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Recent preclinical trials have shown that alginate injections are a promising treatment for ischemic heart disease. Although improvements in heart function and global structure have been reported following alginate implants, the underlying structure is poorly understood. Using high resolution ex vivo MRI and DT-MRI of the hearts of normal control swine (n = 8), swine with induced heart failure (n = 5), and swine with heart failure and alginate injection treatment (n = 6), we visualized and quantified the fibre distribution and implant material geometry. Our findings show that the alginate injectates form solid ellipsoids with a retention rate of 68.7% ± 21.3% (mean ± SD) and a sphericity index of 0.37 ± 0.03. These ellipsoidal shapes solidified predominantly at the mid-wall position with an inclination of -4.9° ± 31.4° relative to the local circumferential direction. Overall, the change to left ventricular wall thickness and myofiber orientation was minor and was associated with heart failure and not the presence of injectates. These results show that alginate injectates conform to the pre-existing tissue structure, likely expanding along directions of least resistance as mass is added to the injection sites. The alginate displaces the myocardial tissue predominantly in the longitudinal direction, causing minimal disruption to the surrounding myofiber orientations.

Purpose: Biomaterial and stem cell delivery are promising approaches to treating myocardial infarction. However, the mechanical and biochemical mechanisms underlying the therapeutic benefits require further clarification. This study aimed to assess the deformation of stem cells injected with the biomaterial into the infarcted heart., Methods: A microstructural finite element model of a mid-wall infarcted myocardial region was developed from ex vivo microcomputed tomography data of a rat heart with left ventricular infarct and intramyocardial biomaterial injectate. Nine cells were numerically seeded in the injectate of the microstructural model. The microstructural and a previously developed biventricular finite element model of the same rat heart were used to quantify the deformation of the cells during a cardiac cycle for a biomaterial elastic modulus (E inj ) ranging between 4.1 and 405,900 kPa., Results: The transplanted cells' deformation was largest for E inj = 7.4 kPa, matching that of the cells, and decreased for an increase and decrease in E inj . The cell deformation was more sensitive to E inj changes for softer (E inj ≤ 738 kPa) than stiffer biomaterials., Conclusions: Combining the microstructural and biventricular finite element models enables quantifying micromechanics of transplanted cells in the heart. The approach offers a broader scope for in silico investigations of biomaterial and cell therapies for myocardial infarction and other cardiac pathologies., Competing Interests: Declarations. Competing Interests: The authors declare that they have no competing interests., (© 2024. The Author(s).)

Introduction: Alcohol dependence is a global issue with many negative consequences, including alcohol-related brain damage (ARBD). Assessment of the sociodemographic and cognitive characteristics of individuals with confirmed or suspected ARBD presenting to alcohol services warrants further investigation., Methods: This study retrospectively examined rates of cognitive impairment using Montreal Cognitive Assessment (MoCA) data from 300 adults who visited three alcohol support services. We demonstrate that 55.3% of the sample had significant levels of cognitive impairment. Females' cognitive performance was disproportionately negatively affected by historical alcohol use relative to males., Results: The analysis identified four categories of participants, and the majority had a long history (+10 years) of alcohol use and were still actively drinking. Those taking part in active treatment for ARBD or practising abstinence demonstrated lower levels of cognitive impairment. Additionally, prior access to specialised ARBD care was associated with higher MoCA scores., Discussion: This research has identified a range of key service engagement, sociodemographic and cognitive characteristics that could be used to optimise support for those with alcohol dependence, whilst also highlighting some critical questions to be addressed in future research., Competing Interests: The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest., (Copyright © 2024 Davies, Lewis, John, Quelch and Roderique-Davies.)

Cells mechanically interact with their environment to sense, for example, topography, elasticity and mechanical cues from other cells. Mechano-sensing has profound effects on cellular behaviour, including motility. The current study aims to develop a mathematical model of cellular mechano-sensing on planar elastic substrates and demonstrate the model's predictive capabilities for the motility of individual cells in a colony. In the model, a cell is assumed to transmit an adhesion force, derived from a dynamic focal adhesion integrin density, that locally deforms a substrate, and to sense substrate deformation originating from neighbouring cells. The substrate deformation from multiple cells is expressed as total strain energy density with a spatially varying gradient. The magnitude and direction of the gradient at the cell location define the cell motion. Cell-substrate friction, partial motion randomness, and cell death and division are included. The substrate deformation by a single cell and the motility of two cells are presented for several substrate elasticities and thicknesses. The collective motility of 25 cells on a uniform substrate mimicking the closure of a circular wound of 200 µm is predicted for deterministic and random motion. Cell motility on substrates with varying elasticity and thickness is explored for four cells and 15 cells, the latter again mimicking wound closure. Wound closure by 45 cells is used to demonstrate the simulation of cell death and division during migration. The mathematical model can adequately simulate the mechanically induced collective cell motility on planar elastic substrates. The model is suitable for extension to other cell and substrates shapes and the inclusion of chemotactic cues, offering the potential to complement in vitro and in vivo studies., (© 2023. The Author(s), under exclusive licence to Springer-Verlag GmbH Germany, part of Springer Nature.)

Intramyocardial delivery of biomaterials is a promising concept for treating myocardial infarction. The delivered biomaterial provides mechanical support and attenuates wall thinning and elevated wall stress in the infarct region. This study aimed at developing a biventricular finite element model of an infarcted rat heart with a microstructural representation of an in situ biomaterial injectate, and a parametric investigation of the effect of the injectate stiffness on the cardiac mechanics. A three-dimensional subject-specific biventricular finite element model of a rat heart with left ventricular infarct and microstructurally dispersed biomaterial delivered 1 week after infarct induction was developed from ex vivo microcomputed tomography data. The volumetric mesh density varied between 303 mm -3 in the myocardium and 3852 mm -3 in the injectate region due to the microstructural intramyocardial dispersion. Parametric simulations were conducted with the injectate's elastic modulus varying from 4.1 to 405,900 kPa, and myocardial and injectate strains were recorded. With increasing injectate stiffness, the end-diastolic median myocardial fibre and cross-fibre strain decreased in magnitude from 3.6% to 1.1% and from -6.0% to -2.9%, respectively. At end-systole, the myocardial fibre and cross-fibre strain decreased in magnitude from -20.4% to -11.8% and from 6.5% to 4.6%, respectively. In the injectate, the maximum and minimum principal strains decreased in magnitude from 5.4% to 0.001% and from -5.4% to -0.001%, respectively, at end-diastole and from 38.5% to 0.06% and from -39.0% to -0.06%, respectively, at end-systole. With the microstructural injectate geometry, the developed subject-specific cardiac finite element model offers potential for extension to cellular injectates and in silico studies of mechanotransduction and therapeutic signalling in the infarcted heart with an infarct animal model extensively used in preclinical research., (© 2023 The Authors. International Journal for Numerical Methods in Biomedical Engineering published by John Wiley & Sons Ltd.)

