The authors would like to thank Prof. Paul Van Tassel and Prof. Chinedum Osuji for their thoughtful conversations and materials science expertise. Funding for this work was provided by the Dubinsky New Initiative Award and National Institutes of Health NIBIB BRPR01 EB16629-01A1.

Please read Material Safety Data Sheet (MSDS) of all materials prior to use and use safety precautions at all times.
1. Synthesis of Zinc Oxide Needles
<ol>
	<li>Prepare 250 mL of a 0.04 M Zn(NO3)2*6H2O solution by adding 2.9749 g of zinc nitrate to 250 mL of water.</li>
	<li>Prepare 150 mL of 1 M NaOH by adding 6 g of NaOH to 150 mL of water.</li>
	<li>Set up a mineral oil bath on a hot plate with stirrer, and submerge a 500-mL round bottom flask into the oi...

<ol>
	<li>Domogatskaya, A., Rodin, S., Tryggvason, K. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Functional+diversity+of+laminins.">Functional diversity of laminins.</a> Annu Rev Cell Dev Biol. 28, 523-553 (2012).</li><li>Howat, W. J., Holmes, J. A., Holgate, S. T., Lackie, P. M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Basement+membrane+pores+in+human+bronchial+epithelium:+a+conduit+for+infiltrating+cells.">Basement membrane pores in human bronchial epithelium: a conduit for infiltrating cells.</a> Am J Pathol. 158, 673-680 (2001).</li><li>Lauridsen, H. M., Pober, J. S., Gonzalez, A. L. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=A+composite+model+of+the+human+postcapillary+venule+for+investigation+of+microvascular+leukocyte+recruitment.">A composite model of the human postcapillary venule for investigation of microvascular leukocyte recruitment.</a> FASEB J. 28, 1166-1180 (2014).</li><li>Mul, F. P., 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=Sequential+migration+of+neutrophils+across+monolayers+of+endothelial+and+epithelial+cells.">Sequential migration of neutrophils across monolayers of endothelial and epithelial cells.</a> J Leukoc Biol. 68, 529-537 (2000).</li><li>Hermanns, M. I., Unger, R. E., Kehe, K., Peters, K., Kirkpatrick, C. J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Lung+epithelial+cell+lines+in+coculture+with+human+pulmonary+microvascular+endothelial+cells:+development+of+an+alveolo-capillary+barrier+in+vitro.">Lung epithelial cell lines in coculture with human pulmonary microvascular endothelial cells: development of an alveolo-capillary barrier in vitro.</a> Lab Invest. 84, 736-752 (2004).</li><li>Birkness, K. A., 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=An+in+vitro+tissue+culture+bilayer+model+to+examine+early+events+in+Mycobacterium+tuberculosis+infection.">An in vitro tissue culture bilayer model to examine early events in Mycobacterium tuberculosis infection.</a> Infect Immun. 67, 653-658 (1999).</li><li>Wang, L., 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=Human+alveolar+epithelial+cells+attenuate+pulmonary+microvascular+endothelial+cell+permeability+under+septic+conditions.">Human alveolar epithelial cells attenuate pulmonary microvascular endothelial cell permeability under septic conditions.</a> PLoS One. 8, 55311 (2013).</li><li>Pellowe, A. S., Gonzalez, A. L. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Extracellular+matrix+biomimicry+for+the+creation+of+investigational+and+therapeutic+devices.">Extracellular matrix biomimicry for the creation of investigational and therapeutic devices.</a> Wiley Interdiscip Rev Nanomed Nanobiotechnol. 8, 5-22 (2016).</li><li>Peyton, S. R., Raub, C. B., Keschrumrus, V. P., Putnam, A. J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=The+use+of+poly(ethylene+glycol)+hydrogels+to+investigate+the+impact+of+ECM+chemistry+and+mechanics+on+smooth+muscle+cells.">The use of poly(ethylene glycol) hydrogels to investigate the impact of ECM chemistry and mechanics on smooth muscle cells.</a> Biomaterials. 27, 4881-4893 (2006).</li><li>West, J. L. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Protein-patterned+hydrogels:+Customized+cell+microenvironments.">Protein-patterned hydrogels: Customized cell microenvironments.</a> Nat Mater. 10, 727-729 (2011).</li><li>DeLong, S. A., Gobin, A. S., West, J. L. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Covalent+immobilization+of+RGDS+on+hydrogel+surfaces+to+direct+cell+alignment+and+migration.">Covalent immobilization of RGDS on hydrogel surfaces to direct cell alignment and migration.</a> J Control Release. 109, 139-148 (2005).</li><li>Engler, A. J., Sen, S., Sweeney, H. L., Discher, D. E. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Matrix+elasticity+directs+stem+cell+lineage+specification.">Matrix elasticity directs stem cell lineage specification.</a> Cell. 126, 677-689 (2006).</li><li>Taite, L. 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=Bioactive+hydrogel+substrates:+probing+leukocyte+receptor-ligand+interactions+in+parallel+plate+flow+chamber+studies.">Bioactive hydrogel substrates: probing leukocyte receptor-ligand interactions in parallel plate flow chamber studies.</a> Ann Biomed Eng. 34, 1705-1711 (2006).</li><li>Lauridsen, H. M., Walker, B. J., Gonzalez, A. L. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Chemically-+and+mechanically-tunable+porated+polyethylene+glycol+gels+for+leukocyte+integrin+independent+and+dependent+chemotaxis.">Chemically- and mechanically-tunable porated polyethylene glycol gels for leukocyte integrin independent and dependent chemotaxis.</a> Technology. 02, 133-143 (2014).</li><li>DeLong, S. A., Moon, J. J., West, J. L. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Covalently+immobilized+gradients+of+bFGF+on+hydrogel+scaffolds+for+directed+cell+migration.">Covalently immobilized gradients of bFGF on hydrogel scaffolds for directed cell migration.</a> Biomaterials. 26, 3227-3234 (2005).</li><li>Lauridsen, H. M., Gonzalez, A. L. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Biomimetic,+ultrathin+and+elastic+hydrogels+regulate+human+neutrophil+extravasation+across+endothelial-pericyte+bilayers.">Biomimetic, ultrathin and elastic hydrogels regulate human neutrophil extravasation across endothelial-pericyte bilayers.</a> PLOS one. 12, 0171386-0171405 (2017).</li><li>Peters, E. B., Christoforou, N., Leong, K. W., Truskey, G. A., West, J. L. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Poly(Ethylene+Glycol+Hydrogel+Scaffolds+Containing+Cell-Adhesive+and+Protease-Sensitive+Peptides+Support+Microvessel+Formation+by+Endothelial+Progenitor+Cells.">Poly(Ethylene Glycol Hydrogel Scaffolds Containing Cell-Adhesive and Protease-Sensitive Peptides Support Microvessel Formation by Endothelial Progenitor Cells.</a> Cellular and Molecular Bioengineering. 9, 38-54 (2016).</li><li>Schwartz, M. P., 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+synthetic+strategy+for+mimicking+the+extracellular+matrix+provides+new+insight+about+tumor+cell+migration.">A synthetic strategy for mimicking the extracellular matrix provides new insight about tumor cell migration.</a> Integr Biol (Camb). 2, 32-40 (2010).</li><li>Booth, A. 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=Acellular+normal+and+fibrotic+human+lung+matrices+as+a+culture+system+for+in+vitro+investigation.">Acellular normal and fibrotic human lung matrices as a culture system for in vitro investigation.</a> Am J Respir Crit Care Med. 186, 866-876 (2012).</li><li>Kalluri, R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Basement+membranes:+structure,+assembly+and+role+in+tumour+angiogenesis.">Basement membranes: structure, assembly and role in tumour angiogenesis.</a> Nat Rev Cancer. 3, 422-433 (2003).</li><li>Roudsari, L. C., Keffs, S. E., Witt, A. S., Gill, B. J., West, J. L. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=A+3D+Poly(ethylene+glycol)-based+Tumor+Angiogenesis+Model+to+Study+the+Influence+of+Vascular+Cells+on+Lung+Tumor+Cell+Behavior.">A 3D Poly(ethylene glycol)-based Tumor Angiogenesis Model to Study the Influence of Vascular Cells on Lung Tumor Cell Behavior.</a> Scientific Reports. 6, 1-15 (2016).</li><li>Bermudez, L. E., Sangari, F. J., Kolonoski, P., Petrofsky, M., Goodman, J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=The+efficiency+of+the+translocation+of+Mycobacterium+tuberculosis+across+a+bilayer+of+epithelial+and+endothelial+cells+as+a+model+of+the+alveolar+wall+is+a+consequence+of+transport+within+mononuclear+phagocytes+and+invasion+of+alveolar+epithelial+cells.">The efficiency of the translocation of Mycobacterium tuberculosis across a bilayer of epithelial and endothelial cells as a model of the alveolar wall is a consequence of transport within mononuclear phagocytes and invasion of alveolar epithelial cells.</a> Infect Immun. 70, 140-146 (2002).</li></ol>

