Biocompatible and biodegradable porous scaffolds with adjustable pore structure have aroused increasing interest in bone tissue engineering. Here, we report a facile method to fabricate hierarchical ...macroporous biocompatible (HmPB) scaffolds by combining Pickering high internal phase emulsion (HIPE) templates with three-dimensional (3D) printing. HmPB scaffolds composed of a polymer matrix of poly(l-lactic acid), PLLA, and poly(ε-caprolactone), PCL, are readily fabricated by solvent evaporation of 3D printed Pickering HIPEs which are stabilized by hydrophobically modified silica nanoparticles (h-SiO2). The pore structure of HmPB scaffolds is easily tailored to be similar to natural extracellular matrix (ECM) by varying the fabrication conditions of the Pickering emulsion or adjusting the printing parameters. In addition, in vivo drug release studies which employ enrofloxacin (ENR) as a model drug indicate the potential of HmPB scaffolds as a drug carrier. Furthermore, in vivo cell culture assays prove that HmPB scaffolds that possess good biocompatibility as mouse bone mesenchymal stem cells (mBMSCs) can adhere and proliferate well on them. All the results suggest that HmPB scaffolds hold great potential in bone tissue engineering applications.
Display omitted
Bioactive and biocompatible scaffolds possessing hierarchical porous structures and tunable multi-functional performance have attracted increasing interest in the biomedical field, ...especially in bone tissue engineering. In this work, we report a convenient and effective approach to construct bioactive nanoparticle/poly(ε-caprolactone) (BNPCL) scaffolds with hierarchical porous structures based on solvent evaporation of 3D printed water-in-oil high internal phase emulsion (HIPE) templates, containing hydrophobically modified hydroxyapatite and silica nanoparticles in the oil phase. The hierarchical porous structures consist of mm-scale macropores formed by 3D printing and μm-scale micropores from HIPE templates. The micropore structures and mechanical properties of BNPCL scaffolds are easily tailored by varying the preparation conditions of the HIPE templates. An in vitro biomineralization study shows that BNPCL scaffolds possess excellent bioactivity because of effective formation of apatite particles on them. Moreover, the in vitro drug release studies using ibuprofen display the potential of BNPCL scaffolds as drug carriers. Furthermore, cell culture assays prove that BNPCL scaffolds have good cytocompatibility to effectively support cell adhesion, growth and proliferation. All the results imply that combining solvent evaporation with 3D printing of HIPE templates is a promising alternative approach to fabricate hierarchical porous scaffolds for bone tissue engineering applications.
Novel oil‐in‐water (O/W) emulsions are prepared which are stabilised by a cationic surfactant in combination with similarly charged alumina nanoparticles at concentrations as low as 10−5 m and 10−4 ...wt %, respectively. The surfactant molecules adsorb at the oil‐water interface to reduce the interfacial tension and endow droplets with charge ensuring electrical repulsion between them, whereas the charged particles are dispersed in the aqueous films between droplets retaining thick lamellae, reducing water drainage and hindering flocculation and coalescence of droplets. This stabilization mechanism is universal as it occurs with different oils (alkanes, aromatic hydrocarbons and triglycerides) and in mixtures of anionic surfactant and negatively charged nanoparticles. Further, such emulsions can be switched between stable and unstable by addition of an equimolar amount of oppositely charged surfactant which forms ion pairs with the original surfactant destroying the repulsion between droplets.
Getting Al emulsional: Oil‐in‐water emulsions are prepared which are stabilised by a cationic surfactant in combination with similarly charged alumina nanoparticles at very low concentrations. The stabilisation mechanism is applicable to different oils and is universal for positively charged particles with cationic surfactant and negatively charged particles with anionic surfactant.
Display omitted
•Stable edible oil foams without added foaming agent.•Air bubbles coated by crystals of long-chain, unsaturated triglycerides.•Packing density of crystals at air bubble surfaces in ...oil depends on oil type.•Thermo-responsiveness of oil foams.•Chemical composition of high melting triglyceride crystals.
Can vegetable oils containing long-chain triglycerides be aerated to yield stable oil foams? This is based on the idea that cooling of vegetable oil results in the formation of crystals of certain triglyceride chain lengths and composition dispersed in liquid oil of other chain lengths and composition. Do such oleogels allow the formation of oil foams stabilised by adsorbed crystals?
Using two vegetable oils, the temperatures for crystal formation are determined. Crystal dispersions were characterised using rheology and optical microscopy. Oleogels were aerated using a double beater and the effects of temperature and aeration time were investigated. The stability and microstructure of the oil foams were studied visually and using microscopy. A stable oil foam was progressively destabilised on heating.
Upon cooling/warming vegetable oils, crystals of high melting triglyceride form in a low melting liquid oil - an oleogel. Such oleogels can be whipped to fabricate oil foams stabilised by fat crystals. Optimum foaming yields an over-run of ~ 40% for peanut oil and ~ 110% for olive oil. Oil foams which do not exhibit drainage, coarsening or coalescence result. We show that high melting triglyceride crystals possess a higher fraction of saturated fatty acids than the original oil. Ultra-stable oil foams can be rendered unstable by heating upon approaching the melting point of the crystals.
Incompatible hydrophilic and hydrophobic anti-cancer drugs are co-encapsulated in biomass nanoparticles stabilized HIPPEs and realize synergistic cancer therapy.
Display omitted
The stability of ...anti-cancer drugs and the adverse drug reactions (ADRs) caused by drug-drug interactions (DDIs) are two major challenges of combination chemotherapy. In this work, hydrophilic drug loaded lignin-based nanoparticles were applied to stabilize high internal phase Pickering emulsions (HIPPEs) containing hydrophobic drug in the oil phase, which not only improved the stability of anti-cancer drugs, but also reduced the risk of DDIs.
