The C57BL/6 mice were purchased from Zhejiang University School of Medicine Sir Run Run Shaw Hospital. The New Zealand rabbits were purchased from Zhejiang University. The animals were maintained in natural light-dark cycle conditions and given food and drinking water freely. All experimental procedures were approved ethically by the institutional guidelines of the Zhejiang University Ethics Committee standard guidelines (ZJU20200156) and Zhejiang University School of Medicine Sir Run Run Shaw Hospital Animal Care and Use Committee, which conformed to the NIH Guide for the Care and Use of Laboratory Animals (SRRSH202107106).
1. Synthesis of NB-COOH
<ol>
	<li>Prepare 4-hydroxy-3-(methoxy-D3) benzaldehyde (8.90 g, 58.5 mM, 1.06 equivalents [eq.]), potassium carbonate (10.2 g, 73.8 mM, 1.34 eq.), and methyl 4-bromobutyrate (9.89 g, 55.0 mM, 1.0 eq.) based on the protocol proposed in the previous study10. Dissolve the compounds in 40 mL of N, N-dimethylformamide (DMF) and stir at ambient temperature for 16 h.</li>
	<li>Add 200 mL of 0 &#176;C water to the mixture and precipitate the mixture to obtain a crude product.</li>
	<li>Repeatedly dissolve the crude product in DMF and then precipitate for five cycles. Precipitate the crude product and dry it at 80 &#176;C for 2 h to obtain the early product.</li>
</ol>
2. Chemical modification and processing
<ol>
	<li>Perform the ipso substitution of methyl 4-(4-formyl-2-methoxyphenoxy methoxyphenyl) butanoic acid methyl ester as described below.</li>
	<li>Add 9.4 g of methyl 4-(4-formyl-2-methoxyphenoxy) butanoate (37.3 mM, 1 eq.) slowly to a precooled (-2 &#176;C) solution of 70% nitric acid (140 mL) and stir at -2 &#176;C for 3 h. 
	NOTE: Depending on the temperature of the nitration reaction, the ipso substitution of the formyl moiety will occur.</li>
	<li>Filter the mixture (~9.0 g) with 200 mL of 0 &#176;C water, then purify it in DMF to precipitate a solid product.</li>
	<li>Hydrolyze the solid product in trifluoroacetic acid (TFA)/H2O, 1:10 v/v (100 mL) at 90 &#176;C and dry. Remove the solvent under 80 kPa to obtain the final intermediate product, a dry pale-yellow powder.</li>
	<li>Dissolve the intermediate product (7.4 g, 23.8 mM, 1.0 eq.) in tetrahydrofuran (THF)/ethanol, 1:1 v/v (100 mL). Then add 1.43 g of NaBH4 (35.7 mM, 1.5 eq.) slowly at 0 &#176;C. After 3 h, remove all solvents under a vacuum and suspend the residue in a 1:1 water and dichloromethane solution (50 mL each).</li>
	<li>Prepare dichloromethane to extract the product from the aqueous layer. Remove the organic layer and dry over magnesium sulfate.</li>
	<li>Purify the crude product by silica gel column chromatography using DCM/MeOH at a 10:1 ratio (1% TEA). Finally, obtain 5.31 g (18.6 mM, 78.3%) of relatively pure yellowish powder NB-COOH.</li>
</ol>
3. Synthesis of gelatin-NB
<ol>
	<li>Prepare 5 g of gelatin for one batch of modification. Prepare a homogeneous gelatin solution by dissolving 5 g of gelatin in 100 mL of deionized water and store at 37 &#176;C. 
	NOTE: Here, the original 33 x 10-5 moles &#949;-amino groups/g gelatin11 is defined.</li>
	<li>Define the feed ratio (FR) as the molar ratio between NB groups and primary amino groups in gelatin. In this study, 53 mg of NB with 1 g of gelatin was defined as FRNB = 1.</li>
	<li>Dissolve 1,060 mg of NB-COOH in 5 mL of dimethyl sulfoxide (DMSO) to activate the carboxyl groups of NB-COOH. Since the NB-group is sensitive to ultraviolet (UV) light when in solution, always keep it away from light.</li>
	<li>Add 746 mg of 1-(3-dimethylaminopropyl)-3-ethylcarbodimide hydrochloride (EDC) into the NB-COOH DMSO solution and stir for 5 min. After EDC has dissolved, add 448 mg of N-hydroxysuccinimide (NHS) and stir for 5 min.</li>
	<li>Use a dropping funnel to slowly drop the mixture at a rate of 0.5 mL/min into the dissolved gelatin solution with vigorous stirring to react at 45 &#176;C for 4 h.</li>
</ol>
4. Purification and storage of the product
<ol>
	<li>Dialyze the gelatin-NB solution against excess deionized water for at least 3 days, then collect, freeze, and lyophilize it to obtain the gelatin-NB foams. Keep the foams in a desiccator in the dark for further use.</li>
	<li>Dissolve the freeze-dried gelatin-NB foams in deionized water at 37 &#176;C, immediately before use.</li>
</ol>

