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 border="1" fo:keep-together.within-page="1" fo:keep-with-next.within-page="always">
	<tbody>
		<tr>
			<td>Octamethylcyclotetrasiloxane (D4), 97 %</td>
			<td>ABCR GmbH</td>
			<td>AB111277</td>
			<td>presumably impairs fertility, must be degassed before use 
			CAS:&#160;556-67-2</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 
			CAS:&#160;2469-55-8</td>
		</tr>
		<tr>
			<td>2,4,6,8-Tetramethyl-2,4,6,8-tetraphenylcyclotetrasiloxane&#160;</td>
			<td>Sigma Aldrich</td>
			<td>40094</td>
			<td>technical grade 
			CAS:&#160;77-63-4</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 
			CAS:&#160;10424-65-4</td>
		</tr>
		<tr>
			<td>4,4&#162;-Methylenbis(cyclohexylisocyanate) (H12MDI)</td>
			<td>Covestro via CSC J&#228;kle Chemie GmbH &#38; Co. KG</td>
			<td></td>
			<td>toxic if inhaled, skin and eye irritant 
			CAS:&#160;5124-30-1</td>
		</tr>
		<tr>
			<td>Tetrahydrofuran (anhydrous) 99.8 %</td>
			<td>Alfa Aesar</td>
			<td>44608</td>
			<td>stabilized with BHT 
			CAS:&#160;109-99-9</td>
		</tr>
		<tr>
			<td>Chloroform 99 %</td>
			<td>Gr&#252;ssing GmbH Analytica</td>
			<td>1025125000</td>
			<td>stabilized with ethanol, presumably carcinogenic, can impair fertility and cause damage to an unborn child 
			CAS:&#160;67-66-3</td>
		</tr>
		<tr>
			<td>Chloroform-d, 99.8 %</td>
			<td>Sigma Aldrich</td>
			<td>151823</td>
			<td>CAS:&#160;865-49-6</td>
		</tr>
		<tr>
			<td>Dulbecco&#39;s modified Eagle&#39;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&#160;</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&#160;</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&#160;</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 &#38; 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.remotexs.ntu.edu.sg/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.remotexs.ntu.edu.sg/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.remotexs.ntu.edu.sg/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.remotexs.ntu.edu.sg/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.remotexs.ntu.edu.sg/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.remotexs.ntu.edu.sg/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.remotexs.ntu.edu.sg/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.remotexs.ntu.edu.sg/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.remotexs.ntu.edu.sg/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.remotexs.ntu.edu.sg/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.remotexs.ntu.edu.sg/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.remotexs.ntu.edu.sg/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

Nanyang Technological University

Research

JoVE Journal

Chemistry

12.4K Views.  Reutlingen University. 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.

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

Synthesis, Cellular Delivery and In vivo Application of Dendrimer-based pH Sensors

The development of fluorescent indicators represented a revolution for life sciences. Genetically encoded and synthetic fluorophores with sensing abilities allowed the visualization of biologically relevant species with high spatial and temporal resolution. Synthetic dyes are of particular interest thanks to their high tunability and the wide range of measureable analytes. However, these molecules suffer several limitations related to small molecule behavior (poor solubility, difficulties in targeting, often no ratiometric imaging allowed). In this work we introduce the development of dendrimer-based sensors and present a procedure for pH measurement in vitro, in living cells and in vivo. We choose dendrimers as ideal platform for our sensors for their many desirable properties (monodispersity, tunable properties, multivalency) that made them a widely used scaffold for several biomedical devices. The conjugation of fluorescent pH indicators to the dendrimer scaffold led to an enhancement of their sensing performances. In particular dendrimers exhibit reduced cell leakage, improved intracellular targeting and allow ratiometric measurements. These novel sensors were successfully employed to measure pH in living HeLa cells and in vivo in mouse brain.

Synthesis, Cellular Delivery and In vivo Application of Dendrimer-based pH Sensors

Fluorescence sensors are powerful tools in life science. Here we describe a methodology to synthesize and use dendrimer-based fluorescent sensors to measure pH in living cells and in vivo. The dendritic scaffold enhances the properties of conjugated fluorescent dyes leading to improved sensing properties.

The development of  fluorescent indicators represented a revolution for life sciences. Genetically  encoded and synthetic fluorophores with sensing ...

