Porous Anisometric PNIPAM Microgels: Tailored Porous Structure and Thermal Response.

The porous structure of microgels significantly influences their properties and, thus, their suitability for various applications, in particular as building blocks for tissue scaffolds. Porosity is one of the crucial features for microgel-cell interactions and significantly increases the cells' accumulation and proliferation. Consequently, tailoring the porosity of microgels in an effortless way is important but still challenging, especially for nonspherical microgels. This work presents a straightforward procedure to fabricate complex-shaped poly(N-isopropyl acrylamide) (PNIPAM) microgels with tuned porous structures using the so-called cononsolvency effect during microgel polymerization. Therefore, the classical solvent in the reaction solution is exchanged from water to water-methanol mixtures in a stop-flow lithography process. For cylindrical microgels with a higher methanol content during fabrication, a greater degree of collapsing is observed, and their aspect ratio increases. Furthermore, the collapsing and swelling velocities change with the methanol content, indicating a modified porous structure, which is confirmed by electron microscopy micrographs. Furthermore, swelling patterns of the microgel variants occur during cooling, revealing their thermal response as a highly heterogeneous process. These results show a novel procedure to fabricate PNIPAM microgels of any elongated 2D shape with tailored porous structure and thermoresponsiveness by introducing the cononsolvency effect during stop-flow lithography polymerization.

About a Membrane with Microfluidic Porous-Wall Channels of Cylindrical Shape for Droplet Formation.

A low-energy emulsification process is hollow-fiber emulsification. In this process, the lumen diameter of the membrane mostly determines the droplet size. To gain smaller droplets, approaches for downsizing the inner diameter of membranes have to be carried out. In this work, we describe a new method for the fabrication of parallel microfluidic porous-wall channels of a homogeneous cylindrical shape with lumen diameters down to 7 µm. Parallel and symmetric porous-wall channels are induced into polyvinylidene fluoride membranes during the casting process. The technique comprises liquid-induced phase separation and phase-separation micromolding using thin glass and carbon fibers as molds and an in-house designed tool to position the fibers. The channel positioning and alignment are verified within this work. We show and investigate the droplet formation in these porous-wall channels via hollow-fiber emulsification. The formed droplets are very small in diameter and size distribution. The droplet formation at varying flow rates and channel diameters is examined in detail. Moreover, an area of sufficient operating conditions is given using Weber and capillary numbers. As a numbering-up approach, we show the simultaneous formation of spherical droplets in two parallel channels. With the proposed membrane fabrication using micromolding, we push the downscaling approach of hollow-fiber emulsification to lower micron ranges of the channel diameter. With these small channels, droplets with a diameter down to 25 µm were produced, which are more attractive for most applications.

Soft temperature-responsive microgels of complex shape in stop-flow lithography.

Stop-flow lithography (SFL) has emerged as a facile high-throughput fabrication method for µm-sized anisometric particles; yet, the fabrication of soft, anisometric microgels has not frequently been addressed in the literature. Furthermore, and to the best of the authors' knowledge, no soft, complex-shaped microgels with temperature-responsive behavior have been fabricated with this technology before. However, such microgels have tremendous potential as building blocks and actuating elements in rapidly developing fields, such as tissue engineering and additive manufacturing of soft polymeric building blocks, bio-hybrid materials, or soft micro-robotics. Given their great potential, we prove in this work that SFL is a viable method for the fabrication of soft, temperature-responsive, and complex-shaped microgels. The microgels, fabricated in this work, consist of poly(N-isopropylacrylamide) (pNIPAm), which is crosslinked with N,N'-methylenebis(acrylamide). The results confirm that the shape of the pNIPAm microgels is determined by the transparency mask, used in SFL. Furthermore, it is shown that, in order to realize stable microgels, a minimum threshold of crosslinker concentration of 2 wt% is required. Above this threshold, the stiffness of pNIPAm microgels can be deliberately altered by adjusting the concentration of the crosslinker. The fabricated pNIPAm microgels show the targeted temperature-responsive behavior. Within this context, temperature-dependent reversible swelling is confirmed, even for fractal-like geometries, such as micro snowflakes. Thus, these microgels provide the targeted unique combination of softness, shape complexity, and temperature responsiveness and increase the freedom of design for actuated building blocks.

From Batch to Continuous Precipitation Polymerization of Thermoresponsive Microgels.