RNA interference is a promising therapeutical approach presently hindered by delivery concerns such as rapid RNA degradation and targeting of individual tissues. Injectable hydrogels are one potentially simple and direct route towards overcoming these barriers. Here we report on the utility of a combination of a mildly modified form of the clinically utilised fibrin hydrogel with Invivofectamine ® 3.0, a lipid nonviral transfection vector, for local and sustained release. PEGylation of fibrin allowed for controlled release of small interfering RNA (siRNA)-lipopolyplexes for at least 10 days and greatly increased the stability of fibrin in vitro and in vivo . A 3D cell culture model and a release study showed transfection efficacy of siRNA-lipopolyplexes was retained for a minimum of 7 days. Injection in conjunction with PEGylated-fibrinogen significantly increased retention of siRNA-lipopolyplexes in mouse skeletal muscle and enhanced knockdown of myostatin mRNA that correlated with muscle growth. Thus, the increased efficacy observed here for the combination of a lipid nanoparticle, the only type of nonviral vector approved for the clinic, with fibrin, might allow for more rapid translation of injectable hydrogel-based RNA interference., (© The Author(s) 2022. Published by Oxford University Press.)

During chemotherapy, structural and mechanical changes in malignant cells have been observed in several cancers, including leukaemia and pancreatic and prostate cancer. Such cellular changes may act as physical biomarkers for chemoresistance and cancer recurrence. This study aimed to determine how exposure to paclitaxel affects the intracellular stiffness of human oesophageal cancer of South African origin in vitro. A human oesophageal squamous cell carcinoma cell line WHCO1 was cultured on glass substrates (2D) and in collagen gels (3D) and exposed to paclitaxel for up to 48 h. Cellular morphology and stiffness were assessed with confocal microscopy, visually aided morpho-phenotyping image recognition and mitochondrial particle tracking microrheology at 24 and 48 h. In the 2D environment, the intracellular stiffness was higher for the paclitaxel-treated than for untreated cells at 24 and 48 h. In the 3D environment, the paclitaxel-treated cells were stiffer than the untreated cells at 24 h, but no statistically significant differences in stiffness were observed at 48 h. In 2D, paclitaxel-treated cells were significantly larger at 24 and 48 h and more circular at 24 but not at 48 h than the untreated controls. In 3D, there were no significant morphological differences between treated and untreated cells. The distribution of cell shapes was not significantly different across the different treatment conditions in 2D and 3D environments. Future studies with patient-derived primary cancer cells and prolonged drug exposure will help identify physical cellular biomarkers to detect chemoresistance onset and assess therapy effectiveness in oesophageal cancer patients., (© The Author(s) 2022. Published by Oxford University Press. All rights reserved. For permissions, please e-mail: journals.permissions@oup.com.)

The regenerative promise of nanosized extracellular vesicles (EVs) secreted by cells is widely explored. Recently, the capacity of EVs purified from blood to elicit regenerative effect has begun to be evaluated. Blood might be a readily available source of EVs, avoiding need for extensive cell culturing, but there are specific issues that complicate use of the biofluid in this area. We assess the evidence for blood containing regenerative material, progress made towards delivering blood derived EVs as regenerative therapeutics, difficulties that relate to the complexity of blood and the promise of hydrogel-based delivery of EVs., Competing Interests: Declaration of competing interest The authors declare no conflicts of interest., (Copyright © 2021 Elsevier B.V. and Société Française de Biochimie et Biologie Moléculaire (SFBBM). All rights reserved.)

Existing in silico models for single cell mechanics feature limited representations of cytoskeletal structures that contribute substantially to the mechanics of a cell. We propose a micromechanical hierarchical approach to capture the mechanical contribution of actin stress fibres. For a cell-specific fibroblast geometry with membrane, cytoplasm and nucleus, the Mori-Tanaka homogenization method was employed to describe cytoplasmic inhomogeneities and constitutive contribution of actin stress fibres. The homogenization was implemented in a finite element model of the fibroblast attached to a substrate through focal adhesions. Strain in cell membrane, cytoplasm and nucleus due to uniaxial substrate stretch was assessed for different stress fibre volume fractions and different elastic modulus of the substrate. A considerable decrease of the peak strain with increasing stress fibre content was observed in cytoplasm and nucleus but not the membrane, whereas the peak strain in cytoplasm, nucleus and membrane increased for increasing elastic modulus of the substrate. Finite element mesh of reconstructed human fibroblast and intracellular strain distribution in cell subjected to substrate stretch., (© 2021. International Federation for Medical and Biological Engineering.)

Obstructive sleep apnoea (OSA) is a serious debilitating condition with significant morbidity and mortality affecting almost one billion adults globally. The current gold standard in the non-surgical management of airway collapse is continuous positive airway pressure (CPAP). However, non-compliance leads to a high abandon rate (27-46%). While there are multiple sites of airway obstruction during sleep, the tongue base is recognized as the key player in the pathogenesis of OSA. Poor outcomes of current tongue suspension devices are due to fracture, slippage or migration of devices. Three tongue tethering device groups, namely a polydioxanone/polyurethane combination (PDO + PU) treatment group, a PDO analytical control group, and a polypropylene (PP) descriptive control group, were implanted into 22 sheep (75-85 kg) in a two-phased study. After implant times of 8, 16, and 32 weeks, sheep were serially euthanized to allow for explantation of their tongues and chins. The PDO + PU devices remodeled during the 32-week implant period into a hybrid biological tendon-like tether through the process of gradual degradation of the PDO and collagen deposition as shown by electrophoresis, histology and mechanical testing. The control PDO device degraded completely after 32 weeks and the PP devices remained intact. The hybrid biological tendon-like tether exhibited a break-strength of 60 N, thus exceeding the maximum force to overcome upper airway collapse., (© 2020 Wiley Periodicals LLC.)

Background & Aims: Failure to control oesophago-gastric variceal bleeding (OGVB) and acute-on-chronic liver failure (ACLF) are both important prognostic factors in cirrhosis. The aims of this study were to determine whether ACLF and its severity define the risk of death in OGVB and whether insertion of rescue transjugular intrahepatic shunt (TIPS) improves survival in patients with failure to control OGVB and ACLF., Methods: Data on 174 consecutive eligible patients, with failure to control OGVB between 2005 and 2015, were collected from a prospectively maintained intensive care unit registry. Rescue TIPS was defined as technically successful TIPS within 72 hours of presentation with failure to control OGVB. Cox-proportional hazards regression analyses were applied to explore the impact of ACLF and TIPS on survival in patients with failure to control OGVB., Results: Patients with ACLF (n = 119) were significantly older, had organ failures and higher white cell count than patients with acute decompensation (AD, n = 55). Mortality at 42-days and 1-year was significantly higher in patients with ACLF (47.9% and 61.3%) than in those with AD (9.1% and 12.7%, p <0.001), whereas there was no difference in the number of endoscopies and transfusion requirements between these groups. TIPS was inserted in 78 patients (AD 21 [38.2%]; ACLF 57 [47.8%]; p = 0.41). In ACLF, rescue TIPS insertion was an independent favourable prognostic factor for 42-day mortality. In contrast, rescue TIPS did not impact on the outcome of patients with AD., Conclusions: This study shows that in patients with failure to control OGVB, the presence and severity of ACLF determines the risk of 42-day and 1-year mortality. Rescue TIPS is associated with improved survival in patients with ACLF., Lay Summary: Variceal bleeding that is not controlled by initial endoscopy is associated with high risk of death. The results of this study showed that in the occurrence of failure of the liver and other organs defines the risk of death. In these patients, insertion of a shunt inside the liver to drain the portal vein improves survival., Competing Interests: Conflict of interest Rajiv Jalan has research collaborations with Yaqrit and Takeda. Rajiv Jalan is the inventor of OPA, which has been patented by UCL and licensed to Mallinckrodt Pharma. He is also the founder of Yaqrit Ltd, a spin out company from University College London. He is also a Founder of Thoeris Ltd. All the other authors do not have any potential conflict of interest to declare. Please refer to the accompanying ICMJE disclosure forms for further details., (Copyright © 2020 European Association for the Study of the Liver. Published by Elsevier B.V. All rights reserved.)