<ol>
	<li>Tam, R. Y., Smith, L. J., Shoichet, M. S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Engineering+cellular+microenvironments+with+photo-+and+enzymatically+responsive+hydrogels:+toward+biomimetic+3D+cell+culture+models.">Engineering cellular microenvironments with photo- and enzymatically responsive hydrogels: toward biomimetic 3D cell culture models.</a> Accounts of Chemical Research. 50 (4), 703-713 (2017).</li><li>Xu, X., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Bioadhesive+hydrogels+demonstrating+pH-independent+and+ultrafast+gelation+promote+gastric+ulcer+healing+in+pigs.">Bioadhesive hydrogels demonstrating pH-independent and ultrafast gelation promote gastric ulcer healing in pigs.</a> Science Translational Medicine. 12 (558), (2020).</li><li>Zheng, J., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Directed+self-assembly+of+herbal+small+molecules+into+sustained+release+hydrogels+for+treating+neural+inflammation.">Directed self-assembly of herbal small molecules into sustained release hydrogels for treating neural inflammation.</a> Nature Communications. 10 (1), 1604 (2019).</li><li>Seif-Naraghi, S. B., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Safety+and+efficacy+of+an+injectable+extracellular+matrix+hydrogel+for+treating+myocardial+infarction.">Safety and efficacy of an injectable extracellular matrix hydrogel for treating myocardial infarction.</a> Science Translational Medicine. 5 (173), (2013).</li><li>Mao, Q., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=GelNB+molecular+coating+as+a+biophysical+barrier+to+isolate+intestinal+irritating+metabolites+and+regulate+intestinal+microbial+homeostasis+in+the+treatment+of+inflammatory+bowel+disease.">GelNB molecular coating as a biophysical barrier to isolate intestinal irritating metabolites and regulate intestinal microbial homeostasis in the treatment of inflammatory bowel disease.</a> Bioactive Materials. 19, 251-267 (2022).</li><li>Nan, J., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=A+highly+elastic+and+fatigue-resistant+natural+protein-reinforced+hydrogel+electrolyte+for+reversible-compressible+quasi-solid-state+supercapacitors.">A highly elastic and fatigue-resistant natural protein-reinforced hydrogel electrolyte for reversible-compressible quasi-solid-state supercapacitors.</a> Advanced Science. 7 (14), 2000587 (2020).</li><li>Matsumoto, K., Sakikawa, N., Miyata, T. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Thermo-responsive+gels+that+absorb+moisture+and+ooze+water.">Thermo-responsive gels that absorb moisture and ooze water.</a> Nature Communications. 9 (1), 2315 (2018).</li><li>Liu, R., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=resilient,+adhesive,+and+anti-freezing+hydrogels+cross-linked+with+a+macromolecular+cross-linker+for+wearable+strain+sensors.">resilient, adhesive, and anti-freezing hydrogels cross-linked with a macromolecular cross-linker for wearable strain sensors.</a> ACS Applied Materials &amp; Interfaces. 13 (35), 42052-42062 (2021).</li><li>Hong, Y., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=A+strongly+adhesive+hemostatic+hydrogel+for+the+repair+of+arterial+and+heart+bleeds.">A strongly adhesive hemostatic hydrogel for the repair of arterial and heart bleeds.</a> Nature Communications. 10 (1), 2060 (2019).</li><li>Yang, Y., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Tissue-integratable+and+biocompatible+photogelation+by+the+imine+crosslinking+reaction.">Tissue-integratable and biocompatible photogelation by the imine crosslinking reaction.</a> Advanced Materials. 28 (14), 2724-2730 (2016).</li><li>Ofner, C. M., Bubnis, W. A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Chemical+and+swelling+evaluations+of+amino+group+crosslinking+in+gelatin+and+modified+gelatin+matrices.">Chemical and swelling evaluations of amino group crosslinking in gelatin and modified gelatin matrices.</a> Pharmaceutical Research. 13 (12), 1821-1827 (1996).</li><li>Zhang, Y., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=A+long-term+retaining+molecular+coating+for+corneal+regeneration.">A long-term retaining molecular coating for corneal regeneration.</a> Bioactive Materials. 6 (12), 4447-4454 (2021).</li><li>Liang, Y., Li, Z., Huang, Y., Yu, R., Guo, B. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Dual-dynamic-bond+cross-linked+antibacterial+adhesive+hydrogel+sealants+with+on-demand+removability+for+post-wound-closure+and+infected+wound+healing.">Dual-dynamic-bond cross-linked antibacterial adhesive hydrogel sealants with on-demand removability for post-wound-closure and infected wound healing.</a> ACS Nano. 15 (4), 7078-7093 (2021).</li></ol>