Microgels are commonly synthesized in batch experiments, yielding quantities sufficient to perform characterization experiments for physical property studies. With increasing attention on the application potential of microgels, little attention is yet paid to the questions (a) whether they can be produced continuously on a larger scale, (b) whether synthesis routes can be easily transferred from batch to continuous synthesis, and (c) whether their properties can be precisely controlled as a function of synthesis parameters under continuous flow reaction conditions. We present a new continuous synthesis process of two typical but different microgel systems. Their size, size distribution, and temperature-responsive behavior are compared in depth to those of microgels synthesized using batch processes, and the influence of premixing and surfactant is also investigated. For the surfactant-free poly( N-vinylcaprolactam) and poly( N-isopropylacrylamide) systems, microgels are systematically smaller, while the actual size is depending on the premixing of the reaction solutions. However, by the use of a surfactant, the size difference between batch and continuous preparation diminishes, resulting in equal-sized microgels. Temperature-induced swelling-deswelling of microgels synthesized under continuous flow conditions was similar to that of their analogues synthesized using the batch polymerization process. Additionally, investigation of the internal microgel structure using static light scattering showed no significant changes between microgels prepared under batch and continuous conditions. The work encourages synthesis concepts of sequential chemical conditions in continuous flow reactors to prepare precisely tuned new microgel systems.

Climate, altitude, and blood pressure.

The effects of climate and altitude on casual blood pressure are examined from the perspectives of initial exposure, acclimatization, long-term residence, and birthplace. Hot arid and hot humid climates seem to have little effect on blood pressure, although a slight reduction may be found in some naturally acclimatized groups. Exposure of the total body to mild cold likewise has little apparent effect. Local exposure of the extremities to severe cold occasions significant increases in blood pressure during exposure but not at other times. Acclimatization reduces but does not eliminate that response. The effects of altitude on blood pressure are variable. There is initial hypertension, followed by gradual normalization. After years of residence at high altitude blood pressure may actually be lower than that observed among residents at sea level.

Migration and acculturation among Samoans: some sources of stress and support.

Daily excretion of the stress hormone, epinephrine, has been employed to study potential stressors associated with acculturation and migration. Young men and women from Samoan communities in Hawaii (HI), American Samoa (AS) and Western Samoa (WS) which differ in exposure to American culture were included. Psychosocial factors associated with elevations in hormone excretion were assumed to be stressors, while associations with reduced excretions were assumed to be supportive or buffers. Hormone excretion levels were similar in all locations, but there were different associations which could be attributed to migration and acculturation. Among all migrants (HI) ethnic networks were apparent stressors, while a high degree of community involvement was stressful for migrant women. In sites of culture contact (HI, AS) certain adult members of the extended family were supportive, as was a superior knowledge of Samoan cultural concepts. For women in Samoa (WS, AS) community involvement was supportive. In contrast for men in WS and AS, but not in HI, being of mixed ancestry or having close family of mixed ancestry was stressful. It is concluded that hormone analysis can provide meaningful clues concerning social stressors in acculturating or migrant communities. Also that migration or acculturation do not necessarily result in increased levels of stress.

Psychosocial factors in blood pressure variation: a comparative study of young Samoans.

Traditional peoples contacting modern cultures frequently experience increased levels of blood pressure. The aim of this investigation was to identify some acculturation-related psychosocial factors which might contribute to those elevations. Young Samoans living in a traditional village, in modernizing American Samoa, and as migrants in Hawaii were studied. Casual blood pressure, anthropometric measurements, and extensive interview data were collected. The most important factor predicting variation in blood pressure was body mass (BMI). This finding was particularly evident among the acculturated and migrant Samoans. In those locations women's abandonment of breast feeding may contribute to their higher BMI. Among acculturated and migrant women, measures of social support favored lower blood pressures. Among men in all locations a greater number of close social ties was linked to higher blood pressures with the exception of ties with parents. Parental ties were linked to substantially lower blood pressures. A knowledge of Samoan traditions favored lower blood pressure among migrant men, while knowledge of American culture favored higher pressures. Coping strategies and complaint behavior were also significant contributors in all locations.

Acculturation and symptoms: a comparative study of reported health symptoms in three Samoan communities.

A health questionnaire, which included a 91 item list of symptoms was administered to three groups of young Samoan adults. These young adults resided in a traditional Samoan village in Western Samoa (n = 50), several villages in modernizing American Samoa (n = 50) and in urban Honolulu, Hawaii (n = 52). Each yes response to a symptom was followed by an expanded interview providing details. The yes answer frequency and the contents of the expanded answers were examined with respect to site of residence. Western Samoan responses differed from the other sites in a number of areas suggesting possible differences related to the process of modernization. These response differences suggest four areas in which the stressors of modernization may have health influences: (1) wage employment outside of the family, (2) increased size of support networks by including non-family members and non-Samoans (3) the greater availability of alcohol, and (4) changes in the perceptions of food.

