Experimental and theoretical analyses of compression induced muscle damage : aetiological factors in pressure ulcers

Pressure ulcers form a major problem in health care. They often occur when patients are bedridden, wheelchair bound or wearing prostheses. The ulcers can be very painful for the patient and often lead to prolonged hospitalization. In addition, the huge costs involved with treatment and prevention put a heavy burden on heath care budgets. Pressure ulcers occur often: between 14% and 33% of the patients in health care institutions develop an ulcer, ranging from discolouration of the skin to severe wounds involving necrosis of epidermis, extending to underlying bone, tendon and joints. It is clear that pressure ulcers are caused by prolonged mechanical loading, applied at the interface between skin and support surfaces. However, the aetiology of pressure ulcers is poorly understood. This forms an important obstacle in decreasing the unacceptably high prevalence figures. It is anticipated that a better understanding of the mechanobiological pathways leading to cell and tissue damage can lead to a breakthrough in reducing pressure ulcer prevalence. In addition, a solid scientific base may establish tools for objective risk assessment and judgement of preventive measures. The present study focuses on deep ulcers that initiate in skeletal muscle tissue, since deep ulcers are more extensive and often difficult to prevent. To obtain insight into the aetiology of these deep ulcers, it is necessary to understand the transfer from externally applied loads at the skin, to the local conditions that the cells experience within the tissue. In addition, the question which local conditions are harmful to the cell needs to be investigated. By combining knowledge on "what a cell feels" with knowledge on potentially harmful conditions, a better judgement of dangerous situations may be achieved. Although several causes of cell damage may play a role in the initiation of pressure ulcers, the present study focussed on the impact of cell deformations. To investigate the hypothesis that prolonged cell deformations lead to cell damage at clinically relevant strains, an experimental model system was developed. A key requirement of this experimental model is the possibility to study the role of cell deformation on cell damage independently of other possible causes of damage. To achieve this, in-vitro engineered muscle tissue constructs were developed. These constructs were compressed using a newly developed compression device. A custom made incubator system was developed to allow monitoring of the constructs for extended periods of time. In addition, a novel assay was developed to determine the viability of the cells during compression. This assay provides quantitative and spatial information on cell damage throughout a construct in a non-invasive manner, making use of fluorescent dyes which are visualized by confocal microscopy. The compression of the engineered muscle tissue constructs indicated that a significant increase in cell death occurs within 1-2 hours and that higher strain levels led to an earlier increase in damage. In addition, it was demonstrated that cell damage was uniformly distributed across the indented area of the construct, without a gradient in percentage dead cells between the centre and periphery of the constructs. The results strongly suggest that prolonged cell deformation was the predominant cause of cell damage in these experiments. This puts a new light on observations in literature which suggested that ischaemia is not the sole determinant for the onset of pressure ulcers. Nevertheless, more experiments are needed to clarify the role of prolonged cell deformations on cell damage. First, it is recommended that the actual local cell deformations are quantified during compression of the constructs. Furthermore, from the present experiments it could not be excluded that the compression of the constructs decreased the permeability of the construct and hence affected cellular metabolism. In future, measuring diffusion pathways of both small molecules and larger vital molecules, may indicate whether this change in permeability is significant. A numerical model was developed to predict local cell deformations, in response to tissue compression. Since the local cell deformations cannot be a-priori determined on the basis of homogenized tissue deformations, a multilevel finite element approach was adopted. In this approach, cell deformations are predicted from detailed nonlinear finite element analyses of the local microstructures of the tissue, which consist of an arrangement of cells embedded in a matrix material. To avoid unacceptably large computational times, the multilevel model was designed to run on a parallel computer system. Application of the multilevel model showed that the heterogeneity of the microstructure of the tissue has a profound impact on local cell deformations, which highly exceeded macroscopic tissue deformations. Moreover, microstructural heterogeneity led to complex cell shapes and caused non-uniform deformations within the cells. To investigate the evolution of compression induced damage in skeletal muscle tissue, the multilevel model was extended with a damage law, which was derived from the in-vitro experiments. With this model, the compression of muscle tissue against a bony prominence was simulated. The percentage of cell damage in the microstructure of the tissue was computed, which could be extrapolated to the bulk tissue level. In the present form, a schematic geometry was considered that intended to elucidate general patterns of tissue damage evolution. The simulations confirmed that it is not feasible to predict the onset of tissue damage on the basis of externally applied loading conditions at the skin surface alone, since these externally applied loads are not indicative of the local mechanical conditions that the cells experience within the tissue. In addition, the simulations showed that it is necessary to consider the local load history of the cells, and the tolerance of the tissue. These findings may explain why a strikingly large variability in load/time threshold values was found in animal studies, which attempted to relate external mechanical to tissue damage, thereby ignoring the local mechanical conditions within the tissue. At present, it is premature to utilize the models presented in this thesis in clinical practice, since the extrapolation towards human patients requires more research. Clearly, further extensions and validation of the numerical model with experimental animal models will be required. This should finally lead to the application in more realistic cases, involving patient data on geometry and tissue properties. Nevertheless, the present models provided an essential step towards evidence based risk assessment and prevention

