Multiple patterns of polymer gels in microspheres due to the interplay among phase separation,wetting, and gelation

We report the spontaneous patterning of polymer microgels by confining a polymer blend within microspheres. A poly(ethylene glycol) (PEG) and gelatin solution was confined inside water-in-oil (W/O) microdroplets coated with a layer of zwitterionic lipids: dioleoylphosphatidylethanolamine (PE) and dioleoylphosphatidylcholine (PC). The droplet confinement affected the kinetics of the phase separation, wetting, and gelation after a temperature quench, which determined the final microgel pattern. The gelatin-rich phase completely wetted to the PE membrane and formed a hollow microcapsule as a stable state in the PE droplets. Gelation during phase separation varied the relation between the droplet size and thickness of the capsule wall. In the case of the PC droplets, phase separation was completed only for the smaller droplets, wherein the microgel partially wetted the PC membrane and had a hemisphere shape. In addition, the temperature decrease below the gelation point increased the interfacial tension between the PEG/gelatin phases and triggered a dewetting transition. Interestingly, the accompanying shape deformation to minimize the interfacial area was only observed for the smaller PC droplets. The critical size decreased as the gelatin concentration increased, indicating the role of the gel elasticity as an inhibitor of the deformation. Furthermore, variously patterned microgels with spherically asymmetric shapes, such as discs and stars, were produced as kinetically trapped states by regulating the incubation time, polymer composition, and droplet size. These findings demonstrate a way to regulate the complex shapes of microgels using the interplay among phase separation, wetting, and gelation of confined polymer blends in microdroplets.The regulation of the 3D shapes of biopolymer gels at the mesoscale has numerous applications in the biomedical, cosmetic, and food materials industries, among others (1). Recently, top-down and bottom-up approaches have been reported to control the mesoscopic patterns of polymer gels. For example, photolithography and two-photon polymerization allow the regulation of gel patterns at the mesoscale (2–4). The advanced design of the molecules enables polymerization with a self-assembly and produces nonspherical microgels: spherical particles with a cavity, capsules, and cubic particles (5–7). However, these methods require highly specialized equipment and are generally difficult to adapt for biopolymer gels.Dynamical coupling between phase separation and sol–gel transition in polymer blends has also been investigated for the spontaneous formation of spherical microgels and a porous gel (8, 9). Ma et al. (10) and Choi et al. (11) confined aqueous two-phase systems (ATPSs) in microdroplets and fabricated microgels by selective polymerization. In such a confined space, phase separation accompanies wetting of a polymer to the substrate (12–15). Although the selective polymerization of phase-separated polymers in microdroplets has a great potential to produce variously shaped microgels, the dynamical coupling among the phase separation, wetting, and gelation of polymers in a confined space remains unclear (16). If it was better understood, the shapes of polymer microgels could be regulated in a self-organized manner.In the present work, we used gelatin, one of the most popular biopolymer gels, and poly(ethylene glycol) (PEG) as the desolvating agent because PEG leads to phase separation for various biopolymers, such as proteins and DNA (17). The gelatin/PEG solution was confined in water-in-oil (W/O) microdroplets coated by a lipid layer, wherein the phase separation and sol–gel transition of the gelatin occur with a decrease in the temperature (18–20). This process led to gelation after and during the phase separation in the presence of the interactions between the polymers and lipid membranes. We analyzed the pattern formation of the gelatin microgel as a function of the temperature history, droplet size, and polymer composition. We found that variously shaped microgels appeared as stable states and kinetically trapped states. These findings yield a method to regulate the shapes of polymer microgels using the interplay among the interfacial tensions, elastic properties of the gels, and interactions between the polymers and the surfaces of the droplets.     