The authors have nothing to disclose.

Adhesive materials are a new class of material. More and more researchers are committed to the synthesis of various types of adhesive materials, and are trying to find their applications in biotechnology, tissue engineering, regenerative medicine, and other fields, which has led to vigorous development in recent years. In addition to focusing on the strong adhesion of adhesive materials, researchers are also paying more attention to other properties, such as injectability, self-healing, hemostatic, antibacterial, control...

Hydrogel is a type of three-dimensional polymer formed by water swelling. In particular, hydrogel derived from an extracellular matrix is widely used in the field of biosynthesis and regenerative medicine because of its excellent biocompatibility and therapeutic effectiveness1. Hydrogels have been reported for the treatment of gastric ulcers, neuritis, myocardial infarction2,3,4, and other diseases. Further, it has been proved that gelatin-NB can promote the outcome of inflammation ininflammatory bowel disease (IBD)5. Traditional hydrogels include gellan gum, gelatin, hyaluronic acid, polyethylene glycol (PEG), layered, hydrophobic/hydrophilic, alginate/polyacrylamide, double network, and polyamphoteric hydrogels6, all of which have good histocompatibility and mechanical properties. However, these traditional hydrogels are vulnerable to moisture and air in the environment. If they are exposed to air for a long time, they will lose water and dry; if they are immersed in the water for a long time, they will absorb water and expand7, thus reducing their flexibility and mechanical function. In addition, maintaining the tissue adhesion of conventional hydrogels is a major challenge8.
Based on this, we designed and synthesized a nanoscale hydrogel gelatin-NB, which is a novel hydrogel formed by modifying biological gelatin with NB (Figure 1). NB has a strong adhesion ability to -NH2 on the tissue, which can form a large number of C = N bonds, thus increasing the adhesiveness of the hydrogel-tissue interface. This strong adhesion can make the hydrogel firmly adhere to the tissue surface, thus forming a nano-level molecular coating. In the team&#39;s previous studies, it has been confirmed that this kind of modified hydrogel coating has improved tissue adhesion9; it can stably adhere to corneal and intestinal organs and tissues and play anti-inflammation, barrier isolation, and regeneration promotion roles. The goal is to introduce the specific synthesis process of gelatin-NB in detail here, so that gelatin-NB can be applied in more scenarios of damage repair. Moreover, we encourage other researchers to further strengthen and expand the nature of this material to suit more application scenarios.

