Polyurethane Microgel Based Microtissue: Interface-Guided Assembly and Spreading.

Colloidal gels are three-dimensional networks of microgel particles and can be utilized to design microtissues where the differential adhesive interactions between the particles and cells, guided by their surface energetics, are engineered to spatially assemble the cellular and colloidal components into three-dimensional microtissues. In this work we utilized a colloidal interaction approach to design cell-polyurethane (PU) microgel bimodal microtissues using endothelial cells (ECs) as a normal cell model and a nonmalignant breast cancer cell line (MCF-7) as a cancer cell model. PU microgels were developed from a library of segmental polyurethanes with poly(ethylene glycol) soft segment and aliphatic diisocyanate/l-tyrosine based chain extender as hard segment to modulate the interactions between PU colloidal particles and cells. The surface energies of the microgel particles and cells were estimated using Zisman's critical surface tension and van Oss-Good-Chaudhury theory (vOGCT) from liquid contact angle analysis. Binary interaction potentials between colloidal PU particles and cells and the ternary interaction between colloidal PU particle, cell, and collagen I/Matrigel were calculated to explain the formation of microtissues and their spreading in extraneous biomatrix respectively by using classical and extended DLVO theory (XDLVO). Furthermore, rheological analysis and in silico simulations were used to analyze the assembly and spreading of the PU microgel based microtissues. In vitro experiments showed that ECs and MCF-7 displayed more differentiated (EC spreading/MCF-7 lumen formation) character when mixed with microgel particles that were stable in aqueous medium and more undifferentiated character (EC nonspreading/MCF-7 spreading) when mixed with microgel particles unstable in aqueous medium.

Comparative surface energetic study of Matrigel® and collagen I interactions with endothelial cells.

Understanding of the surface energetic aspects of the spontaneously deposited proteins on biomaterial surfaces and how this influences cell adhesion and differentiation is an area of regenerative medicine that has not received adequate attention. Current controversies surround the role of the biomaterial substratum surface chemistry, the range of influence of said substratum, and the effects of different surface energy components of the protein interface. Endothelial cells (ECs) are a highly important cell type for regenerative medicine applications, such as tissue engineering, and In-vivo they interact with collagen I based stromal tissue and basement membranes producing different behavioral outcomes. The surface energetic properties of these tissue types and how they control EC behavior is not well known. In this work we studied the surface energetic properties of collagen I and Matrigel® on various previously characterized substratum polyurethanes (PU) via contact angle analysis and examined the subsequent EC network forming characteristics. A combinatorial surface energy approach was utilized that compared Zisman's critical surface tension, Kaelble's numerical method, and van Oss-Good-Chaudhury theory (vOGCT). We found that the unique, rapid network forming characteristics of ECs on Matrigel® could be attributed to the apolar or monopolar basic interfacial characteristics according to Zisman/Kaelble or vOGCT, respectively. We also found a lack of significant substratum influence on EC network forming characteristics for Matrigel® but collagen I showed a distinct influence where more apolar PU substrata tended to produce higher Lewis acid character collagen I interfaces which led to a greater interaction with ECs. Collagen I interfaces on more polar PU substrata lacked Lewis acid character and led to similar EC network characteristics as Matrigel®. We hypothesized that bipolar character of the protein film favored cell-substratum over cell-cell adhesive interactions which resulted in less rapidly forming but more stable networks.

Interfacial energetics approach for analysis of endothelial cell and segmental polyurethane interactions.

Understanding the physicochemical interactions between endothelial cells and biomaterials is vital for regenerative medicine applications. Particularly, physical interactions between the substratum interface and spontaneously deposited biomacromolecules as well as between the induced biomolecular interface and the cell in terms of surface energetics are important factors to regulate cellular functions. In this study, we examined the physical interactions between endothelial cells and segmental polyurethanes (PUs) using l-tyrosine based PUs to examine the structure-property relations in terms of PU surface energies and endothelial cell organization. Since, contact angle analysis used to probe surface energetics provides incomplete interpretation and understanding of the physical interactions, we sought a combinatorial surface energetics approach utilizing water contact angle, Zisman's critical surface tension (CST), Kaelble's numerical method, and van Oss-Good-Chaudhury theory (vOGCT), and applied to both substrata and serum adsorbed matrix to correlate human umbilical vein endothelial cell (HUVEC) behavior with surface energetics of l-tyrosine based PU surfaces. We determined that, while water contact angle of substratum or adsorbed matrix did not correlate well with HUVEC behavior, overall higher polarity according to the numerical method as well as Lewis base character of the substratum explained increased HUVEC interaction and monolayer formation as opposed to organization into networks. Cell interaction was also interpreted in terms of the combined effects of substratum and adsorbed matrix polarity and Lewis acid-base character to determine the effect of PU segments.