A Comparative Evaluation of Selected Prose by Maarten Maartens

Maarten Maartens (1858-1915) is the penname of Joost Maria Willem van der Poorten Schwartz, a Dutchman who wrote poetic plays, novels and short stories in English between 1890 and 1914. But "Maarten Maartens" is more than just a pseudonym chosen because it sounded Dutch while it could still easily be pronounced by his English readers. Under his own name, Schwartz lived retired in the country in the Netherlands while, under his heteronym Maarten Maartens, he led a life as a writer and a man of the world. His works were published in Britain, in the United States and in Germany. Due to the variety of settings in different countries as well as well as due to the interest he took in all layers of society, Maartens can be considered a European rather than a Dutch or British writer; he is perhaps the first author worthy of such name. However, the fact that his themes were not limited to a particular social and cultural setting has never been fully acknowledged, because reviewers and critics continued to focus their interest mainly on the Dutch element in his works, i.e., the representation of Dutch life and morals. As Maartens phrased it in the preface to his fifth novel The Greater Glory (1894): "The morals I seek to describe are those of the entire human race. It is only by the merest accident that my scene is laid in Holland, a country whose inhabitants, I suppose, are no better, nor worse, than my neighbours." In this dissertation, Maartens is placed for the first time within the literary-historical context of the late nineteenth century and the question is explored whether Maartens is merely to be considered a minor author favouring the realistic mode of writing, who still gives us captivating glimpses into a social microcosm long gone by, or whether, and to which extent, he achieved his aim to surpass this aspect. For the general assessment, apart from the published works, a number of unpublished manuscripts are included, amongst which there are a play, several complete and fragmentary novels as well as short stories, private and literary correspondence and some notebooks containing philosophical and literary reflections. While Maartens successfully published both novels and short stories, this dissertation argues that his predilection for literary tableaux quite naturally points at the short story as its most suitable form. Stripped of all non-essential detail and moralizing, the short story enabled the artist to escape from the calling of the preacher. Not only did its moral impact remain untainted; it became more persuasive. In his short stories, Maartens did not feel compelled to tackle the larger social issues that preoccupied him. The short form allowed him to ignore the changes in literary tastes and fashions, giving his attention exclusively to the essential detail, which, to him, represented a universal truth. If he had more thoroughly exploited its potential to give shape to his unique observations, the short story in the English language would have been the richer for it. A number of short stories have remained unpublished to this day, but there are four collections, as well as a number of uncollected stories published in magazines that offer invaluable insights into prevailing attitudes of the late nineteenth and early twentieth centuries. To this day Maarten Maartens? novels and in particular his short stories continue to be unique literary explorations of the human condition.Maarten Maartens (1858-1915) ist das Pseudonym von Joost Maria Willem van der Poorten Schwartz, einem Holländer, der zwischen 1890 und 1914 lyrische Theaterstücke, Romane und Kurzgeschichten in der englischen Sprache verfasste. Aber "Maarten Maartens" ist mehr als nur ein Pseudonym, das ausgewählt worden war, weil es holländisch klang und doch leicht von englischen Lesern ausgesprochen werden konnte. Unter seinem eigenen Namen lebte Schwartz ein zurückgezogenes Leben auf seinem holländischen Landgut, während er unter seinem Heteronym Maarten Maartens das Leben eines Autors und eines Mannes von Welt führte. Seine Werke wurden in England, Amerika und Deutschland veröffentlicht. Wegen der Internationalität seiner Schauplätze und Themen, sowie auch wegen des Interesses, das er an allen sozialen Schichten zeigte, muss Maartens eher als europäischer denn als niederländischer oder britischer Autor betrachtet werden; vielleicht ist er sogar der erste Autor, der den europäischen Namen verdient. Die Tatsache, dass seine Themen nicht auf das Holländische beschränkt sind, wurde allerdings von der Kritik vernachlässigt, weil Rezensenten und Kritiker sich immer hauptsächlich auf die holländischen Elemente in seinen Werken konzentrierten. Doch wie es Maartens selbst im Vorwort zu seinem fünften Roman The Greater Glory (1894) formulierte: "Die moralischen Werte, die ich zu beschreiben suche, sind die der ganzen Menschheit. Es ist reiner Zufall, dass meine Schauplätze in Holland liegen, einem Land, dessen Einwohner, wie ich annehme, weder besser noch schlechter sind als meine Nachbarn." In dieser Dissertation wird Maartens zum ersten Mal in den literar-historischen Kontext des späten neunzehnten Jahrhunderts eingeordnet, und es wird untersucht, ob Maartens als minor author gelten sollte, der in seiner realistischen Schreibweise noch heute interessante Einblicke in einen längst vergangenen sozialen Mikrokosmos gewährt, bzw. in welchem Maße er sein selbst definiertes Ziel erreicht, über diesen Aspekt hinauszugehen. Für die allgemeine Bewertung wurden neben publizierten Werken auch eine Anzahl unveröffentlichter Manuskripte herangezogen, sowie auch Auszüge aus seiner privaten und literarischen Korrespondenz. Hinzu kommen einige (unveröffentlichte) Notizbücher mit privaten und philosophischen Betrachtungen. Maartens war erfolgreicher Autor von Romanen und Kurzgeschichten, aber es wird in der vorliegenden Arbeit die These vertreten, dass ihn seine Vorliebe für literarische tableaux eigentlich für die kurze Form prädestinierte. Da hier das Einfügen zahlloser Einzelheiten und ausführlicher moralisch-bewertender Erzählerkommentare gattungsbedingt nicht möglich war, musste sich Maartens auf das Wesentliche beschränken, so dass die Geschichten für sich selbst sprachen. Die Kurzgeschichte ermöglichte ihm, geschmacksgeschichtliche Veränderungen zu ignorieren und sich ausschließlich auf solche Details zu konzentrieren, die für ihn universelle Wahrheiten enthielten. Hätte er sich verstärkt dieser Form gewidmet, um seine besonderen Einblicken festzuhalten, wäre die englische Kurzgeschichte reicher geworden. Einige seiner Romane und Kurzgeschichten sind unveröffentlicht, doch es sind vier Erzählbände erschienen; weitere einzelne Geschichten wurden in Zeitschriften publiziert. Bis heute bleiben Maarten Maartens Romane, doch v.a. seine Kurzgeschichten einzigartige Untersuchungen der condition humaine

