydrazide and aldehyde-functionalized PNIPAM or POEGMA oligomers with molecular weights below the renal filtration limit. Specifically, methods to fabricate degradable thermoresponsive bulk hydrogels (using a double barrel syringe technique), hydrogel particles (on both the microscale through the use of a microfluidics platform facilitating simultaneous mixing and emulsification of the precursor polymers and the nanoscale through the use of a thermally-driven self-assembly and cross-linking method), and hydrogel nanofibers (using a reactive electrospinning strategy) are described. In each case, hydrogels with temperature-responsive properties similar to those achieved via conventional free radical cross-linking processes can be achieved, but the hydrazone cross-linked network can be degraded over time to re-form the oligomeric precursor polymers and enable clearance. As such, we anticipate these methods (which may be generically applied to any synthetic water-soluble polymer, not just smart materials) will enable easier translation of synthetic smart materials to clinical applications.

Protocols are described for the fabrication of degradable thermoresponsive hydrogels based on hydrazone cross-linking of polymeric oligomers on the bulk scale, microscale, and nanoscale, the latter for preparation of both gel nanoparticles and nanofibers.

While various smart materials have been explored for a variety of biomedical applications (e.g., drug delivery, tissue engineering, bioimaging, etc.), ...

An Additive Manufacturing Technique for the Facile and Rapid Fabrication of Hydrogel-based Micromachines with Magnetically Responsive Components

Polyethylene glycol (PEG)-based hydrogels are biocompatible hydrogels that have been approved for use in humans by the FDA. Typical PEG-based hydrogels have simple monolithic architectures and often function as scaffolding materials for tissue engineering applications. More sophisticated structures typically take a long time to fabricate and do not contain moving components. This protocol describes a photolithography method that allows for facile and rapid microfabrication of PEG structures and devices. This strategy involves an in-house developed fabrication stage that allows for the rapid fabrication of 3D structures by building upwards in a layer-by-layer fashion. Independent moving components can also be aligned and assembled onto support structures to form integrated devices. These independent components are doped with superparamagnetic iron oxide nanoparticles that are sensitive to magnetic actuation. In this manner, the fabricated devices can be actuated using external magnets to yield movement of the components within. Hence, this technique allows for the fabrication of sophisticated MEMS-like devices (micromachines) that are composed entirely out of a biocompatible hydrogel, able to function without an onboard power source, and respond to a contact-less method of actuation. This manuscript describes the fabrication of both the fabrication set-up as well as the step-by-step method for the microfabrication of these hydrogels-based MEMS-like devices.

An additive manufacturing strategy for processing UV-crosslinkable hydrogels has been developed. This strategy allows for the layer-by-layer assembly of microfabricated hydrogel structures as well as the assembly of independent components, yielding integrated devices containing moving components that are responsive to magnetic actuation.

Polyethylene glycol (PEG)-based hydrogels are biocompatible hydrogels that have been approved for use in humans by the FDA. Typical PEG-based hydrogels ...

Photodegradable Hydrogel Interfaces for Bacteria Screening, Selection, and Isolation

Biologists have long attempted to understand the relationship between phenotype and genotype. To better understand this connection, it is crucial to develop practical technologies that couple microscopic cell screening with cell isolation at high purity for downstream genetic analysis. Here, the use of photodegradable poly(ethylene glycol) hydrogels for screening and isolation of bacteria with unique growth phenotypes from heterogeneous cell populations is described. The method relies on encapsulating or entrapping cells with the hydrogel, followed by culture, microscopic screening, then use of a high-resolution light patterning tool for spatiotemporal control of hydrogel degradation and release of selected cells into a solution for retrieval. Applying different light patterns allows for control over the morphology of the extracted cell, and patterns such as rings or crosses can be used to retrieve cells with minimal direct UV light exposure to mitigate DNA damage to the isolates. Moreover, the light patterning tool delivers an adjustable light dose to achieve various degradation and cell release rates. It allows for degradation at high resolution, enabling cell retrieval with micron-scale spatial precision. Here, the use of this material to screen and retrieve bacteria from both bulk hydrogels and microfabricated lab-on-a-chip devices is demonstrated. The method is inexpensive, simple, and can be used for common and emerging applications in microbiology, including isolation of bacterial strains with rare growth profiles from mutant libraries and isolation of bacterial consortia with emergent phenotypes for genomic characterizations.

