The rapid development of additive manufacturing techniques, also known as three‐dimensional (3D) printing, is driving innovations in polymer chemistry, materials science, and engineering. Among ...current 3D printing techniques, direct ink writing (DIW) employs viscoelastic materials as inks, which are capable of constructing sophisticated 3D architectures at ambient conditions. In this perspective, polymer designs that meet the rheological requirements for direct ink writing are outlined and successful examples are summarized, which include the development of polymer micelles, co‐assembled hydrogels, supramolecularly cross‐linked systems, polymer liquids with microcrystalline domains, and hydrogels with dynamic covalent cross‐links. Furthermore, advanced polymer designs that reinforce the mechanical properties of these 3D printing materials, as well as the integration of functional moieties to these materials are discussed to inspire new polymer designs for direct ink writing and broadly 3D printing.
New ink: Polymer designs for direct ink writing are outlined, with emphasis on strategies aimed at fulfilling the rheological requirements, reinforcing the mechanical properties, and integrating functional moieties (see figure).
► The normal adult liver contains populations of polyploid and aneuploid hepatocytes. ► Aneuploidy affects 60% of hepatocytes in mice and 30–90% of hepatocytes in humans. ► Hepatic aneuploidy is ...random, affecting chromosomes equally. ► Ploidy reversal events by polyploid hepatocytes generate diploid cells. ► Aneuploid hepatocytes promote adaptation to chronic liver injury.
Polyploidy has been described in the liver for over 100 years. The frequency of polyploid hepatocytes varies by age and species, but up to 90% of mouse hepatocytes and approximately 50% of human hepatocytes are polyploid. In addition to alterations in the entire complement of chromosomes, variations in chromosome copy number have been recently described. Aneuploidy in the liver is pervasive, affecting 60% of hepatocytes in mice and 30–90% of hepatocytes in humans. Polyploidy and aneuploidy in the liver are closely linked, and the ploidy conveyor model describes this relationship. Diploid hepatocytes undergo failed cytokinesis to generate polyploid cells. Proliferating polyploid hepatocytes, which form multipolar spindles during cell division, generate reduced ploidy progeny (e.g., diploid hepatocytes from tetraploids or octaploids) and/or aneuploid daughters. New evidence suggests that random hepatic aneuploidy can promote adaptation to liver injury. For instance, in response to chronic liver damage, subsets of aneuploid hepatocytes that are differentially resistant to the injury remain healthy, regenerate the liver and restore function. Future work is required to elucidate the mechanisms regulating dynamic chromosome changes in the liver and to understand how these processes impact normal and abnormal liver function.
Covalently linked single-crystalline porous organic materials are highly desired for structure–property analysis; however, periodically polymerizing organic entities into high dimensional networks is ...challenging. Here, we report a series of topologically divergent single-crystalline hydrogen-bonded cross-linked organic frameworks (HCOFs) with visible guest-induced elastic expansions, which mutually integrate high structural order and high flexibility into one framework. These HCOFs are synthesized by photo-cross-linking molecular crystals with alkyldithiols of different chain lengths. Their detailed structural information was revealed by single-crystal X-ray analysis and experimental investigations of HCOFs and their corresponding single-crystalline analogues. Upon guest adsorption, HCOF-2 crystals composed of a 3D self-entangled polymer network undergo anisotropic expansion to more than twice their original size, while the 2D-bilayer HCOF-3 crystals exhibit visible, layered sorption bands and form delaminated sheets along the plane of its 2D layers. The dynamic expansion of HCOF networks creates guest-induced porosity with over 473% greater volume than their permanent voids, as calculated from their record-breaking aqueous iodine adsorption capacities. Temperature-gated DMSO sorption investigations illustrated that the flexible nature of cross-linkers in HCOFs provides positive entropy from the coexistence of multiple conformations to allow for elastic expansion and contraction of the frameworks.
Stem Cells and Liver Regeneration Duncan, Andrew W; Dorrell, Craig; Grompe, Markus
Gastroenterology (New York, N.Y. 1943),
08/2009, Letnik:
137, Številka:
2
Journal Article
Recenzirano
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One of the defining features of the liver is the capacity to maintain a constant size despite injury. Although the precise molecular signals involved in the maintenance of liver size are not ...completely known, it is clear that the liver delicately balances regeneration with overgrowth. Mammals, for example, can survive surgical removal of up to 75% of the total liver mass. Within 1 week after liver resection, the total number of liver cells is restored. Moreover, liver overgrowth can be induced by a variety of signals, including hepatocyte growth factor or peroxisome proliferators; the liver quickly returns to its normal size when the proliferative signal is removed. The extent to which liver stem cells mediate liver regeneration has been hotly debated. One of the primary reasons for this controversy is the use of multiple definitions for the hepatic stem cell. Definitions for the liver stem cell include the following: (1) cells responsible for normal tissue turnover, (2) cells that give rise to regeneration after partial hepatectomy, (3) cells responsible for progenitor-dependent regeneration, (4) cells that produce hepatocyte and bile duct epithelial phenotypes in vitro, and (5) transplantable liver-repopulating cells. This review will consider liver stem cells in the context of each definition.
