Name: synthesis of soft polysiloxane-urea elastomers for intraocular lens application
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Description: Watch this Scientific Journal Video about Synthesis of Soft Polysiloxane-urea Elastomers for Intraocular Lens Application at JoVE.com

The authors would like to thank the Federal Ministry of Education and Research (BMBF) for funding this work under grant number 13FH032I3. Financial support by the Deutsche Forschungsgemeinschaft (DFG, Gepris project 253160297) is gratefully acknowledged. The authors further like to express their thanks to Priska Kolb and Paul Schuler from the University of T&#252;bingen for performing 1H-NMR and 29Si-NMR measurements. Thanks are also due to CSC J&#228;kle Chemie GmbH &#38; Co. KG for their supply of H12MDI. The authors would like to thank Herbert Thelen and Andr&#233; Lemme from Biotronik for performing ethylene oxide sterilization of the PSU samples and Lada Kitaeva (Reutlingen University) for her support with stress-strain and hysteresis measurements.

The authors have nothing to declare.

To achieve high-molecular-weight aminopropyl-terminated PDMS via ring-chain equilibration, using an anhydrous, strongly basic catalyst is crucial. Other typically applied catalysts, such as tetramethylammonium hydroxide (TMAH) or potassium hydroxide (KOH), contain water residues, which promote side reactions; hence, a mixture of difunctional, monofunctional, and nonfunctional PDMS chains with similar molecular weights is obtained44. Furthermore, if TMAH is used, the reaction requires &#62;48 h for completion and does not always proceed with complete monomer consumption44.
In particular, the weighing of the endblocker APTMDS is critical to obtain the desired molecular weight of PDMS. For example, instead of 0.9 g of APTMDS, if 0.85 g is used to synthesize PDMS, as described in section 2.1 of the protocol, this would lead to a theoretical molecular weight of approximately &#62;900 g&#183;mol-1. In addition, the theoretical molecular weight is dependent on the conversion. If the cyclic side products are not considerably removed via vacuum distillation, a high conversion value will be obtained. For example, to use the same synthesis procedure (as in section 2.1 of the protocol), a calculated conversion of 90% would lead to a theoretically calculated molecular weight; this value is 910 g&#183;mol-1 greater than that if a conversion of 85% is presumed. Deviations in the polysiloxane molecular weight determination by titration are possibly related to the weighing of PDMS into the flasks, particularly if a 50 mL burette is used for titration. A deviation related to the weighing of 0.06 g of polysiloxane might lead to a calculated difference of ~650 g&#183;mol-1. Hence, the use of a semiautomatic titrator is recommended.
The refractive index of PDMS can be increased by the incorporation of phenyl groups17,51, halogenated phenyl groups52, or sulfur-containing groups53. Attempts to incorporate phenyl groups into PDMS via the copolymerization of octaphenylcyclotetrasiloxane (D4Ph) as described by Yilg&#246;r, Riffle, and McGrath54 were unsuccessful under the applied reaction conditions, possibly because the bulky ring backbone made it impossible for the applied catalyst to break up the siloxane bonds at the selected reaction temperature. The D4Ph ring can be opened if KOH is used at a reaction temperature of 160 &#176;C. However, polysiloxanes of extremely high molecular weight are obtained, which presumably contain high amounts of nonfunctional impurities. In addition, the removal of the catalyst KOH in those copolymers is not straightforward and requires a neutralization step using ethanolic HCl, followed by an aqueous extraction of the catalyst. Then, the PDMS has to be dissolved in an organic solvent, such as CH2Cl2, to separate the aqueous phase from the organic PDMS-containing phase. Finally, the organic phase must be dried over MgSO4, followed by filtration and vacuum distillation using a rotary evaporator54. In contrast, the method presented in this manuscript allows the catalyst to be removed immediately via thermal decomposition. Therefore, instead of using solid monomer D4Ph, phenyl groups are successfully introduced into the PDMS backbone by the copolymerization of the liquid monomer D4Me,Ph, as confirmed by 29Si-NMR spectroscopy50.
The synthesized PSU elastomers exhibited YM of 0.6 - 5.5 MPa and high elasticity with elongation values of up to 1,000%. Such high elongation values were related not only to the polymer segmented structure but also to the high molecular weights of the PSU elastomers (<img alt="Equation 1" src="/files/ftp_upload/58590/58590eq1.jpg" style="opacity: 0.9; font-size: 14px;" /> &#62; 100,000 g&#183;mol-1)48. An instantaneous reaction occurs between the amino groups and aliphatic isocyanyate groups at room temperature, leading to rapidly increasing molecular weight. This result was further supported by conducting the reaction in a solvent, because a slight increase in viscosity did not appear to slow down the reaction speed significantly, which would otherwise dramatically affect the molecular weight for a nearly balanced stoichiometric ratio. In contrast, when a short chain diol, such as 1,4-butanediol, was used as the chain extender, the resulting polyurethane-urea elastomers were not only less elastic but also lost considerable mechanical stability, particularly if high-molecular-weight PDMS was used for synthesis. This result was presumably related to the considerably low molecular weights of the elastomers (results not published), corresponding to the incomplete conversion of all isocyanate groups at the last stage of polyaddition. In addition, differences in reactivity between the amino and hydroxyl groups toward aliphatic diisocyanates dramatically affected the results obtained from in vitro cytotoxicity tests. Extracts of the PSU elastomer prepared from the amino-chain extender APTMDS did not exhibit any cytotoxic effect on the HaCaT cells (Figure 12). However, if extracts of a siloxane-based polyurethane-urea elastomer were used, the cell viability was drastically reduced (results not published), which was possibly related to the low-molecular-weight leachables and residual unreacted isocyanate groups.
This protocol describes a convenient method for preparing amino-functional polysiloxanes, which can be subsequently used as macrodiamines for synthesizing high-molecular-weight, soft, and elastic polysiloxane-urea elastomers. As the mechanical properties of the PSUs can be varied according to the PDMS molecular weight, it is possible to use these polymers in other application fields. Furthermore, the procedure for preparing amino-functional polysiloxanes can be used for the introduction of side groups, such as vinyl groups, via the copolymerization of a cyclic siloxane with pendant vinyl groups (results not shown). This may open up new application fields, including the preparation of soft crosslinked polysiloxane gels (e.g., by Pt-catalyzed hydrosilylation with a hydride-functional silicone or by UV-activated thiol-ene addition of mercapto-functional PDMS) (results not shown).

