Graft mechanical compliance in vascular patency

With the growing age of average population throughout the world, progress of biomaterials research is important to overcome current limitations. Vascular graft is one of the examples. Currently, synthetic vascular grafts made using expanded polytetrafluoroethylene (ePTFE) or Dacron are commercially available as treatments to cardiovascular diseases. These synthetic vascular grafts have good patency, which is a measure used to determine the success of the grafts, and are actively used in more than 400,000 life-saving procedures in the United States alone. However, the available synthetic grafts have limitations – their patency is poor when used in small-diameter application. Synthetic small diameter vascular graft (sSDVG) is defined by synthetic vascular grafts with internal diameter less than 6mm. sSDVG face limited success due to vascular wall thickening known as intimal hyperplasia (IH). IH develop at the distal anastomosis of the graft and are due to over proliferation and abnormal migration of vascular smooth muscle cells (VSMC). Mechanical compliance mismatch of the sSDVG is proposed as one of the key factors that contribute to the formation and development of IH. Compliance in vascular engineering is referring to the radial elasticity of the vascular graft or the blood vessel. Native blood vessels are highly elastic; compliance of human internal mammary artery with the diameter of 1-2 mm is reported to be 12% per 100mmHg. The compliance of sSDVG, however, is very low. The compliance of ePTFE graft, for example, is reported to be 1.2±0.3 % per 100mmHg. This discrepancy in the compliance of the native blood vessels and sSDVG is called compliance mismatch. Compliance mismatch is suggested to play an important role in IH because of mechanotransduction. Mechanotransduction refers to the cellular responses to mechanical stimuli. In the literature, many biological molecules inside VSMC, such as platelet-derived growth factor-BB (PDGF-BB), platelet-derived growth factor receptor, phosphorylated myosin light-chain kinase (pMLCK), have been found to be influenced by the mechanical stimulation. Compliance mismatch forces the cells around the anastomosis to be exposed to abnormal mechanical stimulation, which is translated to biological responses to increase proliferation and migration of VSMC. Different biomaterials are being studied to develop compliant sSDVG. For example, polyurethane is being studied as a potential compliant vascular graft. Polyurethane vascular grafts were modified with gelatin and collagen to enhance endothelial cell adhesion and were modified using heparin to reduce thrombogenesis. Likewise, poly(vinyl alcohol) (PVA) vascular grafts were developed in 2008. PVA hydrogel is bio-inert, low-thrombogenic, and non-cytotoxic biomaterial with easily modified mechanical properties. The compliance of PVA vascular graft developed by Chaouat et al. had comparable compliance to the native blood vessels. However, the compliance, as well as other mechanical properties, of the PVA grafts were heavily influenced by the conditions in which the crosslinking of the hydrogel occurred. While the variation was observed, it was not studied systematically to identify the effects of the fabrication conditions on mechanical properties. In this thesis, the roles crosslinking density and interlayer adhesion play in compliance and burst pressure of PVA vascular grafts were studied. Fabrication parameters were categorized based on their effects on either crosslinking density or interlayer adhesion. PVA tubes with different fabrication conditions were made to yield tubes with lower crosslinking density, higher crosslinking density, lower interlayer adhesion, and higher interlayer adhesion. It was found that the higher crosslinking density resulted in higher burst pressure and lower compliance. Furthermore, it was found that higher interlayer adhesion resulted in higher burst pressure and lower compliance as well. Elastic modulus and suture-retention strength of the control, higher interlayer adhesion, and higher crosslinking density were compared as well. The result displayed that only the circumferential elastic modulus was affected by the interlayer adhesion and crosslinking density. Therefore, the study concluded that it is important to balance crosslinking density and interlayer adhesion to fabricate PVA grafts with desired compliance. Consistency is important for research to ensure reliable result. In part due to the sensitivity to fabrication condition, the consistency of PVA vascular graft suffered from person-to-person variation in fabrication process. PVA vascular grafts are fabricated using dip-casting method. In this method, a cylindrical mold is dipped into PVA crosslinking solution to produce thin layer of PVA hydrogel on the mold. The dipping is repeated until the PVA graft reach desired wall thickness. Also, while PVA hydrogel crosslinked using chemical crosslinking method is observed to be non-degradable, the stability of PVA grafts were not studied. The batch-to-batch consistency of PVA tubes made using automated process was studied, as well as the long-term stability of PVA grafts. The automated fabrication method developed displayed similar capacity as those made using manual fabrication method. The grafts made using automated process displayed consistent variation in wall thickness, burst pressure, and compliance. The grafts made using automated process and manual process exhibited comparable burst pressure and compliance when accounting for the wall thickness. Lastly, physical dimensions were compared to study long-term stability of the PVA grafts. Wall thickness, graft length, and dry weights displayed less than 5% change after 180 days of incubation. PVA hydrogel is also a good platform to study the effects of compliance mismatch on VSMC. Mechanical stimulation is essential for understanding the responses of VSMC on formation of IH. Studies have found that PDGF-BB and pMLCK are upregulated when VSMC are exposed to cyclic stretching. Furthermore, VSMC have been observed increase in proliferation and changes to migratory phenotype when exposed to cyclic strain. However, understanding the isolated effects of compliance mismatch has been difficult due to lack of continuous sample with two distinct regions of stiffness. In this thesis, a hybrid method using both physical and chemical crosslinking was developed to form continuous compliance mismatched samples using PVA hydrogel. The samples were characterized and found to be continuous in both parallel and perpendicular to the mismatch line. The samples were then used to perform in vitro experiments using human umbilical arterial smooth muscle cells (HUASMC) with exposure to cyclic stretching at 10% strain for 4 hours. Exposure to mechanical stimulation resulted in higher proliferation, change into migratory phenotype, compactification of PDGF-BB, and higher expression of pMLCK for the all the groups Among the stretched groups, compliance mismatch resulted in highest proliferation, pMLCK expression, and highest number of cells with concentrated PDGF-BB signal. However, no nuclear localization of yes-associated protein (YAP) was observed. The experiments were repeated with samples with higher compliance mismatch. Nuclear localization of PDGF-BB and YAP was observed when HUASMC cultured on higher compliance mismatched samples were exposed to cyclic stretch of 10% strain for 4 hours. Therefore, it can be concluded that not only does compliance mismatch affect cellular responses to cyclic stretching, but also the extent of compliance mismatch plays a role in the responses

