Silsesquioxane Research Articles

Silsesquioxanes as molecular analogues of single-site heterogeneous catalysts

We discuss herein selected examples of metal complexes of polyhedral oligosilses-quioxanes (POSSs) as models of single-site heterogeneous surface catalysts. The utility of these compounds as such models is illustrated when employed as analogues of single-site titanium species supported on a silica surface. Deep insights into structure–functionality relationships can be gained. In particular, it was possible to probe the relationship between accessibility of the reactive centre and turnover frequencies in a manner that is impossible for a purely heterogeneous catalyst. We also report that the partially dehydroxylated SiO 2 surface alone is an effective radical polymerization initiation catalyst. This surface reactivity is modelled by the solution reactions between the olefin substrate and two POSSs, the completely condensed triganol prism, Si 6 Cy 6 O 9 ( a6b0 , Cy = Cyclohexyl, C 6 H 11 ), and the incompletely condensed partial cube, Si 7 Cy 7 O 9 (OH) 3 ( a7b3 ). The former, with six-membered Si 3 O 3 rings, is a catalyst. The latter, without this feature, is not. Similar reactivity discrimination is observed in the gas phase reactions of these POSSs with the olefin substrate, examined using atmospheric pressure chemical ionization- and collision-induced decomposition spectroscopies. Silsesquioxane a6b0 , containing Si 3 O 3 rings, reacts with the olefin, forming grafted olefin monomers and dimers, while this reactivity is not observed with silsesquioxane a7b3 .

Do Self-cleaning Surfaces Repel Ice?

The effects of nano- and micro-roughness as well as the chemical composition of surface treatments on self-cleaning properties and their suitability for ice repellency were investigated. In the first part of the study, the thermodynamics of water wettability of coated surfaces was evaluated both theoretically and experimentally. Accordingly, relationships were derived between the interfacial adhesion strength of a liquid drop to a polymer surface of a given composition, the mass of the drop, the measured contact angles, and the sliding angle. To verify the proposed model various hydrophobic coatings having different surface nanoand micro-roughnesses were prepared using polycarbonate as a substrate. The surface treatment was based on fluoroalkylsilane. Roughness was introduced by means of silica (microparticle) and POSS — Polyhedral Oligomeric Sil Sesquioxane (hybrid inorganic-organic nanoparticle) using a two tier topography. Using optimal compositions and processing conditions transparent ultrahydrophobic (superhydrophobic) characteristics were obtained. In these cases the contact angle was above 160° and the sliding angle was below 5°. In the second part of the investigation, the relationship between water wettability and ice repellency represented by ice adhesion to the coated surfaces was studied. Consequently, the surfaces were tailored using nanotechnology approach for their chemistry as well as their nanostructure in order to obtain fully wetting (hydrophilic) having a contact angle close to zero and the fully dewetting (ultrahydrophobic) (self-cleaning) surfaces where the contact angle approaches 180°. Ice adhesion test results have shown that the lower the surface energy the lower is the ice adhesion. The lowest adhesion values were obtained where ultra-hydrophobicity was present, with a combination of very low sliding angle with very high contact angle. These novel ultra-hydrophobic surface coatings and the associated model were used to develop and design surfaces for a variety of applications such as self-cleaning, glazing and anti-icing surfaces.

Sulfonated poly(ether ether ketone)/ethylene glycol/polyhedral oligosilsesquioxane hybrid membranes for fuel cell applications

The paper describes the preparation of hybrid membranes using a trisilanol phenyl polyhedral oligosilsesquioxane (TSP POSS) as filler, ethylene glycol (EG) as cross-linker and sulfonated poly(ether ether ketone) [SPEEK] (DS ∼65%) as polymer matrix.The performance of membranes has been evaluated in terms of thermal stability [by thermogravimetric analysis (TGA), differential scanning calorimetery (DSC)], water uptake, proton conductivity and X-ray diffraction (XRD) analysis. Morphology of the membranes has been investigated using scanning electron microscopy with energy dispersive X-ray (SEM-EDX) and atomic force microscopy (AFM). The addition of EG has increased the proton conductivity and dimensional stability of SPEEK matrix whereas incorporation of a small amount of TSP POSS to SPEEK/EG membranes has resulted in the decrease in water uptake and proton conductivity of the hybrid membranes.