Senile cataract, affecting the age group of &#8805; 60 years, leads to the advanced opacification of the natural crystalline lens. This age-related condition is probably caused by oxidative changes that are accelerated by UV irradiation1,2,3. Conventional treatment for senile cataract involves the surgical extraction of the cataractous lens, followed by the implantation of an artificial intraocular lens (IOL) into an empty lens capsule via an injection system2. However, a majority of IOLs are manufactured from acrylic polymers (hydrophobic and hydrophilic acrylate or methacrylate polymers) with extremely rigid structures; hence, the eye loses its ability to accommodate to various distances2,4. Therefore, patients with monofocal IOL implants are dependent on spectacles for near vision (e.g., while reading a newspaper or a book)5.
Different approaches to restoring the accommodation ability after cataract surgery have been reported. Among these approaches, two principal strategies can be distinguished: refilling the empty lens capsule by injecting a liquid or gel-like polymers and developing soft, foldable a-IOLs6,7,8. The concept of &#34;lens refilling&#34; is promising because gels can be prepared with Young&#39;s moduli as low as those of the natural human eye lens (ca. 1 - 2 kPa)9; however, this approach is still experimental8, and studies are only conducted on animal eyes.
Lens capsules have been refilled by implanting inflatable silicone balloons10 filled with liquid silicone or by directly injecting silicone11,12 that was subsequently cured in the capsule via hydrosilylation. However, issues related to surface wrinkles on the balloons, a lower accommodation amplitude compared to the preoperative state, and the formation of severe secondary cataracts (anterior and posterior capsule opacification) have been noted7,8,12,13. In particular, long curing times (70 min - 12 h) cause an increased risk of leakage into the surrounding eye compartments, leading to postoperative inflammation10,14. Therefore, other materials for replacing the crystalline lens are recommended, including hydrogels based on polyethylene glycol diacrylate, acrylate-modified copolymers of vinyl alcohol (N-vinylpyrrolidone)15, methacrylate-modified polysiloxanes16,17, poloxamer18, and diisocyanate-crosslinked polyalcohols9. However, the monomer viscosity (i.e., gel swelling after the injection and crosslinking), extremely low or high refractive indices, mechanical stability and integrity, unpredictable postoperative refraction, low accommodation range, and after-cataract formation constitute the main issues6,7,8,9,15,18. Commercially, the accommodation ability is mainly restored by developing foldable a-IOLs. Such a-IOLs should provide accommodation by the movement of the IOL optic to the anterior site of the lens capsule via the contraction of the ciliary muscle. Several models have been introduced in the market in 1996, 2001, and 20027,8. However, during clinical studies, the estimated accommodation amplitudes for those implanted a-IOLs were extremely low (&#8804; 1.5 D) to permit unaided reading (3 - 4 D)6,7,8,19,20. Therefore, an a-IOL comprising two connected optics (dual-optic IOL) is being developed for increasing the accommodation range6,21. The design of only one lens has been examined for its accommodative performance in human eyes, albeit conflicting results have been reported22,23,24,25.
Typically, silicone elastomers are regarded to be biologically inert and nontoxic; therefore, silicone elastomers have a long history of being applied as biocompatible materials in medicine and medical engineering (e.g., in breast implants, craniofacial implants, joint prosthetics, wound dressings, catheters, drains, and shunts)26,27. Owing to their softness, transparency, and high oxygen permeability, silicone elastomers also find applications as contact lenses and IOLs2,28,29. However, silicones must be covalently crosslinked and often require reinforcing fillers to gain sufficient mechanical integrity. Crosslinking is disadvantageous as it prohibits&#160;the subsequent processing of elastomers either by thermoplastic methods (e.g., injection molding) or by processing from solutions (e.g., solvent casting). In contrast, thermoplastic polyurethanes exhibit mechanical stability but are susceptible to degradation within the biological environment, particularly if polyester- or polyether-based macrodiols are used. Therefore, efforts to combine flexibility and hydrolytic or oxidative stability with excellent mechanical properties are concentrated on the incorporation of hydroxyl- or amino-functional PDMS as soft segments into polyurethanes, polyurethane-ureas, and polyureas27. To enhance the compatibility of the polar urethane or urea hard segment with a highly nonpolar PDMS soft segment and to improve mechanical properties, different polyether-based macrodiols are incorporated along with PDMS30,31,32. Particularly, the Thilak Gunatillake group has systematically investigated the development of silicone polyurethanes with improved biostability and mechanical properties for long-term biomedical applications such as pacemaker insulation or artificial heart valves33. They synthesized aromatic polyurethanes with mixed soft segments comprising hydroxyl-terminated PDMS and different polyethers, as well as aliphatic polycarbonate diols. Among all the synthesized polyurethanes, the combination of polyhexamethylene oxide (PHMO) and PDMS exhibits the best mechanical properties with respect to hard segment compatibility30. In subsequent studies, they further examined the effect of the PDMS-to-PHMO ratio and the incorporation of a disiloxane-based chain extender on the mechanical properties of silicone polyurethanes34,35,36. The results revealed that a macrodiol composition of 80 wt% PDMS and 20 wt% PHMO, in addition to a co-chain extender, such as 1,3-bis(4-hydroxybutyl)-tetramethyldisiloxane (BHTD), yields softer polyurethanes with good mechanical properties and thermoplastic processability. Furthermore, these silicone-polyurethanes exhibit an enhanced biostability compared to a commonly applied soft polyether urethane37,38,39.
The biocompatibility and stability of similar materials and their use for cardiovascular applications have also been reported40,41,42. Based on these results, silicone-based polyurea elastomers (or PSUs) with a disiloxane-based chain extender are thought to yield high flexibilities and softness, albeit with sufficient mechanical strength, to retain their shape after the application of repeated stress. For instance, Hermans et al. have constructed an experimental polyurethane-based dual-optic a-IOL prototype because the design, which was previously used for a fabrication using silicone, was extremely soft to handle the applied loads within enucleated pig eyes43.
This article describes the synthesis of a soft siloxane-based PSU, which is optimized in terms of mechanical and optical properties for applications as an accommodating IOL. As the mechanical properties of the PSU elastomers can be altered by the siloxane molecular weight, the same procedure can be applied to developing siloxane-based PSUs, which may find applications in coatings and skin dressings. In addition, this procedure can be used to prepare siloxane-based polyurethane or polyurethane-urea elastomers if carbinol-terminated PDMS is used. Depending on the type of diisocyanate (i.e., aliphatic or aromatic) used for synthesis, reaction conditions (including time, temperature, and perhaps the solvent composition) may have to be altered. For the application of aliphatic diisocyanates such as 4,4-methylenebis(cyclohexylisocyanate) (H12MDI) or isophorone diisocyanate, the reaction has to be accelerated using an organotin catalyst, such as dibutyltin dilaurate or diacetoxytetrabutyl distannoxane. For example, the reaction between a hydroxypropyl-terminated PDMS and H12MDI proceeds in the presence of a catalyst. Furthermore, the reaction temperature needs to be increased to 50 - 60 &#176;C.For the application of an aromatic diisocyanate such as 4,4-methylenebis(phenylisocyanate) (MDI), the reaction temperature must be moderately but sufficiently increased as aromatic diisocyanates are typically more reactive toward nucleophilic groups than aliphatic diisocyanates are. The reaction of MDI with carbinol-terminated PDMS can be promoted by using the solvent mixtures of anhydrous tetrahydrofuran (THF) and dimethylformamide (DMF) or dimethylacetamide (DMAc) as tertiary amines exhibit some catalytic activity.