Due to the abundance of lipoproteins in blood, it is challenging to characterize the biological functions and components of blood-derived extracellular vesicles. The aim of this study was to develop a multiple-step purification protocol to separate serum exosomes from serum proteins and lipoproteins and assess their regenerative potential. Exosomes were isolated by concentrating them in human serum using ultracentrifugation (UC), followed sequentially by density gradient (DG) UC and size exclusion chromatography (SEC). Purity and characterization were assessed by western blots, Lipoprint®, enzyme-linked immunosorbent assay, electron microscopy, mass spectrometry, and nanoparticle tracking analysis. Functionality was assessed by cell proliferation analysis and with an in vivo subcutaneous angiogenesis model. SEC alone isolated nano-sized vesicles possessing vesicle markers TSG101 and CD9, but there was a substantial presence of apolipoprotein B, predominantly derived from very-low- and intermediate-density lipoprotein particles. This was reduced to an undetectable level using the combined UC DG SEC approach. Mass spectrometry identified 224 proteins in UC DG SEC isolates relative to the 135 from SEC, with considerable increases in exosome-related proteins and reductions in lipoproteins. A consistent but limited increase in human dermal fibroblast proliferation and evidence of neovascularization enhancement were observed after exposure to UC DG SEC exosomes. An UC DG SEC purification protocol considerably improved the removal of lipoproteins during isolation of serum exosomes. The purified exosomes stimulated cell proliferation and potentially increased an in vivo angiogenic response. This multistep purification allows for more accurate identification of serum exosome functional activity and composition., (© 2020 John Wiley & Sons Ltd.)

The concept of tissue engineering evolved long before the phrase was forged, driven by the thromboembolic complications associated with the early total artificial heart programs of the 1960s. Yet more than half a century of dedicated research has not fulfilled the promise of successful broad clinical implementation. A historical account outlines reasons for this scientific impasse. For one, there was a disconnect between distinct eras each characterized by different clinical needs and different advocates. Initiated by the pioneers of cardiac surgery attempting to create neointimas on total artificial hearts, tissue engineering became fashionable when vascular surgeons pursued the endothelialisation of vascular grafts in the late 1970s. A decade later, it were cardiac surgeons again who strived to improve the longevity of tissue heart valves, and lastly, cardiologists entered the fray pursuing myocardial regeneration. Each of these disciplines and eras started with immense enthusiasm but were only remotely aware of the preceding efforts. Over the decades, the growing complexity of cellular and molecular biology as well as polymer sciences have led to surgeons gradually being replaced by scientists as the champions of tissue engineering. Together with a widening chasm between clinical purpose, human pathobiology and laboratory-based solutions, clinical implementation increasingly faded away as the singular endpoint of all strategies. Moreover, a loss of insight into the healing of cardiovascular prostheses in humans resulted in the acceptance of misleading animal models compromising the translation from laboratory to clinical reality. This was most evident in vascular graft healing, where the two main impediments to the in-situ generation of functional tissue in humans remained unheeded-the trans-anastomotic outgrowth stoppage of endothelium and the build-up of an impenetrable surface thrombus. To overcome this dead-lock, research focus needs to shift from a biologically possible tissue regeneration response to one that is feasible at the intended site and in the intended host environment of patients. Equipped with an impressive toolbox of modern biomaterials and deep insight into cues for facilitated healing, reconnecting to the "user needs" of patients would bring one of the most exciting concepts of cardiovascular medicine closer to clinical reality., (Copyright © 2020 Zilla, Deutsch, Bezuidenhout, Davies and Pennel.)

Purpose: The lack of long-term patency of synthetic vascular grafts currently available on the market has directed research towards improving the performance of small diameter grafts. Improved radial compliance matching and tissue ingrowth into the graft scaffold are amongst the main goals for an ideal vascular graft., Methods: Biostable polyurethane scaffolds were manufactured by electrospinning and implanted in subcutaneous and circulatory positions in the rat for 7, 14 and 28 days. Scaffold morphology, tissue ingrowth, and mechanical properties of the scaffolds were assessed before implantation and after retrieval., Results: Tissue ingrowth after 24 days was 96.5 ± 2.3% in the subcutaneous implants and 77.8 ± 5.4% in the circulatory implants. Over the 24 days implantation, the elastic modulus at 12% strain decreased by 59% in direction of the fibre alignment whereas it increased by 1379% transverse to the fibre alignment of the highly aligned scaffold of the subcutaneous implants. The lesser aligned scaffold of the circulatory graft implants exhibited an increase of the elastic modulus at 12% strain by 77% in circumferential direction., Conclusion: Based on the observations, it is proposed that the mechanism underlying the softening of the highly aligned scaffold in the predominant fibre direction is associated with scaffold compaction and local displacement of fibres by the newly formed tissue. The stiffening of the scaffold, observed transverse to highly aligned fibres and for more a random fibre distribution, represents the actual mechanical contribution of the tissue that developed in the scaffold.

Despite positive initial outcomes emerging from preclinical and early clinical investigation of alginate hydrogel injection therapy as a treatment for heart failure, the lack of knowledge about the mechanism of action remains a major shortcoming that limits the efficacy of treatment design. To identify the mechanism of action, we examined previously unobtainable measurements of cardiac function from in vivo, ex vivo, and in silico states of clinically relevant heart failure (HF) in large animals. High-resolution ex vivo magnetic resonance imaging and histological data were used along with state-of-the-art subject-specific computational model simulations. Ex vivo data were incorporated in detailed geometric computational models for swine hearts in health (n = 5), ischemic HF (n = 5), and ischemic HF treated with alginate hydrogel injection therapy (n = 5). Hydrogel injection therapy mitigated elongation of sarcomere lengths (1.68 ± 0.10μm [treated] vs. 1.78 ± 0.15μm [untreated], p<0.001). Systolic contractility in treated animals improved substantially (ejection fraction = 43.9 ± 2.8% [treated] vs. 34.7 ± 2.7% [untreated], p<0.01). The in silico models realistically simulated in vivo function with >99% accuracy and predicted small myofiber strain in the vicinity of the solidified hydrogel that was sustained for up to 13 mm away from the implant. These findings suggest that the solidified alginate hydrogel material acts as an LV mid-wall constraint that significantly reduces adverse LV remodeling compared to untreated HF controls without causing negative secondary outcomes to cardiac function. STATEMENT OF SIGNIFICANCE: Heart failure is considered a growing epidemic and hence an important health problem in the US and worldwide. Its high prevalence (5.8 million and 23 million, respectively) is expected to increase by 25% in the US alone by 2030. Heart failure is associated with high morbidity and mortality, has a 5-year mortality rate of 50%, and contributes considerably to the overall cost of health care ($53.1 billion in the US by 2030). Despite positive initial outcomes emerging from preclinical and early clinical investigation of alginate hydrogel injection therapy as a treatment for heart failure, the lack of knowledge concerning the mechanism of action remains a major shortcoming that limits the efficacy of treatment design. To understand the mechanism of action, we combined high-resolution ex vivo magnetic resonance imaging and histological data in swine with state-of-the-art subject-specific computational model simulations. The in silico models realistically simulated in vivo function with >99% accuracy and predicted small myofiber strain in the vicinity of the solidified hydrogel that was sustained for up to 13 mm away from the implant. These findings suggest that the solidified alginate hydrogel material acts as a left ventricular mid-wall constraint that significantly reduces adverse LV remodeling compared to untreated heart failure controls without causing negative secondary outcomes to cardiac function. Moreover, if the hydrogel can be delivered percutaneously rather than via the currently used open-chest procedure, this therapy may become routine for heart failure treatment. A minimally invasive procedure would be in the best interest of this patient population; i.e., one that cannot tolerate general anesthesia and surgery, and it would be significantly more cost-effective than surgery., (Copyright © 2020. Published by Elsevier Ltd.)