Polyploidy, a balanced amplification of the genome, is common in the liver. The function of hepatic polyploidy is not entirely clear, but growing evidence shows that polyploidy can protect the liver ...from tumor formation. In this issue of EMBO Reports, Sladky and colleagues identify the PIDDosome as a polyploidy sensor that regulates liver cancer (Sladky et al, 2020b).
Polyploidy is common in the liver and can protect the organ from tumor formation. A study in this issue identifies the PIDDosome as a polyploidy sensor that regulates liver cancer.
MEASURING SAMPLE QUALITY WITH DIFFUSIONS Gorham, Jackson; Duncan, Andrew B.; Vollmer, Sebastian J. ...
The Annals of applied probability,
10/2019, Letnik:
29, Številka:
5
Journal Article
Recenzirano
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Stein’s method for measuring convergence to a continuous target distribution relies on an operator characterizing the target and Stein factor bounds on the solutions of an associated differential ...equation. While such operators and bounds are readily available for a diversity of univariate targets, few multivariate targets have been analyzed. We introduce a new class of characterizing operators based on Itô diffusions and develop explicit multivariate Stein factor bounds for any target with a fast-coupling Itô diffusion. As example applications, we develop computable and convergence-determining diffusion Stein discrepancies for log-concave, heavy-tailed and multimodal targets and use these quality measures to select the hyperparameters of biased Markov chain Monte Carlo (MCMC) samplers, compare random and deterministic quadrature rules and quantify bias-variance tradeoffs in approximate MCMC. Our results establish a near-linear relationship between diffusion Stein discrepancies and Wasserstein distances, improving upon past work even for strongly log-concave targets. The exposed relationship between Stein factors and Markov process coupling may be of independent interest.
The aim of the How Farm Vets Cope project was to co-design, with farm veterinary surgeons, a set of web-based resources to help them and others deal with the different situations that they can face. ...As part of the wider project, participants were recruited for one-to-one semi-structured phone interviews. These interviews focused on elements of job satisfaction and how the participants coped during periods of poor mental wellbeing or with setbacks and failure.
Transcripts of these interviews were analysed using both quantitative methods of sentiment analysis and text mining, including term frequency/inverse document frequency and rapid automated keyword extraction, and qualitative content analysis. The twin aims of the analysis were identifying the important themes discussed by the participants and comparing the results of the two methods to see what differences, if any, arose.
Analysis using the afinn and nrc sentiment lexicons identified emotional themes of anticipation and trust. Rapid automated keyword extraction highlighted issues around age of vets and support, whilst using term frequency/inverse document frequency allowed for individual themes, such as religion, not present across all responses, to be identified. Content analysis supported these findings, pinpointing examples of trust around relationships with farmers and more experienced vets, along with some examples of the difference good support networks can make, particularly to younger vets.
This work has confirmed previous results in identifying the themes of trust, communication and support to be integral to the experience of practicing farm veterinary surgeons. Younger or less experienced vets recognised themselves as benefiting from further support and signposting, leading to a discussion around the preparation of veterinary students for entry into a farm animal vet practice. The two different approaches taken showed very good agreement in their results. The quantitative approaches can be scaled to allow a larger number of interviews to be utilised in studies whilst still allowing the important qualitative results to be identified.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
Polymers with the ability to repair themselves after sustaining damage could extend the lifetimes of materials used in many applications. Most approaches to healable materials require heating the ...damaged area. Here we present metallosupramolecular polymers that can be mended through exposure to light. They consist of telechelic, rubbery, low-molecular-mass polymers with ligand end groups that are non-covalently linked through metal-ion binding. On exposure to ultraviolet light, the metal-ligand motifs are electronically excited and the absorbed energy is converted into heat. This causes temporary disengagement of the metal-ligand motifs and a concomitant reversible decrease in the polymers' molecular mass and viscosity, thereby allowing quick and efficient defect healing. Light can be applied locally to a damage site, so objects can in principle be healed under load. We anticipate that this approach to healable materials, based on supramolecular polymers and a light-heat conversion step, can be applied to a wide range of supramolecular materials that use different chemistries.
Celotno besedilo
Dostopno za:
DOBA, IJS, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
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