<table><tbody><tr><td>Octamethylcyclotetrasiloxane (D4), 97 %</td><td>ABCR GmbH</td><td>AB111277</td><td>presumably impairs fertility, must be degassed before use&lt;br/&gt; &lt;strong&gt;CAS&lt;/strong&gt;:&amp;nbsp;556-67-2&lt;br/&gt; </td></tr><tr><td>1,3-Bis(3-aminopropyl)-tetramethyldisiloxane, 97%</td><td>ABCR GmbH</td><td>110832</td><td>sensitive to air, must be stored under nitrogen&lt;br/&gt; &lt;strong&gt;CAS&lt;/strong&gt;:&amp;nbsp;2469-55-8&lt;br/&gt; </td></tr><tr><td>2,4,6,8-Tetramethyl-2,4,6,8-tetraphenylcyclotetrasiloxane&amp;nbsp;</td><td>Sigma Aldrich</td><td>40094</td><td>technical grade&lt;br/&gt; &lt;strong&gt;CAS&lt;/strong&gt;:&amp;nbsp;77-63-4&lt;br/&gt; </td></tr><tr><td>Tetramethylammonium hydroxide pentahydrate</td><td>Alfa Aesar</td><td>L09658</td><td>toxic if swallowed and upon skin contact, strong base, sensitive to air, hygroscopic, store under refrigeration and under nitrogen&lt;br/&gt; &lt;strong&gt;CAS&lt;/strong&gt;:&amp;nbsp;10424-65-4&lt;br/&gt; </td></tr><tr><td>4,4&amp;cent;-Methylenbis(cyclohexylisocyanate) (H12MDI)</td><td>Covestro via CSC J&amp;auml;kle Chemie GmbH &amp;amp; Co. KG</td><td></td><td>toxic if inhaled, skin and eye irritant&lt;br/&gt; &lt;strong&gt;CAS&lt;/strong&gt;:&amp;nbsp;5124-30-1&lt;br/&gt; </td></tr><tr><td>Tetrahydrofuran (anhydrous) 99.8 %</td><td>Alfa Aesar</td><td>44608</td><td>stabilized with BHT&lt;br/&gt; &lt;strong&gt;CAS&lt;/strong&gt;:&amp;nbsp;109-99-9&lt;br/&gt; </td></tr><tr><td>Chloroform 99 %</td><td>Gr&amp;uuml;ssing GmbH Analytica</td><td>1025125000</td><td>stabilized with ethanol, presumably carcinogenic, can impair fertility and cause damage to an unborn child&lt;br/&gt; &lt;strong&gt;CAS&lt;/strong&gt;:&amp;nbsp;67-66-3&lt;br/&gt; </td></tr><tr><td>Chloroform-d, 99.8 %</td><td>Sigma Aldrich</td><td>151823</td><td>&lt;strong&gt;CAS&lt;/strong&gt;:&amp;nbsp;865-49-6&lt;br/&gt; </td></tr><tr><td>Dulbecco&#039;s modified Eagle&#039;s medium (DMEM) high glucose</td><td>Thermo Fisher Scientific Life Technologies GmbH</td><td>41965-039</td><td></td></tr><tr><td>Fetal bovine serum (FBS)</td><td>Thermo Fisher Scientific Life Technologies GmbH</td><td>A3160801</td><td></td></tr><tr><td>Trypsin/EDTA, 0.25 % phenol red</td><td>Thermo Fisher Scientific Life Technologies GmbH</td><td>25200056</td><td></td></tr><tr><td>Cell Titer Aqueous One Solution cell proliferation assay (MTS)</td><td>Promega GmbH</td><td>G3580</td><td></td></tr><tr><td>HaCaT-cells</td><td>CLS Cell Lines Service GmbH</td><td>300493</td><td></td></tr><tr><td>BioComFold&amp;nbsp;</td><td>Morcher GmbH</td><td></td><td>foldable accommodating intraocular lens</td></tr><tr><td>Accommodative 1CU</td><td>Human Optics AG</td><td></td><td>foldable accommodating intraocular lens</td></tr><tr><td>CrystaLens&amp;nbsp;</td><td>Bausch and Lomb Inc.</td><td></td><td>foldable accommodating intraocular lens</td></tr><tr><td>Silmer OH-Di10</td><td>Siltech Corp.</td><td></td><td>Carbinol-terminated Polydimethylsiloxane</td></tr><tr><td>Synchrony&amp;nbsp;</td><td>Visiogen Inc.</td><td></td><td>dual-optic foldable accommodating intraocular lens</td></tr><tr><td>Elast-Eon</td><td>AorTech International plc</td><td></td><td>thermoplastic PDMS-PHMO-based polyurethane for medical applications</td></tr><tr><td>Pellethane 2363-80A</td><td>Lubrizol Life Sciences</td><td></td><td>thermoplastic polyether-based polyurethane for medical applications</td></tr><tr><td>Zwick universal tensile testing machine model 81565 and software testXpert II</td><td>Zwick GmbH &amp;amp; Co. KG</td><td></td><td>tensile testing machine</td></tr><tr><td>CASY</td><td>Roche Innovatis AG</td><td></td><td>cell counting system</td></tr><tr><td>Multisizer</td><td>Beckman Coulter Life Sciences</td><td></td><td>cell counting system</td></tr></tbody></table>

