Polymeric scaffolds serve as valuable supports for biological cells since they offer essential features for guiding cellular organization and tissue development. The main challenges for scaffold fabrication are i) to tune an internal structure and ii) to load bio-molecules such as growth factors and control their local concentration and distribution. Here, a new approach for the design of hollow polymeric scaffolds using porous CaCO3 particles (cores) as templates is presented. The cores packed into a microfluidic channel are coated with polymers employing the layer-by-layer (LbL) technique. Subsequent core elimination at mild conditions results in formation of the scaffold composed of interconnected hollow polymer microspheres. The size of the cores determines the feature dimensions and, as a consequence, governs cellular adhesion: for 3T3 fibroblasts an optimal microsphere size is 12 μm. By making use of the carrier properties of the porous CaCO3 cores, the microspheres are loaded with BSA as a model protein. The scaffolds developed here may also be well suited for the localized release of bio-molecules using external triggers such as IR-light.
The attractive colloidal and physicochemical
properties of cellulose
nanofibers (CNFs) at interfaces have recently been exploited in the
facile production of a number of environmentally benign materials,
e.g. foams, emulsions, and capsules. Herein, these unique properties
are exploited in a new type of CNF-stabilized perfluoropentane droplets
produced via a straightforward and simple mixing protocol. Droplets
with a comparatively narrow size distribution (ca. 1–5 μm
in diameter) were fabricated, and their potential in the acoustic
droplet vaporization process was evaluated. For this, the particle-stabilized
droplets were assessed in three independent experimental examinations,
namely temperature, acoustic, and ultrasonic standing wave tests.
During the acoustic droplet vaporization (ADV) process, droplets were
converted to gas-filled microbubbles, offering enhanced visualization
by ultrasound. The acoustic pressure threshold of about 0.62 MPa was
identified for the cellulose-stabilized droplets. A phase transition
temperature of about 22 °C was observed, at which a significant
fraction of larger droplets (above ca. 3 μm in diameter) were
converted into bubbles, whereas a large part of the population of
smaller droplets were stable up to higher temperatures (temperatures
up to 45 °C tested). Moreover, under ultrasound standing wave
conditions, droplets were relocated to antinodes demonstrating the
behavior associated with the negative contrast particles. The combined
results make the CNF-stabilized droplets interesting in cell-droplet
interaction experiments and ultrasound imaging.
Green, all-polysaccharide based microcapsules with mechanically robust capsule walls and fast, stimuli-triggered, and switchable permeability behavior show great promise in applications based on selective and timed permeability. Taking a cue from nature, the build-up and composition of plant primary cell walls inspired the capsule wall assembly, because the primary cell walls in plants exhibit high mechanical properties despite being in a highly hydrated state, primarily owing to cellulose microfibrils. The microcapsules (16 ± 4 μm in diameter) were fabricated using the layer-by-layer technique on sacrificial CaCO templates, using plant polysaccharides (pectin, cellulose nanofibers, and xyloglucan) only. In water, the capsule wall was permeable to labeled dextrans with a hydrodynamic diameter of ∼6.6 nm. Upon exposure to NaCl, the porosity of the capsule wall quickly changed allowing larger molecules (∼12 nm) to permeate. However, the porosity could be restored to its original state by removal of NaCl, by which permeants became trapped inside the capsule's core. The high integrity of cell wall was due to the CNF and the ON/OFF alteration of the permeability properties, and subsequent loading/unloading of molecules, could be repeated several times with the same capsule demonstrating a robust microcontainer with controllable permeability properties.
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