Synthesis of Hypervalent Iodonium Alkynyl Triflates for the Application of Generating Cyanocarbenes

The procedures described in this article involve the synthesis and isolation of hypervalent iodonium alkynyl triflates (HIATs) and their subsequent reactions with azides to form cyanocarbene intermediates. The synthesis of hypervalent iodonium alkynyl triflates can be facile, but difficulties stem from their isolation and reactivity. In particular, the necessity to use filtration under inert atmosphere at -45 &deg;C for some HIATs requires special care and equipment. Once isolated, the compounds can be stored and used in reactions with azides to form cyanocarbene intermediates. 
The evidence for cyanocarbene generation is shown by visible extrusion of dinitrogen as well as the characterization of products that occur from O-H insertion, sulfoxide complexation, and cyclopropanation. A side reaction of the cyanocarbene formation is the generation of a vinylidene-carbene and the conditions to control this process are discussed. There is also potential to form a hypervalent iodonium alkenyl triflate and the means of isolation and control of its generation are provided. The O-H insertion reaction involves using a HIAT, sodium azide or tetrabutylammonium azide, and methanol as solvent/substrate. The sulfoxide complexation reaction uses a HIAT, sodium azide or tetrabutylammonium azide, and dimethyl sulfoxide as solvent. The cyclopropanations can be performed with or without the use of solvent. The azide source must be tetrabutylammonium azide and the substrate shown is styrene.

Herein is described the synthesis, isolation, and reactions of hypervalent iodonium alkynyl triflates (HIATs) with azides to generate cyanocarbenes. The procedures will involve air-sensitive and cryogen techniques, including cold filtration under an inert atmosphere. Handling and safety of the synthesized compounds will also be discussed.

The procedures described in this article involve the synthesis and isolation of hypervalent iodonium alkynyl triflates (HIATs) and their subsequent ...

Synthesis of Indoxyl-glycosides for Detection of Glycosidase Activities

Indoxyl glycosides proved to be valuable and versatile tools for monitoring glycosidase activities. Indoxyls are released by enzymatic hydrolysis and are rapidly oxidized, for example by atmospheric oxygen, to indigo type dyes. This reaction enables fast and easy screening in vivo without isolation or purification of enzymes, as well as rapid tests on agar plates or in solution (e.g., blue-white screening, micro-wells) and is used in biochemistry, histochemistry, bacteriology and molecular biology. Unfortunately the synthesis of such substrates proved to be difficult, due to various side reactions and the low reactivity of the indoxyl hydroxyl function. Especially for glucose type structures low yields were observed. Our novel approach employs indoxylic acid ester as key intermediates. Indoxylic acid esters with varied substitution patterns were prepared on scalable pathways. Phase transfer glycosylations with those acceptors and peracetylated glycosyl halides can be performed under common conditions in high yields. Ester cleavage and subsequent mild silver mediated glycosylation yields the peracetylated indoxyl glycosides in high yields. Finally deprotection is performed according to Zempl&#233;n.

Indoxyl glycosides are well-established and widely used tools for enzyme screening and enzyme activity monitoring. Especially for glucose type structures previous syntheses proved to be challenging and low yielding. Our novel approach employs indoxylic acid esters as precious intermediates to yield a considerable number of indoxyl glycosides in good yields.

Indoxyl glycosides proved to be valuable and versatile tools for monitoring glycosidase activities. Indoxyls are released by enzymatic hydrolysis and are ...

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 ...

Synthesis of Cd-free InP/ZnS Quantum Dots Suitable for Biomedical Applications

Fluorescent nanocrystals, specifically quantum dots, have been a useful tool for many biomedical applications. For successful use in biological systems, quantum dots should be highly fluorescent and small/monodisperse in size. While commonly used cadmium-based quantum dots possess these qualities, they are potentially toxic due to the possible release of Cd2+ ions through nanoparticle degradation. Indium-based quantum dots, specifically InP/ZnS, have recently been explored as a viable alternative to cadmium-based quantum dots due to their relatively similar fluorescence characteristics and size. The synthesis presented here uses standard hot-injection techniques for effective nanoparticle growth; however, nanoparticle properties such as size, emission wavelength, and emission intensity can drastically change due to small changes in the reaction conditions. Therefore, reaction conditions such temperature, reaction duration, and precursor concentration should be maintained precisely to yield reproducible products. Because quantum dots are not inherently soluble in aqueous solutions, they must also undergo surface modification to impart solubility in water. In this protocol, an amphiphilic polymer is used to interact with both hydrophobic ligands on the quantum dot surface and bulk solvent water molecules. Here, a detailed protocol is provided for the synthesis of highly fluorescent InP/ZnS quantum dots that are suitable for use in biomedical applications.

