Mz75 microsystems

Surface roughness of different area of microcapsules was determined by atomic force microscopy (AFM). APA capsules without cells were used as control. Surface roughness of empty APA capsules (n = 4), APA capsules (n = 4) and multilayer capsules (n = 4) with cells was studied on day 30 post-encapsulation using a Bruker dimensions 3100 atomic force microscopy. Topographic imaging of capsules was performed at room temperature using the tapping mode21 (link)60 (link). Briefly single capsules were carefully sorted using a dissection microscope (Leica MZ75 microsystems), washed with demineralized water and placed on microscopic slides. The excess of water was carefully aspirated. The surface of the microcapsules was scanned by the tip of a silicon nitride cantilever (Nanoprobes GmbH, Darmstadt, Germany), spring constant k was set to 0.05 N/m, which was vertically oscillating (z-oscillating) near its resonant frequency with a tapping frequency (x-y raster scanning) less than 1 Hz. Surface roughness (Rq) was evaluated by using the root mean square average of height deviations taken from the mean image data plane at a 5 µm scan. NanoScope V software was used to analyze the raw data of AFM.

Empty beads of 3.4% intermediate-G alginate beads and 2% high-G alginate were made using air driven droplet generator using 23 g needle, gelled in 100 mM CaCl₂ for 5 minutes as previously described by us19 (link). Mechanical stability of alginate capsule can be quantified using different methods like burst pressure55 (link), ultrasound56 , Young's modulus57 , however we prefer to calculate the mechanical stability based on force and time required to resist compression19 (link). The mechanical stability was quantified with a Texture Analyzer XT plus (Stable Micro Systems, Godalming, UK) equipped with a force transducer with a resolution of 1 mN as previously described by us19 (link). Texture Exponent software version 6.0 was used for analyzing the data. Briefly individual beads of size 500 µm micrometer were carefully sorted using a dissection microscope (Leica MZ75 microsystems) equipped with an ocular micrometer with an accuracy of 25 µm. Individual beads were carefully placed on plate, storage solution was carefully removed. The mechanical stability of beads was measured by compressing individual microcapsules to 60% using P/25L mobile probe with a pretest speed of 0.5 mm/sec, a test speed of 0.01 mm/sec, and a posttest speed of 2 mm/sec. The trigger force was set to 2 grams. The force exerted by the probe to compress the bead was recorded as function of time.