The potential to control the rate of replacement of a biodegradable implant by a tissue would be advantageous. Here, we demonstrate that tissue invasion can be tuned through the novel approach of overlaying an enzymatically degradable hydrogel with an increasingly hydrolytically degradable environment. Poly(ethylene glycol) (PEG) hydrogels were formed from varying proportions of PEG-vinyl sulfone and PEG-acrylate (PEG-AC) monomers via a Michael-type addition reaction with a dithiol-containing matrix-metalloproteinase-susceptible peptide cross-linker. Swelling studies showed that PEG hydrogels with similar initial stiffnesses degraded more rapidly as the PEG-AC content increased. The replacement of subcutaneously implanted PEG hydrogels was also found to be proportional to their PEG-AC content. In addition, it would in many instances be desirable that these materials have the ability to stimulate their neovascularization. These hydrogels contained covalently bound heparin, and it was shown that a formulation of the hydrogel that allowed tissue replacement to occur over 1 month could trap and release growth factors and increase neovascularization by 50% over that time.

Myocardial infarction (MI), a type of cardiovascular disease, affects a significant proportion of people around the world. Traditionally, non-communicable chronic diseases were largely associated with aging populations in higher income countries. It is now evident that low- to middle-income countries are also affected and in these settings, younger individuals are at high risk. Currently, interventions for MI prolong the time to heart failure. Regenerative medicine and stem cell therapy have the potential to mitigate the effects of MI and to significantly improve the quality of life for patients. The main drawback with these therapies is that many of the injected cells are lost due to the vigorous motion of the heart. Great effort has been directed toward the development of scaffolds which can be injected alongside stem cells, in an attempt to improve retention and cell engraftment. In some cases, the scaffold alone has been seen to improve heart function. This study focuses on a synthetic polyethylene glycol (PEG) based hydrogel which is injected into the heart to improve left ventricular function following MI. Many studies in literature characterize PEG as a Newtonian fluid within a specified shear rate range, on the macroscale. The aim of the study is to characterize the flow of a 20 kDa PEG on the microscale, where the behavior is likely to deviate from macroscale flow patterns. Micro particle image velocimetry (μPIV) is used to observe flow behavior in microchannels, representing the gaps in myocardial tissue. The fluid exhibits non-Newtonian, shear-thinning behavior at this scale. Idealized two-dimensional computational fluid dynamics (CFD) models of PEG flow in microchannels are then developed and validated using the μPIV study. The validated computational model is applied to a realistic, microscopy-derived myocardial tissue model. From the realistic tissue reconstruction, it is evident that the myocardial flow region plays an important role in the distribution of PEG, and therefore, in the retention of material.

Recent preclinical trials have shown that alginate injections are a promising treatment for ischemic heart disease. Although improvements in heart function and global structure have been reported following alginate implants, the underlying structure is poorly understood. Using high resolution ex vivo MRI and DT-MRI of the hearts of normal control swine (n = 8), swine with induced heart failure (n = 5), and swine with heart failure and alginate injection treatment (n = 6), we visualized and quantified the fibre distribution and implant material geometry. Our findings show that the alginate injectates form solid ellipsoids with a retention rate of 68.7% ± 21.3% (mean ± SD) and a sphericity index of 0.37 ± 0.03. These ellipsoidal shapes solidified predominantly at the mid-wall position with an inclination of -4.9° ± 31.4° relative to the local circumferential direction. Overall, the change to left ventricular wall thickness and myofiber orientation was minor and was associated with heart failure and not the presence of injectates. These results show that alginate injectates conform to the pre-existing tissue structure, likely expanding along directions of least resistance as mass is added to the injection sites. The alginate displaces the myocardial tissue predominantly in the longitudinal direction, causing minimal disruption to the surrounding myofiber orientations., (Copyright © 2018. Published by Elsevier Ltd.)

Background: Mesenchymal stromal cells (MSC) repair infarcted hearts mainly through paracrine mechanisms. Low cell engraftment limits the release of soluble paracrine factors (SF) over time and, consequently, MSC efficacy. We tested whether a synthetic extracellular matrix mimic, a hydrogel containing heparin (H-HG), could ameliorate MSC engraftment and binding/release of SF, thus improving MSC therapy efficacy., Methods and Results: In vitro, rat bone-marrow MSC (rBM-MSC) were seeded and grown into H-HG. Under normoxia, the hydrogel did not affect cell survival (rBM-MSC survival >90% at each time point tested); vice versa, under hypoxia the biomaterial resulted to be protective for the cells (p < .001 vs rBM-MSC alone). H-HG or control PEG hydrogels (HG) were incubated with VEGF or bFGF for binding/release quantification. Data showed significantly higher amount of VEGF and bFGF bound by H-HG compared with HG (p < .05) and a constant release over time. In vivo, myocardial infarction (MI) was induced in female Sprague Dawley rats by permanent coronary ligation. One week later, saline, rBM-MSC, H-HG or rBM-MSC/H-HG were injected in the infarct zone. The co-injection of rBM-MSC/H-HG into infarcted hearts significantly increased cardiac function. Importantly, we observed a significant gain in MSC engraftment, reduction of ventricular remodeling and stimulation of neo-vasculogenesis. We also documented higher amounts of several pro-angiogenic factors in hearts treated with rBM-MSC/H-HG., Conclusions: Our data show that H-HG increases MSC engraftment, efficiently fine tunes the paracrine MSC actions and improves cardiac function in infarcted rat hearts., Statement of Significance: Transplantation of MSC is a promising treatment for ischemic heart disease, but low cell engraftment has so far limited its efficacy. The enzymatically degradable H-HG that we developed is able to increase MSC retention/engraftment and, at the same time, to fine-tune the paracrine effects mediated by the cells. Most importantly, the co-transplantation of MSC and H-HG in a rat model of ischemic cardiomyopathy improved heart function through a significant reduction in ventricular remodeling/scarring and amelioration in neo-vasculogenesis/endogenous cardiac regeneration. These beneficial effects are comparable to those obtained by others using a much greater number of cells, strengthening the efficacy of the biomaterial used in increasing the therapeutic effects of MSC. Given its efficacy and safety, documented by the absence of immunoreaction, our strategy appears readily translatable to clinical scenarios., (Copyright © 2018 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.)