The protocol detailed here has allowed us to create a tunable PEG hydrogel to serve as a biomimetic BM scaffold. Specifically, by varying PEG molecular weights, peptide conjugation strategies, and zinc oxide microcrystalline structures or concentrations, the elastic modulus, biochemical properties, and porous structure of the hydrogels can be modified, respectively. The ultrathin PEG scaffold features a higher pore density and a smaller pore diameter that is more mimetic of the features found in in vivo basement...

Extracellular matrices (ECM) make up the protein scaffolds that support cell attachment and serve as barriers between distinct cell types and are an essential component of complex tissues and organs. In contrast to interstitial connective tissue, the basement membrane (BM) is a specialized type of ECM that acts as a barrier to divide tissue compartments from one another. BMs are approximately 100 &#181;m thick, and therefore allow for direct and indirect communication between cells on either side. Two common examples of BMs are vascular BMs, found in the microvascular wall between pericytes and endothelial cells, and airway BMs that are found between endothelial and epithelial cells. BMs serve an important role in regulating cell function, such as cell polarity and migration, in health and disease.1 The composition, stiffness, architecture, and porosity of BMs varies across organ systems to facilitate distinct physiological functions. For example, BM pores are critical for maintaining cell-cell communication, soluble molecule diffusion, and for migration of immune cells during inflammation or bacteria during infection. In the airways, pores span the full thickness of the BM, with diameters ranging from 0.75 to 3.86 &#181;m.2
The thin nature of the BM ensures that although cell types are physically separated from one another, intercellular communication via paracrine- and contact-mediated signaling is preserved. Thus, to study human disease in vitro, researchers have relied on porous permeable support inserts to culture cellular bilayers.3 These models have been critical for understanding the cellular communication that plays a role in health and disease.3,4,5,6,7 Permeable support inserts satisfy the basic requirements for understanding how cell-cell signaling regulates physiological processes, such as leukocyte recruitment and bacterial infiltration; however, the inserts have significant limitations and fail to mimic a human BM. Permeable support inserts lack both mechanical and biochemical tunability, and the simplistic porous structure does not mimic the fibrous structure that creates the irregular pores typical of BMs. Therefore, there is a growing need for tunable systems that can recreate the native BM properties that influence cellular processes.
Polymer-based substrates are ideal candidates for the development of biomimetic BMs to study cellular bilayers in a context that more closely mimics the in vivo environment.8,9,10,11,12 Polymers are mechanically tunable and can be chemically modified to incorporate biomimetic peptide fragments.11,12,13 The bioinert polymer polyethylene glycol (PEG) can be used to construct biomimetic BMs, and recent work has detailed the synthesis of mechanically tunable PEG arginine-glycine-aspartic acid (RGD) gels with porous networks that support cell growth and inflammatory cell chemotaxis.14 Although published PEG-based substrates provided a more realistic model of a human ECM than permeable supports, many of these models are extremely thick, with a depth of roughly 775 &#181;m that limits the ability to create bilayer cultures with cell-cell contacts.14
Here, we present a protocol for the creation of a PEG polymer-based BM mimic that overcomes many of the limitations of current cell bilayer culture technologies. We have developed a templating method that incorporates zinc oxide, an extensively used material for the manufacture of microcrystalline production, into the polymer during synthesis and crosslinking, which is subsequently and selectively removed from the resulting bulk polymer. This process generates a random porous network, mimicking the tortuous and interconnected pore network of human BMs. Further, the porosity can be altered by changing the size and shape of the zinc oxide microcrystals via modification of the reaction stoichiometry during needle production. The technique developed here creates an ultrathin hydrogel that mimics the thickness of human BM. Lastly, the mechanics, the porosity, and the biochemical composition of these BM-like constructs can easily be altered to generate a microenvironment that is most similar to that seen in vivo.

<table border="0" cellpadding="0" cellspacing="0" style="width:737px;" width="738">
	<colgroup>
		<col />
		<col />
		<col />
		<col />
	</colgroup>
	<tbody>
		<tr height="21">
			<td height="21" style="height:21px;width:335px;">1M Hydrogel Chloride (HCl)</td>
			<td style="width:117px;">EMD</td>
			<td style="width:119px;">HX0603-75 2.5L</td>
			<td style="width:167px;">Sterile. Use in fume hood with eye protection and gloves.</td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:335px;">1X PBS</td>
			<td style="width:117px;">Gibco</td>
			<td style="width:119px;">14040-133 500 mL</td>
			<td>None</td>
		</tr>
		<tr height="25">