<table><tbody><tr><td>1-(3Dimethylaminopropyl)-3-ethylcarbodimide hydrochloride (EDC)</td><td>Aladdin</td><td>L287553</td><td></td></tr><tr><td>4-Hydroxy-3-(methoxy-D3) benzaldehyde</td><td>Shanghai Acmec Biochemical Co., Ltd</td><td>H946072</td><td></td></tr><tr><td>DCM</td><td>Aladdin</td><td>D154840</td><td></td></tr><tr><td>Dichloromethane</td><td>Sigma-Aldrich</td><td>270997</td><td></td></tr><tr><td>Dimethyl sulfoxide (DMSO)</td><td>Sigma-Aldrich</td><td>20-139</td><td></td></tr><tr><td>dimethylformamide (DMF)</td><td>Sigma-Aldrich</td><td>PHR1553</td><td></td></tr><tr><td>gelatin</td><td>Sigma-Aldrich</td><td>1288485</td><td></td></tr><tr><td>magnesium sulfate</td><td>Sigma-Aldrich</td><td>M7506</td><td></td></tr><tr><td>MeOH</td><td>Sigma-Aldrich</td><td>1424109</td><td></td></tr><tr><td>methyl 4-(4-formyl-2-methoxyphenoxy methoxyphenyl) butanoic acid methyl ester</td><td>chemsrc</td><td>141333-27-9</td><td></td></tr><tr><td>methyl 4-bromobutyrate</td><td>Aladdin</td><td>M158832</td><td></td></tr><tr><td>NaBH4</td><td>Sigma-Aldrich</td><td>215511</td><td></td></tr><tr><td>N-hydroxysuccinimide (NHS)</td><td>Aladdin</td><td>D342712</td><td></td></tr><tr><td>nitric acid</td><td>Sigma-Aldrich</td><td>225711</td><td></td></tr><tr><td>potassium carbonate</td><td>Sigma-Aldrich</td><td>209619</td><td></td></tr><tr><td>SEM (Nova Nano 450)</td><td>Thermo FEI</td><td>17024560</td><td></td></tr><tr><td>THF/EtOH</td><td>Aladdin</td><td>D380010</td><td></td></tr><tr><td>trifluoroacetic acid (TFA)</td><td>Sigma-Aldrich</td><td>8.0826</td><td></td></tr></tbody></table>

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.

Figure 2A shows a schematic of the main chemical reactions involved in the synthesis of gelatin-NB, which promotes tissue integration by grafting NB groups onto gelatin. Figure 2B shows that the O-nitrobenzene of the gelatin-NB hydrogel converts to an NB group immediately after UV irradiation, and then the active aldehyde group can be crosslinked with an amino group to form a Schiff base. Figure 2C indicates that different ratios of...

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Synthesis of Strong Adhesive Hydrogel, Gelatin O-Nitrosobenzaldehyde

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 - ...

synthesis-of-strong-adhesive-hydrogel-gelatin-o-nitrosobenzaldehyde

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Bioengineering

2.3K Views.  Zhejiang University School of Medicine. Ons protocol beschrijft de synthese van een nieuwe klevende hydrogel, gelatine o-nitrosobenzaldehyde, in detail. Het lost vooral het probleem op van het maximaliseren van de hechting van hydrogel. In onze technologie worden chemische groepen in de waterstof gemodificeerd, waardoor de activiteit van chemische reactie met chemische groepen op het oppervlak van dierlijk weefsel wordt verkregen om nauwe buiging en aandacht te bereiken.Het product dat door onze techniek wordt gesynthetiseer...

Video: Synthesis of Strong Adhesive Hydrogel, Gelatin O-Nitrosobenzaldehyde

Synthesis of an Intein-mediated Artificial Protein Hydrogel

We present the synthesis of a highly stable protein hydrogel mediated by a split-intein-catalyzed protein trans-splicing reaction. The building blocks of this hydrogel are two protein block-copolymers each containing a subunit of a trimeric protein that serves as a crosslinker and one half of a split intein. A highly hydrophilic random coil is inserted into one of the block-copolymers for water retention. Mixing of the two protein block copolymers triggers an intein trans-splicing reaction, yielding a polypeptide unit with crosslinkers at either end that rapidly self-assembles into a hydrogel. This hydrogel is very stable under both acidic and basic conditions, at temperatures up to 50 &#176;C, and in organic solvents. The hydrogel rapidly reforms after shear-induced rupture. Incorporation of a &#34;docking station peptide&#34; into the hydrogel building block enables convenient incorporation of &#34;docking protein&#34;-tagged target proteins. The hydrogel is compatible with tissue culture growth media, supports the diffusion of 20 kDa molecules, and enables the immobilization of bioactive globular proteins. The application of the intein-mediated protein hydrogel as an organic-solvent-compatible biocatalyst was demonstrated by encapsulating the horseradish peroxidase enzyme and corroborating its activity.