Enhanced electrochemical performance of polyaniline/sulfonated polyhedral oligosilsesquioxane nanocomposites with porous and ordered hierarchical nanostructure

In this work, polyhedral oligosilsesquioxane (POSS) was functionalized by direct sulfonation, and the porous and ordered hierarchical nanostructure of polyaniline/sulfonated polyhedral oligosilsesquioxane (PANI/SOPS) was subsequently fabricated by in situ polymerization. The morphologies of the PANI/SOPS nanocomposites can be controlled by adjusting the concentration of SOPS. The measurement of X-ray diffraction pattern and ultraviolet-visible spectra demonstrates the molecular level dispersion of SPOS in the PANI matrix. Synergetic interaction between PANI and SOPS significantly improves the porosity and the stability of the electrode, yielding excellent electrochemical properties. Compared to pure PANI, the PANI/SOPS electrode exhibits a higher specific capacitance of 1810 F g−1, faster oxidation/reduction at high current changes and better cyclic stability, which is attributed to the nano-architecture of the electrode materials and the support of the SOPS nanoparticles. This result suggests that the construction of the porous and ordered hierarchical nanostructure is a novel and effective way for improving the electrochemical properties of conducting polymers.

Preparation of Ionic Silsesquioxanes with Regular Structures and Their Hybridization

This paper deals with our recent studies on the preparation of ionic silsesquioxanes (SQs) with regular structures. Cationic ladder-like polySQs (PSQs) with hexagonally stacked structures were successfully prepared by the sol-gel reactions of amino group-containing organotrialkoxysilanes in strong acid aqueous solutions. Self-organization of an ion pair (a salt) prepared from the amino group in the organotrialkoxysilane and an acid is the key factor for the formation of such regular structures of the PSQs. It is also reported that the control of the conformational structure of the PSQs was performed by the introduction of the chiral moieties. In addition, we investigated the correlation between the of acid-catalysts and the structures of SQs prepared by the hydrolytic condensation of amino group-containing organotrialkoxysilane, that is, the use of the superacid aqueous solution resulted in the formation of cage-like octaSQ, while the ladder-like PSQs with hexagonally stacked structures were formed from the strong acid aqueous solutions under the same reaction conditions. Furthermore, anion-exchange behaviors of the cationic ladder-like PSQ were investigated with various organic and inorganic compounds, such as anionic surfactants, a polymer, and layered clay minerals, to obtain the functional hybrid materials.

Quaternary ammonium salt substituted polyhedral oligosilsesquioxanes (POSSes) as structure directing agents in the generation of porous silica materials

AbstractThe sol-gel base catalysed hydrolytic polycondensations of tetramethoxysilane (TMOS) were studied in the presence of quaternary ammonium chloride substituted polyhedral oligosilsesquioxanes (POSSes): octa{3-[(2- hydroxyethyl)dimethylammonio]propyl chloride}octasilsesquioxane or octa[3-(noctyldimethylammonio) propyl chloride]octasilsesquioxane. Small amounts of these POSSes added to the sol-gel system markedly affected the morphology of the silica gel polycondensation products. The morphology was highly dependent on the POSS concentration. Amorphous mesoporous silica gels were obtained showing a high porosity and the surface area up to 615 m2g-1. Most of gels had a fairly large average pore diameters, 4-11 nm and pore volume 0.4-1.3 cm3g-1. TMOS having inserted hexamethyltrisiloxane chain, 1,1,1,7-tetramethoxyhexamethyltetra siloxane, (TMOSD3) in the mixture with TMOS was also used as the monomer in the sol-gel polycondensation; but obtained gels showed a low porosity.

Beads on a Chain (BOC) Polymers Formed from the Reaction of NH2PhSiO1.5]x[PhSiO1.5]10–x and [NH2PhSiO1.5]x[PhSiO1.5]12–x Mixtures (x = 2–4) with the Diglycidyl Ether of Bisphenol A