Highly biocompatible enzymatic hydrolysis lignin/chitosan oligosaccharide (EHL/COS-x) nanoparticles were prepared and used to load hydrophilic cytarabine (Ara-C). The morphology, loading capacity, encapsulation efficiency and emulsifying properties of nanoparticles were characterized and predicted. Subsequently, these nanoparticles were applied to stabilize HIPPEs with soybean oil containing hydrophobic curcumin as dispersed phase. The effects of the morphology, amphipathy and concentration of nanoparticles and oil/water ratio on the microstructure and stability of HIPPEs were investigated. Meanwhile, the controlled release, protective performance, cytotoxicity and bio-activity of HIPPEs were also evaluated.
EHL/COS-x nanoparticles loaded with Ara-C could stabilize HIPEs with 85 vol% soybean oil containing curcumin. The two drugs were separately loaded in same delivery system, which effectively lowered the risk of DDIs. Meanwhile, HIPPEs provided outstanding UV, thermal and oxidation protection for these two environmentally sensitive anti-cancer drugs. In addition, HIPPEs displayed a good pH-responsive release in a tumor environment. In vitro experiments show that the killing efficiency of two drugs co-loaded HIPPEs against the leukemia cell is two times higher than that of single drug loaded systems. This strategy can be extended to the synergistic therapy of two or more drugs with different physicochemical properties.
Sorbitan esters have been extensively used as surfactants to stabilize emulsions in many fields. However, the preparation of an oleofoam with sorbitan ester alone has not been reported. Here, we ...apply a novel protocol to fabricate stable oleofoams of high air volume fraction from mixtures of vegetable oil and sorbitan ester. To incorporate more air bubbles into the oil matrix, aeration is first carried out in the one-phase region at high temperatures, during which the highest over-run can reach 280%. Due to foam instability at high temperatures, the foam is then submitted to rapid cooling, followed by storage at low temperatures. For high-melting sorbitan monostearate, the resulting foams containing many crystal-encased air bubbles are ultrastable to drainage, coarsening, and coalescence for several months. On the contrary, the cooled foams with low-melting sorbitan monooleate go through a gradual decay lasting for more than 1 month. We highlight the importance of hydrogen bond formation between surfactant and oil in enhancing foam stability. The generic nature of the above findings is demonstrated by preparing oil foams with various vegetable oils and sorbitan monooleate.
Colloidal particles act in many ways like surfactant molecules, particularly if adsorbed to a fluid–fluid interface. Just as the water or oil-liking tendency of a surfactant is quantified in terms of ...the hydrophile–lipophile balance (HLB) number, so can that of a spherical particle be described in terms of its wettability via contact angle. Important differences exist, however, between the two types of surface-active material, due in part to the fact that particles are strongly held at interfaces. This review attempts to correlate the behaviour observed in systems containing either particles or surfactant molecules in the areas of adsorption to interfaces, partitioning between phases and solid-stabilised emulsions and foams.
We have investigated a new class of food-grade particles, whey protein microgels, as stabilisers of triglyceride-water emulsions. The sub-micron particles stabilized oil-in-water emulsions at all pH ...with and without salt. All emulsions creamed but exhibited exceptional resistance to coalescence. Clear correlations exist between the properties of the microgels in aqueous dispersion and the resulting emulsion characteristics. For conditions in which the particles were uncharged, fluid emulsions with relatively large drops were stabilised, whereas emulsions stabilized by charged particles contained smaller flocculated drops. A combination of optical microscopy of the drops and spectrophotometry of the resolved aqueous phase allowed us to estimate the interfacial adsorption densities of the particles using the phenomenon of limited coalescence. We deduce two classes of particle arrangement. Complete adsorption of the particles was obtained when they were neutral or when their charges were screened by salt resulting in at least one particle monolayer at the interface. By contrast, only around 50% of the particles adsorbed when they were charged with emulsion drops being covered by less than half a monolayer. These findings were supported by direct visualization of drop interfaces using cryo-scanning electron microscopy. Uncharged particles were highly aggregated and formed a continuous 2-D network at the interface. Otherwise particles organized as individual aggregates separated by particle-free regions. In this case, we suggest that some particles spread at the interface leading to the formation of a continuous protein membrane. Charged particles displayed the ability to bridge opposing interfaces of neighbouring drops to form dense particle disks protecting drops against coalescence; this is the main reason for the flocculation and stability of emulsions containing sparsely covered drops.
We develop a novel strategy to more effectively and controllably process continuous enzymatic or homogeneous catalysis reactions based on nonaqueous Pickering emulsions. A key element of this ...strategy is “bottom-up” construction of a macroscale continuous flow reaction system through packing catalyst-containing micron-sized ionic liquid (IL) droplet in oil in a column reactor. Due to the continuous influx of reactants into the droplet microreactors and the continuous release of products from the droplet microreactors, catalysis reactions in such a system can take place without limitations arising from establishment of the reaction equilibrium and catalyst separation, inherent in conventional batch reactions. As proof of the concept, enzymatic enantioselective trans-esterification and CuI-catalyzed cycloaddition reactions using this IL droplet-based flow system both exhibit 8 to 25-fold enhancement in catalysis efficiency compared to their batch counterparts, and a durability of at least 4000 h for the enantioselective trans-esterification of 1-phenylethyl alcohol, otherwise unattainable in their batch counterparts. We further establish a theoretical model for such a catalysis system working under nonequilibrium conditions, which not only supports the experimental results but also helps to predict reaction progress at a microscale level. Being operationally simple, efficient, and adaptive, this strategy provides an unprecedented platform for practical applications of enzymes and homogeneous catalysts even at a controllable level.
PDF