synthesis of soft polysiloxane-urea elastomers for intraocular lens application

This study discusses a synthesis route for soft polysiloxane-based urea (PSU) elastomers for their applications as accommodating intraocular lenses (a-IOLs). Aminopropyl-terminated polydimethylsiloxanes (PDMS) were previously prepared via the ring-chain equilibration of the cyclic siloxane octamethylcyclotetrasiloxane (D4) and 1,3-bis(3-aminopropyl)-tetramethyldisiloxane (APTMDS). Phenyl groups were introduced into the siloxane backbone via the copolymerization of D4 and 2,4,6,8-tetramethyl-2,4,6,8-tetraphenyl-cyclotetrasiloxane (D4Me,Ph). These polydimethyl-methyl-phenyl-siloxane-block copolymers were synthesized for increasing the refractive indices of polysiloxanes. For applications as an a-IOL, the refractive index of the polysiloxanes must be equivalent to that of a young human eye lens. The polysiloxane molecular weight is controlled by the ratio of the cyclic siloxane to the endblocker APTMDS. The transparency of the PSU elastomers is examined by the transmittance measurement of films between 200 and 750 nm, using a UV-Vis spectrophotometer. Transmittance values at 750 nm (upper end of the visible spectrum) are plotted against the PDMS molecular weight, and &#62; 90% of the transmittance is observed until a molecular weight of 18,000 g&#183;mol&#8722;1. Mechanical properties of the PSU elastomers are investigated using stress-strain tests on die-cut dog-bone-shaped specimens. For evaluating mechanical stability, mechanical hysteresis is measured by repeatedly stretching (10x) the specimens to 5% and 100% elongation. Hysteresis considerably decreases with the increase in the PDMS molecular weight. In vitro cytotoxicity of some selected PSU elastomers is evaluated using an MTS cell viability assay. The methods described herein permit the synthesis of a soft, transparent, and noncytotoxic PSU elastomer with a refractive index approximately equal to that of a young human eye lens.

