Funding for this project was through NSF CBET Award 1061834. The authors would like to acknowledge CIBA for a sample of photoinitiator.

1. Preparing Solutions for Use in Microgel Fabrication
<ol>
	<li>Before beginning the precipitation reaction, make the necessary solutions and warm them to 37 &#176;C. The required solutions include 0.5% photoinitiator, 1.5 M Na2SO4, buffer solution, 200 mg/ml PEG-diacrylate (PEG-DA) solution, and 1x phosphate buffered saline (PBS). Note: Acrylate all PEG precursors according to published methods and store at -20 &#176;C under argon until use12.</li>
	<li>Weigh out photoinitiator and di...

<ol>
	<li>McNaught, A. D., Wilkinson, A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=.">.</a> IUPAC Compendium of Chemical Terminology (The Gold Book). 2nd edn. , (1997).</li><li>Lu, S. X., Anseth, K. S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Release+behavior+of+high+molecular+weight+solutes+from+poly(ethylene+glycol)-based+degradable+networks.">Release behavior of high molecular weight solutes from poly(ethylene glycol)-based degradable networks.</a> Macromolecules. 33, 2509-2515 (2000).</li><li>Peppas, N. A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=.">.</a> Hydrogels in Medicine. 1, (1986).</li><li>West, J. L., Hubbell, J. A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Photopolymerized+hydrogel+materials+for+drug+delivery+applications.">Photopolymerized hydrogel materials for drug delivery applications.</a> React. Polym. 25, 139-147 (1995).</li><li>Hunkeler, D., 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> Theories and Mechanism of Phase Transitions, Heterophase Polymerizations, Homopolymerization, Addition Polymerization. Advances in Polymer Science. 112, 115-133 (1994).</li><li>Arshady, R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Suspension,+emulsion,+and+dispersion+polymerization:+A+methodological+survey.">Suspension, emulsion, and dispersion polymerization: A methodological survey.</a> Colloid Polym. Sci. 270, 717-732 (1992).</li><li>Bai, F., Yang, X. L., Huang, W. Q. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Synthesis+of+narrow+or+monodisperse+poly(divinylbenzene)+microspheres+by+distillation-precipitation+polymerization.">Synthesis of narrow or monodisperse poly(divinylbenzene) microspheres by distillation-precipitation polymerization.</a> Macromolecules. 37, 9746-9752 (2004).</li><li>Bailey, F., Callard, R. W. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Some+properties+of+poly(ethylene+oxide)+in+aqueous+solution.">Some properties of poly(ethylene oxide) in aqueous solution.</a> J. Appl. Polym. Sci. 1, 56-62 (1959).</li><li>Cruise, G. M., Scharp, D. S., Hubbell, J. 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The authors declare that they have no competing financial interests.

Physical properties of PEG microgels were examined for changes in polymerization conditions. For this precipitation reaction, a buffer solution, 20% (w/v)&#160;PEG-diacrylate (MW 3,000, 4,600, or 6,000 Da) solution, and photoinitiator were mixed and warmed to 37 &#176;C. Addition of 1.5 M Na2SO4, a kosmotrophic salt that increases the interactions between water molecules, caused PEG to momentarily precipitate upon its addition. This effect is more prominent with higher molecular weight PEG8</su...