			<td height="25" style="height:25px;width:335px;">Zinc Nitrate Hexahydrate (Zn(NO3)2&#8226;6H2O)</td>
			<td style="width:117px;">Sigma-Aldrich</td>
			<td style="width:119px;">228737-500g</td>
			<td>Use with eye protection and gloves.</td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:335px;">Sodium Hydroxide (NaOH)</td>
			<td style="width:117px;">Macron Chemicals</td>
			<td style="width:119px;">278408-500g</td>
			<td>Use with eye protection and gloves.</td>
		</tr>
		<tr height="44">
			<td height="44" style="height:44px;width:335px;">Zinc Acetate Dihydrate ((CH3O2)2Zn2+&#8226;2H2O)</td>
			<td style="width:117px;">Fisher Scientific</td>
			<td style="width:119px;">AC45180010 1 kg</td>
			<td>Use with eye protection and gloves.</td>
		</tr>
		<tr height="25">
			<td height="25" style="height:25px;width:335px;">Methanol (CH3OH)</td>
			<td style="width:117px;">J.T. Baker</td>
			<td style="width:119px;">9070-05 4L</td>
			<td>Use in fume hood with eye protection and gloves.</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:335px;">VWR Life Science Seradigm Premium Grade FBS</td>
			<td style="width:117px;">VWR</td>
			<td style="width:119px;">97068-085</td>
			<td>Sterile filter. 5 mL FBS in 45 mL PBS</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:335px;">Mineral oil</td>
			<td style="width:117px;">CVS&#160;</td>
			<td style="width:119px;">PLD-B280B</td>
			<td>None</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:335px;">Round bottom flask</td>
			<td style="width:117px;">ChemGlass</td>
			<td style="width:119px;"></td>
			<td>N/A</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:335px;">Thermometer</td>
			<td style="width:117px;"></td>
			<td style="width:119px;"></td>
			<td>N/A</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:335px;">Stir bar</td>
			<td style="width:117px;"></td>
			<td style="width:119px;"></td>
			<td>N/A</td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:335px;">Plain precleaned microscope slides 3&#34;x1&#34;x1&#34; mm thick</td>
			<td style="width:117px;">Thermo Scientific</td>
			<td style="width:119px;">420-004T</td>
			<td>Spray with ethanol and let dry prior to use.</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:335px;">Glass pasteur pipets</td>
			<td style="width:117px;"></td>
			<td style="width:119px;"></td>
			<td>N/A</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:335px;">1 mL rubber bulbs</td>
			<td style="width:117px;"></td>
			<td style="width:119px;"></td>
			<td>N/A</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:335px;">Plastic 100 mm petri dishes</td>
			<td style="width:117px;"></td>
			<td style="width:119px;"></td>
			<td>N/A</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:335px;">Sterile forceps</td>
			<td style="width:117px;"></td>
			<td style="width:119px;"></td>
			<td>N/A</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:335px;">Silicone isolators</td>
			<td style="width:117px;"></td>
			<td style="width:119px;"></td>
			<td>0.8 mm thick</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:335px;">Polydimethylsiloxane (PDMS) punches</td>
			<td style="width:117px;"></td>
			<td style="width:119px;"></td>
			<td>N/A</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:335px;">Glass bottles</td>
			<td style="width:117px;"></td>
			<td style="width:119px;"></td>
			<td>N/A</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:335px;">6 well plates</td>
			<td style="width:117px;">Cellstar</td>
			<td style="width:119px;">657 160</td>
			<td>N/A</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:335px;">Filter Paper</td>
			<td style="width:117px;">Whatman</td>
			<td align="right" style="width:119px;">8519</td>
			<td>N/A</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:335px;">Stirrer-hot plate</td>
			<td style="width:117px;">VWR Dya-Dual</td>
			<td style="width:119px;">12620-970</td>
			<td>Use with eye protection and gloves.</td>
		</tr>
		<tr height="46">
			<td height="46" style="height:46px;width:335px;">2,2-Dimethoxy-2-phenylacetophenone (C6H5COC(OCH3)2C6H5</td>
			<td style="width:117px;">Sigma-Aldrich</td>
			<td style="width:119px;">24650-42-8</td>
			<td>Use with eye protection and gloves.</td>
		</tr>
		<tr height="24">
			<td height="24" style="height:24px;">1-Vinyl-2-pyrrolidone (C6H9NO)</td>
			<td style="width:117px;">Aldrich</td>
			<td style="width:119px;"></td>
			<td>Use with eye protection and gloves.</td>
		</tr>
		<tr height="46">
			<td height="46" style="height:46px;width:335px;">Polyethylene Glycol 10,000 (H(OCH2CH2)10,000OH)</td>
			<td style="width:117px;">Fluka</td>
			<td style="width:119px;">81280-1kg</td>
			<td>Use with eye protection and gloves.</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:335px;">RGDS</td>
			<td style="width:117px;">Life Tein</td>
			<td align="right" style="width:119px;">180190</td>
			<td>Use with eye protection and gloves.</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:335px;">Blak-Ray long wave UV lamp</td>
			<td style="width:117px;">UVP</td>
			<td style="width:119px;">Model B 100AP</td>
			<td>N/A</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:335px;">Eppendorf tubes</td>
			<td style="width:117px;">USA Scientific</td>
			<td style="width:119px;">1615-5500</td>
			<td>N/A</td>
		</tr>
	</tbody>
</table>