We recently reported that catalytic amounts of F– cause rapid rearrangement of silsesquioxane (SQ) T8 cages in THF at room temperature. These rearrangements lead primarily to the T10 and T12 cages as long as the F– is trapped for example using CaCl2 to form insoluble CaF2 in situ. In this report, we use this approach to make di- and triaminophenyl, phenyl silsesquioxane T10 and T12 mixtures: (NH2Ph)2xPh10/12–x(SiO1.5)10/12. Thereafter, we isolate the fraction that consists primarily of x = 2–3 via column chromatography. We then explore the reaction of this fraction (fraction 3) with the diglycidyl ether of bisphenol A (DGEBA) to form a soluble epoxy resin wherein the cage SQs are contained in the chain backbone. We call these products beads on a chain (BoC) polymers. The use of 1:1 mole ratios of [epoxide]:[NH2Ph] of DGEBA and (NH2Ph)2xPh10/12–x(SiO1.5)10/12 leads to insoluble products. However, the reaction of 0.8:1 mole ratio of [epoxide]:[NH2Ph] provides a soluble but bimodal distribution of products (after 24 h reaction at 90 °C in THF). The low MW component is much more soluble in THF than the higher MW component, allowing simple separation. The low MW polymer has a Mn of 6000 Da with a PDI of 1.6. The higher MW material has an Mn of 21 000 000 Da with a PDI of 21. Both components offer similar ceramic yields (to SiO2) of 32 ± 1%, indicating that the relative contents of cages are identical. They also exhibit very similar FTIR spectra, suggesting that they are the same material. Two explanations are possible for the bimodal size distribution. One is that the positioning of the NH2 groups on the cage leads to cyclic trimers given that the average monomer unit will mass ≈1700–1900 Da, which represents the low MW fraction. Alternately and more likely, the higher molecular weight component consists of di- and triamino functionalities such that in the growing chain, once the first two amine groups on the cage react, the third group is likely sterically protected. Thus, only late in the reaction will the quantities of the third group exceed those of the diamino components, allowing a slow tertiary functionalization and likely some degree of cross-linking (or internal cyclization) to occur. That this happens is suggested by the much poorer solubility of the higher MW materials as well as the very large PDI. These studies serve as a model for other possible studies targeting BoC polymers.

Polymer nanocomposite coatings based on polyhedral oligosilsesquioxanes: route for industrial manufacturing and barrier properties

A route to a large variety of functionalized POSS compounds by a two-step procedure has been developed. Up-scaling to high volume industrial applications is feasible. In the first step, an amino-functionalized silane such as 3-aminopropyltriethoxy silane is converted to amino-functionalized POSS (amine-POSS) by a sol–gel process. In the second step, the amine groups of amine-POSS are converted by state-of-the-art amine chemistry. A large number of reactants including carboxylic acids, esters, anhydrides, isocyanates, carbonates, epoxides, and acrylates as well as reactants suitable for nucleophilic substitution can be applied. Conversion of an amine-POSS with hexanoic acid leads to an amide-POSS. Amine chemistry can usually be performed under mild conditions, which suppresses degradation and/or cross-linking reactions of the amine-POSS during the conversion. MALDI-TOF mass spectroscopy and dynamic light scattering (particle size: 3–6 nm) have been applied to prove the conversion of an amine-POSS to an amide-POSS. 1H-NMR and TGA-MS prove the presence of amide-POSS and its thermal stability. Gas barrier properties of nanocomposite coatings based on functionalized POSS are characterized.

Characterization and diffusion behavior of chitosan–poss composite membranes

AbstractFour types of polyhedral oligosilsesquioxanes (POSS) were incorporated into chitosan by solution blending to fabricate composite membranes. The thermal stability of the composite membranes was improved compared with the neat chitosan membrane. For the mechanical properties, the stiffness of the composite membranes was weakened by the presence of POSS. However, the effects of POSS on the strength and elongation at break of the composite membranes depended on the type of POSS incorporated. Hydrophilic POSS increased the ductility of the composite membranes and maintained their strength, while hydrophobic POSS made the membranes more brittle and less rigid compared with the neat chitosan membranes. These significant differences were due to the different compatibility and interfacial adhesion between POSS and chitosan. The permeation of sodium chloride and riboflavin in the composite membranes was also influenced by the type and content of POSS in the membranes. Composite membranes containing hydrophilic POSS showed higher partition coefficients but lower diffusion coefficients of riboflavin, compared with the composite membranes containing hydrophobic POSS. This indicates that the transport of riboflavin is retarded by the interactions between riboflavin and the membrane. This study suggests that the structure and physical properties of chitosan membrane can be modified by the incorporation of a small amount of POSS molecules. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011