We present the synthesis of a split-intein-mediated protein hydrogel. The building blocks of this hydrogel are two protein copolymers each containing a subunit of a trimeric protein that serves as a crosslinker and one half of a split intein. Mixing of the two protein copolymers triggers an intein trans-splicing reaction, yielding a polypeptide unit that self-assembles into a hydrogel. This hydrogel is highly pH- and temperature-stable, compatible with organic solvents, and easily incorporates functional globular proteins.

We present the synthesis of a highly stable protein hydrogel mediated by a split-intein-catalyzed protein trans-splicing reaction. The building blocks of ...

Synthesis of Thermogelling Poly(N-isopropylacrylamide)-graft-chondroitin Sulfate Composites with Alginate Microparticles for Tissue Engineering

Injectable biomaterials are defined as implantable materials that can be introduced into the body as a liquid and solidify in situ. Such materials offer the clinical advantages of being implanted minimally invasively and easily forming space-filling solids in irregularly shaped defects. Injectable biomaterials have been widely investigated as scaffolds for tissue engineering. However, for the repair of certain load-bearing areas in the body, such as the intervertebral disc, scaffolds should possess adhesive properties. This will minimize the risk of dislocation during motion and ensure intimate contact with the surrounding tissue, providing adequate transmission of forces. Here, we describe the preparation and characterization of a scaffold composed of thermally sensitive poly(N-isopropylacrylamide)-graft-chondroitin sulfate (PNIPAAM-g-CS) and alginate microparticles. The PNIPAAm-g-CS copolymer forms a viscous solution in water at RT, into which alginate particles are suspended to enhance adhesion. Above the lower critical solution temperature (LCST), around 30 &#176;C, the copolymer forms a solid gel around the microparticles. We have adapted standard biomaterials characterization procedures to take into account the reversible phase transition of PNIPAAm-g-CS. Results indicate that the incorporation of 50 or 75 mg/ml&#160;alginate particles into 5% (w/v) PNIPAAm-g-CS solutions quadruple the adhesive tensile strength of PNIPAAm-gCS alone (p&#60;0.05). The incorporation of alginate microparticles also significantly increases swelling capacity of PNIPAAm-g-CS (p&#60;0.05), helping to maintain a space-filling gel within tissue defects. Finally, results of the in vitro toxicology assay kit, 2,3-bis-(2-methoxy-4-nitro-5-sulfophenyl)-2H-tetrazolium-5-carboxanilide (XTT) and Live/Dead viability assay indicate that the adhesive is capable of supporting the survival and proliferation of encapsulated Human Embryonic Kidney (HEK) 293 cells over 5 days.

Synthesis of Thermogelling PolyN-isopropylacrylamide-graft-chondroitin Sulfate Composites with Alginate Microparticles for Tissue Engineering

An injectable tissue engineering scaffold composed of poly(N-isopropylacrylamide)-graft-chondroitin sulfate (PNIPAAm-g-CS)-containing alginate microparticles was prepared. The adhesive strength, swelling properties and in vitro biocompatibility are analyzed in this study. The characterization techniques developed here may be applicable to other thermogelling systems.

Injectable biomaterials are defined as implantable materials that can be introduced into the body as a liquid and solidify in situ. Such materials offer ...