By definition, microgels are hydrogels of any shape with an equivalent diameter of approximately 0.1-100 &#956;m1. Because of their size and characteristics, polymeric microgels present a versatile tool for advancing drug delivery and tissue engineering systems. While bulk hydrogels are extensively utilized as tissue engineering scaffolds and drug delivery vehicles with great success2-4, a recent shift to microscale control of scaffolds provides a unique opportunity for microgels to be used as base materials for building scaffolds. In addition, microgels have a high surface area to volume ratio for cellular interactions and in solution have a low viscosity that makes them ideal for injections. Finally, microgels can be formed using numerous polymers by a variety of methods dependent on the desired microgel characteristics, making them highly customizable for a variety of applications.
Techniques to produce microgels include suspension, emulsion, dispersion, or precipitation polymerizations. Emulsion and suspension polymerizations typically require organic solvents and surfactants or stabilizers to form the microgels. The nature of these methods yield a highly disperse particle size distribution5. Dispersion and precipitation reactions render particles with a lower polydispersity6; however particles formed by dispersion polymerization still require the use of stabilizing agents6. Microgels formed by precipitation reactions are unique in that they form particles of uniform size and shape without the use of stabilizers or surfactants. Microgel formation is achieved when growing polymer chains phase separate from the continuous phase by enthalpic or entropic precipitation7. Precipitation polymerization is often at high temperatures that can be lowered by the use of kosmotrophic salts, which decrease the solubility of the polymer in the solvent8. This work focuses on microgels formed from poly(ethylene glycol) (PEG) by a photopolymerized precipitation reaction under biologically-compatible conditions, with variations to alter microgel properties and encapsulate molecules for drug delivery applications.
Previous studies with PEG hydrogels show that the polymerization conditions greatly influence the physical and mechanical properties of hydrogels, namely the hydrogel water content and compressive modulus3,9. These crosslinked materials are of interest because the relationship between structural and physical properties described by Flory10 can be utilized to tailor the crosslinked hydrogel for specific applications. These principles are similar for microgels. Precipitation-formed PEG microgels have been found to have potential for regenerative medicine11, however further investigation into the microgel properties was necessary to enhance their repertoire for future biomedical applications. This report describes the procedure to fabricate microgels by precipitation reaction and alter characteristics, such as microparticle diameter, polydispersity index (PDI), density, and swelling, that would be important to further develop these materials for drug delivery or regenerative medicine.

<table border="0" cellpadding="0" cellspacing="0" width="1293">
	<colgroup>
		<col />
		<col />
		<col />
		<col />
		<col />
		<col />
		<col />
		<col />
		<col />
	</colgroup>
	<tbody>
		<tr height="42">
			<td height="42" style="height:42px;width:195px;">Phosphate Buffered Saline (PBS)</td>
			<td style="width:99px;">MP Biomedical</td>
			<td style="width:136px;">2810305</td>
			<td style="width:108px;"></td>
			<td style="width:63px;"></td>
			<td style="width:315px;">ThermoStat plus</td>
			<td style="width:123px;">Eppendorf</td>
			<td style="width:155px;">5352YL404573</td>
			<td style="width:104px;">Tube Warmer</td>
		</tr>
		<tr height="63">
			<td height="63" style="height:63px;width:195px;">Triethanolamine (TEOA)</td>
			<td style="width:99px;">J.T. Baker</td>
			<td style="width:136px;">9468-01</td>
			<td style="width:108px;">Preheat to 37 &#176;C prior to pipetting</td>
			<td></td>
			<td>LSE Vortex Mixer</td>
			<td>Corning</td>
			<td>S004164</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:195px;">Hydrochloric acid (HCl)</td>
			<td style="width:99px;">BDH Aristar</td>
			<td style="width:136px;">BDH3028</td>
			<td style="width:108px;"></td>
			<td></td>
			<td>XP205 Analytical Balance</td>
			<td>Mettler Toledo</td>
			<td>11106024</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:195px;">Sodium Sulfate</td>
			<td style="width:99px;">J.T. Baker</td>
			<td style="width:136px;">3891-01</td>
			<td style="width:108px;"></td>
			<td></td>
			<td>CureSpot 50</td>
			<td>ADAC Systems</td>
			<td>A121-031</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:195px;">Irgacure 2959</td>
			<td style="width:99px;">Ciba</td>
			<td style="width:136px;">029891301PS04</td>
			<td style="width:108px;"></td>
			<td></td>
			<td style="width:315px;">SevenMulti pH Meter&#160;</td>
			<td style="width:123px;">Mettler Toledo</td>
			<td>51302813</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:195px;">Ovalbumin (OVA)</td>
			<td style="width:99px;">Invitrogen</td>
			<td style="width:136px;">34782</td>
			<td style="width:108px;"></td>
			<td></td>
			<td style="width:315px;">Class II, Type A2 Biological Safety Cabinet</td>
			<td style="width:123px;">Nuaire</td>
			<td align="right">1.39284E+11</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:195px;">PEG 1,500</td>
			<td style="width:99px;">Alfa Aesar</td>
			<td style="width:136px;">A16241</td>
			<td style="width:108px;"></td>
			<td></td>
			<td style="width:315px;">Centrifuge 5430 R</td>
			<td>Eppendorf</td>
			<td>5428AH010419</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:195px;">PEG 3,000</td>
			<td style="width:99px;">Fluka</td>
			<td style="width:136px;">03997-1KG</td>
			<td style="width:108px;"></td>
			<td></td>
			<td style="width:315px;">Sonicator 8890</td>
			<td>Cole Parmer</td>
			<td>8890R-DTH</td>
			<td>SN QAC039907293D</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:195px;">PEG 4,000</td>
			<td style="width:99px;">Alfa Aesar</td>
			<td style="width:136px;">A16151</td>
			<td style="width:108px;"></td>
			<td></td>
			<td>Coverslip 22 mm x 30 mm, 1.5 thickness</td>
			<td style="width:123px;">Fisherbrand</td>
			<td>12-544-A</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:195px;">PEG 4,600</td>
			<td style="width:99px;">Sigma</td>
			<td style="width:136px;">373001-250G</td>
			<td style="width:108px;"></td>
			<td></td>
			<td style="width:315px;">Inverted Microscope with camera</td>
			<td style="width:123px;">Zeiss</td>
			<td>1022923629</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:195px;">PEG 6,000</td>
			<td style="width:99px;">Fluka</td>
			<td style="width:136px;">03394-1KG</td>
			<td style="width:108px;"></td>
			<td></td>
			<td style="width:315px;"></td>
			<td style="width:123px;"></td>
			<td></td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:195px;">PEG 10,000</td>
			<td style="width:99px;">Alfa Aesar</td>
			<td style="width:136px;">B21955</td>
			<td style="width:108px;"></td>
			<td></td>
			<td></td>
			<td></td>
			<td></td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:195px;">Dextran 70</td>
			<td style="width:99px;">TCI</td>
			<td>D1449</td>
			<td style="width:108px;"></td>
			<td></td>
			<td></td>
			<td></td>
			<td></td>
			<td></td>
		</tr>
	</tbody>
</table>