How multiplicity determines entropy and the derivation of the maximum entropy principle for complex systems

The maximum entropy principle (MEP) is a method for obtaining the most likely distribution functions of observables from statistical systems by maximizing entropy under constraints. The MEP has found hundreds of applications in ergodic and Markovian systems in statistical mechanics, information theory, and statistics. For several decades there has been an ongoing controversy over whether the notion of the maximum entropy principle can be extended in a meaningful way to nonextensive, nonergodic, and complex statistical systems and processes. In this paper we start by reviewing how Boltzmann–Gibbs–Shannon entropy is related to multiplicities of independent random processes. We then show how the relaxation of independence naturally leads to the most general entropies that are compatible with the first three Shannon–Khinchin axioms, the -entropies. We demonstrate that the MEP is a perfectly consistent concept for nonergodic and complex statistical systems if their relative entropy can be factored into a generalized multiplicity and a constraint term. The problem of finding such a factorization reduces to finding an appropriate representation of relative entropy in a linear basis. In a particular example we show that path-dependent random processes with memory naturally require specific generalized entropies. The example is to our knowledge the first exact derivation of a generalized entropy from the microscopic properties of a path-dependent random process.Many statistical systems can be characterized by a macrostate for which many microconfigurations exist that are compatible with it. The number of configurations associated with the macrostate is called the phase-space volume or multiplicity, M. Boltzmann entropy is the logarithm of the multiplicity,and has the same properties as the thermodynamic (Clausius) entropy for systems such as the ideal gas (1). We set . Boltzmann entropy scales with the degrees of freedom f of the system. For example, for N noninteracting point particles in three dimensions, . Systems where scales with system size are called extensive. The entropy per degree of freedom is a system-specific constant. Many complex systems are nonextensive, meaning that if two initially insulated systems A and B, with multiplicities and , respectively, are brought into contact, the multiplicity of the combined system is . For such systems, which are typically strongly interacting, non-Markovian, or nonergodic, and the effective degrees of freedom do no longer scale as N. Given the appropriate scaling for , the entropy is a finite and nonzero constant in the thermodynamic limit, .A crucial observation in statistical mechanics is that the distribution of all macrostate variables gets sharply peaked and narrow as system size N increases. The reason behind this is that the multiplicities for particular macrostates grow much faster with N than those for other states. In the limit the probability of measuring a macrostate becomes a Dirac delta, which implies that one can replace the expectation value of a macrovariable by its most likely value. This is equivalent to maximizing the entropy in Eq. 1 with respect to the macrostate. By maximizing entropy one identifies the “typical” microconfigurations compatible with the macrostate. This typical region of phase space dominates all other possibilities and therefore characterizes the system. Probability distributions associated with these typical microconfigurations can be obtained in a constructive way by the maximum entropy principle (MEP), which is closely related to the question of finding the most likely distribution functions (histograms) for a given system.We demonstrate the MEP in the example of coin tossing. Consider a sequence of N independent outcomes of coin tosses, , where is either head or tail. The sequence x contains heads and tails. The probability of finding a sequence with exactly heads and tails iswhere is the binomial factor. We use the shorthand notation for the histogram of heads and tails and for the marginal probabilities for throwing head or tail. For the relative frequencies we write . We also refer to θ as the “biases” of the system. The probability of observing a particular sequence x with histogram k is given by . It is invariant under permutations of the sequence x because the coin tosses are independent. All possible sequences x with the same histogram k have identical probabilities. is the respective multiplicity, representing the number of possibilities to throw exactly heads and tails. As a consequence Eq. 2 becomes the probability of finding the distribution function p of relative frequencies for a given N. The MEP is used to find the most likely p. We denote the most likely histogram by and the most likely relative frequencies by .We now identify the two components that are necessary for the MEP to hold. The first is that in Eq. 2 factorizes into a multiplicity that depends on k only and a factor that depends on k and the biases θ. The second necessary component is that the multiplicity is related to an entropy expression. By using Stirling’s formula, the multiplicity of Eq. 2 can be trivially rewritten for large N,where an entropy functional of Shannon type (2) appears,The same arguments hold for multinomial processes with sequences x of N independent trials, where each trial takes one of W possible outcomes (3). In that case the probability for finding a given histogram k is is the multinomial factor and . Asymptotically holds. Extremizing Eq. 5 for fixed N with respect to k yields the most likely histogram, . Taking logarithms on both sides of Eq. 5 givesObviously, extremizing Eq. 6 leads to the same histogram . The term in Eq. 6 is sometimes called relative entropy or Kullback–Leibler divergence (4). We identify the first term on the right-hand side of Eq. 6 with Shannon entropy , and the second term is the so-called cross-entropy . Eq. 6 states that the cross-entropy is equal to entropy plus the relative entropy. The constraints of the MEP are related to the cross-entropy. For example, let the marginal probabilities be given by the so-called Boltzmann factor, , for the “energy levels” , where β is the inverse temperature and α the normalization constant. Inserting the Boltzmann factor into the cross-entropy, Eq. 6 becomeswhich is the MEP in its usual form, where Shannon entropy gets maximized under linear constraints. α and β are the Lagrangian multipliers for the normalization and the “energy” constraint , respectively. Note that in Eq. 6 we used to scale . Any other nonlinear would yield nonsensical results in the limit of , either 0 or ∞. Comparing with Eq. 1 shows that indeed, up to a constant multiplicative factor, . This means that the Boltzmann entropy per degree of freedom of a (uncorrelated) multinomial process is given by a Shannon-type entropy functional. Many systems that are nonergodic, are strongly correlated, or have long memory will not be of multinomial type, implying that is not invariant under permutations of a sequence x. For this situation it is not a priori evident that a factorization of into a θ-independent multiplicity and a θ-dependent term, as in Eq. 5, is possible. Under which conditions such a factorization is both feasible and meaningful is discussed in the next section.     