The Synthesis of RGD-functionalized Hydrogels as a Tool for Therapeutic Applications

The use of polymers as biomaterials has provided significant advantages in therapeutic applications. In particular, the possibility to modify and functionalize polymer chains with compounds that are able to improve biocompatibility, mechanical properties, or cell viability allows the design of novel materials to meet new challenges in the biomedical field. With the polymer functionalization strategies, click chemistry is a powerful tool to improve cell-compatibility and drug delivery properties of polymeric devices. Similarly, the fundamental need of biomedicine to use sterile tools to avoid potential adverse-side effects, such as toxicity or contamination of the biological environment, gives rise to increasing interest in the microwave-assisted strategy.
The combination of click chemistry and the microwave-assisted method is suitable to produce biocompatible hydrogels with desired functionalities and improved performances in biomedical applications. This work aims to synthesize RGD-functionalized hydrogels. RGD (arginylglycylaspartic acid) is a tripeptide that can mimic cell adhesion proteins and bind to cell-surface receptors, creating a hospitable microenvironment for cells within the 3D polymeric network of the hydrogels. RGD functionalization occurs through Huisgen 1,3-dipolar cycloaddition. Some PAA carboxyl groups are modified with an alkyne moiety, whereas RGD is functionalized with azido acid as the terminal residue of the peptide sequence. Finally, both products are used in a copper catalyzed click reaction to permanently link the peptide to PAA. This modified polymer is used with carbomer, agarose and polyethylene glycol (PEG) to synthesize a hydrogel matrix. The 3D structure is formed due to an esterification reaction involving carboxyl groups from PAA and carbomer and hydroxyl groups from agarose and PEG through microwave-assisted polycondensation. The efficiency of the gelation mechanism ensures a high degree of RGD functionalization. In addition, the procedure to load therapeutic compounds or biological tools within this functionalized network is very simple and reproducible.

We present a protocol for the synthesis of RGD-functionalized hydrogels as devices for cell and drug delivery. The procedure involves copper catalyzed alkyne-azide cycloaddition (CuAAC) between alkyne-modified polyacrylic acid (PAA) and a RGD-azide derivative. The hydrogels are formed using microwave-assisted polycondensation and their physicochemical properties are investigated.

The use of polymers as biomaterials has provided significant advantages in therapeutic applications. In particular, the possibility to modify and ...

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.), ...

Patterning Bioactive Proteins or Peptides on Hydrogel Using Photochemistry for Biological Applications

There are many biological stimuli that can influence cell behavior and stem cell differentiation. General cell culture approaches rely on soluble factors within the medium to control cell behavior. However, soluble additions cannot mimic certain signaling motifs, such as matrix-bound growth factors, cell-cell signaling, and spatial biochemical cues, which are common influences on cells. Furthermore, biophysical properties of the matrix, such as substrate stiffness, play important roles in cell fate, which is not easily manipulated using conventional cell culturing practices. In this method, we describe a straightforward protocol to provide patterned bioactive proteins on synthetic polyethylene glycol (PEG) hydrogels using photochemistry. This platform allows for the independent control of substrate stiffness and spatial biochemical cues. These hydrogels can achieve a large range of physiologically relevant stiffness values. Additionally, the surfaces of these hydrogels can be photopatterned with bioactive peptides or proteins via thiol-ene click chemistry reactions. These methods have been optimized to retain protein function after surface immobilization. This is a versatile protocol that can be applied to any protein or peptide of interest to create a variety of patterns. Finally, cells seeded onto the surfaces of these bioactive hydrogels can be monitored over time as they respond to spatially specific signals.

In this method, we use photopolymerization and click chemistry techniques to create protein or peptide patterns on the surface of polyethylene glycol (PEG) hydrogels, providing immobilized bioactive signals for the study of cellular responses in vitro.

There are many biological stimuli that can influence cell behavior and stem cell differentiation. General cell culture approaches rely on soluble factors ...

Synthesis of Stimuli-responsive Nanogels using Aqueous One-step Crosslinking and Co-nanopolymerization