ultrathin porated elastic hydrogels as a biomimetic basement membrane for dual cell culture

The basement membrane is a critical component of cellular bilayers that can vary in stiffness, composition, architecture, and porosity. In vitro studies of endothelial-epithelial bilayers have traditionally relied on permeable support models that enable bilayer culture, but permeable supports are limited in their ability to replicate the diversity of human basement membranes. In contrast, hydrogel models that require chemical synthesis are highly tunable and allow for modifications of both the material stiffness and the biochemical composition via incorporation of biomimetic peptides or proteins. However, traditional hydrogel models are limited in functionality because they lack pores for cell-cell contacts and functional in vitro migration studies. Additionally, due to the thickness of traditional hydrogels, incorporation of pores that span the entire thickness of hydrogels has been challenging. In the present study, we use poly-(ethylene-glycol) (PEG) hydrogels and a novel zinc oxide templating method to address the previous shortcomings of biomimetic hydrogels. As a result, we present an ultrathin, basement membrane-like hydrogel that permits the culture of confluent cellular bilayers on a customizable scaffold with variable pore architectures, mechanical properties, and biochemical composition.

PEG-RGD hydrogels were formed by sandwiching the polymer solution between two sacrificial zinc oxide layers and creating pore templates with zinc oxide needles. Sacrificial zinc oxide components were then removed with hydrochloric acid, generating ultrathin PEG hydrogels with continuous pores (Figure 1). The morphology of zinc oxide needles was confirmed by scanning electron microscopy (SEM), and the average length and width were determined to be 3.92 &#177;&...

Watch this Scientific Journal Video about Ultrathin Porated Elastic Hydrogels As a Biomimetic Basement Membrane for Dual Cell Culture at JoVE.com

Ultrathin Porated Elastic Hydrogels As a Biomimetic Basement Membrane for Dual Cell Culture

Current bilayer culture models do not allow for functional in vitro studies that mimic in vivo microenvironments. Using polyethylene glycol and a zinc oxide templating method, this protocol describes the development of an ultrathin biomimetic basement membrane with tunable stiffness, porosity, and biochemical composition that closely mimics in vivo extracellular matrices.

The basement membrane is a critical component of cellular bilayers that can vary in stiffness, composition, architecture, and porosity. In vitro studies ...