Cell-material interactions on biphasic polyurethane matrix.

Cell-matrix interaction is a key regulator for controlling stem cell fate in regenerative tissue engineering. These interactions are induced and controlled by the nanoscale features of extracellular matrix and are mimicked on synthetic matrices to control cell structure and functions. Recent studies have shown that nanostructured matrices can modulate stem cell behavior and exert specific role in tissue regeneration. In this study, we have demonstrated that nanostructured phase morphology of synthetic matrix can control adhesion, proliferation, organization and migration of human mesenchymal stem cells (MSCs). Nanostructured biodegradable polyurethanes (PU) with segmental composition exhibit biphasic morphology at nanoscale dimensions and can control cellular features of MSCs. Biodegradable PU with polyester soft segment and hard segment composed of aliphatic diisocyanates and dipeptide chain extender were designed to examine the effect polyurethane phase morphology. By altering the polyurethane composition, morphological architecture of PU was modulated and its effect was examined on MSC. Results show that MSCs can sense the nanoscale morphology of biphasic polyurethane matrix to exhibit distinct cellular features and, thus, signifies the relevance of matrix phase morphology. The role of nanostructured phases of a synthetic matrix in controlling cell-matrix interaction provides important insights for regulation of cell behavior on synthetic matrix and, therefore, is an important tool for engineering tissue regeneration.

Multi-criteria assessment of tensions in resource use at continental scale: a proof of concept with Australian rangelands.

The purpose of this study was to help to inform policy development for the Australian rangelands, and provide a proof of concept for application of a multi-criteria analysis approach to assessment of competing resource use at continental scale. The study aimed to identify and locate key natural resource and agricultural production assets in the rangelands, define a number of measures of potentially threatening processes, and use a multi-criteria approach to identify areas where threatening processes, agricultural production problems, or valuable natural resources coincided. The analysis used 35 readily available, continental spatial data layers at 5-km pixel resolution ranked from 1 (low) to 5 (high) under three themed groupings: natural resource base, production base, and threatening processes. These measures were aggregated into composite indicators to define attributes such as environmental sensitivity and total grazing pressure. The composites were then compared in a two-way analysis to explore particular interactions between threatening processes such as pastoralism and mining, and the condition of production and natural resource assets. These interactions were defined as "tensions" for purposes of this analysis. Example "tensions" included the association of high grazing intensity with areas of high environmental sensitivity, indicating a risk of land degradation under adverse climatic conditions. A summary of patterns of tension was obtained by extracting area proportions of high-tension classes for selected Natural Heritage Trust Regions, which are a basis for Australian Government funding of improved environmental management. The study provides a basis for further examination of trade-offs in the use of natural assets, opportunities for improved productivity and sustainability, and social and economic implications.

Guanylin and uroguanylin induce natriuresis in mice lacking guanylyl cyclase-C receptor.

BACKGROUND: Guanylin (GN) and uroguanylin (UGN) are intestinally derived peptide hormones that are similar in structure and activity to the diarrhea-causing Escherichia coli heat-stable enterotoxins (STa). These secretagogues have been shown to affect fluid, Na+, K+, and Cl- transport in both the intestine and kidney, presumably by intracellular cyclic guanosine monophosphate (cGMP)-dependent signal transduction. However, the in vivo consequences of GN, UGN, and STa on renal function and their mechanism of action have yet to be rigorously tested. METHODS: We hypothesized that intravenous administration of GN, UGN, or STa would cause an increase in natriuresis in wild-type mice via cGMP and guanylyl cyclase-C (GC-C, Gucy2c), the only known receptor for these peptide-hormones, and that the peptide-induced natriuresis would be blunted in genetically altered mice devoid of GC-C receptors (GC-C(-/-) null). RESULTS: In wild-type mice using a modified renal clearance model, GN, UGN, and STa elicited significant natriuresis, kaliuresis, and diuresis as well as increased urinary cGMP levels in a time- and dose-dependent fashion. Absolute and fractional urinary sodium excretion levels were greatest approximately 40 minutes following a bolus infusion with pharmacologic doses of these peptides. Unexpectedly, GC-C(-/-) null mice also responded to the GN peptides similarly to that observed in wild-type mice. Glomerular filtration rate (GFR), blood pressure, and plasma cGMP in the mice (wild-type or GC-C(-/-) null) did not significantly vary between the vehicle- and peptide-treatment groups. The effects of UGN may also influence long-term renal function due to down-regulation of the Na+/K+ ATPase gamma-subunit and the Cl- channel ClC-K2 by 60% and 75%, respectively, as assessed by differential display polymerase chain reaction (PCR) (DD-PCR) and Northern blot analysis of kidney mRNA from mice treated with UGN. CONCLUSION: GN, UGN, and STa act on the mouse kidney, in part, through a cGMP-dependent, GC-C-independent mechanism, causing significant natriuresis by renal tubular processes. UGN may have further long-term effects on the kidney by altering the expression of such transport-associated proteins as Na+/K+ ATPase and ClC-K2.