Nanogels consisting of crosslinked-polymeric nanoparticles have been developed for the delivery of numerous chemical and biological therapeutics, owing to their versatile bottom-up synthesis and biocompatibility. While various methods have been employed for nanogel synthesis to date, very few have achieved it without the use of harsh organic solvents or high temperatures that can damage the integrity of the biological payload. In contrast, the methodology presented here accomplishes the synthesis of sub-100 nm sized, protein-loaded nanogels using mild reaction conditions. Here, we present a method for the non-covalent encapsulation of protein-based payloads within nano-gels that were synthesized using an aqueous-based, single-step, crosslinking copolymerization technique. In this technique, we initially electrostatically bind a protein-based payload to a cationic quaternary ammonium monomer and simultaneously cross-link and co-polymerize it using ammonium persulfate and N,N,N&#39;,N&#39;-tetramethylethylenediamine to form nanogels that entrap the protein payload. The size and polydispersity index of the nanogels is determined using dynamic light scattering (DLS), while the surface morphology is assessed by transmission electron microscopy (TEM). The mass of protein entrapped within nanogels is determined by calculating the encapsulation efficiency. Furthermore, the controlled-release ability of the nanogels via the gradual degradation of redox-responsive structural elements is also assessed in bioreduction assays. We provide examples of nanoparticle optimization data to demonstrate all caveats of nanogel synthesis and characterization using this technique. In general, uniformly sized nanogels were obtained with an average size of 57 nm and a polydispersity index value of 0.093. A high encapsulation efficiency of 76% was achieved. Furthermore, the nanogels exhibited controlled release of up to 86% of the encapsulated protein by gradual degradation of novel redox-responsive components in the presence of glutathione over 48 h.

Nanogels are an excellent and versatile nanoparticle platform for the delivery of biologics. Stimuli-responsive poly(ethylene) glycol-based polymeric nano-gels, capable of encapsulating protein-based payloads, were synthesized using a one-step cross-linking co-nanopolymerization strategy in aqueous conditions. The optimal fabrication and characterization of these novel nanoparticles are presented here.

Nanogels consisting of crosslinked-polymeric nanoparticles have been developed for the delivery of numerous chemical and biological therapeutics, owing to ...

Chemistry

3D Printed Porous Cellulose Nanocomposite Hydrogel Scaffolds

This work demonstrates the use of three-dimensional (3D) printing to produce porous cubic scaffolds using cellulose nanocomposite hydrogel ink, with controlled pore structure and mechanical properties. Cellulose nanocrystals (CNCs, 69.62 wt%) based hydrogel ink with matrix (sodium alginate and gelatin) was developed and 3D printed into scaffolds with uniform and gradient pore structure (110-1,100 &#181;m). The scaffolds showed compression modulus in the range of 0.20-0.45 MPa when tested in simulated in vivo conditions (in distilled water at 37 &#176;C). The pore sizes and the compression modulus of the 3D scaffolds matched with the requirements needed for cartilage regeneration applications. This work demonstrates that the consistency of the ink can be controlled by the concentration of the precursors and porosity can be controlled by the 3D printing process and both of these factors in return defines the mechanical properties of the 3D printed porous hydrogel scaffold. This process method can therefore be used to fabricate structurally and compositionally customized scaffolds according to the specific needs of patients.&#160;

The three critical steps of this protocol are i) developing the right composition and consistency of the cellulose hydrogel ink, ii) 3D printing of scaffolds into various pore structures with good shape fidelity and dimensions and iii) demonstration of the mechanical properties in simulated body conditions for cartilage regeneration.

This work demonstrates the use of three-dimensional (3D) printing to produce porous cubic scaffolds using cellulose nanocomposite hydrogel ink, with ...

Protocols of 3D Bioprinting of Gelatin Methacryloyl Hydrogel Based Bioinks

Gelatin methacryloyl (GelMA) has become a popular biomaterial in the field of bioprinting. The derivation of this material is gelatin, which is hydrolyzed from mammal collagen. Thus, the arginine-glycine-aspartic acid (RGD) sequences and target motifs of matrix metalloproteinase (MMP) remain on the molecular chains, which help achieve cell attachment and degradation. Furthermore, formation properties of GelMA are versatile. The methacrylamide groups allow a material to become rapidly crosslinked under light irradiation in the presence of a photoinitiator. Therefore, it makes great sense to establish suitable methods for synthesizing three-dimensional (3D) structures with this promising material. However, its low viscosity restricts GelMA's printability. Presented here are methods to carry out 3D bioprinting of GelMA hydrogels, namely the fabrication of GelMA microspheres, GelMA fibers, GelMA complex structures, and GelMA-based microfluidic chips. The resulting structures and biocompatibility of the materials as well as the printing methods are discussed. It is believed that this protocol may serve as a bridge between previously applied biomaterials and GelMA as well as contribute to the establishment of GelMA-based 3D architectures for biomedical applications.