Poly(L-Lactide) Composite Nanofibers Incorporating POSS-MWNTs

We report the electrospun poly(L-lactide) (PLA) nanofibers incorporating polyhedral oligosilsesquioxane (POSS)-modified multiwalled carbon nanotubes (MWNTs). FT-IR, transmission electron microscopy (TEM) and Raman analysis confirmed the existence of POSS macromers bonded to the MWNTs as an extra phase. The thermal and microstructure properties of the PLA hybrid nanofibers with POSS-modified MWNTs were investigated by thermogravimetric analysis (TGA) and Wide-angle X-ray diffraction (WAXD).

Self-Assembled Core-Shell Poly(ethylene glycol)-POSS Nanocarriers for Drug Delivery

In this work, novel nanostructured core-shell poly(ethylene glycol) (PEG)-polyhedral oligosilsesquioxane (POSS) nanoparticles were used to encapsulate insulin as new drug delivery carriers. The morphologies, particle size and ζ potential of the pure nanostructured core-shell PEG-POSS and the corresponding insulin-loaded PEG-POSS nanoparticles were investigated by transmission electron microscopy (TEM) and laser diffraction particle sizer. TEM analysis demonstrated that pure and insulin-loaded self-assembled PEG-POSS nanoparticles were of spherical shape with core-shell nanostructure, and were well-dispersed and uniform in size distribution. Insulin release test showed that insulin was well-protected inside PEG-POSS nanoparticles at gastric pH for 2hrs, and was released at intestinal pH (pH 6-7) where the absorption and activation of the drug are necessary. We therefore believe that such nanostructured PEG-POSS nanoparticles could be useful as a potential carrier for insulin drug delivery systems.

Pervaporation performance of novel chitosan‐POSS hybrid membranes: Effects of POSS and operating conditions

AbstractFour types of polyhedral oligosilsesquioxane (POSS)–octaanion, octaammonium, octanitrophenyl, and octaaminophenyl–were incorporated into chitosan (CS) to fabricate inorganic–organic hybrid membranes. The hybrid membranes were employed for the pervaporation dehydration of ethanol aqueous solutions. The performance of the hybrid membranes was found to be influenced by the type and loading amount of POSS. In comparison with the neat CS membranes which showed a separation factor of 65.2 for 10 wt % water in the feed at 303 K, the hybrid membranes containing 5 wt % of octaanion and octaaminophenyl POSS showed high separation factors of 305.6 and 373.3, respectively. The effects of the operating conditions such as the feed composition and temperature on the pervaporation performance of the membranes were investigated. Activation energies for permeation in the membranes were estimated from Arrhenius relationship. The activation energies for ethanol permeation in the hybrid membranes were much higher than that in the CS membrane, which may account for the large enhancements in the selectivity of the hybrid membranes. © 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2010

Blends of Paclitaxel with POSS-Based Biodegradable Polyurethanes: Morphology, Miscibility, and Specific Interactions

The morphology, miscibility, and specific interactions of paclitaxel (PTx) with a family of polyhedral oligosilsesquioxane (POSS)-based biodegradable thermoplastic polyurethanes (POSS TPUs) were investigated systematically using wide-angle X-ray diffraction (WAXD), differential scanning calorimetry (DSC), and Fourier transform infrared spectroscopy (FTIR). These POSS TPUs incorporate an alternating multiblock structure formed by POSS hard segments and the soft segments composed of polylactide/caprolactone copolymer (P(DLLA-co-CL)). They feature variable poly(ethylene glycol) (PEG) content from 0 to 14 wt % through adjusting the poly(ethylene glycol) (PEG) molecular weight in P(DLLA-co-CL) soft segments of fixed molar mass of Mn = 12 kg/mol and further to 52 wt % utilizing pure PEG Mn = 1 kg/mol in the soft segments. Using WAXD, it was found that PTx is amorphous in all proportions in the PTx/POSS TPU blends prepared using a solution-casting method. Interestingly, the PTx not only exhibits excellent misc...