The use of photodegradable hydrogels to isolate bacterial cells by utilizing a high-resolution light pattering tool is reported. Essential experimental procedures, results, and advantages of the process are reviewed. The method enables rapid and inexpensive isolation of targeted bacteria showing rare or unique functions from heterogeneous communities or populations.

Biologists have long attempted to understand the relationship between phenotype and genotype. To better understand this connection, it is crucial to ...

Synthesis of Strong Adhesive Hydrogel, Gelatin O-Nitrosobenzaldehyde

Adhesive materials have become popular biomaterials in the field of biomedical and tissue engineering. In our previous work, we presented a new material - gelatin o-nitrosobenzaldehyde (gelatin-NB) - which is mainly used for tissue regeneration and has been validated in animal models of corneal injury and inflammatory bowel disease. This is a novel hydrogel formed by modifying biological gelatin with o-nitrosobenzaldehyde (NB). Gelatin-NB was synthesized by activating the carboxyl group of NB-COOH and reacting with gelatin through 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride (EDC) and N-hydroxysuccinimide (NHS). The obtained compound was purified to generate the final product, which can be stably stored for at least 18 months. NB has a strong adhesion to -NH2 on the tissue, which can form many C = N bonds, thus increasing the adhesion of gelatin-NB to the tissue interface. The preparation process comprises steps for the synthesis of the NB-COOH group, modification of the group, synthesis of gelatin-NB, and purification of the compound. The goal is to describe the specific synthesis process of gelatin-NB in detail and to demonstrate the application of gelatin-NB to damage repair. Moreover, the protocol is presented to further strengthen and expand the nature of the material produced by the scientific community for more applicable scenarios.

The protocol presented here shows the synthesis of a strong adhesive hydrogel gelatin o-nitrosobenzaldehyde (gelatin-NB). Gelatin-NB has rapid and efficient tissue adhesion ability, which can form a strong physical barrier to protect wound surfaces, so it is expected to be applied to the field of injury repair biotechnology.

Adhesive materials have become popular biomaterials in the field of biomedical and tissue engineering. In our previous work, we presented a new material - ...

Embedding CFPS Reactions in a Variety of Hydrogel Matrices

Methods for Embedding Cell-Free Protein Synthesis Reactions in Macro-Scale Hydrogels

Synthetic gene networks provide a platform for scientists and engineers to design and build novel systems with functionality encoded at a genetic level. While the dominant paradigm for the deployment of gene networks is within a cellular chassis, synthetic gene networks may also be deployed in cell-free environments. Promising applications of cell-free gene networks include biosensors, as these devices have been demonstrated against biotic (Ebola, Zika, and SARS-CoV-2 viruses) and abiotic (heavy metals, sulfides, pesticides, and other organic contaminants) targets. Cell-free systems are typically deployed in liquid form within a reaction vessel. Being able to embed such reactions in a physical matrix, however, may facilitate their broader application in a wider set of environments. To this end, methods for embedding cell-free protein synthesis (CFPS) reactions in a variety of hydrogel matrices have been developed. One of the key properties of hydrogels conducive to this work is the high-water reconstitution capacity of hydrogel materials. Additionally, hydrogels possess physical and chemical characteristics that are functionally beneficial. Hydrogels can be freeze-dried for storage and rehydrated for use later. Two step-by-step protocols for the inclusion and assay of CFPS reactions in hydrogels are presented. First, a CFPS system can be incorporated into a hydrogel via rehydration with a cell lysate. The system within the hydrogel can then be induced or expressed constitutively for complete protein expression through the hydrogel. Second, cell lysate can be introduced to a hydrogel at the point of polymerization, and the entire system can be freeze-dried and rehydrated at a later point with an aqueous solution containing the inducer for the expression system encoded within the hydrogel. These methods have the potential to allow for cell-free gene networks that confer sensory capabilities to hydrogel materials, with the potential for deployment beyond the laboratory.

Author Spotlight: A Novel Approach for Embedding Cell-Free Protein Synthesis Reactions in Hydrogels 

Here, we present two protocols for embedding cell-free protein synthesis reactions in macro-scale hydrogel matrices without the need for an external liquid phase.

Synthetic gene networks provide a platform for scientists and engineers to design and build novel systems with functionality encoded at a genetic level. ...