In recent years, there has been an increasing interest in endovascular iliofemoral vein stenting to prevent/ alleviate symptoms related to proximal venous outflow obstruction. Maintaining long-term stent patency is one of the main challenges, and risk factors for the development of re-thrombosis are not well understood. Published data on the safety and efficacy of the procedure predominantly come from cohort studies mainly focusing on mechanical aspects relating to stent placement and flow. Aetiology of thrombus formation and thrombotic tendencies of patients due to underlying medical conditions are not captured well or linked to clinical outcomes, and the impact of choice and length of antithrombotic therapy have not been specifically investigated. Here, we review different procedure-related factors and patient characteristics that might increase the risk of re-thrombosis and the utility of antithrombotic treatment options currently available., (Copyright© Bentham Science Publishers; For any queries, please email at epub@benthamscience.net.)

Spontaneous endothelialization of synthetic vascular grafts may occur via three independent or concurrent modalities: transanastomotic (TA) outgrowth, transmural (TM) ingrowth or fallout (FO) from the blood. The limited TA and FO endothelialization, which occurs in humans, results in poor long-term patency in the small diameter position, where TM ingrowth may offer a clinically relevant alternative. To achieve sequential analysis of each mode of healing, loop grafts comprising anastomotically isolated angiopermissive polyurethane control grafts were abluminally sealed using either ePTFE wraps or solid polyurethane skins and implanted in the rat infrarenal aortic loop model for twelve weeks. Positive control grafts showed improved endothelialization and patency compared to the abluminally isolated mid-grafts. Furthermore, the mid-graft healing was accelerated with surface heparin and heparin-growth factor (VEGF, PDGF) modification in a three-week sub-study. We are thus able to distinguish between the three vascular graft endothelialization modes, and conclude that fallout plays a secondary role to TM healing. The increased endothelialisation for growth factor presenting grafts indicates the promise of this simple approach but further optimization is required., Statement of Significance: In addition to the full elucidation of, and differentiation between, the three healing/endothelialisation modes of vascular grafts, the significance of the work relates to the near-complete lack of endothelialisation of small diameter vascular grafts in humans (1-2 cm transanastomotic outgrowth on a graft that may be 60 cm long) even after decades of implantation. The concomitant retained midgraft thrombogenicity leads, together with anastomotic hyperplastic responses, to poor long-term outcomes. The large impact of successful translation of the current research to the achievement of full endothelialisation of long peripheral grafts in humans via transmural ingrowth (half a millimetre distance; thickness of the graft wall), is evident, and supported by the large improvements in clinical patencies achievable in by pre-seeding of ePTFE grafts with confluent endothelia., (Copyright © 2017 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.)

Surface modification with heparin has previously been shown to increase vascularization of porous scaffolds. In order to determine its efficacy with sustained release, heparin (Hep) was covalently incorporated into degradable (Type D) and non-degradable (Type N) polyethylene glycol (PEG) hydrogels. After in vitro characterization of their physicochemical properties, growth factor (GF) loaded, heparinised Type D gels were formed within the pores of porous polyurethane disks, which were then implanted and evaluated in a subcutaneous model. Type N gels formed faster (3.1±0.1 vs. 7.2±0.2min), were stiffer (10.0±0.5kPa vs. 7.1±1.2kPa) and more stable than degradable gels (>6month stability vs. disintegration ⩽22d in vitro; all p<0.001). Sustained release of covalently incorporated (CI) heparin from Type N (56days; first order kinetics) and Type D (21days; zero order kinetics) was achieved, as opposed to non-covalently incorporated (NI) heparin that eluted in a burst release within the first 2days. While Type D gels initially impeded tissue ingrowth into the porous scaffolds, they were completely degraded and replaced by ingrown tissue after 28days in vivo. At the latter timepoint disks containing gels without Hep or with non-covalently incorporated Hep were less vascularized than empty (no gel) controls. In contrast, the incorporation of covalently heparinized (no GF) and GF containing gels (no Hep) resulted in a 50% and 42% (p<0.05) improvement in vascularization, while an increase of 119% (p<0.001) was achieved with a combination of covalently attached Hep and GF. These gels thus provide a sustained release system for heparin and GF that extends the duration of their action to local tissue ingrowth., Statement of Significance: The paper describes the modification and covalent incorporation of heparin into degradable and non-degradable polyethylene glycol hydrogels in a way that provides for the hydrolytic cleavage of the linker for the release of the heparin in original and active form, and in an extended (21-56d) controlled (zero and first order respectively) manner. The successful use of these gels as growth-factor containing and releasing matrices for the improvement of in vivo vascularization holds promise for many potential uses in tissue engineering and regenerative medicine applications, such as vascular grafts and myocardial infarction therapy, where the antithrombotic and/or growth factor binding/potentiating properties are required., (Copyright © 2016 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.)

Biomaterial injectates are promising as a therapy for myocardial infarction to inhibit the adverse ventricular remodeling. The current study explored interrelated effects of injectate volume and infarct size on treatment efficacy. A finite element model of a rat heart was utilized to represent ischemic infarcts of 10%, 20%, and 38% of left ventricular wall volume and polyethylene glycol hydrogel injectates of 25%, 50%, and 75% of the infarct volume. Ejection fraction was 49.7% in the healthy left ventricle and 44.9%, 46.4%, 47.4%, and 47.3% in the untreated 10% infarct and treated with 25%, 50%, and 75% injectate, respectively. Maximum end-systolic infarct fiber stress was 41.6, 53.4, 44.7, 44.0, and 45.3 kPa in the healthy heart, the untreated 10% infarct, and when treated with the three injectate volumes, respectively. Treating the 10% and 38% infarcts with the 25% injectate volume reduced the maximum end-systolic fiber stress by 16.3% and 34.7% and the associated strain by 30.2% and 9.8%, respectively. The results indicate the existence of a threshold for injectate volume above which efficacy does not further increase but may decrease. The efficacy of an injectate in reducing infarct stress and strain changes with infarct size. Copyright © 2016 John Wiley & Sons, Ltd., (Copyright © 2016 John Wiley & Sons, Ltd.)

Predictive computational modelling in biomedical research offers the potential to integrate diverse data, uncover biological mechanisms that are not easily accessible through experimental methods and expose gaps in knowledge requiring further research. Recent developments in computing and diagnostic technologies have initiated the advancement of computational models in terms of complexity and specificity. Consequently, computational modelling can increasingly be utilised as enabling and complementing modality in the clinic-with medical decisions and interventions being personalised. Myocardial infarction and heart failure are amongst the leading causes of death globally despite optimal modern treatment. The development of novel MI therapies is challenging and may be greatly facilitated through predictive modelling. Here, we review the advances in patient-specific modelling of cardiac mechanics, distinguishing specificity in cardiac geometry, myofibre architecture and mechanical tissue properties. Thereafter, the focus narrows to the mechanics of the infarcted heart and treatment of myocardial infarction with particular attention on intramyocardial biomaterial delivery.