In vivo kinetic degradation analysis and biocompatibility of aliphatic polyester polyurethanes

Polyester polyurethanes incorporating polyhedral oligosilsesquioxane (POSS) as the crystalline hard block were evaluated for biocompatibility and degradation over 24 weeks in vivo. In vitro studies were also used to predict the onset of mass loss. The molecular weight of each sample was found to decrease quickly over an 8 week period and then became constant due to the nondegrading POSS hard block. Kinetic analysis of the initial molecular weight change indicated that the degradation rate was dependent on the soft block composition. Crystallinity, melting temperature, and heat of fusion of the polyurethanes were found to increase during degradation as the amorphous polyester soft segments were hydrolyzed. The histological analysis of each polymer demonstrated rapid resolution of the acute and chronic inflammatory responses and the development of expected, normal foreign body reaction, consisting of adherent macrophages and foreign body giant cells on the surface of the polymers, and fibrous capsule formation around the polymer. No acute and/or chronic inflammation was seen after 3 weeks, indicating that the polymers in film form and biodegraded form, that is, particles, were biocompatible and did not elicit inflammatory responses expected for toxic or nonbiocompatible materials.

Generation of 3-Chloropropylsilanetriol: Monomer for the Synthesis of 3-Chloropropyl Substituted Oligosilsesquioxanes

Controlled hydrolysis of 3-chloropropyltrimethoxysilane in water or in methanol–water (1:1 or 1:2 V/V) mixture in a slightly acidic system followed by solvent evaporation under reduced pressure leads to crystalline 3-chloropropylsilanetriol containing 5–10%, of the self-condensation dimer, 1,3-di(3-chloropropyl)1,1,3,3-tetrahydroxydisiloxane. Polycondensation of 3-chloropropylsilanetriol may be used for synthesis of polyhedral oligosilsesquioxanes bearing the chloropropyl group.

Synthesis, Self-assembly, and Crystal Structure of a Shape-Persistent Polyhedral-Oligosilsesquioxane-Nanoparticle-Tethered Perylene Diimide

A novel organic−inorganic hybrid with two polyhedral oligosilsesquioxane (POSS) nanoparticles covalently attached to perylene diimide (PDI) via a rigid 1,4-phenylene linkage (POSS-PDI-POSS) was designed and synthesized to examine the effect of bulky and well-defined nanoparticle side chains on the self-assembly behavior of PDI derivatives. The molecules were self-assembled directly by slow evaporation of a cast drop from solution in tetrahydrofuran to give rise to uniform crystalline nanobelts with dimensions typically of 0.2 mm × 1 μm × 50 nm. The phase behavior and crystal structure of the sample were then elucidated via a combination of different experimental techniques such as differential scanning calorimetry (DSC), wide-angle X-ray diffraction (WAXD), selected area electron diffraction (SAED) in transmission electron microscopy (TEM), polarized light microscopy, and atomic force microscopy. One-dimensional (1D) WAXD and DSC revealed that only one crystalline phase exists. Based on the 2D WAXD fiber ...

Fluoride Rearrangement Reactions of Polyphenyl- and Polyvinylsilsesquioxanes as a Facile Route to Mixed Functional Phenyl, Vinyl T10and T12Silsesquioxanes

Polyphenylsilsesquioxane [PhSiO(1.5)](n) (PPS) and polyvinylsilsesquioxane [vinylSiO(1.5)](n) (PVS) are polymeric byproducts of the syntheses of the related T(8) octamers [PhSiO(1.5)](8) and [vinylSiO(1.5)](8). Here we demonstrate that random-structured PPS and PVS rearrange in the presence of catalytic amounts of Bu(4)N(+)F(-) in THF to form mixed-functionality polyhedral T(10) and T(12) silsesquioxane (SQ) cages in 80-90% yields. Through control of the initial ratio of starting materials, we can statistically tailor the average values for x for the vinyl(x)Ph(10-x)T(10) and vinyl(x)Ph(12-x)T(12) products. Metathetical coupling of x approximately = 2 vinyl cages with 4-bromostyrene produces SQs with an average of two 4-bromostyrenyl substituents. These products can be reacted via Heck coupling with vinylSi(OEt)(3) to produce SQs with vinylSi(OEt)(3) end-caps. Alternately, Heck coupling with the originally produced x approximately = 2 vinyl SQs leads to "beads on a chain" SQ oligomers joined by conjugated organic tethers. The functionalized T(10) and T(12) cages, metathesis, and Heck compounds were characterized by standard analytical methods (MALDI-TOF MS, (1)H and (13)C NMR spectroscopy, TGA, and GPC). MALDI confirms the elaboration of the cages after each synthetic step, and GPC verifies the presence of higher molecular weight SQ oligomers. TGA shows that all of these compounds are thermally stable in air (>300 degrees C). The UV-vis absorption and emission behavior of the Heck oligomers reveals exceptional red-shifts (> or = 60 nm) compared to the vinylSi(OEt)(3) end-capped model compounds, suggesting electronic interactions through the SQ silica cores. Such phenomena may imply 3-D conjugation through the cores themselves.