The ring-chain equilibration of D4 and D4Me,Ph with the endblocker APTMDS yielded aminopropyl-terminated polydimethylsiloxanes and polydimethyl-methyl-phenyl-siloxane-copolymers, respectively, which were synthesized with molecular weights between 3,000 and 33,000 g&#183;mol-1 by adjusting the monomer ratio between D4 and APTMDS (Figure 6). Molecular weights&#160;<img alt="Equation 1" src="/files/ftp_upload/58590/58590eq1.jpg" /> of the prepared PDMS, which were determined from 1H-NMR spectra (Figure 5), were similar to the values obtained from titration. These values were in agreement with the calculated theoretical molecular weights of up to 15,000 g&#183;mol-1. During the preparation of PDMS with higher molecular weights, the obtained molecular weights were slightly greater than those presumed by theoretical calculation.The copolymerization of the cyclic siloxane with pendant phenyl groups D4Me,Ph was deemed successful for slightly increasing the refractive index of polysiloxanes. The refractive index (determined using the Abbe refractometer at 37 &#176;C) increased from 1.401 (unmodified PDMS) to 1.4356 (14 mol% methyl-phenyl-siloxane) (Figure 7).PSU elastomers were synthesized in two steps using the prepared aminopropyl-terminated PDMS, aliphatic diisocyanate H12MDI, and APTMDS, using THF as the solvent. This method permitted the construction of high-molecular-weight PSUs with a segmented structure of soft segments (PDMS) and hard segments (diisocyanate + urea). Inline FTIR spectroscopy confirmed the extremely rapid reaction of the isocyanate groups with the amino groups from the PDMS and the chain extender APTMDS (Figure 3 and Figure 8). Unlike the preparation of the polyurethane elastomers, which takes several hours, the preparation of the PSU elastomers was convenient.The transparency and mechanical properties of PSU elastomers were dependent on the PDMS molecular weight. Transparent PSU elastomer films exhibited a transmittance of &#62;90% up to a PDMS molecular weight of 18,000 g&#183;mol-1. At higher PDMS molecular weights, the PSU films became increasingly opaque (Figure 9).With the increase in the PDMS molecular weight, soft PSU elastomers could be prepared. The Young&#39;s modulus of PSU elastomers decreased from ~5.5 MPa (with a PDMS molecular weight of 3,000 g&#183;mol-1) to 0.6 MPa (with a PDMS molecular weight of &#8805;26,000 g&#183;mol-1) (Figure 10).Furthermore, mechanical hysteresis, which was used to evaluate the mechanical stability under repeated applied stress, was reduced for the PSU elastomers when they were prepared from high-molecular-weight PDMS. The hysteresis values for the first cycle at a 100% strain decreased from 54% (with a PDMS molecular weight of 3,000 g&#183;mol-1) to 6% (with a PDMS molecular weight of 33,000 g&#183;mol-1) (Figure 11).The applied synthesis method permitted the preparation of PSU elastomers that do not release cytotoxic residuals as examples shown in cell viability tests performed with extracts of some selected PSU elastomers on HaCaT cells (Figure 12).
<img alt="Figure 1" class="xfigimg" src="/files/ftp_upload/58590/58590fig1.jpg" /> 
Figure 1: Synthesis of the tetramethylammonium-3-aminopropyl-dimethylsilanolate catalyst. 
Tetramethylammonium hydroxide pentahydrate (TMAH) and 1,3-Bis(3-aminopropyl)-tetramethyldisiloxane (APTMDS) were reacted 2 h in THF at 80 &#176;C. The catalyst tetramethylammonium-3-aminopropyl-dimethylsilanolate is received as a white solid after washing the crude product with THF. <a href="https://www.jove.com/files/ftp_upload/58590/58590fig1large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 2" class="xfigimg" src="/files/ftp_upload/58590/58590fig3.jpg" /> 
Figure 2: Synthesis route for aminopropyl-terminated polydimethylsiloxanes (PDMS) and polydimethyl-methyl-phenyl-siloxane-copolymers. Cyclic monomers D4/D4Me,Ph are equilibrated using a disiloxane endblocker APTMDS at 80 &#176;C for 24 h using the tetramethylammonium-3-aminopropyl-dimethylsilanolate catalyst. This figure has been modified from Riehle et al.48. <a href="https://www.jove.com/files/ftp_upload/58590/58590fig3large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 3" class="xfigimg" src="/files/ftp_upload/58590/58590fig2.jpg" /> 
Figure 3: Two-step synthesis of segmented polysiloxane-based urea elastomers (PSU). In the first step, a prepolymer containing active isocyanate groups is formed after the reaction of H12MDI with aminopropyl-terminated polysiloxane (R = CH3: PDMS; R = Ph; copolymer). In the second step, the polymer molecular weight is increased via the reaction of the remaining active isocyanate groups with the chain extender APTMDS. The resulting elastomer is a segmented polymer comprising urea hard segments and silicone soft segments. This figure has been modified from Riehle et al.48. <a href="https://www.jove.com/files/ftp_upload/58590/58590fig2large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 4" class="xfigimg" src="/files/ftp_upload/58590/58590fig4.jpg" /> 
Figure 4: Specification of the dog-bone-shaped test specimen for stress-strain tests. This figure has been modified from Keiper45. <a href="https://www.jove.com/files/ftp_upload/58590/58590fig4large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 5" class="xfigimg" src="/files/ftp_upload/58590/58590fig5.jpg" /> 
Figure 5: 1H-NMR spectrum of aminopropyl-terminated polydimethylsiloxane. For the molecular weight calculation, integral values of the methylene protons d (&#948; 2.69 ppm) and b (&#948; 0.56 ppm) and methyl protons a (&#948; ~ 0.07 ppm) were utilized. The peak c (&#948; ~1.5 ppm) is overlaid by the HDO peak49, corresponding to the proton exchange of water traces with solvent CDCl3; hence, this peak is not used to calculate the molecular weight. The PDMS molecular weight in this spectrum is ~16,365 g&#183;mol-1. <a href="https://www.jove.com/files/ftp_upload/58590/58590fig5large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 6" class="xfigimg" src="/files/ftp_upload/58590/58590fig6.jpg" /> 
Figure 6: Linear correlation between the molecular weight <img alt="Equation 6" src="/files/ftp_upload/58590/58590eq6.jpg" /> of aminopropyl-terminated polydimethylsiloxanes and endblocker concentration. <img alt="Equation 1" src="/files/ftp_upload/58590/58590eq1.jpg" /> values were determined via&#160;1H-NMR spectroscopy, the titration of amino end groups, and the theoretical calculation according to equation (1). This figure is reprinted with permission from Riehle et al.48. <a href="https://www.jove.com/files/ftp_upload/58590/58590fig6large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 7" class="xfigimg" src="/files/ftp_upload/58590/58590fig7.jpg" /> 
Figure 7: Refractive indices of aminopropyl-terminated polydimethyl-methyl-phenyl-siloxane-copolymers. Refractive indices (RI) of polydimethyl-methyl-phenyl-siloxane-copolymers were determined at 20 &#176;C (black squares) and 37 &#176;C (red circles) using an Abbe refractometer. The RI values linearly increased with the amount of the incorporated methyl-phenyl-siloxane units. RI values at 0 mol% represent those from unmodified PDMS with a molecular weight comparable to the polydimethyl-methyl-phenyl-siloxane-copolymers. An optimal RI of 1.4346 (37 &#176;C) was obtained for a copolymer with 14 mol% of methyl-phenyl-siloxane. This figure has been reprinted with permission from Riehle et al.48. <a href="https://www.jove.com/files/ftp_upload/58590/58590fig7large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 8" class="xfigimg" src="/files/ftp_upload/58590/58590fig8.jpg" /> 
Figure 8: Isocyanate conversion during the synthesis of polydimethylsiloxane-urea (PSU). This figure shows a time-dependent plot of the NCO absorption band at 2,266 cm1 followed by inline FTIR-ATR spectroscopy during the synthesis of PSU.After the addition of aminopropyl-terminated polydimethylsiloxane, the height of the NCO band decreased, indicative of the formation of NCO-terminated prepolymer chains. After the addition of the chain extender APTMDS, the NCO band completely disappeared from the IR spectra. This figure has been reprinted with permission from Riehle et al.50. <a href="https://www.jove.com/files/ftp_upload/58590/58590fig8large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 9" class="xfigimg" src="/files/ftp_upload/58590/58590fig9.jpg" /> 
Figure 9: Dependence of the transmittance of PSU elastomer films at 750 nm and the molecular weight of polydimethylsiloxane. The transmittance of the PSU films was determined by UV-Vis spectroscopy. The transmittance of PSUs at 750 nm (the upper edge of the visible spectrum) was &#62;90% if PSUs were synthesized using PDMS with molecular weights ranging between 3,000 and 18,000 g&#183;mol-1. With an increasing molecular weight of PDMS, the opacity of films increased. This figure has been reprinted with permission from Riehle et al.48. <a href="https://www.jove.com/files/ftp_upload/58590/58590fig9large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 10" class="xfigimg" src="/files/ftp_upload/58590/58590fig10.jpg" /> 
Figure 10: Young&#39;s modulus of PSU elastomers as a function of the molecular weight of polydimethylsiloxane. Young&#39;s moduli (YM) were determined from stress-strain measurements of the PSU films. The values are expressed as a mean value obtained from five repeated measurements. The error bars represent the standard deviation. The highest decrease of YM was observed for PSUs synthesized from PDMS ranging from 3,000 to 9,000 g&#183;mol-1. At PDMS molecular weights between 12,000 and 18,000 g&#183;mol-1, YM values were between 1.5 MPa and 1.0 MPa. At molecular weights greater than 26,000 g&#183;mol-1, YM values were ~0.6 MPa. This figure has been reprinted with permission from Riehle et al.48. <a href="https://www.jove.com/files/ftp_upload/58590/58590fig10large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 11" class="xfigimg" src="/files/ftp_upload/58590/58590fig11.jpg" /> 
Figure 11: 100% hysteresis curves of PSU elastomers. The first-cycle hysteresis curves of the PSU elastomers at 100% elongation are shown. The polymer notation refers to the PDMS molecular weight (e.g., PSU-3T is a polyurea elastomer prepared from PDMS with a molecular weight of 3,000 g&#183;mol-1). The highest mechanical hysteresis (43% - 54%) was observed in PSU elastomers synthesized from low-molecular-weight PDMS, as indicated by the pronounced hysteresis curves. Hysteresis decreased with the increase in the PDMS molecular weight from 14% (15,000 g&#183;mol-1) to 6% (33,000 g&#183;mol-1). This figure has been reprinted with permission from Riehle et al.48. <a href="https://www.jove.com/files/ftp_upload/58590/58590fig11large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 12" class="xfigimg" src="/files/ftp_upload/58590/58590fig12.jpg" /> 
Figure 12: Results of in vitro cytotoxicity tests on HaCaT cells treated with PSU extracts. This figure shows the cell proliferation of the HaCaT cells treated with the cell medium extracts of PSU elastomers. The values are expressed as the mean value obtained from three tested extracts per sample, with six repeated measurements for each extract (18 replicates in total). The error bars represent the standard deviation from these measurements.The blank represents the cell medium DMEM (without the sample), which was treated analogous to the cell medium used for extraction. A medical-grade polyether urethane was selected as the reference material. Silicone-based polyurea elastomers (PSU-18T, PSU-16T, and PSU-14Ph) were selected as representative test samples, which were based on PDMS with molecular weights of 18,000 and 16,000 g&#183;mol-1 (PSU-18T and PSU-16T), whereas PSU-14Ph was based on a polydimethyl-methyl-phenyl-siloxane-copolymer with 14 mol% of methyl-phenyl-siloxane and a molecular weight of ~16,600 g&#183;mol-1.&#160;The mean proliferation of HaCaT cells, treated with the extracts of the PSU elastomers, and the reference polyurethane was 100% and higher. Therefore, the extracts of the PSU elastomers and reference polyurethane are not cytotoxic. <a href="https://www.jove.com/files/ftp_upload/58590/58590fig12large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>