In this protocol, the synthesis of Cd-free InP/ZnS quantum dots (QDs) is detailed. InP-based QDs are gaining popularity due to the toxicity of Cd2+ ions that may be released through nanoparticle degradation. After synthesis, QDs are solubilized in water using an amphiphilic polymer for use in biomedical applications.

Fluorescent nanocrystals, specifically quantum dots, have been a useful tool for many biomedical applications. For successful use in biological systems, ...

Protocol for the Synthesis of Ortho-trifluoromethoxylated Aniline Derivatives

Molecules bearing trifluoromethoxy (OCF3) group often show desired pharmacological and biological properties. However, facile synthesis of trifluoromethoxylated aromatic compounds remains a formidable challenge in organic synthesis. Conventional approaches often suffer from poor substrate scope, or require use of highly toxic, difficult-to-handle, and/or thermally labile reagents. Herein, we report a user-friendly protocol for the synthesis of methyl 4-acetamido-3-(trifluoromethoxy)benzoate using 1-trifluoromethyl-1,2-benziodoxol-3(1H)-one (Togni reagent II). Treating methyl 4-(N-hydroxyacetamido)benzoate (1a) with Togni reagent II in the presence of a catalytic amount of cesium carbonate (Cs2CO3) in chloroform at RT afforded methyl 4-(N-(trifluoromethoxy)acetamido)benzoate (2a). This intermediate was then converted to the final product methyl 4-acetamido-3-(trifluoromethoxy)benzoate (3a) in nitromethane at 120 &#176;C. This procedure is general and can be applied to the synthesis of a broad spectrum of ortho-trifluoromethoxylated aniline derivatives, which could serve as useful synthetic building blocks for the discovery and development of new pharmaceuticals, agrochemicals, and functional materials.

Protocol for the Synthesis of Ortho-trifluoromethoxylated Aniline Derivatives

An operationally simple procedure for the synthesis of ortho-trifluoromethoxylated aniline derivatives via a two-step sequence of O-trifluoromethylation of N-aryl-N-hydroxyacetamide followed by thermally induced intramolecular OCF3-migration is reported.

Molecules bearing trifluoromethoxy (OCF3) group often show desired pharmacological and biological properties. However, facile synthesis of ...

Synthesis and Characterization of Supramolecular Colloids

Control over colloidal assembly is of utmost importance for the development of functional colloidal materials with tailored structural and mechanical properties for applications in photonics, drug delivery and coating technology. Here we present a new family of colloidal building blocks, coined supramolecular colloids, whose self-assembly is controlled through surface-functionalization with a benzene-1,3,5-tricarboxamide (BTA) derived supramolecular moiety. Such BTAs interact via directional, strong, yet reversible hydrogen-bonds with other identical BTAs. Herein, a protocol is presented that describes how to couple these BTAs to colloids and how to quantify the number of coupling sites, which determines the multivalency of the supramolecular colloids. Light scattering measurements show that the refractive index of the colloids is almost matched with that of the solvent, which strongly reduces the van der Waals forces between the colloids. Before photo-activation, the colloids remain well dispersed, as the BTAs are equipped with a photo-labile group that blocks the formation of hydrogen-bonds. Controlled deprotection with UV-light activates the short-range hydrogen-bonds between the BTAs, which triggers the colloidal self-assembly. The evolution from the dispersed state to the clustered state is monitored by confocal microscopy. These results are further quantified by image analysis with simple routines using ImageJ and Matlab. This merger of supramolecular chemistry and colloidal science offers a direct route towards light- and thermo-responsive colloidal assembly encoded in the surface-grafted monolayer.

A protocol for the synthesis and characterization of colloids coated with supramolecular moieties is described. These supramolecular colloids undergo self-assembly upon the activation of the hydrogen-bonds between the surface-anchored molecules by UV-light.

Control over colloidal assembly is of utmost importance for the development of functional colloidal materials with tailored structural and mechanical ...