A Study on Radiant Heat Application to the Curing Process for Improvement of Free-form Concrete Panel Productivity

As free-form panel production takes a long time, it extends the construction period and increases construction expenses. This study suggests a method to apply radiant heat to concrete for the purpose of shortening the curing and removal process in free-form panel production. The optimal temperature and time for removal are determined based on the results of constant temperature/humidity curing experiments and quartz tube heater curing experiments. Through an experiment in various time settings, the general time of FCP (Free-form Concrete Panel) production is measured to examine whether the productivity is enhanced. It is expected that findings of this study contribute to shortening the construction period and reducing construction expenses as well as future studies on the FCP manufacturing equipment

Exploring Data-Driven Components of Socially Intelligent AI through Cooperative Game Paradigms

The development of new approaches for creating more “life-like” artificial intelligence (AI) capable of natural social interaction is of interest to a number of scientific fields, from virtual reality to human–robot interaction to natural language speech systems. Yet how such “Social AI” agents might be manifested remains an open question. Previous research has shown that both behavioral factors related to the artificial agent itself as well as contextual factors beyond the agent (i.e., interaction context) play a critical role in how people perceive interactions with interactive technology. As such, there is a need for customizable agents and customizable environments that allow us to explore both sides in a simultaneous manner. To that end, we describe here the development of a cooperative game environment and Social AI using a data-driven approach, which allows us to simultaneously manipulate different components of the social interaction (both behavioral and contextual). We conducted multiple human–human and human–AI interaction experiments to better understand the components necessary for creation of a Social AI virtual avatar capable of autonomously speaking and interacting with humans in multiple languages during cooperative gameplay (in this case, a social survival video game) in context-relevant ways

Glycaemic status, insulin resistance, and risk of infection-related mortality:a cohort study

Importance: the impact of non-diabetic hyperglycaemia and insulin resistance on infection-related mortality risk remains unknown.Objective: we investigated the association of glycaemic status and insulin resistance with infection-related mortality in individuals with and without diabetes.Design: cohort study based on Kangbuk Samsung Health Study and national death records.Participants: about 666 888 Korean adults who underwent fasting blood measurements including glucose, glycated haemoglobin (HbA1c), and insulin during health-screening examinations were followed for up to 15.8 years.Main outcome and measures: infection-related mortality, therefore we used Cox proportional hazards regression analyses to estimate hazard ratios (HRs) and 95% CIs for infection-related mortality. Vital status and infection-related mortality were ascertained through national death records. Variable categories were created based on established cut-offs for glucose and HbA1c levels and homeostatic model assessment of insulin resistance (HOMA-IR) quintiles.Results: during a median follow-up of 8.3 years, 313 infectious disease deaths were dentified. The associations of glucose and HbA1c levels with infection-related mortality were J-shaped (P for quadratic trend&lt;.05). The multivariable-adjusted HR (95% CIs) for infection-related mortality comparing glucose levels &lt;5, 5.6-6.9, and ≥7.0 mmol/L to 5.0–5.5 mmol/L (the reference) were 2.31 (1.47–3.64), 1.65 (1.05–2.60), and 3.41 (1.66–7.00), respectively. Among individuals without diabetes, the multivariable-adjusted HR for infection-related mortality for insulin resistance (HOMA-IR ≥75th centile versus &lt;75th centile) was 1.55 (1.04–2.32).Conclusions and relevance: both low and high glycaemic levels and insulin resistance were independently associated with increased infection-related mortality risk, indicating a possible role of abnormal glucose metabolism in increased infection-related mortality.<br/

CTCF cooperates with CtIP to drive homologous recombination repair of double-strand breaks