Watch this Scientific Journal Video about Synthesis of Soft Polysiloxane-urea Elastomers for Intraocular Lens Application at JoVE.com

Synthesis of Soft Polysiloxane-urea Elastomers for Intraocular Lens Application

This study describes synthetic routes for aminopropyl-terminated polydimethylsiloxanes and polydimethyl-methyl-phenyl-siloxane-block copolymers and for soft polysiloxane-based urea (PSU) elastomers. It presents the application of PSUs as accommodating an intraocular lens. An evaluation method for in vitro cytotoxicity is also described.

This study discusses a synthesis route for soft polysiloxane-based urea (PSU) elastomers for their applications as accommodating intraocular lenses ...

synthesis-soft-polysiloxane-urea-elastomers-for-intraocular-lens

Research

JoVE Journal

Chemistry

12.5K Views.  Reutlingen University. De methoden aangetoond in deze video tonen een handige manier om amino-beëindigd polysiloxanes en zachte polysiloxane-gebaseerde polyurea's die geschikt zijn voor de toepassing als opvang intraoculaire lens synthetiseren. Het belangrijkste voordeel van deze technieken is dat synthese en analyse van de polymeren gemakkelijk volgens standaardmethoden kunnen worden uitgevoerd zonder ingewikkelde experimentele setup. De implicatie van deze technologie uit te breiden tot cataract therapie, omdat ...

Video: Synthesis of Soft Polysiloxane-urea Elastomers for Intraocular Lens Application

Microbubble Fabrication of Concave-porosity PDMS Beads

Microbubble fabrication (by use of a fine emulsion) provides a means of increasing the surface-area-to-volume (SAV) ratio of polymer materials, which is particularly useful for separations applications. Porous polydimethylsiloxane (PDMS) beads can be produced by heat-curing such an emulsion, allowing the interface between the aqueous and aliphatic phases to mold the morphology of the polymer. In the procedures described here, both polymer and crosslinker (triethoxysilane) are sonicated together in a cold-bath sonicator. Following a period of cross-linking, emulsions are added dropwise to a hot surfactant solution, allowing the aqueous phase of the emulsion to separate, and forming porous polymer beads. We demonstrate that this method can be tuned, and the SAV ratio optimized, by adjusting the electrolyte content of the aqueous phase in the emulsion. Beads produced in this way are imaged with scanning electron microscopy, and representative SAV ratios are determined using Brunauer&#8211;Emmett&#8211;Teller (BET) analysis. Considerable variability with the electrolyte identity is observed, but the general trend is consistent: there is a maximum in SAV obtained at a specific concentration, after which porosity decreases markedly.

Procedures used to generate microstructured concave-porosity polydimethylsiloxane beads are presented. Effects of electrolyte concentration and identity within the aqueous phase are particularly emphasized.

Microbubble fabrication (by use of a fine emulsion) provides a means of increasing the surface-area-to-volume (SAV) ratio of polymer materials, which is ...

Synthesis of Programmable Main-chain Liquid-crystalline Elastomers Using a Two-stage Thiol-acrylate Reaction

This study presents a novel two-stage thiol-acrylate Michael addition-photopolymerization (TAMAP) reaction to prepare main-chain liquid-crystalline elastomers (LCEs) with facile control over network structure and programming of an aligned monodomain. Tailored LCE networks were synthesized using routine mixing of commercially available starting materials and pouring monomer solutions into molds to cure. An initial polydomain LCE network is formed via a self-limiting thiol-acrylate Michael-addition reaction. Strain-to-failure and glass transition behavior were investigated as a function of crosslinking monomer, pentaerythritol tetrakis(3-mercaptopropionate) (PETMP). An example non-stoichiometric system of 15 mol% PETMP thiol groups and an excess of 15 mol% acrylate groups was used to demonstrate the robust nature of the material. The LCE formed an aligned and transparent monodomain when stretched, with a maximum failure strain over 600%. Stretched LCE samples were able to demonstrate both stress-driven thermal actuation when held under a constant bias stress or the shape-memory effect when stretched and unloaded. A permanently programmed monodomain was achieved via a second-stage photopolymerization reaction of the excess acrylate groups when the sample was in the stretched state. LCE samples were photo-cured and programmed at 100%, 200%, 300%, and 400% strain, with all samples demonstrating over 90% shape fixity when unloaded. The magnitude of total stress-free actuation increased from 35% to 115% with increased programming strain. Overall, the two-stage TAMAP methodology is presented as a powerful tool to prepare main-chain LCE systems and explore structure-property-performance relationships in these fascinating stimuli-sensitive materials.

