Elastic Sponges Research Articles

Superamphiphobic, Magnetic, and Elastic Silicone Sponges with Excellent Temperature Stability

It is very challenging to create bioinspired superamphiphobic 3D porous materials that resist wetting of organic liquids with low surface tension. Here, preparation of superamphiphobic, magnetic, and elastic (SAME) silicone sponges is reported with excellent temperature stability. The SAME silicone sponges are prepared by hydrolytic condensation of methyltrimethoxysilane and dimethoxydimethylsilane in the presence of urea, n‐hexadecyltrimethyl ammonium bromide, and the Fe3O4@SiO2 nanoparticles, followed by surface modification with 1H,1H,2H,2H‐perfluorodecyltriethoxysilane (PFDTES) and tetraethoxysilane (TEOS). The SAME silicone sponges are characterized using a wide range of analytical techniques including scanning electron microscopy, X‐ray photoelectron spectroscopy, and thermal gravimetric analysis. It is found that the wettability of the SAME silicone sponges can be controllable simply by regulating their surface topography and surface chemical composition, in other words, the volume ratio of PFDTES and TEOS. The residual silanol groups on the pore surface of the silicone sponge act as the active sites for the hydrolytic condensation of PFDTES and TEOS. The SAME silicone sponges feature excellent superamphiphobicity for water and various organic liquids of low surface tension, fast magnetic responsiveness, high compressibility (90%), and stretchability (35%) as well as high stability in a wide range of temperature (−196–300 °C).

Electrochemical cathodic deposition of hydroxyapatite: Improvements in adhesion and crystallinity

To improve on the biological performance of titanium and its alloys hydroxyapatite coatings are applied to the surface. Although plasma spraying is currently the clinically accepted deposition technique, it has drawbacks including being a line-of-site method which greatly limits its uses for coating either irregular-shapes or the low elastic moduli porous materials and metallic sponges now being developed for implants. Electrochemical cathodic deposition is an alternative technique but this also has disadvantages, mainly the crystallinity of the deposited hydroxyapatite and its adhesion to the substrate. In the present study it is demonstrated that increased adhesion and crystallinity are obtained by either pre-treating the Ti substrate with NaOH followed by a heat treatment at 600 °C or the addition of H 2O 2 to the electrolyte. The increased adhesion is believed to result in the former case from the development of a titanate binding layer. In the latter case the local alkaline conditions required for deposition are obtained from the reduction of the peroxide, thereby negating the need to evolve hydrogen that can damage the film. Rotating the substrate at low revolutions is also beneficial for adhesion however; at high rotation rates bulk precipitation is favoured over film formation.

Carbopol gels: Elastoviscoplastic and slippery glasses made of individual swollen sponges: Meso- and macroscopic properties, constitutive equations and scaling laws

This paper gives details of new data on neutralized Carbopol 940 dispersions. Appropriate techniques have been used to characterize the physical properties of the bulk gel and inter-phase slip at the wall. Previously published data are analysed and used wherever possible. Terminology and measurement difficulties are also addressed. The structure of Carbopol dispersions can be described in terms of polydisperse glasses made of individual swollen hydrophylic elastic sponges. They display elastoplasticity, and significant dissipation both below and above their yield stress. Hardly any creep was observed over 10 months of experiments. Scaling laws are proposed for Carbopol mechanical properties as a function of concentration. Carbopol behaviour varies with the value of concentration, and in particular when comparing percolation concentration with close-packing concentration. Constitutive equations for bulk shear stresses and for friction slip at the wall can be deduced from contact mechanics which fit rheometry data and scaling laws. Herschel–Bulkley constitutive equations may be used by ignoring elasticity, normal shear stresses and transients.

Synthetic elastin hydrogels derived from massive elastic assemblies of self-organized human protein monomers

A key objective of bioengineering is the development of new scaffolding biomaterials with appropriate mechanical and biological properties such as strength, elasticity and biocompatibility that mimic the native host connective tissue. Here we describe the production and properties of massive synthetic elastin assemblies formed by chemically cross-linking recombinant human tropoelastin with bis(sulfosuccinimidyl) suberate, permitting the construction of elastic sponges, sheets and tubes. The innate characteristics of synthetic elastin constructs are common with those of native elastin. The Young's Modulus ranged from 220 to 280 kPa with linearity of extension to at least 150%. Synthetic elastin was extensible by 200–370%. The constructs behaved as hydrogels and displayed stimuli-responsive characteristics towards temperature and salt concentrations. Intrinsic fluorescence spectroscopy demonstrated that the elastin fluorophore is a feature of the polypeptide. Scanning electron microscopy allowed us to construct a model of elastin assembly that was driven by the lateral association of small twisted rope-like fibrils. FT–Raman spectra at 100% strain gave amide I and III peaks that correlated with a stretch-dependent increase in α-helical content. Growth and proliferation of cells were supported in vitro while in vivo implants were well tolerated. We conclude that synthetic elastin has potential as a novel biomaterial that can be easily molded into a variety of shaped tissue substrates and has a range of properties that are required for elastic, cell-interacting and compliant applications. Furthermore, its in vitro construction provides a powerful tool to probe the early stages of elastin assembly and the molecular basis for its elasticity.