Functionalization of Single-walled Carbon Nanotubes with Thermo-reversible Block Copolymers and Characterization by Small-angle Neutron Scattering

We demonstrate a protocol for single-walled carbon nanotube functionalization using thermo-sensitive PEO-PPO-PEO triblock copolymers in an aqueous solution. In a carbon nanotube/PEO105-PPO70-PEO105 (poloxamer 407) aqueous solution, the amphiphilic poloxamer 407 adsorbs onto the carbon nanotube surfaces and self-assembles into continuous layers, driven by intermolecular interactions between constituent molecules. The addition of 5-methylsalicylic acid changes the self-assembled structure from spherical-micellar to a cylindrical morphology. The fabricated poloxamer 407/carbon nanotube hybrid particles exhibit thermo-responsive structural features so that the density and thickness of poloxamer 407 layers are also reversibly controllable by varying temperature. The detailed structural properties of the poloxamer 407/carbon nanotube particles in suspension can be characterized by small-angle neutron scattering experiments and model fit analyses. The distinct curve shapes of the scattering intensities depending on temperature control or addition of aromatic additives are well described by a modified core-shell cylinder model consisting of a carbon nanotube core cylinder, a hydrophobic shell, and a hydrated polymer layer. This method can provide a simple but efficient way for the fabrication and in-situ characterization of carbon nanotube-based nano particles with a structure-tunable encapsulation.

A method for the functionalization of carbon nanotubes with structure-tunable polymeric encapsulation layers and structural characterization using small-angle neutron scattering is presented.

We demonstrate a protocol for single-walled carbon nanotube functionalization using thermo-sensitive PEO-PPO-PEO triblock copolymers in an aqueous ...

Synthesis of Protein Bioconjugates via Cysteine-maleimide Chemistry

The chemical linking or bioconjugation of proteins to fluorescent dyes, drugs, polymers and other proteins has a broad range of applications, such as the development of antibody drug conjugates (ADCs) and nanomedicine, fluorescent microscopy and systems chemistry. For many of these applications, specificity of the bioconjugation method used is of prime concern. The Michael addition of maleimides with cysteine(s) on the target proteins is highly selective and proceeds rapidly under mild conditions, making it one of the most popular methods for protein bioconjugation.
We demonstrate here the modification of the only surface-accessible cysteine residue on yeast cytochrome c with a ruthenium(II) bisterpyridine maleimide. The protein bioconjugation is verified by gel electrophoresis and purified by aqueous-based fast protein liquid chromatography in 27% yield of isolated protein material. Structural characterization with MALDI-TOF MS and UV-Vis is then used to verify that the bioconjugation is successful. The protocol shown here is easily applicable to other cysteine - maleimide coupling of proteins to other proteins, dyes, drugs or polymers.

Synthesis of Protein Bioconjugates via Cysteine-maleimide Chemistry

This protocol details the important steps required for the bioconjugation of a cysteine containing protein to a maleimide, including reagent purification, reaction conditions, bioconjugate purification and bioconjugate characterization.

The chemical linking or bioconjugation of proteins to fluorescent dyes, drugs, polymers and other proteins has a broad range of applications, such as the ...

Hydroquinone Based Synthesis of Gold Nanorods

Gold nanorods are an important kind of nanoparticles characterized by peculiar plasmonic properties. Despite their widespread use in nanotechnology, the synthetic methods for the preparation of gold nanorods are still not fully optimized. In this paper we describe a new, highly efficient, two-step protocol based on the use of hydroquinone as a mild reducing agent. Our approach allows the preparation of nanorods with a good control of size and aspect ratio (AR) simply by varying the amount of hexadecyl trimethylammonium bromide (CTAB) and silver ions (Ag+) present in the "growth solution". By using this method, it is possible to markedly reduce the amount of CTAB, an expensive and cytotoxic reagent, necessary to obtain the elongated shape. Gold nanorods with an aspect ratio of about 3 can be obtained in the presence of just 50 mM of CTAB (versus 100 mM used in the standard protocol based on the use of ascorbic acid), while shorter gold nanorods are obtained using a concentration as low as 10 mM.

This paper describes a protocol for the synthesis of gold nanorods, based on the use of hydroquinone as reducing agent, plus the different mechanisms for controlling their size and aspect ratio.

Gold nanorods are an important kind of nanoparticles characterized by peculiar plasmonic properties. Despite their widespread use in nanotechnology, the ...