A novel methodology is presented to synthesize and program main-chain liquid-crystalline elastomers using commercially available starting monomers. A wide range of thermomechanical properties was tailored by adjusting the amount of crosslinker, while the actuation performance was dependent on the amount of applied strain during programming.

This study presents a novel two-stage thiol-acrylate Michael addition-photopolymerization (TAMAP) reaction to prepare main-chain liquid-crystalline ...

Fabrication Process of Silicone-based Dielectric Elastomer Actuators

This contribution demonstrates the fabrication process of dielectric elastomer transducers (DETs). DETs are stretchable capacitors consisting of an elastomeric dielectric membrane sandwiched between two compliant electrodes. The large actuation strains of these transducers when used as actuators (over 300% area strain) and their soft and compliant nature has been exploited for a wide range of applications, including electrically tunable optics, haptic feedback devices, wave-energy harvesting, deformable cell-culture devices, compliant grippers, and propulsion of a bio-inspired fish-like airship. In most cases, DETs are made with a commercial proprietary acrylic elastomer and with hand-applied electrodes of carbon powder or carbon grease. This combination leads to non-reproducible and slow actuators exhibiting viscoelastic creep and a short lifetime. We present here a complete process flow for the reproducible fabrication of DETs based on thin elastomeric silicone films, including casting of thin silicone membranes, membrane release and prestretching, patterning of robust compliant electrodes, assembly and testing. The membranes are cast on flexible polyethylene terephthalate (PET) substrates coated with a water-soluble sacrificial layer for ease of release. The electrodes consist of carbon black particles dispersed into a silicone matrix and patterned using a stamping technique, which leads to precisely-defined compliant electrodes that present a high adhesion to the dielectric membrane on which they are applied.

This manuscript shows the fabrication process for the manufacture of dielectric elastomer soft actuators based on silicone membranes. The three key stages of production are presented in detail: blade casting of thin silicone membranes; pad printing of compliant electrodes; and the assembly of all the components.

This contribution demonstrates the fabrication process of dielectric elastomer transducers (DETs). DETs are stretchable capacitors consisting of an ...

Engineering

Thin Film Composite Silicon Elastomers for Cell Culture and Skin Applications: Manufacturing and Characterization

In this protocol, we present methods to fabricate thin elastomer composite films for advanced cell culture applications and for the development of skin adhesives. Two different poly-(dimethyl siloxanes) (PDMS and soft skin adhesive (SSA)), have been used for in depth investigation of biological effects and adhesive characteristics. The composite films consist of a flexible backing layer and an adhesive top coating. Both layers have been manufactured by doctor blade application technique. In the present investigation, the adhesive behavior of the composite films has been investigated as a function of the layer thickness or a variation of the Young&#39;s modulus of the top layer. The Young&#39;s modulus of PDMS has been changed by varying the base to crosslinker mixing ratio. In addition, the thickness of SSA films has been varied from approx. 16 &#181;m to approx. 320 &#181;m. Scanning electron microscopy (SEM) and optical microscopy have been used for thickness measurements. The adhesive properties of elastomer films depend strongly on the film thickness, the Young&#39;s modulus of the polymers and surface characteristics. Therefore, normal adhesion of these films on glass substrates exhibiting smooth and rough surfaces has been investigated. Pull-off stress and work of separation are dependent on the mixing ratio of silicone elastomers.
Additionally, the thickness of the soft skin adhesive placed on top of a supportive backing layer has been varied in order to produce patches for skin applications. Cytotoxicity, proliferation and cellular adhesion of L929 murine fibroblasts on PDMS films (mixing ratio 10:1) and SSA films (mixing ratio 50:50) have been conducted. We have shown here, for the first time, the side by side comparison of thin composite films manufactured of both polymers and present the investigation of their biological- and adhesive properties.

A protocol for the manufacturing process of polymeric thin film composite structures possessing either different Young&#39;s moduli or thicknesses is presented. Films are produced for advanced cell culture studies or as skin adhesives.

In this protocol, we present methods to fabricate thin elastomer composite films for advanced cell culture applications and for the development of skin ...

Developmental Biology

Drawing and Hydrophobicity-patterning Long Polydimethylsiloxane Silicone Filaments

Polydimethylsiloxane (PDMS) silicone is a versatile polymer that cannot readily be formed into long filaments. Traditional spinning methods fail because PDMS does not exhibit long-range fluidity at melting. We introduce an improved method to produce filaments of PDMS by a stepped temperature profile of the polymer as it cross-links from a fluid to an elastomer. By monitoring its warm-temperature viscosity, we estimate a window of time when its material properties are amendable to drawing into long filaments. The filaments pass through a high-temperature tube oven, curing them sufficiently to be harvested. These filaments are on the order of hundreds of micrometers in diameter and tens of centimeters in length, and even longer and thinner filaments are possible. These filaments retain many of the material properties of bulk PDMS, including switchable hydrophobicity. We demonstrate this capability with an automated corona-discharge patterning method. These patternable PDMS silicone filaments have applications in silicone weavings, gas-permeable sensor components, and model microscale foldamers.

Here, we present a protocol to produce long filaments of polydimethylsiloxane (PDMS) silicone by gravity-drawing through a furnace. Filaments are on the order of hundreds of micrometers in diameter and tens of centimeters in length and are hydrophobically patternable via an Arduino-controlled corona discharge system.

Polydimethylsiloxane (PDMS) silicone is a versatile polymer that cannot readily be formed into long filaments. Traditional spinning methods fail because ...

Double Emulsion Generation Using a Polydimethylsiloxane (PDMS) Co-axial Flow Focus Device

Double emulsions are useful in a number of biological and industrial applications in which it is important to have an aqueous carrier fluid. This paper presents a polydimethylsiloxane (PDMS) microfluidic device capable of generating water/oil/water double emulsions using a coaxial flow focusing geometry that can be fabricated entirely using soft lithography. Similar to emulsion devices using glass capillaries, double emulsions can be formed in channels with uniform wettability and with dimensions much smaller than the channel sizes. Three dimensional flow focusing geometry is achieved by casting a pair of PDMS slabs using two layer soft lithography, then mating the slabs together in a clamshell configuration. Complementary locking features molded into the PDMS slabs enable the accurate registration of features on each of the slab surfaces. Device testing demonstrates formation of double emulsions from 14 &#181;m to 50 &#181;m in diameter while using large channels that are robust against fouling and clogging.