Understanding the passive mechanical properties of infarcted tissue at different healing stages is essential to explore the emerging biomaterial injection-based therapy for myocardial infarction (MI). Although rats have been widely used as animal models in such investigations, the data in literature that quantify the passive mechanical properties of rat heart infarcts is very limited. MI was induced in rats and hearts were harvested immediately (0 day), 7, 14 and 28 days after infarction onset. Left ventricle anterioapical samples were cut and underwent equibiaxial and non equibiaxial tension followed by uniaxial compression mechanical tests. Histological analysis was conducted to confirm MI and to quantify the size of the induced infarcts. Infarcts maintained anisotropy and the nonlinear biaxial and compressive mechanical behaviour throughout the healing phases with the circumferential direction being stiffer than the longitudinal direction. Mechanical coupling was observed between the two axes in all infarct groups. The 0, 7, 14 and 28 days infarcts showed 438, 693, 1048 and 1218kPa circumferential tensile moduli. The 28 day infarct group showed a significantly higher compressive modulus compared to the other infarct groups (p=0.0060, 0.0293, and 0.0268 for 0, 7 and 14 days groups). Collagen fibres were found to align in a preferred direction for all infarct groups supporting the observed mechanical anisotropy. The presented data are useful for developing material models for healing infarcts and for setting a baseline for future assessment of emerging mechanical-based MI therapies., (Copyright © 2016 Elsevier Ltd. All rights reserved.)

Myocardial infarction was experimentally induced in rat hearts and harvested immediately, 7, 14 and 28 days after the infarction induction. Anterior wall infarct samples underwent biaxial tensile and uniaxial compressive testing. Orientation of collagen fibres was analysed following mechanical testing. In this paper, we present the tensile and compressive stress-strain raw data, the calculated tensile and compressive moduli and the measured angles of collagen orientation. The presented data is associated with the research article titled "Characterisation of the mechanical properties of infarcted myocardium in the rat under biaxial tension and uniaxial compression" (Sirry et al., 2016) [1].

Directed cell motility, as controlled by soluble factors, is crucial for many biological processes, including development, cancer progression, and wound healing. The use of directed cell motility also shows promise for applications in regenerative medicine such as therapeutic angiogenesis. Unfortunately, current in vitro 3-D migration and invasion models limit our understanding and application of these processes. Here, we present a novel and cost-effective 3-D chemotaxis assay for assessing the invasive response of cells to a chemoattractant extracellular matrix (ECM). Our system takes advantage of a custom-casting chamber to set two gels in contact with each other along a defined front, one containing a suitable chemoattractant and the other the cells. Rotation of the chamber allows easy visualization of invasion across the interface. The effectiveness of the assay was demonstrated by studying the invasion of both human dermal fibroblasts (FBs) and smooth muscle cells (SMCs) into a polyethylene glycol (PEG) hydrogel containing basic fibroblast growth factor (bFGF). Incorporation of bFGF resulted in significantly increased and directional invasion for both cell groups.

Introduction: The renin-angiotensin system (RAS) is a dynamic network that plays a critical role in blood pressure regulation and fluid and electrolyte homeostasis. Modulators of the RAS, such as angiotensin-converting enzyme (ACE) inhibitors, are widely used to treat hypertension, heart failure and myocardial infarction., Methods: The effect of ACE inhibitors (lisinopril and C-domain-selective LisW-S) on the constituent peptides of the RAS following myocardial infarction was examined in rats. Ten angiotensin peptides were analysed using a sensitive LC-MS/MS-based assay to examine both the circulating and equilibrium levels of these peptides., Results: Administration of lisinopril or LisW-S caused a significant decrease in Ang 1-8/Ang 1-10 ratios as determined by circulating and equilibrium peptide level analysis. Furthermore, Ang 1-7 levels were elevated by both ACE inhibitors, but only lisinopril decreased the Ang 1-5/Ang 1-7 ratio. This indicates LisW-S C-domain specificity as Ang 1-5 is generated by hydrolysis of Ang 1-7 by the N-domain. Further corroboration of LisW-S C-domain specificity is that only lisinopril increased the circulating levels of the N-domain ACE substrate Ac-SDKP., Conclusion: LisW-S is able to effectively block ACE in vivo by C-domain-selective inhibition. The LC-MS/MS-based assay allows the evaluation of the pharmacologic impact of RAS inhibitors in different pathophysiological conditions., (© The Author(s) 2015.)

Regenerative therapies to improve prognosis after heart attack and mitigate the onset of heart failure are urgently needed. To this end, we developed a bioactive therapy of sustained release of the morphogen Sonic hedgehog (Shh) and the anti-inflammatory cytokine interleukin-10 (IL-10) from a coacervate delivery vehicle. This is combined with a structural therapy consisting of a biodegradable polyethylene glycol (PEG) hydrogel, harnessing the benefits of both components. Upon injection into the hearts of rats after heart attack, we found that each component synergistically improved the benefit of the other. Furthermore, their combination was critical to preserve heart function. These findings indicate that, when combined, growth factor delivery and an injectable hydrogel represent a promising therapeutic approach for treatment after heart attack.

Regulation of the rate of cell ingrowth into and within a matrix is desirable for efficient tissue regeneration. Polyethylene glycol hydrogels crosslinked with matrix metalloproteinase (MMP) susceptible peptide sequences permit cell-controlled invasion. In this study, hydrogels of the same stiffness polymerised using different ratios of a readily degradable MMP peptide sequence (PAN-MMP) and a MMP peptide with a limited degradation capacity (MMP-9) were assessed both in vitro and in vivo for cellular invasion. The degree of invasion into the various hydrogels was found to be tightly linked to the relative proportion of each peptide both in vitro and in vivo. Furthermore a good correlation between in vitro and in vivo ingrowth was observed. These findings demonstrate a highly tunable model for regulating cellular invasion which is readily translatable to in vivo models. This finding may allow for further optimisation of aspects of regenerative scaffolds such as tissue invasion, growth factor release and cellular encapsulation., Statement of Significance: Degradable hydrogels are used in a wide range of tissue regeneration approaches. A particularly advantageous variant of these hydrogels is where due to peptide based crosslinking of the polymeric hydrogels, cell invasion rate is dependent on cellular enzymatic activity. This present study demonstrates a further refinement whereby both cellular and tissue invasion rates are finely regulated through the polymerisation of a hydrogel with varying combinations of enzymatically degradable peptides. Importantly this allows for invasion rates to be controlled without altering the biomechanical properties of the hydrogel such as stiffness. The latter can further influence cellular behaviour thus potentially interfering with the desired outcome., (Copyright © 2015 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.)

Biomaterial injection-based therapies have showed cautious success in restoration of cardiac function and prevention of adverse remodelling into heart failure after myocardial infarction (MI). However, the underlying mechanisms are not well understood. Computational studies utilised simplified representations of the therapeutic myocardial injectates. Wistar rats underwent experimental infarction followed by immediate injection of polyethylene glycol hydrogel in the infarct region. Hearts were explanted, cryo-sectioned and the region with the injectate histologically analysed. Histological micrographs were used to reconstruct the dispersed hydrogel injectate. Cardiac magnetic resonance imaging data from a healthy rat were used to obtain an end-diastolic biventricular geometry which was subsequently adjusted and combined with the injectate model. The computational geometry of the injectate exhibited microscopic structural details found the in situ. The combination of injectate and cardiac geometry provides realistic geometries for multiscale computational studies of intra-myocardial injectate therapies for the rat model that has been widely used for MI research.