Presented here is a method for the 3D bioprinting of gelatin methacryloyl.

Gelatin methacryloyl (GelMA) has become a popular biomaterial in the field of bioprinting. The derivation of this material is gelatin, which is hydrolyzed ...

Gelatin Methacryloyl Granular Hydrogel Scaffolds: High-throughput Microgel Fabrication, Lyophilization, Chemical Assembly, and 3D Bioprinting

The emergence of granular hydrogel scaffolds (GHS), fabricated via assembling hydrogel microparticles (HMPs), has enabled microporous scaffold formation in situ. Unlike conventional bulk hydrogels, interconnected microscale pores in GHS facilitate degradation-independent cell infiltration as well as oxygen, nutrient, and cellular byproduct transfer. Methacryloyl-modified gelatin (GelMA), a (photo)chemically crosslinkable, protein-based biopolymer containing cell adhesive and biodegradable moieties, has widely been used as a cell-responsive/instructive biomaterial. Converting bulk GelMA to GHS&#160;may open a plethora of opportunities for tissue engineering and regeneration. In this article, we demonstrate the procedures of high-throughput GelMA microgel fabrication, conversion to resuspendable dry microgels (micro-aerogels), GHS formation via the chemical assembly of microgels, and granular bioink fabrication for extrusion bioprinting. We show how a sequential physicochemical treatment via cooling and photocrosslinking enables the formation of mechanically robust GHS.&#160;When light is inaccessible (e.g., during deep tissue injection), individually crosslinked GelMA HMPs may be bioorthogonally assembled via enzymatic crosslinking using transglutaminases. Finally, three-dimensional (3D) bioprinting of microporous GHS&#160;at low HMP packing density is demonstrated via the interfacial self-assembly of heterogeneously charged nanoparticles.

This article describes protocols for high-throughput gelatin methacryloyl microgel fabrication using microfluidic devices, converting microgels to resuspendable powder (micro-aerogels), the chemical assembly of microgels to form granular hydrogel scaffolds, and developing granular hydrogel bioinks with preserved microporosity for 3D bioprinting.

The emergence of granular hydrogel scaffolds (GHS), fabricated via assembling hydrogel microparticles (HMPs), has enabled microporous scaffold formation ...

Studying Tissue Rigidity and Shear Stress Effects on Endothelial Cells

In Vitro Model Integrating Substrate Stiffness and Flow to Study Endothelial Cell Responses

We present an innovative in vitro model aimed at investigating the combined effects of tissue rigidity and shear stress on endothelial cell (EC) function, which are crucial for understanding vascular health and the onset of diseases such as atherosclerosis. Traditionally, studies have explored the impacts of shear stress and substrate stiffness on ECs, independently. However, this integrated system combines these factors to provide a more precise simulation of the mechanical environment of the vasculature. The objective is to examine EC mechanotransduction across various tissue stiffness levels and flow conditions using human ECs. We detail the protocol for synthesizing gelatin methacrylate (GelMA) hydrogels with tunable stiffness and seeding them with ECs to achieve confluency. Additionally, we describe the design and assembly of a cost-effective flow chamber, supplemented by computational fluid dynamics simulations, to generate physiological flow conditions characterized by laminar flow and appropriate shear stress levels. The protocol also incorporates fluorescence labeling for confocal microscopy, enabling the assessment of EC responses to both tissue compliance and flow conditions. By subjecting cultured ECs to multiple integrated mechanical stimuli, this model enables comprehensive investigations into how factors such as hypertension and aging may affect EC function and EC-mediated vascular diseases. The insights gained from these investigations will be instrumental in elucidating the mechanisms underlying vascular diseases and in developing effective treatment strategies.

We synthesized and characterized a tunable gelatin-based substrate for culturing vascular endothelial cells (ECs) under relevant vascular flow conditions. This biomimetic surface replicates both physiological and pathological conditions, enabling the study of mechanical forces on EC behavior and advancing our understanding of vascular health and disease mechanisms.

We present an innovative in vitro model aimed at investigating the combined effects of tissue rigidity and shear stress on endothelial cell (EC) function, ...

Synthesis of Strong Adhesive Hydrogel, Gelatin O-Nitrosobenzaldehyde

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