The pleiotropic CCCTC-binding factor (CTCF) plays a role in homologous recombination (HR) repair of DNA double-strand breaks (DSBs). However, the precise mechanistic role of CTCF in HR remains largely unclear. Here, we show that CTCF engages in DNA end resection, which is the initial, crucial step in HR, through its interactions with MRE11 and CtIP. Depletion of CTCF profoundly impairs HR and attenuates CtIP recruitment at DSBs. CTCF physically interacts with MRE11 and CtIP and promotes CtIP recruitment to sites of DNA damage. Subsequently, CTCF facilitates DNA end resection to allow HR, in conjunction with MRE11-CtIP. Notably, the zinc finger domain of CTCF binds to both MRE11 and CtIP and enables proficient CtIP recruitment, DNA end resection and HR. The N-terminus of CTCF is able to bind to only MRE11 and its C-terminus is incapable of binding to MRE11 and CtIP, thereby resulting in compromised CtIP recruitment, DSB resection and HR. Overall, this suggests an important function of CTCF in DNA end resection through the recruitment of CtIP at DSBs. Collectively, our findings identify a critical role of CTCF at the first control point in selecting the HR repair pathway

Role of histamine-mediated macrophage differentiation in clearance of metastatic bacterial infection

Macrophages are highly heterogeneous immune cells with a role in maintaining tissue homeostasis, especially in activating the defense response to bacterial infection. Using flow cytometric and single-cell RNA-sequencing analyses of peritoneal cells, we here show that small peritoneal macrophage and immature macrophage populations are enriched in histamine-deficient (Hdc-/-) mice, characterized by a CD11bmiF4/80loCCR2+MHCIIhi and CD11bloF4/80miTHBS1+IL-1α+ phenotype, respectively. Molecular characterization revealed that immature macrophages represent an abnormally differentiated form of large peritoneal macrophages with strong inflammatory properties. Furthermore, deficiency in histamine signaling resulted in significant impairment of the phagocytic activity of peritoneal macrophage populations, conferring high susceptibility to bacterial infection. Collectively, this study reveals the importance of histamine signaling in macrophage differentiation at the molecular level to maintain tissue homeostasis, offering a potential therapeutic target for bacterial infection-mediated diseases

Swine gut microbiome associated with non-digestible carbohydrate utilization

Non-digestible carbohydrates are an unavoidable component in a pig’s diet, as all plant-based feeds contain different kinds of non-digestible carbohydrates. The major types of non-digestible carbohydrates include non-starch polysaccharides (such as cellulose, pectin, and hemicellulose), resistant starch, and non-digestible oligosaccharides (such as fructo-oligosaccharide and xylo-oligosaccharide). Non-digestible carbohydrates play a significant role in balancing the gut microbial ecology and overall health of the swine by promoting the production of short chain fatty acids. Although non-digestible carbohydrates are rich in energy, swine cannot extract this energy on their own due to the absence of enzymes required for their degradation. Instead, they rely on gut microbes to utilize these carbohydrates for energy production. Despite the importance of non-digestible carbohydrate degradation, limited studies have been conducted on the swine gut microbes involved in this process. While next-generation high-throughput sequencing has aided in understanding the microbial compositions of the swine gut, specific information regarding the bacteria involved in non-digestible carbohydrate degradation remains limited. Therefore, it is crucial to investigate and comprehend the bacteria responsible for the breakdown of non-digestible carbohydrates in the gut. In this mini review, we have discussed the major bacteria involved in the fermentation of different types of non-digestible carbohydrates in the large intestine of swine, shedding light on their potential roles and contributions to swine nutrition and health

Calcitonin receptor N-glycosylation enhances peptide hormone affinity by controlling receptor dynamics

The class B G protein-coupled receptor (GPCR) calcitonin receptor (CTR) is a drug target for osteoporosis and diabetes. N-glycosylation of asparagine 130 in its extracellular domain (ECD) enhances calcitonin hormone affinity with the proximal GlcNAc residue mediating this effect through an unknown mechanism. Here, we present two crystal structures of salmon calcitonin-bound, GlcNAc-bearing CTR ECD at 1.78 and 2.85 Å resolutions and analyze the mechanism of the glycan effect. The N130 GlcNAc does not contact the hormone. Surprisingly, the structures are nearly identical to a structure of hormone-bound, N-glycan-free ECD, which suggested that the GlcNAc might affect CTR dynamics not observed in the static crystallographic snapshots. Hydrogen-deuterium exchange mass spectrometry and molecular dynamics simulations revealed that glycosylation stabilized a β-sheet adjacent to the N130 GlcNAc and the N-terminal α-helix near the peptide-binding site, while increasing flexibility of the peptide-binding site turret loop. These changes due to N-glycosylation increased the ligand on-rate and decreased its off rate. The glycan effect extended to RAMP-CTR amylin receptor complexes and was also conserved in the related CGRP receptor. These results reveal that N-glycosylation can modulate GPCR function by altering receptor dynamics