Silk Fibroin-Based Shape-Memory Organohydrogels with Semicrystalline Microinclusions.

Inspired by nature, we designed organohydrogels (OHGs) consisting of a silk fibroin (SF) hydrogel as the continuous phase and the hydrophobic microinclusions based on semicrystalline poly(n-octadecyl acrylate) (PC18A) as the dispersed phase. SF acts as a self-emulsifier to obtain oil-in-water emulsions, and hence, it is a versatile and green alternative to chemical emulsifiers. We first prepared a stable oil-in-water emulsion without an external emulsifier by dispersing the n-octadecyl acrylate (C18A) monomer in an aqueous SF solution. To stabilize the emulsions for longer times, gelation in the continuous SF phase was induced by the addition of ethanol, which is known to trigger the conformational transition in SF from random coil to ß-sheet structures. In the second step, in situ polymerization of C18A droplets in the emulsion system was conducted under UV light in the presence of a photoinitiator to obtain high-strength OHGs with shape-memory function, and good cytocompatibility. The incorporation of hydrophilic N,N-dimethylacrylamide and noncrystallizable hydrophobic lauryl methacrylate units in the hydrogel and organogel phases of OHGs, respectively, further improved their mechanical and shape-memory properties. The shape-memory OHGs presented here exhibit switchable viscoelasticity and mechanics, a high Young's modulus (up to 4.3 ± 0.1 MPa), compressive strength (up to 2.5 ± 0.1 MPa), and toughness (up to 0.68 MPa).

Performance of butyl rubber-based macroporous sorbents as passive samplers.

In this study, two macroporous butyl rubber (BR)-based sorbents prepared in benzene (H-BR) and in cyclohexane (L-BR) with different porosities were synthesized by cryogelation technique. Their performances as a passive sampler were studied and then compared with commercially available silicon rubber (polydimethylsiloxane, PDMS) passive sampler. For that aim, polycyclic aromatic hydrocarbon (PAH) absorption rates of the sorbents in the short-term and their accumulation capacities in the long-term periods were investigated. Four PAHs (naphthalene, phenanthrene, fluoranthene, and pyrene) with a different number of aromatic rings were utilized. The concentrations of the PAHs in solutions were quantified by fluorescence spectrophotometer. The results showed that the BR sampler prepared in benzene (H-BR) generally has the highest absorption rates for all PAHs. The rate constants k (h-1) of the H-BR, L-BR, and PDMS samplers were found as 1.07, 0.55, and 0.55 for naphthalene; 0.73, 0.16, and 0.09 for phenanthrene; 0.24, 0.26, and 0.08 for fluoranthene; and 0.97, 0.38, and 0.17 for pyrene, respectively. The highest PAH absorption capacity was found for the BR sorbents prepared in benzene for all PAHs. Thus, benzene was selected as the organic solvent rather than cyclohexane for further studies in the preparation of butyl rubber-based samplers. The H-BR possessing the highest absorption rate and capacity underlines their usage as a capable passive sampler for both short- and long-term monitoring activities in the aquatic environments.

Single-, Double-, and Triple-Network Macroporous Rubbers as a Passive Sampler.

Over the past decades, large quantities of organic compounds including polycyclic aromatic hydrocarbons (PAHs) entering aquatic systems create acutely toxic effects and chronic abnormalities in aquatic organisms. Passive sampling is an effective technique to detect organic compounds at very low concentrations in water by accumulating them in their structure to a measurable concentration level. Polymeric passive samplers reported so far have a nonporous structure, and hence, the absorption of organic compounds into the passive sampler is governed by their slow diffusion process. We present here novel macroporous rubber sorbents as monophasic passive samplers with tunable pore morphologies, extraordinary mechanical properties, and high sorption rates and capacities for PAHs. Sorbent materials based on single-network (SN), double-network (DN), and triple-network (TN) butyl rubber were prepared via the cryogelation technique from butyl rubber solutions in benzene as the solvent at -18 °C using a sulfur monochloride cross-linker. To obtain macroporous rubbers with DN and TN structures, the reactions were conducted in the macropores of SN and DN rubber networks, respectively. The porous morphology and the mechanical behavior of the rubbers can be tuned by adjusting the weight ratio wR of the network components. The rubbers exhibit two generations of pores, namely, large and small pores with diameters 40-240 and 14-54 µm, respectively. The sizes of both large and small pores decrease and approach each other as wR is increased. Four PAH compounds, namely, naphthalene, phenanthrene, fluoranthene, and pyrene with two to four aromatic rings, dissolved in filtered seawater with a salinity of 22 ppt were used to highlight the correlations between the properties of macroporous rubbers and their absorption rates and capacities. Nonporous silicone rubber reported before as a passive sampler has the lowest absorption rate and capacity as compared to the macroporous rubbers. The SN rubber absorbs most rapidly PAHs because of its largest porosity, whereas the TN rubber with the smallest pores exhibits the highest sorption capacity.

