A three constituent mixture theory model of cutaneous and subcutaneous tissue in the context of neonatal pressure ulcer etiology and prevention

Localized ischemia, impaired interstitial fluid flow, and sustained mechanical loading of cells have all been hypothesized as mechanisms of pressure ulcer (PrU) etiology. Time-varying loading has experimentally been shown to increase fluid flow in human skin in vivo. Towards the design of prophylactic protocols and treatment modalities for PrU management there is a need for an analytical model to investigate the local fluid flow characteristics of skin tissue under time-varying loading. In this study, a triphasic mixture theory model with constituents of extracellular matrix, interstitial fluid, and blood was calibrated and validated and used to investigate stress and fluid velocity under quasi-static and time-varying loading conditions, respectively. Four input strain profiles were considered, including uniform, geometric circular segment, Gaussian, and Hertz-type strain profiles. Calibrated bulk and shear modulus (κ;=227.7kPa, µ=1.04kPa) were on the same order of magnitude as literature. Fluid velocities were investigated for apparent strain amplitudes of 100-700μϵ and frequencies of 10-80Hz. At the lowest amplitude and frequency, interstitial fluid velocities were on the same order of magnitude as literature values, 1 micrometers/s and 1 mm/s, respectively. Interstitial fluid and blood velocity both experienced significant increases with increasing amplitude and frequency. The study demonstrated the ability to analytically predict quasi-static stress profiles as well as predict fluid velocity increases in cyclically loaded soft tissues by employing quasi-static mechanics and mixture theory models. Consequently, this study builds a strong foundation for use in the development of vibrational support surfaces for use in prophylactic protocols and adjunctive treatment modalities for PrU managemen

Mechanisms of aging-mediated loss of stem cell potency through changes in niche architecture and chromatin accessibility

All multicellular organisms undergo a decline in tissue and organ function as they age. Loss in stem cell number or activity over time is one possible explanation for this decline. However, little is known about mechanisms leading to stem cell exhaustion in aged tissues. This study reveals a mechanism explaining stem cell exhaustion in the hair follicle. Genome-wide analyses revealed that aged hair follicle stem cells displayed widespread reduction of chromatin accessibility, specifically at crucial self-renewal and differentiation genes that were characterized by bivalent promoters occupied by both active and repressive chromatin marks. Aged hair follicle stem cells showed reduced self-renewing capacity and attenuated ability to activate the expression of these bivalent genes upon regeneration. These functional defects were niche-dependent as transplantation of aged hair follicle stem cells into synthetic niches restored stem cell functions and transcription of poised genes. Mechanistically, the old hair follicle stem cell niche displayed widespread alterations in extracellular matrix composition and mechanics, resulting in mechanical stress and concomitant transcriptional repression, shifting these bivalent promoters to a silenced state. Tuning tissue mechanics in vivo and in vitro recapitulated age-related stem cell changes implicating niche mechanics as a central regulator of chromatin state, which, when altered, leads to age-dependent stem cell exhaustion

Stem cell based therapy retards the progression of osteoarthritis and promotes repair of meniscus injury of sheep model knee joint

ABSTRACT The aim of this study to determine if intra-articular injection of autologous bone marrow mesenchymal stem cells (ABMSCs) could repair surgically induced osteoarthritis in sheep model. Eighteen male healthy sheep (weighed 18-20kg) were divided into two test groups and one control group. The control groups were not different from the test groups with respect to age and weight, but the test animals underwent a bone marrow aspira- tion for cell preparation in the same time of osteoarthritis induction. ABMSCs were isolated from sheep bone marrow and divided into two groups, namely test group A; ABMSCs cultured in FD medium supplemented with 10% fetal bovine serum (FBS), Test group B; ABMSCs were cultured in FD medium supplimented with 1% FBS and 10 ng/ml TGFβ-3 for three weeks. OA was induced by complete excision of the medial meniscus and resection of the anterior cruciate ligament (ACL). Sheep were subjected to exercise for three weeks post OA induction. After 6 weeks post-operation, test groups received direct intra-articular injection of a single dose 10x106 cells suspended in basal medium into injured sheep knee joint. Con- trol animals received basal medium alone. Six weeks post- cel injection, the femoral condyle and the tibial plateau from test and control groups were removed,fixed,photographed, and assessed by two blinded evaluators based on ICRS grading system, decalcified. Specimens were sectioned into 5 µm and stained with H & E and Safranin O. The result demonstrated that Gross observation of femoral condyle and tibia plaetue of the operated knee joint had OA. The severe OA was clearly observed in in control group knee joints. Test group received intra-articular injection of ABMSCs alone showed moderate OA. Interestingly test group B that received intra-articularinjection of TGF-β3 induced ABMSCs showed mild OA. The histological examination showed clear evidence of articular cartilage and menicscus regeneration in test group B of sheep injured knee joint that received TGF-β3 induced ABMSCs when compared with other groups