characteristics of precipitation-formed polyethylene glycol microgels are controlled by molecular weight of reactants

This work describes the formation of poly(ethylene glycol) (PEG) microgels via a photopolymerized precipitation reaction. Precipitation reactions offer several advantages over traditional microsphere fabrication techniques. Contrary to emulsion, suspension, and dispersion techniques, microgels formed by precipitation are of uniform shape and size, i.e.&#160;low polydispersity index, without the use of organic solvents or stabilizers. The mild conditions of the precipitation reaction, customizable properties of the microgels, and low viscosity for injections make them applicable for in vivo purposes. Unlike other fabrication techniques, microgel characteristics can be modified by changing the starting polymer molecular weight. Increasing the starting PEG molecular weight increased microgel diameter and swelling ratio. Further modifications are suggested such as encapsulating molecules during microgel crosslinking. Simple adaptations to the PEG microgel building blocks are explored for future applications of microgels as drug delivery vehicles and tissue engineering scaffolds.

Microgel size is dependent on polymerization conditions. Figure 2A illustrates how microgel diameter increases with increasing PEG starting molecular weight and crosslinking time. Representative images of microgels used for sizing for various molecular weights and crosslinked for 30 sec are shown in Figures 2C-G. For PEG with a molecular weight of 3,000 Da, the microgel average diameter increased from 1.65&#177;0.26 to 2.20&#177;0.54 &#956;m as UV exposure increased from 30-600 sec (<str...

Watch this Scientific Journal Video about Characteristics of Precipitation-formed Polyethylene Glycol Microgels Are Controlled by Molecular Weight of Reactants at JoVE.com

Characteristics of Precipitation-formed Polyethylene Glycol Microgels Are Controlled by Molecular Weight of Reactants

This work describes the formation of poly(ethylene glycol) (PEG) microgels via a photopolymerized precipitation reaction. Increasing the PEG molecular weight increased microgel diameter and swelling ratio. Simple adaptations to the PEG microgel precipitation reaction are explored for future applications of microgels as drug delivery vehicles and tissue engineering scaffolds.

This work describes the formation of poly(ethylene glycol) (PEG) microgels via a photopolymerized precipitation reaction. Precipitation reactions offer ...

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11.7K Görüntüleme.  The University of Akron. This work describes the formation of poly(ethylene glycol) (PEG) microgels via a photopolymerized precipitation reaction. Increasing the PEG molecular weight increased microgel diameter and swelling ratio. Simple adaptations to the PEG microgel precipitation reaction are explored for future applications of microgels as drug delivery vehicles and tissue engineering scaffolds.