Cryogel composites based on hyaluronic acid and halloysite nanotubes as scaffold for tissue engineering.

We present here preparation of mechanically strong and biocompatible cryogel composites based on hyaluronic acid (HA) and halloysite nanotubes (HNTs) of various compositions, and their applications as scaffold for different cell growing media. Uniaxial compression tests reveal that the incorporation of HNTs into HA cryogels leads to a ~2.5-fold increase in their Young moduli, e.g., from 38 ±â€¯1 to 99 ±â€¯4 kPa at a HA:HNTs weight ratio of 1:2. Although HA:HNTs based cryogels were found to be blood compatible with 1.37 ±â€¯0.11% hemolysis ratio at a HA:HNTs weight ratio of 1:2, they trigger thrombogenic activity with a blood clotting index of 17.3 ±â€¯4.8. Remarkably, HA:HNTs cryogel composites were found to be excellent scaffold materials in the proliferation of rat mesenchymal stem cells (MSC), human cervical carcinoma cells (HeLa), and human colon cancer cells (HCT116). The cell studies revealed that an increased amount of HNT embedding into HA cryogels leads to an increase of MSC proliferation.

Highly Stretchable and Rapid Self-Recoverable Cryogels Based on Butyl Rubber as Reusable Sorbent.

Cryogels based on hydrophobic polymers combining good mechanical properties with fast responsivity are attractive materials for many applications, such as oil spill removal from water and passive sampler for organic pollutants. We present, here, cryogels based on butyl rubber (BR) with a high stretchability, rapid self-recoverability, and excellent reusability for organic solvents. BR cryogels were prepared at subzero temperatures in cyclohexane and benzene at various BR concentrations in the presence of sulfur monochloride (S2Cl2) as a crosslinker. Although the properties of BR cryogels are independent of the amount of the crosslinker above a critical value, the type of the solvent, the cryogelation temperature, as well as the rubber content significantly affect their properties. It was found that benzene produces larger pore volumes as compared to cyclohexane due to the phase separation of BR from benzene at low temperatures, producing additional pores. Increasing cryogelation temperature from -18 to -2 °C leads to the formation of more ordered and aligned pores in the cryogels. Increasing BR content decreases the amount of unfrozen microphase of the frozen reaction solution, leading to a decrease in the total porosity of the cryogels and the average diameter of pores. Cryogels formed at -2 °C and at 5% (w/v) BR in cyclohexane sustain up to around 1400% stretch ratios. Cryogels swollen in toluene can completely be squeezed under strain during which toluene is released from their pores, whereas addition of toluene to the squeezed cryogels leads to recovery of their original shapes.

High-strength and self-recoverable silk fibroin cryogels with anisotropic swelling and mechanical properties.

Creating mechanically strong macroporous hydrogels with anisotropic properties as observed in many biological tissues is a major challenge in the gel science. Here we describe a directional freezing/cryogelation method of producing high-strength and rapid self-recoverable silk fibroin scaffolds with a high degree of mechanical anisotropy similar to that of tendon. By adjusting the synthesis parameters, we were able to create fibroin scaffolds exhibiting the highest modulus anisotropy so far reported, 21 ±â€¯5, with moduli E = 2.3 ±â€¯0.5 and 0.11 ±â€¯0.03 MPa measured along parallel and perpendicular to the freezing direction, respectively. The cryogels are squeezable under load whereas, upon unloading, the squeezed-out water is taken back immediately. It was shown that the squeezability of the cryogels results in significant viscous stresses and energy dissipation. Cyclic mechanical tests reveal that the friction between the fibroin pore walls is the primary factor responsible for the energy dissipation. Independent on the fibroin concentration or direction of the measurements, 60% of the mechanical energy given to the cryogels are dissipated due to the friction between the pore walls, which is responsible for their almost complete squeezability and self-recoverability.