Shaping Ability of Different Nickel-Titanium Systems in Simulated S-shaped Canals with and without Glide Path

Introduction

The objective of this study was to compare the shaping ability of different rotary and reciprocating nickel-titanium file systems with and without previous glide path preparation in simulated S-shaped canals.

Methods

One hundred twenty S-shaped canals in resin blocks were prepared to an apical size 25 by using Reciproc, WaveOne, HyflexCM, F360, and OneShape systems either with or without previous glide path preparation (Pathfile) (12 canals/group). Material removal was measured at 20 measuring points, beginning 1 mm from the end point of preparation. Incidence of canal aberrations (zip/elbow, ledge formation), preparation time, and instrument failures were also recorded. Statistical analyses were performed by using analysis of variance and Tukey and χ² tests.

Results

For all systems, glide path preparation exerted no significant effect on preparation times (P > .05). Glide path preparation had no influence on the incidence of canal aberrations and instrument fractures (P > .05), with no significant differences between the 5 systems (P > .05). Glide path preparation had no influence on the centering ability of all systems (P > .05). On average, canals prepared with F360, OneShape, and HyflexCM remained better centered compared with those enlarged with WaveOne and Reciproc.

Conclusions

Under the conditions of this study, glide path preparation had no significant impact on canal straightening. Less tapered instruments maintained the original canal curvature better than instruments having greater tapers.     

Focus on Fluorides: Update on the Use of Fluoride for the Prevention of Dental Caries

Improving the efficacy of fluoride therapies reduces dental caries and lowers fluoride exposure.BackgroundFluoride is delivered to the teeth systemically or topically to aid in the prevention of dental caries. Systemic fluoride from ingested sources is in blood serum and can be deposited only in teeth that are forming in children. Topical fluoride is from sources such as community water, processed foods, beverages, toothpastes, mouthrinses, gels, foams, and varnishes. The United States Centers for Disease Control and Prevention (CDC) and the American Dental Association (ADA) have proposed changes in their long standing recommendations for the amount of fluoride in community drinking water in response to concerns about an increasing incidence of dental fluorosis in children. Current research is focused on the development of strategies to improve fluoride efficacy. The purpose of this update is to inform the reader about new research and policies related to the use of fluoride for the prevention of dental caries.MethodsReviews of the current research and recent evidence based systematic reviews on the topics of fluoride are presented. Topics discussed include: updates on community water fluoridation research and policies; available fluoride in dentifrices; fluoride varnish compositions, use, and recommendations; and other fluoride containing dental products. This update provides insights into current research and discusses proposed policy changes for the use of fluoride for the prevention of dental caries.ConclusionsThe dental profession is adjusting their recommendations for fluoride use based on current observations of the halo effect and subsequent outcomes. The research community is focused on improving the efficacy of fluoride therapies thus reducing dental caries and lowering the amount of fluoride required for efficacy.     

Measuring adherence among nurses one year after training in applying the Modified Early Warning Score and Situation-Background-Assessment-Recommendation instruments

Background

Patients with a cardiac arrest or unplanned intensive care admission show gradual decline in clinical condition preceding the event. This can be objectified by measuring the vital parameters and subsequently determining the Modified Early Warning Score (MEWS). Contact with the physician by nurses may be structured using the Situation-Background-Assessment-Recommendation (SBAR) communication instrument. The aim of our study was to evaluate whether nurses trained in the use of MEWS and SBAR tools were more likely to recognize a deteriorating patient.