The overall goal of this protocol is to describe a polyethylene glycol and zinc oxide templating method to create a porous, ultra-thin, biomimetic basement membrane that supports dual cell culture, and has tuneable mechanical and chemical properties. The main advantage of this technique is that we can create hydrogels that are ultra-thin, porated, mechanically and biochemically tuneable. They allow support of either single or dual cell culture.This method can help answer key questions in the tissue engineering field, including how dual cell cultures react to, and interact with, microenvironments that mimic human basement membranes. The implications of this technique extend toward a wide variety of biological systems and tissues, ultimately allowing more biomimetic research with enhanced translation for human disease. Add 250 milliliters of zinc nitrate to a flask and begin stirring the reaction.Then, add 150 milliliters of sodium hydroxide solution. A white precipitate will form briefly and then disappear as the two solutions continue to mix. Stir the mixture for two hours uncovered.Heat the flask to 55 to 60 degrees celsius and continue stirring for 24 hours. Turn off the heat and allow solution to cool to room temperature while stirring. Filter the solution though a Buchner funnel with an 11 micron pore size and allow it to dry overnight, uncovered.When the filter paper is no longer wet from the poured solution and a white powder has formed over the funnel holes, the particles are fully dried. After checking the needle leg morphology of zinc oxide needles, as described in the text protocol, clean three inch by one inch plain microscope slides with 70 percent ethanol and a disposable wipe. Hold the glass slide with tweezers and use a glass pipet with a pipet bulb to coat the slides with five drops of zinc acetate forming a thin layer dispersed on the slide.Allow excess solution to drip back into the stock solution. Then, place the slide into a preheated Petri dish on a hot plate with the zinc acetate coated side facing up for 15 minutes. Remove the slide with tweezers and allow it to cool to room temperature.The slide will appear to be coated with white streaks. Remove any excess zinc that is remaining on the slides, using a disposable wipe to remove permanent white streaks. The surface should be uniform.Suspend 20 milligrams of zinc oxide needles in 270 microliters of ten percent FBS/PBS solution. Vortex to mix for approximately 15 seconds. Briefly spin the solution in a bench top mini centrifuge to bring any zinc oxide aggregates to the base of the tube.Following centrifugation, collect 250 microliters from the top of the zinc oxide solution to ensure that aggregates remain at the bottom of the tube. Combine the collected zinc oxide solution with PEG diacrylate and PEG-RGD to create a PEG solution with approximately 2.5 millimolar RGD. Then vortex to mix for approximately 15 seconds.Next, add two microliters of acetophenone and vinyl pyrrolidone photoinitiator and vortex briefly to mix. Add 20 microliters of the polymer solution along the center of the zinc oxide coated slides. Slowly lower a second slide on top, with the zinc oxide coating facing down so that the PEG solution is between two zinc oxide coated layers.Try to prevent the formation of any air bubbles. Move the slides laterally along their axis to allow any bubbles to escape and to spread the solution into a thin layer. Create a slight overhang with the top slide to ensure that the slides can be pulled apart in their later steps.Finally, cross link the slides under a 365 nanometer UV lamp for 15 minutes. Apply pressure to the overhanging slide and manually pull the two slides apart at a slow pace in order to avoid cracking the slides. Allow the gels to dry for at least five minutes or overnight.Once the gels are dry, place the slide in a sterile 25 milliliter glass Petri dish and gently pour the one molar HCL solution onto the slide using only enough to cover the slide. Gently rock the Petri dish. The gel should begin to lift off the slide as the HCL dissolves the sacrificial zinc coating and needles.Once the gel is free from the slide, pour the HCL back into the stock solution. Rinse the gel by gently pouring approximately 25 milliliters of 1x PBS into the Petri dish until the slide and gel are submerged. Carefully pour off PBS into a waste container.Then, gently pour approximately 25 milliliters of 1x PBS into the Petri dish until the gel is floating in the solution. Use tweezers to carefully slide the silicone isolator under the gel and lift the gel onto it. Transfer the isolator and the gel into a six well dish filled with sterile 1x PBS.Prepare A549 cells as detailed in the text protocol. While cells are spinning down, add a small drop of complete Dulbecco's Modified Eagle Medium to each well of a six well plate. Use tweezers to transfer the silicone isolators with the gels, into a new six well plate such that the gel is resting on the drop of media.Now that the gels are spread into a thin layer, check to ensure that there are no large holes visible to the eye. Add the resuspended cell suspension drop-wise to the center of the gel, trying to maintain a meniscus in the punched out area of the silicone membrane. After allowing the cells to adhere for four hours, add 0.5 milliliters of Dulbecco's Modified Eagle Complete Medium to the well.Incubate overnight at 37 degrees Celsius to allow for complete adhesion. The following day, prepare huvecs for cell seeding as described in the text protocol. Then, add a small drop of Complete Medium 199 to each well in a new six well plate.Place a new silicone isolator in the well with a drop of media in the center of the silicone. Using tweezers, carefully flip the silicone isolators supporting the peg gel with A459 cells onto the isolator in the new six well plate. Add the huvec suspension to the center of the flipped gel drop-wise to maintain a meniscus on the gel within the punched out area of the silicone membrane.After allowing the cells to adhere for two hours, gently add two milliliters of M199 Complete Media to each well. Use a manual pipet to carefully remove the media from the gels, and add approximately 500 microliters of four percent PFA to the center of the gel where the cells are seeded. After the PFA sits for 30 minutes at room temperature, carefully remove the PFA and add approximately 500 microliters of two percent BSA in PBS to each gel.Following one hour incubation at room temperature, carefully remove the BSA. Add 500 microliters of prepared primary antibodies at a dilution of one to 100 in two percent BSA in PBS to each gel. Apply the secondary antibodies and phalloidin as detailed in the text protocol.Then, using tweezers and silicone isolators, transfer one gel to a glass slide. Mount the gel using a DAPI mounting medium. Finally, seal the samples with nail polish and acquire the images.Endothelial cells are able to form confluent monolayers on PEG hydrogels as demonstrated by fluorescent staining for PECAM-1 in red and DAPI in blue. Similarly, fluorescent staining for A549 in red demonstrates that epithelial cells also form confluent monolayers. Furthermore, endothelial cells can form intact cadherin junctions on PEG hydrogels as demonstrated by fluorescent staining for VE-cadherin in green and DAPI in blue.Staining for E-cadherin in green reveals the epithelial cells also form intact cadherin junctions. Following this technique, other methods like migration assays or permeability assays can be performed to understand how dual cell cultures and different microenvironments maintain or attenuate barrier function. After watching this video, you should have a good understanding on how to create ultra-thin PEG gels and modulate their porosity in addition to their mechanical and chemical properties in order to mimic the basement membrane.This technique will pave the way for researchers in the fields of biomaterials and biomedical engineering to explore and decouple mechanical, biochemical, and cell-mediated pathways that contribute to human disease. Though the system is widely applicable to biological applications, it can be applied to any system where cell-cell signaling and mechanical or biochemical extracellular cues can play a role.