Optimization of Biodegradable Sponges as Controlled Release Drug Matrices. I. Effect of Moisture Level on Chitosan Sponge Mechanical Properties

Cross‐linked chitosan sponges as controlled release drug carrier systems were developed. Tramadol hydrochloride, a centrally acting analgesic, was used as a model drug. The sponges were prepared by freeze‐drying 1.25% and 2.5% (w/w) high and low M.wt. chitosan solutions, respectively, using glutaraldehyde as a cross‐linking agent. The hardness of the prepared sponges was a function of glutaraldehyde concentration and volume where the optimum concentration that offered accepted sponge consistency was 5%. Below or above 5%, very soft or very hard and brittle sponges were obtained, respectively. The determined drug content in the prepared sponges was uniform and did not deviate markedly from the calculated amount. Scanning electron microscopy (SEM) was used to characterize the internal structures of the sponges. The SEM photos revealed that cross‐linked high M.wt. chitosan sponges have larger size surface pores that form connections (channels) with the interior of the sponge than cross‐linked low M.wt. ones. Moreover, crystals of the incorporated Tramadol hydrochloride were detected on the lamellae and within pores in both chitosan sponges. Differences in pore size and dissolution medium uptake capacity were crucial factors for the more delayed drug release from cross‐linked low M.wt. chitosan sponges over high M.wt. ones at pH 7.4. Kinetic analysis of the release data using linear regression followed the Higuchi diffusion model over 12 hours. Setting storage conditions at room temperature under 80–92% relative humidity resulted in soft, elastic, and compressible sponges.

Influence of the acid type on the physical and drug liberation properties of chitosan–gelatin sponges

The influence of acid type used to dissolve chitosan on the resulting sponge physical properties, and their consequent effect on the drug liberation were investigated. Chitosan was dissolved in different acid solutions and chitosan–gelatin sponges were produced by frothing up the polymer solution and then freeze-drying the foam. Prednisolone was used as a model drug. Using tartaric or citric acid resulted in instable, soft, elastic and disintegrating sponges with fast drug release. Elastic but harder sponges from stable foams were obtained when hydrochloric or lactic acid were used. The use of acetic or formic acid enabled the production of stable foams, soft and elastic sponges and a slow drug release. The rate of drug release was decreased by crosslinking the polymers with glutaraldehyde, but only if acetic, formic or acetic acid were used. Therefore, it is possible to manipulate the mechanical properties and the drug liberation rate by using different acids to dissolve chitosan.

Sponge-inhabiting barnacles on Red Sea coral reefs

In this study eight different species of barnacles were found within nine species of sponges from the Red Sea. This brings to 11 the number of sponge-symbiotic barnacles reported from the Red Sea, two of these are new Acasta species (not described herein) and one (A. tzetlini Kolbasov) is a new record for this sea. This number is much higher than that of symbiotic barnacles found within sponges from either the N. Atlantic (2) or the Mediterranean (4). Two possible explanations for this are the presence of numerous predators in coral reefs and scarcity of available substrate for settlement. These factors can lead to high incidence of symbiotic relationships. Of the nine sponge species, only one (Suberites cf. clavatus) had previously been known to contain barnacles. Even at the family level, this is the first record of symbiotic barnacles in two out of the seven sponge families (Latrunculiidae, Theonellidae). Our present findings strengthen the apparent rule that the wider the openings in a barnacle shell, the fewer the host taxa with which it will associate, usually from one or two closely related families, and the more frequent it will associate with elastic sponges. Most Neoacasta laevigata found on Carteriospongia foliascens were located on the same side as the sponge's ostia, i.e. facing the incoming water. This adaptation allows the barnacles to catch more suspended particles from the water, provides them with more oxygen and prevents their exposure to discharged sponge waste. The highest density of barnacles observed on one face of a “leaf ” (with ostia) was 0.389 barnacles cm−2 (one barnacle per 2.57 cm2) and on average 0.181 ± 0.68, while the average on the other side was only 0.068 ± 0.52 barnacles cm−2. As indicated by the Morisita index, these barnacles most frequently (58%, n = 12) had a clumped spatial distribution (while the rest were randomly distributed), as is to be expected from such sessile organisms with internal fertilization via copulation. The presence of N. laevigata induced the growth of secondary perpendicular projections of its host C. foliascens. Of the N. laevigata examined, 17% brooded 324 ± 41 embryos each, of 286 ± 17 μm total length; only 5.7% (n = 123) were found to be dead. Size distribution analysis of skeletal elements from dead barnacles showed them to be significantly larger than the skeletal elements of the population of live barnacles ( p < 0.05).