Isochoric freezing to extend the shelf life of pomegranate juice.

Pomegranate juice was treated by isochoric freezing (-15°C/130 MPa) for 24 h and then stored under three different conditions for up to 4 weeks: 4°C/0.1 MPa, 24°C/0.1 MPa, and -10°C/100 MPa. The juice microbiological stability and quality were compared to those using heat treatment at 95°C for 15 s followed by cold storage at 4°C. Heat-treated and isochoric frozen (IF) pomegranate juice stored under isochoric conditions showed no spoilage microorganisms after 4 weeks of storage. Also, IF juice stored at 4 or 24°C for 4 weeks had lower microbial loads than those in fresh pomegranate juice. IF juice stored under isochoric conditions showed greater color stability, antioxidant capacity, and nutrient retention (anthocyanins, ascorbic acid, and total phenolic compounds) than heat-treated juices stored at 4°C. IF juice stored at 4°C also showed greater anthocyanin and ascorbic acid contents compared with heat-treated juice. PRACTICAL APPLICATION: Isochoric freezing storage at -10°C can be used to preserve the quality properties of fresh pomegranate juice. Isochoric freezing at -15°C for 24 h can also be used as a pretreatment to extend the shelf life of refrigerated pomegranate juice since the applied pressures reached total inactivation levels of spoilage microorganisms.

Ice modulatory effect of the polysaccharide FucoPol in directional freezing.

Directional freezing harnesses crystal growth development to create aligned solid structures or etchable patterns, useful for directed ice growth in cryobiology and cryoprinting for tissue engineering. We have delved into the ice-modulating properties of FucoPol, a fucose-rich, bio-based polysaccharide. Previous research on FucoPol revealed its non-colligative hysteresis in kinetic freezing point, reduced crystal dimensions and cryoprotective effect. Here, FucoPol reshaped developing sharp, anisotropic obloid ice dendrites into linearly-aligned, thin, isotropic spicules or tubules (cooling rate-dependent morphology). The effect was enhanced by increased concentration and decreased cooling rate, but major reshaping was observed with 5 µM and below. These structures boasted remarkable enhancements: uniform alignment (3-fold), tip symmetry (5.9-fold) and reduced thickness (5.3-fold). The ice-modulating capability of FucoPol resembles the Gibbs-Thomson effect of antifreeze proteins, in particular the ice reshaping profiles of type I antifreeze proteins and rattlesnake venom lectins, evidenced by a 52.6 ± 2.2° contact angle (θ) and spicular structure generation. The high viscosity of FucoPol solutions, notably higher than that of sucrose, plays a crucial role. This viscosity dynamically intensifies during directional freezing, leading to a diffusion-limited impediment that influences dendritic formation. Essentially, the ice-modulating prowess of FucoPol not only reinforces its established cryoprotective qualities but also hints at its potential utility in applications that harness advantageous ice growth for intentional structuring. For instance, its potential in cryobioprinting is noteworthy, offering an economical, biodegradable resource, of easy removal, sidestepping the need for toxic reagents. Moreover, FucoPol fine-tunes resulting ice structures, enabling the ice-etching of biologically relevant patterns within biocompatible matrices for advanced tissue engineering endeavors.

Temperature-Controlled 3D Cryoprinting Inks Made of Mixtures of Alginate and Agar.

Temperature-controlled 3D cryoprinting (TCC) is an emerging tissue engineering technology aimed at overcoming limitations of conventional 3D printing for large organs: (a) size constraints due to low print rigidity and (b) the preservation of living cells during printing and subsequent tissue storage. TCC addresses these challenges by freezing each printed voxel with controlled cooling rates during deposition. This generates a rigid structure upon printing and ensures cell cryopreservation as an integral part of the process. Previous studies used alginate-based ink, which has limitations: (a) low diffusivity of the CaCl2 crosslinker during TCC's crosslinking process and (b) typical loss of print fidelity with alginate ink. This study explores the use of an ink made of agar and alginate to overcome TCC protocol limitations. When an agar/alginate voxel is deposited, agar first gels at above-freezing temperatures, capturing the desired structure without compromising fidelity, while alginate remains uncrosslinked. During subsequent freezing, both frozen agar and alginate maintain the structure. However, agar gel loses its gel form and water-retaining ability. In TCC, alginate crosslinking occurs by immersing the frozen structure in a warm crosslinking bath. This enables CaCl2 diffusion into the crosslinked alginate congruent with the melting process. Melted agar domains, with reduced water-binding ability, enhance crosslinker diffusivity, reducing TCC procedure duration. Additionally, agar overcomes the typical fidelity loss associated with alginate ink printing.