Characteristics and regional variations of patients with Barrett's oesophagus in the UK.

OBJECTIVES: To establish the patient characteristics and regional variation of Barrett's oesophagus in the UK in a large number (5717) of subjects. Barrett's oesophagus is a precursor lesion of oesophageal adenocarcinoma, the incidence of which is rising more rapidly than any other solid tumour. METHODS: Demographic data of 5717 Barrett's oesophagus patients from 27 UK centres, each registering at least 50 patients, with UK National Barrett's Oesophagus Registry, were analysed. RESULTS: Centres registering patients were distributed evenly throughout the UK. There was an excess of males, with a male to female ratio of 1.7. Mean age at diagnosis was 62.0 years for males and 67.5 years for females. In Scotland, the mean and peak age at diagnosis for males was lower than for the remainder of the UK. In contrast, there was no regional variation in mean and peak age of diagnosis for females. In 3880 Barrett's oesophagus patients with complete data, adenocarcinoma developed in 136 (3.5%). Adenocarcinoma prevalence was 4.0% in males and 2.5% in females. The male/female ratio of patients with adenocarcinoma was 3.0, twice that of Barrett's oesophagus (1.7). The mean age was 64.7 years for males and 74.0 years for females. CONCLUSIONS: These data demonstrate that Barrett's oesophagus occurs with a higher frequency in males, with progression to adenocarcinoma being even more biased towards men in the UK, in contrast to the USA. There are significant regional variations in age of diagnosis of Barrett's oesophagus, especially in younger male patients in Scotland. Studies to identify genetic and environmental determinants of Barrett's oesophagus and cancer risk are needed.

Asymptomatic colorectal neoplasia and fecal characteristics: a case-control study of subjects participating in the nottingham fecal occult blood screening trial.

PURPOSE: The results of previous studies of colorectal neoplasia and fecal composition have been inconsistent, in part because the cases have been symptomatic and the studies small. We sought to test hypotheses relating to fecal bile acids, calcium, and pH in a large sample of asymptomatic subjects who had participated in fecal occult blood screening. METHODS: Fecal samples were obtained from 45 cases of cancer, 129 subjects with adenoma, 167 fecal occult blood-negative controls and 155 fecal occult blood-positive subjects in whom no cancer or adenoma was found. Concentrations of fecal bile acids, steroids, calcium, and pH were assessed blind to case-control status and compared between cases and 1) fecal occult blood-negative controls and 2) fecal occult blood-positive subjects. RESULTS: No association between colorectal cancer and fecal bile acids or pH was observed. Although there was no overall association between colorectal adenomas and fecal bile acids or pH, villous adenomas were associated with increasing concentrations of major bile acids and decreasing concentration of minor bile acids, and there was a suggestion of an inverse association with an acid pH. High levels of fecal calcium were associated with a reduced risk of both colorectal cancer and adenoma, but this was not statistically significant. CONCLUSION: The study does not support an association between colorectal cancer and fecal bile acids or pH. However, there is evidence that increases in major bile acids are associated with villous adenomas.

Lifestyle factors and Barrett's esophagus.

OBJECTIVE: We aimed to investigate lifestyle factors relevant to the development of Barrett's esophagus in the United Kingdom. METHODS: At Ninewells Hospital, Dundee, Scotland, medical records of 136 Barrett's esophagus patients were examined. At Wexham Park Hospital, Slough, Southern England, 50 male and 51 female Barrett's esophagus patients were matched for sex, age, and year of diagnosis (+/- 3 yr) with uncomplicated reflux esophagitis patients. Data were abstracted for tobacco consumption, alcohol intake, and weight. In Dundee, height was also recorded and body mass index calculated. Alcohol and tobacco intake were scored for each patient. RESULTS: In Dundee there is no difference in smoking or drinking habits between men and women under and over 50 yr of age. In Slough there is little difference in drinking or smoking habits between Barrett's esophagus and reflux esophagitis patients and between their mean weights. However, of the Dundee Barrett's esophagus patients younger than 50 yr, 31% of men and 71% of women have body mass indexes over 30 (obese), versus 11% and 13%, respectively, for the general population. In those older than 50 yr, 14% of men and 19% of women have body mass indexes over 30. CONCLUSIONS: There is no difference in smoking or drinking habits in younger and older Barrett's esophagus patients, nor between those with Barrett's esophagus and reflux esophagitis. Obesity is a risk factor for Barrett's esophagus in young people only.