Design and setting

This prospective quasi-experimental trial in the Academic Medical Center in Amsterdam, the Netherlands included three medical and three surgical wards.

Interventions

A group of 47 trained and 48 non-trained nurses were presented with a case of a deteriorating patient, and subsequent assessment and actions regarding the patient case were measured.

Results

Of the trained nurses, 77% versus 58% of the non-trained group assessed the patient immediately. On subsequent assessment of the patient, respiratory rate was measured twice as frequently (53% trained versus 25% non-trained, p = 0.025). No differences were found in the measurement of other vital parameters. The MEWS was determined by 11% of trained nurses. Subsequent notification of the physician was performed by 67% of the trained versus 43% of the non-trained nurses. The SBAR communication tool was used by only one nurse.

Conclusions

Trained nurses are able to identify a deteriorating patient and react more appropriately. However, despite rigorously implementing MEWS/SBAR methodology, these tools were rarely used.     

Model for the physics and physiology of fluid administration

This article describes a model designed to provide an understanding of fluid flow in intravenous systems and human subjects. Experiments were developed which demonstrate that the model can represent common clinical situations. The model depicts physical devices as ideal resistors, pressure sources, and flow sources. The patient's venous system is depicted as a combination of ordinary and Starling resistors. For flows between 0 and 300 ml/hr, both physical devices and patients are adequately represented by a straight line representing the pressure-flow relationship (PFR): pressure = opening pressure + flow × resistance, where the slope is the resistance to fluid flow and the intercept is the opening pressure. The PFR for a normal vein is characterized by a flat slope (vein resistance =22±20 mm Hg/L/hr, mean ± SD) and a low intercept (opening pressure =15±8 mm Hg). The PFR for a partially obstructed vein has a resistance equal to that of an unobstructed vein and an opening pressure elevated approximately equal to the pressure obstructing the vein. For perivascular tissue, the PFR has a steep slope (tissue resistance =1,125±1,376 mm Hg/L/hr), while tissue opening pressure depends on the amount of fluid infused. At the onset of fluid extravasation (infiltration), tissue pressure usually is lower than venous pressure (8±8 versus 15±8 mm Hg), until fluid fills the distensible tissue compartment. In clinical practice, when infiltration or obstruction occurs, flow decreases and the clinician adjusts the roller clamp until correct flow resumes; no problem is obvious. The combined model for the intravenous tubing and venous systems explains the behavior of current clinical infusion devices.Presented in part at the Sixth Medical Monitoring Technology Conference, Vail, CO, March 1986; at the Annual Meeting of the American Society of Anesthesiologists, Las Vegas, NV, October 1986; at the Seventh Medical Monitoring Technology Conference, Vail, CO, March 1987; at a meeting on Computers in Critical Care and Pulmonary Medicine, San Diego, CA, June 1987; at the Annual Meeting of the American Society of Anesthesiologists, Atlanta, GA, October 1987; at the Regional Meeting of the Association for the Advancement of Medical Instrumentation, Cincinnati, OH, October 1987; at the Institute of Electrical and Electronics Engineers Ninth Annual Conference of the Engineering in Medicine and Biology Society, Boston, MA, November 1987; and at a meeting of the American Society of Hospital Pharmacists, Atlanta, GA, December 1987.Supported in part by grants from IVAC Corp.The author thanks the following individuals for important intellectual and/or technical assistance: Peter Basser, PhD, Avital Cnaan, PhD, Adriane Concus, MD, John Fox, MD, David Gissen, MD, David Joseph, MD, Anne Kamara, David Leith, MD, Leonard Lind, MD, Richard Morris, MB, BS, Barbara Orlowitz, MEE, Mary Anne Palleiko, RN, Beverly Philip, MD, Daniel Raemer, PhD, David Scott, MB, BS, John Stelling, MPH, and Marie vanRensberg, MB. At IVAC Corp: Walter Bochenko, BSEE, MBA, Robert Butterfield, BSEE, Douglas Christian, RPh, MBA, Alan Davison, BS, David Doan, PhD, Alan Somerville, BSEE, MS, Robin Wernick, BSEE, MS.     