Double Emulsion Generation Using a Polydimethylsiloxane PDMS Co-axial Flow Focus Device

Microfluidic double emulsions generation typically involves devices with patterned wettability or custom-fabricated glass components. Here we describe the fabrication and testing of an all polydimethylsiloxane (PDMS) double emulsion generator that does not require surface treatment or complicated fabrication processes, and is capable of producing double emulsions down to 14 &#181;m.

Double emulsions are useful in a number of biological and industrial applications in which it is important to have an aqueous carrier fluid. This paper ...

Bioengineering

Preparation of Monodomain Liquid Crystal Elastomers and Liquid Crystal Elastomer Nanocomposites

LCEs are shape-responsive materials with fully reversible shape change and potential applications in medicine, tissue engineering, artificial muscles, and as soft robots. Here, we demonstrate the preparation of shape-responsive liquid crystal elastomers (LCEs) and LCE nanocomposites along with characterization of their shape-responsiveness, mechanical properties, and microstructure. Two types of LCEs &#8212; polysiloxane-based and epoxy-based &#8212; are synthesized, aligned, and characterized. Polysiloxane-based LCEs are prepared through two crosslinking steps, the second under an applied load, resulting in monodomain LCEs. Polysiloxane LCE nanocomposites are prepared through the addition of conductive carbon black nanoparticles, both throughout the bulk of the LCE and to the LCE surface. Epoxy-based LCEs are prepared through a reversible esterification reaction. Epoxy-based LCEs are aligned through the application of a uniaxial load at elevated (160 &#176;C) temperatures. Aligned LCEs and LCE nanocomposites are characterized with respect to reversible strain, mechanical stiffness, and liquid crystal ordering using a combination of imaging, two-dimensional X-ray diffraction measurements, differential scanning calorimetry, and dynamic mechanical analysis. LCEs and LCE nanocomposites can be stimulated with heat and/or electrical potential to controllably generate strains in cell culture media, and we demonstrate the application of LCEs as shape-responsive substrates for cell culture using a custom-made apparatus.

We demonstrate the preparation of siloxane-based and epoxy-based liquid crystal elastomers (LCEs) and LCE nanocomposites. The LCEs are characterized with respect to reversible strain, liquid crystal ordering, and stiffness. As a potential application, we demonstrate their use as shape-responsive substrates in a custom device for active cell culture.

LCEs are shape-responsive materials with fully reversible shape change and potential applications in medicine, tissue engineering, artificial muscles, 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.), ...

Polydimethylsiloxane-polycarbonate Microfluidic Devices for Cell Migration Studies Under Perpendicular Chemical and Oxygen Gradients

This paper reports a microfluidic device made of polydimethylsiloxane (PDMS) with an embedded polycarbonate (PC) thin film to study cell migration under combinations of chemical and oxygen gradients. Both chemical and oxygen gradients can greatly affect cell migration in vivo; however, due to technical limitations, very little research has been performed to investigate their effects in vitro. The device developed in this research takes advantage of a series of serpentine-shaped channels to generate the desired chemical gradients and exploits a spatially confined chemical reaction method for oxygen gradient generation. The directions of the chemical and oxygen gradients are perpendicular to each other to enable straightforward migration result interpretation. In order to efficiently generate the oxygen gradients with minimal chemical consumption, the embedded PC thin film is utilized as a gas diffusion barrier. The developed microfluidic device can be actuated by syringe pumps and placed into a conventional cell incubator during cell migration experiments to allow for setup simplification and optimized cell culture conditions. In cell experiments, we used the device to study migrations of adenocarcinomic human alveolar basal epithelial cells, A549, under combinations of chemokine (stromal cell-derived factor, SDF-1&#945;) and oxygen gradients. The experimental results show that the device can stably generate perpendicular chemokine and oxygen gradients and is compatible with cells. The migration study results indicate that oxygen gradients may play an essential role in guiding cell migration, and cellular behavior under combinations of gradients cannot be predicted from those under single gradients. The device provides a powerful and practical tool for researchers to study interactions between chemical and oxygen gradients in cell culture, which can promote better cell migration studies in more in vivo-like microenvironments.

The control of chemical and oxygen gradients is essential for cell cultures. This paper reports a polydimethylsiloxane-polycarbonate (PDMS-PC) microfluidic device capable of reliably generating combinations of chemical and oxygen gradients for cell migration studies, which can be practically utilized in biological labs without sophisticated instrumentation.

This paper reports a microfluidic device made of polydimethylsiloxane (PDMS) with an embedded polycarbonate (PC) thin film to study cell migration under ...

Synthesis of Biocompatible Liquid Crystal Elastomer Foams as Cell Scaffolds for 3D Spatial Cell Cultures

Here, we present a step-by-step preparation of a 3D, biodegradable, foam-like cell scaffold. These scaffolds were prepared by cross-linking star block co-polymers featuring cholesterol units as side-chain pendant groups, resulting in smectic-A (SmA) liquid crystal elastomers (LCEs). Foam-like scaffolds, prepared using metal templates, feature interconnected microchannels, making them suitable as 3D cell culture scaffolds. The combined properties of the regular structure of the metal foam and of the elastomer result in a 3D cell scaffold that promotes not only higher cell proliferation compared to conventional porous templated films, but also better management of mass transport (i.e., nutrients, gases, waste, etc.). The nature of the metal template allows for the easy manipulation of foam shapes (i.e., rolls or films) and for the preparation of scaffolds of different pore sizes for different cell studies while preserving the interconnected porous nature of the template. The etching process does not affect the chemistry of the elastomers, preserving their biocompatible and biodegradable nature. We show that these smectic LCEs, when grown for extensive time periods, enable the study of clinically relevant and complex tissue constructs while promoting the growth and proliferation of cells.

This study presents a methodology to prepare 3D, biodegradable, foam-like cell scaffolds based on biocompatible side-chain liquid crystal elastomers (LCEs). Confocal microscopy experiments show that foam-like LCEs allow for cell attachment, proliferation, and the spontaneous alignment of C2C12s myoblasts.

Here, we present a step-by-step preparation of a 3D, biodegradable, foam-like cell scaffold. These scaffolds were prepared by cross-linking star block ...

Synthesis of Soft Polysiloxane-urea Elastomers for Intraocular Lens Application

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