Isochoric supercooling cryomicroscopy.

We introduce an isochoric (constant-volume) supercooling cryomicroscope (ISCM), enabling the ice-free study of biological systems and biochemical reactions at subzero temperatures at atmospheric pressure absent ice. This technology draws from thermodynamic findings on the behavior of water in isochoric systems at subfreezing temperatures. A description of the design of the ISCM and a demonstration of the stability of the supercooled solution in the ISCM is followed by an illustration of the possible use of the ISCM in the preservation of biological matter research. A comparison was made between the survival of HeLa cells in the University of Wisconsin (UW) solution in the ISCM at +4 °C under conventional atmospheric conditions and at -5 °C under isochoric supercooled conditions. Continuous real-time monitoring at cryopreservation temperature via fluorescence microscopy showed that after three days of isochoric supercooling storage, the percentage of compromised cells remained similar to fresh controls, while storage at +4 °C yielded approximately three times the mortality rate of cells preserved at -5 °C.

Individual Microparticle Manipulation Using Combined Electroosmosis and Dielectrophoresis through a Si3N4 Film with a Single Micropore.

Porous dielectric membranes that perform insulator-based dielectrophoresis or electroosmotic pumping are commonly used in microchip technologies. However, there are few fundamental studies on the electrokinetic flow patterns of single microparticles around a single micropore in a thin dielectric film. Such a study would provide fundamental insights into the electrokinetic phenomena around a micropore, with practical applications regarding the manipulation of single cells and microparticles by focused electric fields. We have fabricated a device around a silicon nitride film with a single micropore (2-4 µm in diameter) which has the ability to locally focus electric fields on the micropore. Single microscale polystyrene beads were used to study the electrokinetic flow patterns. A mathematical model was developed to support the experimental study and evaluate the electric field distribution, fluid motion, and bead trajectories. Good agreement was found between the mathematic model and the experimental data. We show that the combination of electroosmotic flow and dielectrophoretic force induced by direct current through a single micropore can be used to trap, agglomerate, and repel microparticles around a single micropore without an external pump. The scale of our system is practically relevant for the manipulation of single mammalian cells, and we anticipate that our single-micropore approach will be directly employable in applications ranging from fundamental single cell analyses to high-precision single cell electroporation or cell fusion.

Chemical composition of enamel surface as a predictor of in-vitro shear bond strength.

INTRODUCTION: Orthodontic bond failure varies between patients. It has been speculated that the chemical composition of the enamel surface might play a role in the variations in bond failure. METHODS: X-ray photoelectron spectroscopy was used in analyzing the surface chemical composition of 49 pairs of maxillary right and left first premolars from patients requiring extractions as part of the orthodontic treatment. After x-ray photoelectron spectroscopy analysis, 49 enamel samples were randomly selected for an in-vitro shear bonding study with a materials testing system, Synergie 400 machine (MTS Systems, Eden Prairie, Minn). RESULTS: The in-vitro shear bond strength was found to have a mean of 6.93 +/- 2.71 MPa. Twelve elements were detected; the major ones were calcium, phosphorus, oxygen, nitrogen, and carbon. Regression analysis with the 12 elements explained 33.3% of the variations in bond strength. However, the contribution was not significant (P = 0.170). CONCLUSIONS: The chemical composition of the buccal surface of maxillary first premolars was not significant in predicting in-vitro mean shear bond strength. Other factors are likely to be important contributors to the large variations frequently seen in bond strength studies.

Accuracy of measurements and reliability of landmark identification with computed tomography (CT) techniques in the maxillofacial area: a systematic review.

OBJECTIVE: The objective of this study was to evaluate the available published information on the reliability and accuracy of skeletal CT landmark identification and associated measurement accuracy through CT in the maxillofacial region. STUDY DESIGN: Electronic databases were searched with the help of a senior health sciences librarian. Abstracts that appeared to fulfill the initial selection criteria were selected by consensus. The original articles were then retrieved and their references hand-searched for possible missing articles. RESULTS: A total of 8 articles met the selection criteria. Differences between the magnitudes of errors of landmarks and their associated measurements were discussed. CONCLUSIONS: It was concluded that each landmark exhibited a characteristic pattern of error that contributed to measurement inaccuracy, and with repeated practice of landmark identifications, the error can be reduced to within 0.5 mm for 2-D CT. Considerations have to be given to some of the 3-D CT reliability values because they can have diagnosis implications.