The role of inflammation and cytokines in the pathogenesis of tendinopathy

Tendon disorders - tendinopathies - are the primary reason form musculoskeletal consultation in primary care in the UK and the US. The molecular pathophysiology of tendinopathy remains difficult to interpret while inflammation and its role in tendinopathy have been historically ignored due to its absence in human surgical specimens. This thesis explores the role of inflammation in human tendinopathy and dissects potential molecular pathways involved in its initiation and perpetuation. Firstly I characterize inflammatory cell subtypes within a model of human tendinopathy highlighting a distinct inflammatory infiltrate particularly of mast cells and macrophages. Hypoxia and hypoxic cell death have been a long considered aetiology of tendon degeneration. In this thesis I demonstrate that hypoxia related proteins are present in early tendinopathy biopsies and thereafter in mechanistic studies demonstrate that hypoxia regulates inflammatory and apoptotic mediators in tendon cells associated with a significant shift in collagen matrix synthesis. The cytokines, interleukins 17 and 33 are emerging inflammatory mediators known to play key roles in fibroblast biology. I explored the cellular sources of IL- 17A in human tendinopathy with experiments revealing the majority of IL17A colocalised to mast cells. Moreover IL-17A induced proinflammatory cytokines and apoptosis in vitro and again resulted in a significant switch in collagen extracellular matrix production. IL 33 is a new member of the IL-1 superfamily that signals through the ST2 receptor. Herein I demonstrate that IL-33 expression is up regulated in human tendinopathic biopsies whilst rhIL-33 promotes proinflammatory cytokine release and significantly shifts matrix production toward a collagen III phenotype. WT mice undergoing a tendon injury model showed significant up regulation of IL-33 and ST2 while ST2-/- mice exhibit a reduced collagen response and biomechanical tendon strength at early time points post injury Addition of rh-IL33 increased type III collagen production and reduced the biomechanical strength of WT tendons. Furthermore mechanistic investigations has highlighted a key role for the microRNA 29 family in the modulation of collagen regulation in tendinopathy but also in controlling IL-33 induced changes as a direct target of sST2. Based on these experiments I propose IL-33 as an important and influential alarmin in early tendon injury and tendinopathy, which may be influential in the balance between reparation and degeneration in tendon disease.EThOS - Electronic Theses Online ServiceGBUnited Kingdo

Skin Tissue Models

Skin Tissue Models provides a translational link for biomedical researchers on the interdisciplinary approaches to skin regeneration. As the skin is the largest organ in the body, engineered substitutes have critical medical application to patients with disease and injury - from burn wounds and surgical scars, to vitiligo, psoriasis and even plastic surgery. This volume offers readers preliminary description of the normal structure and function of mammalian skin, exposure to clinical problems and disease, coverage of potential therapeutic molecules and testing, skin substitutes, models as study platforms of skin biology and emerging technologies. The editors have created a table of contents which frames the relevance of skin tissue models for researchers as platforms to study skin biology and therapeutic approaches for different skin diseases, for clinicians as tissue substitutes, and for cosmetic and pharmaceutical industries as alternative test substrates that can replace animal models. Offers descriptions of the normal structure/function of mammalian skin, exposure to clinical problems, and more Presents coverage of skin diseases (cancer, genodermatoses, vitiligo and psoriasis) that extends to clinical requirements and skin diseases in vitro models Addresses legal requirements and ethical concerns in drugs and cosmetics in vitro testing Edited and authored by internationally renowned group of researchers, presenting the broadest coverage possible. © 2018 Elsevier Inc. All rights reserved.(undefined)info:eu-repo/semantics/publishedVersio