Modernization and catecholamine excretion of young Samoan adults.

Urinary catecholamine excretion rates have been used as a cross-culturally valid measure of generalized stress. The purposes of this paper are to examine group differences in catecholamine excretion rates in three Samoan groups who differ in degree of modernization and to compare these findings to rates of norepinephrine and epinephrine excretion in other populations. In 1986-1987, 24-hr urine samples were collected from 18-37-year-old Samoans; 46 rural Western Samoan villagers, 53 American Samoans, and 49 Samoans residing in Honolulu. The results show that norepinephrine excretion is significantly higher in more modernized Samoan groups (P less than 0.05), while epinephrine excretion is not significantly different in the three groups. The higher norepinephrine excretion rate in the more modernized Samoan groups may be related to differences in relative work load associated with changes in body weight, work capacity, and work patterns which accompany modernization. Samoan epinephrine excretion rates are relatively high compared to the results of other population studies, while norepinephrine excretion in three Samoan samples ranged from among the lowest rates observed worldwide to among the highest.

Selective migration from Samoa: a longitudinal study of pre-migration differences in social and psychological characteristics.

In 1981 extensive questionnaire and interview data were collected on some 100 young Samoan adults. Five years later in 1986 we determined their whereabouts and divided the data in accordance with migration status. The answers of the 35 who had migrated in the intervening period were contrasted to those 65 who remained in Samoa. The migrants differed in several distinct areas. Migrants reported a higher degree of peer-reliance as a personal adaptive strategy. Migrants also reported larger numbers of individuals in social support networks, a higher quality of support and more community involvement. They also report less expressive display of anger. Those who did not migrate reported a slightly better view of life in Samoa and abroad, as well as better relations with their friends and neighbors. These findings support a hypothesis that migrants are pre-selected to fit into migrant communities and do not appear to be misfits who are unhappy with life in Samoa.

Similarities and differences in acute cardiovascular responses to alcohol among normal men of European, Japanese, and Chinese ancestry: a univariate and multivariate analysis.

Normal young adult males residing in Hawaii (46 of European ancestry, 30 Japanese, 27 Chinese) were tested for changes in heart rate and blood pressure following a dose of 0.59 g of ethanol/kg. The two Oriental groups did not differ in mean changes but, when pooled, differed from Europeans, having increased heart rate and decreased blood pressure. Within-race analyses showed that, contrary to the literature, all three groups have great interindividual differences in cardiovascular responses. In addition, the three races show a basically similar multivariate response: blood pressure more variable than heart rate and blood pressure changes uncorrelated with heart rate changes.

Metabolic responses of Chinese, Japanese and Europeans to alcohol.

Thirty-nine Chinese, 47 Japanese, and 68 Europeans were tested for rate of alcohol metabolism under standardized conditions. The Japanese and Chinese metabolized at a significantly higher rate. Possible sources of such differences are considered.

Use of coca leaf in southern Peru: adaptation or addiction.

Use of coca leaves among the Quechua Indians of the Peruvian altiplano is considered from the biological and social perspectives. Biologically, coca use seems to reduce the loss of body heat in the cold and to enhance working ability to a small degree. It may also have nutritional value. Socially, coca is well integrated into the economic and social systems, providing functions in both spheres. The equation of coca use with cocaine addiction is also considered and a simple equivalence is rejected.

Marijuana smoking and cold tolerance in man.

Ten men who were marijuana users served as subjects in a study of the effects of marijuana smoking on response to cold. Cold water (28 degrees C for 60 min) and cold air (20 degrees C for 120 min) mediums were utilized with three exposures in each medium. The three exposures followed smoking marijuana, smoking placebo, and a no-smoking control period. Additionally, a breathhold experiment preceded and followed the four smoking periods. Marijuana and placebo smoke were inhaled from a spirometer with each man receiving the smoke of 0.739 g of marijuana and placebo. Smoking marijuana did not greatly modify body heat content, since rectal temperature and most peripheral temperatures were not altered. However, temperatures over voluntary muscles likely to be involved in shivering were elevated. Heat production also greatly increased after marijuana, suggesting that it had stimulated shivering. Marijuana also produced tachycardia and abolished apneic bradycardia. The mechanism of this action is not clear, but some sympathetic involvement is indicated.