Angiotensin-converting enzyme (ACE, EC 3.4.15.1) is a metallopeptidase comprised of two homologous catalytic domains (N- and C-domains). The C-domain cleaves the vasoactive angiotensin II precursor, angiotensin I, more efficiently than the N-domain. Thus, C-domain-selective ACE inhibitors have been designed to investigate the pharmacological effects of blocking the C-terminal catalytic site of the enzyme and improve the side effect profile of current ACE inhibitors. Lisinopril-tryptophan (LisW-S), an analogue of the ACE inhibitor lisinopril, is highly selective for the C-domain. In this study, we have analysed the ex vivo domain selectivity and pharmacokinetic profile of LisW-S. The IC50 value of LisW-S was 38.5 nM in rat plasma using the fluorogenic substrate Abz-FRKP(Dnp)P-OH. For the pharmacokinetics analysis of LisW-S, a sensitive and selective LC-MS/MS method was developed and validated to determine the concentration of LisW-S in rat plasma. LisW-S was administered to Wistar rats at a dose of 1 mg/kg bodyweight intravenously, 5 mg/kg bodyweight orally. The Cmax obtained following oral administration of the drug was 0.082 μM and LisW-S had an apparent terminal elimination half-life of around 3.1 h. The pharmacokinetic data indicate that the oral bioavailability of LisW-S was approximately 5.4%. These data provide a basis for better understanding the absorption mechanism of LisW-S and evaluating its clinical application., (Copyright © 2014 Elsevier B.V. All rights reserved.)

Virus-mediated gene therapy is a promising strategy for numerous tissue engineering applications. Fibrin-based scaffolds have been previously used as vehicles for localised delivery of adenovirus to wound sites. However, their utility in the delivery of adeno-associated viruses to wound repair cells has not yet been determined. The influence of fibrin concentration on efficacy of delivery of AAV-2 to wound tissue was assessed in this study. Fibrin scaffolds containing recombinant AAV-2 encoding for β-galactosidase were polymerised in porous polyurethane discs and implanted subcutaneously in rats. A fibrin scaffold with a concentration of 50 mg/ml showed significantly elevated levels of β-galactosidase activity within explanted discs at 10 days compared to 10 mg/ml and 25 mg/ml fibrin. These findings inform efforts to optimise biodegradable scaffolds for the localised delivery of AAV in tissue engineering.

Myocardial infarction is an increasing health problem worldwide. Because of an under-supply of blood, the cardiomyocytes in the affected region permanently lose their ability to contract. This in turn gradually weakens the overall heart function. A new therapeutic approach based on the injection of a gel into the infarcted area aims to support the healing and to inhibit adverse remodelling that can lead to heart failure. A computational model is the basis for obtaining a better understanding of the heart mechanics, in particular, how myocardial infarction and gel injections affect its pumping performance. A strain invariant-based stored energy function is proposed to account for the passive mechanical behaviour of the model, which also makes provision for active contraction. To incorporate injections an additive homogenization approach is introduced. The numerical framework is developed using an in-house code based on the element-free Galerkin method. The main focus of this contribution is to investigate the influence of gel injections on the mechanics of the left ventricle during the diastolic filling and systolic isovolumetric (isochoric) contraction phases. It is found that gel injections are able to reduce the elevated fibre stresses caused by an infarct., (Copyright © 2013 John Wiley & Sons, Ltd.)

Extracellular mimetic hydrogels formed from peptide crosslinkers and polyethylene glycol monomers permit cell-controlled invasion. The use of matrix metalloproteinase specific peptides might further allow for selective control of different cell-type invasion. In this study, the invasion of fibroblasts and vascular smooth muscle cells (VSMC) into hydrogels polymerised with either a peptide generally permissive for matrix metalloproteinase (MMP) degradation or peptides preferentially cleaved by MMP-14 or MMP-9 enzymes were compared. The two cell-types invaded the MMP permissive hydrogel equally. However, invasion of VSMC into MMP-14 selective peptide crosslinked hydrogels was diametrically opposite in nature to that of fibroblasts whereby VSMC showed a two-fold increase into these hydrogels relative to that observed in permissive hydrogels whilst fibroblasts had a relative two-fold decrease (p < 0.01). These findings are suggestive that invasion and growth of different cell-types in engineered synthetic extracellular matrix mimics may be controlled selectively by the choice of protease specific peptide crosslinker and this could have general utility in tissue regenerative and engineering approaches., (Copyright © 2013 Elsevier Ltd. All rights reserved.)

Myocardial infarction therapies involving biomaterial injections have shown benefits in inhibiting progression towards heart failure. However, the underlying mechanisms remain unclear. A finite element model of the human left ventricle was developed from magnetic resonance images. An anteroapical infarct was represented at acute (AI) and fibrotic (FI) stage. Hydrogel injections in the infarct region were modelled with layered (L) and bulk (B) distribution. In the FI, injectates reduced end-systolic myofibre stresses from 291.6% to 117.6% (FI-L) and 115.3% (FI-B) of the healthy value, whereas all AI models exhibited sub-healthy stress levels (AI: 90.9%, AI-L: 20.9%, AI-B: 30.5%). Reduction in end-diastolic infarct stress were less pronounced for both FI (FI: 294.1%, FI-L: 176.5%, FI-B: 188.2%) and AI (AI: 94.1%, AI-L: 35.3%, AI-B: 41.2%). In the border zone, injectates reduced end-systolic fibre stress by 8-10% and strain from positive (AI) and zero (FI) to negative. Layered and bulk injectates increased ejection fraction by 7.4% and 8.4% in AI and 14.1% and 13.7% in FI. The layered injectate had a greater impact on infarct stress and strain at acute stage, whereas the bulk injectate exhibited greater benefits at FI stage. These findings were confirmed by our previous in vivo results., (Copyright © 2013 John Wiley & Sons, Ltd.)

N-myc downstream regulated gene 1 (NDRG1/Cap43/Drg-1) has previously been shown to be dysregulated in esophageal squamous cell carcinoma (ESCC). In this study, we investigated the role of NDRG1 in the neoplastic progression of ESCC using ectopic gain-of-function and loss-of-function approaches. Stable transfectants of the KYSE30 ESCC cell line with altered NDRG1 levels were generated by lentiviral transduction. Although no measurable effects on in vitro cell proliferation were observed with altered NDRG1 expression, the ectopic overexpression of NDRG1 was positively linked to recognized markers of metastasis, angiogenesis and apoptotic evasion. Accordingly, in the nude mouse xenograft model system, NDRG1 overexpression promoted the in vivo growth of KYSE30 derived xenografts, which could be attributed to the reduced apoptotic and enhanced angiogenic activities associated with this gene. These processes were mediated in part by increased NFκB activity in NDRG1 overexpressing cells. Nevertheless, no significant phenotypic changes were observed in response to NDRG1 knock-down, suggesting that this gene might not be essential for the neoplastic progression of ESCC. Taken together, our results suggest that NDRG1 may play positive but dispensable roles in the progression of esophageal squamous cell carcinoma.

An emerging therapy to limit adverse heart remodelling following myocardial infarction (MI) is the injection of polymers into the infarcted left ventricle (LV). In the few numerical studies carried out in this field, the definition and distribution of the hydrogel in the infarcted myocardium were simplified. In this computational study, a more realistic biomaterial distribution was simulated after which the effect on cardiac function and mechanics was studied. A validated finite element heart model was used in which an antero-apical infarct was defined. Four infarct models were created representing different temporal phases in the progression of a MI. Hydrogel layers were simulated in the infarcted myocardium in each model. Biomechanical and functional improvement of the LV was found after hydrogel inclusion in the ischaemic models representing the early phases of MI. In contrast, only functional but no mechanical restitution was shown in the scar model due to hydrogel presence.