ultrathin-porated-elastic-hydrogels-as-biomimetic-basement-membrane

Research

JoVE Journal

Bioengineering

7.6K Views.  Yale University. The overall goal of this protocol is to describe a polyethylene glycol and zinc oxide templating method to create a porous, ultra-thin, biomimetic basement membrane that supports dual cell culture, and has tuneable mechanical and chemical properties. The main advantage of this technique is that we can create hydrogels that are ultra-thin, porated, mechanically and biochemically tuneable. They allow support of either single or dual cell culture.This method can help answer key questions ...

Video: Ultrathin Porated Elastic Hydrogels As a Biomimetic Basement Membrane for Dual Cell Culture

Rotating Cell Culture Systems for Human Cell Culture: Human Trophoblast Cells as a Model

The field of human trophoblast research aids in understanding the complex environment established during placentation. Due to the nature of these studies, human in vivo experimentation is impossible. A combination of primary cultures, explant cultures and trophoblast cell lines1 support our understanding of invasion of the uterine wall2 and remodeling of uterine spiral arteries3,4 by extravillous trophoblast cells (EVTs), which is required for successful establishment of pregnancy. Despite the wealth of knowledge gleaned from such models, it is accepted that in vitro cell culture models using EVT-like cell lines display altered cellular properties when compared to their in vivo counterparts5,6. Cells cultured in the rotating cell culture system (RCCS) display morphological, phenotypic, and functional properties of EVT-like cell lines that more closely mimic differentiating in utero EVTs, with increased expression of genes mediating invasion (e.g. matrix metalloproteinases (MMPs)) and trophoblast differentiation7,8,9. The Saint Georges Hospital Placental cell Line-4 (SGHPL-4) (kindly donated by Dr. Guy Whitley and Dr. Judith Cartwright) is an EVT-like cell line that was used for testing in the RCCS.
The design of the RCCS culture vessel is based on the principle that organs and tissues function in a three-dimensional (3-D) environment. Due to the dynamic culture conditions in the vessel, including conditions of physiologically relevant shear, cells grown in three dimensions form aggregates based on natural cellular affinities and differentiate into organotypic tissue-like assemblies10,11,12 . The maintenance of a fluid orbit provides a low-shear, low-turbulence environment similar to conditions found in vivo. Sedimentation of the cultured cells is countered by adjusting the rotation speed of the RCCS to ensure a constant free-fall of cells. Gas exchange occurs through a permeable hydrophobic membrane located on the back of the bioreactor. Like their parental tissue in vivo, RCCS-grown cells are able to respond to chemical and molecular gradients in three dimensions (i.e. at their apical, basal, and lateral surfaces) because they are cultured on the surface of porous microcarrier beads. When grown as two-dimensional monolayers on impermeable surfaces like plastic, cells are deprived of this important communication at their basal surface. Consequently, the spatial constraints imposed by the environment profoundly affect how cells sense and decode signals from the surrounding microenvironment, thus implying an important role for the 3-D milieu13.
We have used the RCCS to engineer biologically meaningful 3-D models of various human epithelial tissues7,14,15,16. Indeed, many previous reports have demonstrated that cells cultured in the RCCS can assume physiologically relevant phenotypes that have not been possible with other models10,17-21. In summary, culture in the RCCS represents an easy, reproducible, high-throughput platform that provides large numbers of differentiated cells that are amenable to a variety of experimental manipulations. 
In the following protocol, using EVTs as an example, we clearly describe the steps required to three-dimensionally culture adherent cells in the RCCS.

Traditional, two dimensional cell culture techniques often result in altered characteristics with respect to differentiation markers, cytokines and growth factors. Three-dimensional cell culture in the rotating cell culture system (RCCS) reestablishes expression of many of these factors as shown here with an extravillous trophoblast cell line.

The field of human trophoblast research aids in  understanding the complex environment established during placentation. Due to the  nature of these ...

Three-dimensional Biomimetic Technology: Novel Biorubber Creates Defined Micro- and Macro-scale Architectures in Collagen Hydrogels

Tissue scaffolds play a crucial role in the tissue regeneration process. The ideal scaffold must fulfill several requirements such as having proper composition, targeted modulus, and well-defined architectural features. Biomaterials that recapitulate the intrinsic architecture of in vivo tissue are vital for studying diseases as well as to facilitate the regeneration of lost and malformed soft tissue. A novel biofabrication technique was developed which combines state of the art imaging, three-dimensional (3D) printing, and selective enzymatic activity to create a new generation of biomaterials for research and clinical application. The developed material, Bovine Serum Albumin rubber, is reaction injected into a mold that upholds specific geometrical features. This sacrificial material allows the adequate transfer of architectural features to a natural scaffold material. The prototype consists of a 3D collagen scaffold with 4 and 3 mm channels that represent a branched architecture. This paper emphasizes the use of this biofabrication technique for the generation of natural constructs. This protocol utilizes a computer-aided software (CAD) to manufacture a solid mold which will be reaction injected with BSA rubber followed by the enzymatic digestion of the rubber, leaving its architectural features within the scaffold material.