A virtual reality environment for evaluation of a daily living skill in brain injury rehabilitation: reliability and validity

OBJECTIVE: To establish the stability and validity of information collected in a virtual reality environment from persons with traumatic brain injury (TBI). DESIGN: Prospective correlation design to examine 3-week test-retest results for equivalence reliability between computer-simulated and natural environments. SETTING: A residential rehabilitation center for brain injury. PARTICIPANTS: Fifty-four consecutive patients with TBI who received comprehensive rehabilitation services and who were at different stages of recovery. INTERVENTION: An immersive virtual kitchen was developed in which a meal preparation task involving multiple steps was performed. The subjects completed meal preparation both in a virtual reality kitchen and an actual kitchen twice over a 3-week period. MAIN OUTCOME MEASURES: Time and errors on task completion using virtual reality assessment, actual kitchen performance (analogous to the virtual reality environment), occupational therapy (OT) evaluation, and neuropsychologic tests. RESULTS: The stability of performance using the simulated virtual environment was estimated with intraclass correlation coefficients (ICCs). The ICC value for total performance, based on all steps involved in the meal preparation task, was.76 (P<.01). The construct validity of the simulated environment was examined by correlating performance in the virtual environment with that in the actual kitchen (r=.63, P<.01), the OT evaluation (r=.30, P=.05 for meal preparation; r=.40, P=.01 for cognitive subskills), and neuropsychologic tests (r=.56, P<.01 for the full-scale intelligence quotient [IQ]; r=.40, P<.01 for the verbal IQ; r=.56, P<.01 for the performance IQ). Finally, a multiple regression analysis revealed that the virtual reality environment test was a good predictor for the actual assessment kitchen (beta=.35, P=.01). CONCLUSION: The virtual reality system showed adequate reliability and validity as a method of assessment in persons with brain injury.     

Intra- and inter-observer reliability assessment of widely used classifications and the “Ten-segment classification” of tibial plateau fractures

BackgroundTen-segment classification provides a different approach to the evaluation of tibial plateau fractures. The purpose of this study was to assess the intra- and inter-observer reliability of three widely used classification systems (Schatzker, Arbeitsgemeinschaft für Osteosynthesefragen (AO/OTA), and the updated three-column concept (uTCC)) with ten-segment classification in two-dimensional computed tomography (2D-CT) and three-dimensional computed tomography (3D-CT).MethodNinety 2D-CT and 3D-CT scans of patients with tibial plateau fractures were included in this retrospective cohort study. The included data were independently classified by six observers of different years of seniority and were independently observed and classified again after eight weeks. Inter-observer and intra-observer reliability of the four fracture classifications made by the six observers was analyzed using the kappa statistic. Kappa values were interpreted according to the categorical rating by Landis and Koch.ResultsWhen the inter-observer reliability was based on 2D-CT/3D-CT analysis, the mean Kappa values for the Schatzker, AO/OTA, uTCC, and ten-segment classification were 0.64/0.66, 0.56/0.59, 0.53/0.65, and 0.60/0.73, respectively. When intra-observer reliability was based on 2D-CT/3D-CT, the mean Kappa values for the Schatzker, AO/OTA, uTCC, and ten-segment classification were 0.68/0.83, 0.69/0.83, 0.74/0.85, and 0.80/0.91, respectively.ConclusionsThe use of 3D-CT is important for the reliable diagnosis and recognition of tibial plateau fracture features compared to 2D-CT. When using 3D-CT, ten-segment classification showed high intra- and inter-observer agreement.     

Needs and concerns of patients in isolation care units - learnings from COVID-19: A reflection

With strict measures in place to contain the spread of coronavirus disease 2019, many have been isolated as suspected or confirmed cases. Being isolated causes much inconvenience for the patients and family. Patients' and next-of-kins’ needs and concerns during isolation will be shared together with suggestions for key process improvements. Our hospital’s Senior Patient Experience Managers contact all patients admitted to the isolation wards on a daily basis to provide some form of support. Common issues raised were gathered and strategies to help with their needs and concerns were discussed. Being in isolation is a challenging period for both patients and family. Nonetheless, we can implement measures to mitigate against the adverse effects of isolation. Patient education, effective and efficient means of communication, close monitoring for signs of distress and anxiety, and early intervention could help patients cope better with the whole isolation experience. Nursing management may want to consider implementing the measures shared in the article to manage patient’s stress while not compromising on staff safety.