Biomaterials are increasingly being investigated as a means of reducing stress within the ventricular wall of infarcted hearts and thus attenuating pathological remodelling and loss of function. In this context, we have examined the influence of timing of delivery on the efficacy of a polyethylene glycol hydrogel polymerised with an enzymatically degradable peptide sequence. Delivery of the hydrogel immediately after infarct induction resulted in no observable improvements, but a delay of one week in delivery resulted in significant increases in scar thickness and fractional shortening, as well as reduction in end-systolic diameter against saline controls and immediately injected hydrogel at both 2 and 4 weeks post-infarction (p < 0.05). Hydrogels injected at one week were degraded significantly slower than those injected immediately and this may have played a role in the differing outcomes. The hydrogel assumed markedly different morphologies at the two time points having either a fibrillar or bulky appearance after injection immediately or one week post-infarction respectively. We argue that the different morphologies result from infarction induced changes in the cardiac structure and influence the degradability of the injectates. The results indicate that timing of delivery is important and that very early time points may not be beneficial., (Copyright © 2011 Elsevier Ltd. All rights reserved.)

Tissue regeneration into a three-dimensional scaffold requires the stimulation of blood vessel ingrowth. We have employed a freely interconnecting porous scaffold developed by us to determine the utility of a covalently bound heparin surface coating for the delivery of vascular endothelial growth factor (VEGF) and platelet-derived growth factor BB (PDGF-BB) in vivo. The heparin surface was shown to release VEGF far more rapidly than PDGF-BB in vitro (VEGF: 75 ng/h for 24 h; PDGF-BB: 86 pg/h for >7 days). In rat subcutaneous implants, at 10 days the heparin surface alone increased vessel ingrowth substantially (p<0.05 vs. unmodified scaffold), release of VEGF resulted in a further increase (p<0.05 vs. heparinized scaffold), whereas PDGF-BB had no additional effect. The increase induced by the combination of growth factors was similar to VEGF alone. After 2 months, PDGF-BB, but not VEGF delivery, resulted in a substantial increase in vascularization above that induced by heparin (p<0.05). At the longer time point the combination of growth factors was similar to PDGF-BB. However, only the combination of growth factors significantly elevated the number of ingrowing arterioles (p<0.05 vs. heparinized scaffold). Thus, the covalent modification of a porous scaffold with heparin allows for the differential release of VEGF and PDGF-BB that results in both a rapid and sustained increase in scaffold vascularization.

Purpose. To evaluate whether 3T clinical MRI with a small-animal coil and gradient-echo (GE) sequence could be used to characterize long-term left ventricular remodelling (LVR) following nonreperfused myocardial infarction (MI) using semi-automatic segmentation software (SASS) in a rat model. Materials and Methods. 5 healthy rats were used to validate left ventricular mass (LVM) measured by MRI with postmortem values. 5 sham and 7 infarcted rats were scanned at 2 and 4 weeks after surgery to allow for functional and structural analysis of the heart. Measurements included ejection fraction (EF), end-diastolic volume (EDV), end-systolic volume (ESV), and LVM. Changes in different regions of the heart were quantified using wall thickness analyses. Results. LVM validation in healthy rats demonstrated high correlation between MR and postmortem values. Functional assessment at 4 weeks after MI revealed considerable reduction in EF, increases in ESV, EDV, and LVM, and contractile dysfunction in infarcted and noninfarcted regions. Conclusion. Clinical 3T MRI with a small animal coil and GE sequence generated images in a rat heart with adequate signal-to-noise ratio (SNR) for successful semiautomatic segmentation to accurately and rapidly evaluate long-term LVR after MI.

Porous scaffolds are frequently utilized in tissue regeneration. We have developed a polyurethane (PU) scaffold with a freely interconnecting porosity that can be modified with a covalently linked heparinized surface. The ability of this surface functionality to stimulate vessel and cellular growth into the PU scaffold has been evaluated by subcutaneous implantation of discs in the rat under normoxia and chronic hypoxia (hypobaric chamber) for 10 days. The heparinized surface alone was able to significantly increase vascularization and cellularization under normoxia (p < 0.05), but this response was negated by hypoxia. Addition of vascular endothelial growth factor to heparinized discs resulted in increased vascularity and cellularization under both conditions (p < 0.05). This suggests that endogenous growth factor production was limiting under chronic hypoxia but that an angiogenic response could still occur with exogenous delivery of factors., (Copyright © 2011 Wiley Periodicals, Inc.)

The retention and mass overload of five bases and a quaternary ammonium compound were studied on a bridged ethyl hybrid inorganic/organic phase (XBridge C18) over a pH range 2.7-12.0 using acetonitrile-phosphate and carbonate buffers. Some comparisons were drawn with results on a methyl hybrid (XTerra) phase. At low pH, rapid mass overload was observed with severe decreases in efficiency as sample mass was increased over the range 0.04-5 microg of solute. At intermediate pH (swpH 7.0), generally good peak shapes for small sample mass were still obtained on the ethyl hybrid, but with somewhat increased tailing of bases compared with swpH 2.7. At higher pH (swpH 10), good peak shape and improved loadability were obtained for moderately strong bases, due to their occurrence mostly as neutral species. However, stronger bases gave poor efficiency, attributed to interaction of the charged basic solute with increasingly ionised column silanol groups. Results were broadly similar on the methyl hybrid at swpH 10. At swpH 11, unusual profiles of increasing followed by decreasing efficiency were obtained on the ethyl hybrid for some bases as sample mass was increased; improved results were obtained at swpH 12. While the column loadability increased substantially at the highest pH studied, tailing for small sample mass was still more severe than at low pH, even though all compounds were <1% ionised in the mobile phase.

The retention and overload of bases were studied on two new mixed-mode, silica based phases possessing ionic carboxylate functionalities of different acidity embedded within a hydrophobic ligand (SiELC Primesep). At low pH, good peak shapes were obtained for small solute mass, suggesting that the mere presence of a mixed-mode hydrophobic/ionic retention mechanism is not responsible for the poor peak shape that can occur on conventional reversed-phases with ionised silanols. Somewhat inferior, but still acceptable peak shape for bases was obtained on a column containing a mixture of discrete ion exchange and reversed-phase particles (Hypersil Duet). In both types of column, the ionic sites favourably increased the capacity for ionised bases, reducing considerably the deterioration of peak shape with load observed with conventional RP columns. The combined ionic and reversed-phase interaction can give strong retention of bases under certain conditions, necessitating careful choice of stationary and mobile phase.

The retention and overloading properties for eight basic solutes and two quaternary ammonium compounds were studied over the pH range 2.7-10.0 using phosphate and carbonate buffers. At low pH, a hybrid inorganic-organic silica-ODS phase (XTerra RP-18, 15 cm x 0.46 cm) showed substantial loss in efficiency when sample masses exceeded about 0.5 microg; these results were similar to those obtained previously on pure silica ODS and wholly polymeric phases, suggesting a common overloading mechanism. At pH 7-8.5, substantial improvements in loading capacity were obtained on XTerra due apparently to the unexpectedly strong influence of small decreases in solute ionisation. Data from the quaternary compounds suggested that silanol ionisation on this phase was still small even at intermediate pH. For many bases, loading capacity continued to improve as the pH was raised to 10, in line with the decrease in the proportion of ionised solute. However, for the highest pK(a) solutes, peak shape worsened at high pH, possibly due to the negative influence of increasing column silanol ionisation.