An innovative biofabrication technique was developed to engineer three-dimensional constructs that resemble the architectural features, components, and mechanical properties of in vivo tissue. This technique features a newly developed sacrificial material, BSA rubber, which transfers detailed spatial features, reproducing the in vivo architectures of a wide variety of tissues.

Tissue scaffolds play a crucial role in the tissue regeneration process. The ideal scaffold must fulfill several requirements such as having proper ...

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 ...

Light-mediated Formation and Patterning of Hydrogels for Cell Culture Applications

Click chemistries have been investigated for use in numerous biomaterials applications, including drug delivery, tissue engineering, and cell culture. In particular, light-mediated click reactions, such as photoinitiated thiol&#8722;ene and thiol&#8722;yne reactions, afford spatiotemporal control over material properties and allow the design of systems with a high degree of user-directed property control. Fabrication and modification of hydrogel-based biomaterials using the precision afforded by light and the versatility offered by these thiol&#8722;X photoclick chemistries are of growing interest, particularly for the culture of cells within well-defined, biomimetic microenvironments. Here, we describe methods for the photoencapsulation of cells and subsequent photopatterning of biochemical cues within hydrogel matrices using versatile and modular building blocks polymerized by a thiol&#8722;ene photoclick reaction. Specifically, an approach is presented for constructing hydrogels from allyloxycarbonyl (Alloc)-functionalized peptide crosslinks and pendant peptide moieties and thiol-functionalized poly(ethylene glycol) (PEG) that rapidly polymerize in the presence of lithium acylphosphinate photoinitiator and cytocompatible doses of long wavelength ultraviolet (UV) light. Facile techniques to visualize photopatterning and quantify the concentration of peptides added are described. Additionally, methods are established for encapsulating cells, specifically human mesenchymal stem cells, and determining their viability and activity. While the formation and initial patterning of thiol-alloc hydrogels are shown here, these techniques broadly may be applied to a number of other light and radical-initiated material systems (e.g., thiol-norbornene, thiol-acrylate) to generate patterned substrates.

We describe a sequential process for light-mediated formation and subsequent biochemical patterning of synthetic hydrogel matrices for three-dimensional cell culture applications. The construction and modification of hydrogels with cytocompatible photoclick chemistry is demonstrated. Additionally, facile techniques to quantify and observe patterns and determine cell viability within these hydrogels are presented.

Click chemistries have been investigated for use in numerous biomaterials applications, including drug delivery, tissue engineering, and cell culture. In ...

Tunable Hydrogels from Pulmonary Extracellular Matrix for 3D Cell Culture

Here we present a method for establishing multiple component cell culture hydrogels for in vitro lung cell culture. Beginning with healthy en bloc lung tissue from porcine, rat, or mouse, the tissue is perfused and submerged in subsequent chemical detergents to remove the cellular debris. Histological comparison of the tissue before and after processing confirms removal of over 95% of double stranded DNA and alpha galactosidase staining suggests the majority of cellular debris is removed. After decellularization, the tissue is lyophilized and then cryomilled into a powder. The matrix powder is digested for 48 hr in an acidic pepsin digestion solution and then neutralized to form the pregel solution. Gelation of the pregel solution can be induced by incubation at 37 &#176;C and can be used immediately following neutralization or stored at 4 &#176;C for up to two weeks. Coatings can be formed using the pregel solution on a non-treated plate for cell attachment. Cells can be suspended in the pregel prior to self-assembly to achieve a 3D culture, plated on the surface of a formed gel from which the cells can migrate through the scaffold, or plated on the coatings. Alterations to the strategy presented can impact gelation temperature, strength, or protein fragment sizes. Beyond hydrogel formation, the hydrogel stiffness may be increased using genipin.

This is a method to create a 3-dimensional cell culture scaffold from pulmonary extracellular matrix. Intact lung is processed into hydrogels that can support the growth of cells in three-dimensions.

Here we present a method for establishing multiple component cell culture hydrogels for in vitro lung cell culture. Beginning with healthy en bloc lung ...

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.

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 ...

Hyaluronic-Acid Based Hydrogels for 3-Dimensional Culture of Patient-Derived Glioblastoma Cells

Glioblastoma (GBM) is the most common, yet most lethal, central nervous system cancer. In recent years, many studies have focused on how the extracellular matrix (ECM) of the unique brain environment, such as hyaluronic acid (HA), facilitates GBM progression and invasion. However, most in vitro culture models include GBM cells outside of the context of an ECM. Murine xenografts of GBM cells are used commonly as well. However, in vivo models make it difficult to isolate the contributions of individual features of the complex tumor microenvironment to tumor behavior. Here, we describe an HA hydrogel-based, three-dimensional (3D) culture platform that allows researchers to independently alter HA concentration and stiffness. High molecular weight HA and polyethylene glycol (PEG) comprise hydrogels, which are crosslinked via Michael-type addition in the presence of live cells. 3D hydrogel cultures of patient-derived GBM cells exhibit viability and proliferation rates as good as, or better than, when cultured as standard gliomaspheres. The hydrogel system also enables incorporation of ECM-mimetic peptides to isolate effects of specific cell-ECM interactions. Hydrogels are optically transparent so that live cells can be imaged in 3D culture. Finally, HA hydrogel cultures are compatible with standard techniques for molecular and cellular analyses, including PCR, Western blotting and cryosectioning followed by immunofluorescence staining.