Scaffold Stiffness Influences Cell Behavior: Opportunities for Skeletal Tissue Engineering

Skeletal defects resulting from trauma, tumors, or abnormal development frequently require surgical treatment to restore normal tissue function. To overcome the limitations associated with conventional surgical treatments, several tissue engineering approaches have been developed. In particular, the use of scaffolds enriched with stem cells appears to be a very promising strategy. A crucial issue in this approach is how to control stem cell behavior. In this respect, the effects of growth factors, scaffold surface characteristics, and external ‘active’ loading conditions on stem cell behavior have been investigated. Recently, it has become clear that the stiffness of a scaffold is a highly potent regulator of stem cell differentiation. In addition, the stiffness of a scaffold affects cell migration, which is important for the infiltration of host tissue cells. This review summarizes current knowledge on the role of the scaffold stiffness in the regulation of cell behavior. Furthermore, we discuss how this knowledge can be incorporated in scaffold design which may provide new opportunities in the context of orthopedic tissue engineering

Globalised citizenship and the perceived legitimacy of immigration control: narratives and acts of resistance in immigration detention

This article considers the legitimacy deficits of immigration control in the eyes of unwanted migrants. We explore the consequences of globalisation-related changes in the institution of citizenship for the perceived legitimacy and operation of immigration control. The study is based on ethnographic research and in-depth interviews in 2018 with 35 migrants in the Detention Centre Rotterdam, the Netherlands. We find that immigration detainees use both denationalised and transnational/cosmopolitan definitions of citizenship and belonging to contest the legitimacy of restrictive admission requirements and, to a lesser extent, the authority of states to stipulate and implement admission requirements. Based on these narratives, immigration detainees engage in forms of resistance that are meant to diminish the likelihood of deportation (‘instrumental resistance’) and in forms of resistance that are unlikely to change the outcome of the deportation procedure yet do make immigration control more costly for states (‘expressive resistance’). The narratives and strategies of resistance seem correlated with length of stay: settled migrants seem more inclined to use denationalised repertoires and instrumental resistance. Our analysis confirms the need for migration scholars to pay more attention to changing social norms regarding the perceived legitimacy of immigration control for the operation and outcomes of immigration control. The results are therefore relevant for our thinking about the future of migration governance in the context of globalisation-related changes in the institution of citizenshi