Water-Resistant Poly(Vinyl Alcohol) Hybrid Nanofibers Incorporating Polyhedral Oligosilsesquioxane (POSS)

We have explored a straightforward approach for achieving water-resistant properties of the electrospun PVA nanofibers. The electrospun PVA nanofibers are post-treated with a hydrophobic polyhedral oligosilsesquioxane (POSS) hybrid macromer via a direct urethane reaction between the hydroxyl group of PVA and the isocyanate group of POSS macromers. The POSS-modified PVA nanofibers are characterized by fourier transform infrared spectroscopy (FT-IR), scanning electron microscopy (SEM), thermogravimetric analysis (TGA), and water resistant property. The morphologies of the electrospun PVA nanofibers before and after POSS post-treatments are regular and a narrow distribution of diameters was observed, indicating a uniform post-treatment of POSS macromers onto the PVA nanofibers. Thermal decomposition behavior of the POSS-modified PVA nanofibers was altered compared to the pure PVA nanofibers, suggesting the suppression of thermal decomposition due to the incorporation of POSS macromers. In addition, the pure PVA nanofiber mats immersed in pure water exhibited no characteristic morphology, whereas the POSS-modified PVA nanofiber mats showed the texture morphology, indicating an enhanced water-resistant property.

Reactivity, viscoelastic behaviour and mechanical performances of hybrid systems based on epoxy resins and reactive polyhedral oligosilsesquioxanes

An epoxy formulation was modified by adding various amounts of an epoxy functionalized polyhedral oligomeric silsesquioxane (POSS). The obtained networks were characterized in terms of reactivity, viscoelastic behaviour and mechanical properties. Spectroscopy measurements by FT-NIR demonstrated that the epoxy groups of POSS were almost as reactive as those of the DGEBA in the curing stage, while in the post-curing a lower reactivity of the latter was found, possibly due to steric hindrance effects. The dynamic-mechanical analysis showed an increase in the storage modulus in both glassy and rubbery regions. On the other hand, Tg and Tβ decreased with POSS content. The viscoelastic analysis showed that the addition of POSS enhanced the free volume and the tendency of the network to undergo thermal expansion. In particular, the β transition was made increasingly localized by increasing the POSS content. With respect to mechanical performances, the yield process was facilitated by incorporation of the POSS nanocages within the network, possibly due to an enhancement of the chain mobility. Fracture measurements showed an improvement of the parameters Kc and Gc up to 5wt% of POSS, after which a decrease of toughness was observed. These results were supported by a fractographic analysis.

Antimicrobial Properties of Nanostructured Hydrogel Webs Containing Silver

The need exists for biomaterials that prevent biofilm formation and associated infections. In this report, we have studied the synthesis, processing, and antimicrobial behavior of new silver-containing thermoplastic hydrogel nanofibrous webs. Thermoplastic hydrogels were synthesized from multiblock PEG-POSS polyurethanes (PEG: poly(ethylene gylcol); POSS: polyhedral oligosilsesquioxane) and electrospun into nanofibrous webs (diameter approximately 150 nm), with or without AgNO(3). The nanofibrous hydrogels exhibited unusual shrinkage during water uptake, yielding a uniquely dense structure compared to hydrogels prepared from cast films. Antimicrobial activity was examined using exposure to Escherichia coli with daily refreshment of medium and inoculation to a controlled cell density. Nanofibrous hydrogels without silver featured the most rapid and most extensive biofilm formation, while the silver-containing nanofibrous hydrogel featured outstanding biofilm resistance, with biofilm formation taking hold only after 14 days of incubation in daily refreshed bacterial cultures. We envision application of the unique antimicrobial hydrogels as wound dressings that combine sustained bactericidal properties and lack of volumetric swelling during water uptake.