Here, we present a protocol for three-dimensional culture of patient-derived glioblastoma cells within orthogonally tunable biomaterials designed to mimic the brain matrix. This approach provides an in vitro, experimental platform that maintains many characteristics of in vivo glioblastoma cells typically lost in culture.

Glioblastoma (GBM) is the most common, yet most lethal, central nervous system cancer. In recent years, many studies have focused on how the extracellular ...

Fabrication of a Biomimetic Nano-Matrix with Janus Base Nanotubes and Fibronectin for Stem Cell Adhesion

A biomimetic NM was developed to serve as a tissue-engineering biological scaffold, which can enhance stem cell anchorage. The biomimetic NM is formed from JBNTs and FN through self-assembly in an aqueous solution. JBNTs measure 200-300 &#181;m in length with inner hydrophobic hollow channels and outer hydrophilic surfaces. JBNTs are positively charged and FNs are negatively charged. Therefore, when injected into a neutral aqueous solution, they are bonded together via noncovalent bonding to form the NM bundles. The self-assembly process is completed within a few seconds without any chemical initiators, heat source, or UV light. When the pH of the NM solution is lower than the isoelectric point of FNs (pI 5.5-6.0), the NM bundles will self-release due to the presence of positively charged FN.
NM is known to mimic the extracellular matrix (ECM) morphologically and hence, can be used as an injectable scaffold, which provides an excellent platform to enhance hMSC adhesion. Cell density analysis and fluorescence imaging experiments indicated that the NMs significantly increased the anchorage of hMSCs compared to the negative control.

The goal of this protocol is to show the assembly of a biomimetic nanomatrix (NM) with Janus base nanotubes (JBNTs) and fibronectin (FN). When co-cultured with human mesenchymal stem cells (hMSCs), the NMs exhibit excellent bioactivity in encouraging hMSCs adhesion.

A biomimetic NM was developed to serve as a tissue-engineering biological scaffold, which can enhance stem cell anchorage. The biomimetic NM is formed ...

Injectable Supramolecular Polymer-Nanoparticle Hydrogels for Cell and Drug Delivery Applications

These methods describe how to formulate injectable, supramolecular polymer-nanoparticle (PNP) hydrogels for&#160;use as biomaterials. PNP hydrogels are composed of two components: hydrophobically modified cellulose as the network polymer and self-assembled core-shell nanoparticles that act as non-covalent cross linkers through dynamic, multivalent interactions. These methods describe both the formation of these self-assembled nanoparticles through nanoprecipitation as well as the formulation and mixing of the two components to form hydrogels with tunable mechanical properties. The use of dynamic light scattering (DLS) and rheology to characterize the quality of the synthesized materials is also detailed. Finally, the utility of these hydrogels for drug delivery, biopharmaceutical stabilization, and cell encapsulation and delivery is demonstrated through in vitro experiments to characterize&#160;drug release, thermal stability, and cell settling and viability. Due to its biocompatibility, injectability, and mild gel formation conditions, this hydrogel system is a readily tunable platform suitable for a range of biomedical applications.

This protocol describes the synthesis and formulation of injectable, supramolecular polymer-nanoparticle (PNP) hydrogel biomaterials. Applications of these materials for drug delivery, biopharmaceutical stabilization, and cell encapsulation and delivery are demonstrated.

These methods describe how to formulate injectable, supramolecular polymer-nanoparticle (PNP) hydrogels for&#160;use as biomaterials. PNP hydrogels are ...

Fragmenting Bulk Hydrogels and Processing into Granular Hydrogels for Biomedical Applications

Granular hydrogels are jammed assemblies of hydrogel microparticles (i.e., &#34;microgels&#34;). In the field of biomaterials, granular hydrogels have many advantageous properties, including injectability, microscale porosity, and tunability by mixing multiple microgel populations. Methods to fabricate microgels often rely on water-in-oil emulsions (e.g., microfluidics, batch emulsions, electrospraying) or photolithography, which may present high demands in terms of resources and costs, and may not be compatible with many hydrogels. This work details simple yet highly effective methods to fabricate microgels using extrusion fragmentation and to process them into granular hydrogels useful for biomedical applications (e.g., 3D printing inks). First, bulk hydrogels (using photocrosslinkable hyaluronic acid (HA) as an example) are extruded through a series of needles with sequentially smaller diameters to form fragmented microgels. This microgel fabrication technique is rapid, low-cost, and highly scalable. Methods to jam microgels into granular hydrogels by centrifugation and vacuum-driven filtration are described, with optional post-crosslinking for hydrogel stabilization. Lastly, granular hydrogels fabricated from fragmented microgels are demonstrated as extrusion printing inks. While the examples described herein use photocrosslinkable HA for 3D printing, the methods are easily adaptable for a wide variety of hydrogel types and biomedical applications.

This work describes straightforward, adaptable, and low-cost methods to fabricate microgels with extrusion fragmentation, process the microgels into injectable granular hydrogels, and apply the granular hydrogels as extrusion printing inks for biomedical applications.

Granular hydrogels are jammed assemblies of hydrogel microparticles (i.e., &#34;microgels&#34;). In the field of biomaterials, granular hydrogels have ...