The human somatostatin receptor type 2 as an imaging and suicide reporter gene for pluripotent stem cell-derived therapy of myocardial infarction

Rationale: Pluripotent stem cells (PSCs) are being investigated as a cell source for regenerative medicine since they provide an infinitive pool of cells that are able to differentiate towards every cell type of the body. One possible therapeutic application involves the use of these cells to treat myocardial infarction (MI), a condition where billions of cardiomyocytes (CMs) are lost. Although several protocols have been developed to differentiate PSCs towards CMs, none of these provide a completely pure population, thereby still posing a risk for neoplastic teratoma formation. Therefore, we developed a strategy to (i) monitor cell behavior noninvasively via site-specific integration of firefly luciferase (Fluc) and the human positron emission tomography (PET) imaging reporter genes, sodium iodide symporter (hNIS) and somatostatin receptor type 2 (hSSTr2), and (ii) perform hSSTr2-mediated suicide gene therapy via the clinically used radiopharmacon 177Lu-DOTATATE. Methods: Human embryonic stem cells (ESCs) were gene-edited via zinc finger nucleases to express Fluc and either hNIS or hSSTr2 in the safe harbor locus, adeno-associated virus integration site 1. Firstly, these cells were exposed to 4.8 MBq 177Lu-DOTATATE in vitro and cell survival was monitored via bioluminescence imaging (BLI). Afterwards, hNIS+ and hSSTr2+ ESCs were transplanted subcutaneously and teratomas were allowed to form. At day 59, baseline 124I and 68Ga-DOTATATE PET and BLI scans were performed. The day after, animals received either saline or 55 MBq 177Lu-DOTATATE. Weekly BLI scans were performed, accompanied by 124I and 68Ga-DOTATATE PET scans at days 87 and 88, respectively. Finally, hSSTr2+ ESCs were differentiated towards CMs and transplanted intramyocardially in the border zone of an infarct that was induced by left anterior descending coronary artery ligation. After transplantation, the animals were monitored via BLI and PET, while global cardiac function was evaluated using cardiac magnetic resonance imaging. Results: Teratoma growth of both hNIS+ and hSSTr2+ ESCs could be followed noninvasively over time by both PET and BLI. After 177Lu-DOTATATE administration, successful cell killing of the hSSTr2+ ESCs was achieved both in vitro and in vivo, indicated by reductions in total tracer lesion uptake, BLI signal and teratoma volume. As undifferentiated hSSTr2+ ESCs are not therapeutically relevant, they were differentiated towards CMs and injected in immune-deficient mice with a MI. Long-term cell survival could be monitored without uncontrolled cell proliferation. However, no improvement in the left ventricular ejection fraction was observed.Conclusion: We developed isogenic hSSTr2-expressing ESCs that allow noninvasive cell monitoring in the context of PSC-derived regenerative therapy. Furthermore, we are the first to use the hSSTr2 not only as an imaging reporter gene, but also as a suicide mechanism for radionuclide therapy in the setting of PSC-derived cell treatment

Interstitial Cell Remodeling Promotes Aberrant Adipogenesis in Dystrophic Muscles.

Fibrosis and fat replacement in skeletal muscle are major complications that lead to a loss of mobility in chronic muscle disorders, such as muscular dystrophy. However, the in vivo properties of adipogenic stem and precursor cells remain unclear, mainly due to the high cell heterogeneity in skeletal muscles. Here, we use single-cell RNA sequencing to decomplexify interstitial cell populations in healthy and dystrophic skeletal muscles. We identify an interstitial CD142-positive cell population in mice and humans that is responsible for the inhibition of adipogenesis through GDF10 secretion. Furthermore, we show that the interstitial cell composition is completely altered in muscular dystrophy, with a near absence of CD142-positive cells. The identification of these adipo-regulatory cells in the skeletal muscle aids our understanding of the aberrant fat deposition in muscular dystrophy, paving the way for treatments that could counteract degeneration in patients with muscular dystrophy