Thermal alteration of collagenous tissue subjected to biaxial isometric constraints

Clinical thermal therapies are widespread and gaining in appeal due to improved technology of heating devices and promising results. Outcomes of thermal treatment are often unpredictable and suboptimal, however, due in part to a lack of appreciation of the underlying biothermomechanics. There is a pressing need, therefore, to understand better the role of clinically-controllable parameters on the thermal damage processes of tissue. Heretofore, researchers have primarily sought to understand this process through various uniaxial experiments on tissues containing collagen as their primary constituent. Most biological tissues experience multiaxial loading, however, with complex boundary constraints inclusive of both isotonic and isometric conditions. The primary focus of this work is on the isothermal denaturation of fibrillar collagen subjected to a biaxial isometric constraint. Results from our tests reveal a complicated process, the kinetics of which are not easily measured. Evolving isometric contraction forces during heating do not correlate with resultant mechanical behaviors, as thermal shrinkage does in biaxial isotonic tests. Furthermore, resultant mechanical behaviors at variousdurations of heating reveal a two phase process with a rate dependent on the amount of isometric stretch. For tissues heated at 75oC for 15 minutes, at which point the first phase of mechanical alteration dominates for all constraints herein, resultant mechanical behaviors correlate well with the amount of isometric stretch. The correlation is similar to that between isotonic loads and resultant mechanical behaviors from previous studies. In light of the need for a better measure of thermal damage in isometric tests, we performed a histological analysis of tissues heated under varying constraints. Results show a good correlation between the level of isometric constraint and thermally-induced histological aberrations. Finally, we demonstrate that our seemingly limited and qualitative knowledge can be applied well to a specific clinical application: namely, the use of glycerol as a clearing agent for laser therapies. Our results suggest that glycerol is safe to use for such therapies because it increases the thermal stability of fibrillar collagen, and its hyperosmotic effects on mechanical behavior are fully reversed upon rehydration

Validation of a Three-Dimensional Culture System for the Differentiation of Multipotential Mesenchymal Stromal Cells by Uniaxial Strain

The differentiation potential of multipotential mesenchymal stromal cells is known to be affected by many aspects of the cellular microenvironment, including soluble factors, extracellular matrix composition, the Young’s modulus of the substrate, cellular neighbours and externally applied forces. Despite this, reasonable understanding of harnessing soluble factors only exists. Few studies have investigated mechanotransduction in hMSC, and those published to date primarily employ unsuitable substrates, that do not facilitate the cellular adhesions known to be active in force transmission. In this study, porcine pericardium was decellularised for use as a biologically-relevant, threedimensional scaffold for the mechanostimulation of hMSC in a uniaxial strain bioreactor. Tissue stocks (n=67) were successfully decellularised and confirm biocompatible, sterile and free of contaminating genomic DNA. Histoarchitecture comparable to that of native tissue was also maintained. Tencell-specific seeding rings were found to release cytotoxic residue, and an alternative, nontoxic seeding approach was developed. The Tencell bioreactor was initially unable to maintain cell viability as a culture system, and was validated with respect to chamber humidity, culture temperature and arm displacement. Temperature maintenance was inadequate prior to re-engineering of the heating apparatus and was rectified through the use of an autotunable module. Losses of cell viability were still observed following validation as a result of medium pH changes. A Tencell culture regime utilising the HEPES buffer was successfully developed for the culture of hMSC. No significant differences in gene expression between strained and unstrained samples were found, and the greatest effects were observed between unseeded and other sample types. Additionally, seeded hMSC did not penetrate the scaffold. Overall, this study investigated the differentiation potential of hMSC cultured in a threedimensional scaffold. The Tencell bioreactor was fully validated for use as a uniaxial strain mechanostimulation device, and could be used in future studies to investigate the effect of different frequencies and magnitudes of cyclic strain

An In Vitro Investigation of a Novel, Two-Piece Zirconia Dental Implant System

Implant treatment is currently overriding other prosthetic solutions especially in the case of replacing anterior teeth in the aesthetic zone. Zirconia ceramics exhibit promising aesthetic, periointegration and antibacterial properties that may overcome critical drawbacks associated with titanium based dental implants. They also possess distinctive mechanical properties due to the unique transformation toughening mechanism. However, the effects of low-temperature degradation (LTD) or ageing on the durability of the material is of a major concern. Additionally, the currently available one-piece and two-piece zirconia dental implant designs exhibit sub-standard performance. This study aimed to investigate ageing, mechanical properties and biofunctional characteristics of a new implant system with a novel biomechanical design. The proposed design utilises a relatively low-strength glass fibre composite abutment bonded with resin cement to an injection-moulded, soft tissue level, acid-etched zirconia implant. Hydrothermal treatment was used to simulate in vivo ageing. A battery of complimentary crystallographic and imaging studies was used to characterise hydrothermally- and stress-induced phase transformation. Additionally, the effect of ageing on basic mechanical properties of standard samples was investigated at the macro-, micro- and nano-scales. Dynamic fatigue was performed in order to determine durability and reliability of various components and interfaces of the design under simulated clinical conditions. The acid-etched zirconia surface (MDS) was compared to a high-performance, mechanically and chemically modified titanium surface in terms of; surface topography, biocompatibility and cell biofunctional response. The results of this study indicated that hydrothermal ageing resulted in phase transformation that was localised to the surface of the material without any involvement of the bulk. No evidence of extensive cracking was detected as a result of the used ageing conditions. The aged samples exhibited static mechanical properties that were not significantly different from the control group apart from marginal decreases in surface hardness. The implant samples restored with two different crown materials did not exhibit any premature failures. The engineered weak connection seemed to favour retrievable failures especially when low strength crown material was used to restore the implants. The studied MDS zirconia surface exhibited moderate surface roughness and high biocompatibility when tested with human osteoblast-like cells and human gingival fibroblasts. Cell attachment and bone formation capacity of cells were similar or marginally higher in cells cultured on MDS surface when compared to titanium (SLActive-like) counterpart. Within the limitations of this study, it can be concluded that the studied zirconia material was not drastically affected by hydrothermal ageing and thereby, in vivo LTD may be not of a concern whilst using such material. The current implant design may withstand long-term functional forces in the anterior region of the oral cavity. The MDS surface may reduce the time required for bone and soft tissue healing which is essential for clinical cases require immediate provisionalisation and/or early loading. Soft tissue remodelling may be of a less concern owing to the high soft tissue attachment (periointegration) capacity of the studied MDS zirconia surface

Bridging spatiotemporal scales in biomechanical models for living tissues : from the contracting Esophagus to cardiac growth

Appropriate functioning of our body is determined by the mechanical behavior of our organs. An improved understanding of the biomechanical functioning of the soft tissues making up these organs is therefore crucial for the choice for, and development of, efficient clinical treatment strategies focused on patient-specific pathophysiology. This doctoral dissertation describes the passive and active biomechanical behavior of gastrointestinal and cardiovascular tissue, both in the short and long term, through computer models that bridge the cell, tissue and organ scale. Using histological characterization, mechanical testing and medical imaging techniques, virtual esophagus and heart models are developed that simulate the patient-specific biomechanical organ behavior as accurately as possible. In addition to the diagnostic value of these models, the developed modeling technology also allows us to predict the acute and chronic effect of various treatment techniques, through e.g. drugs, surgery and/or medical equipment. Consequently, this dissertation offers insights that will have an unmistakable impact on the personalized medicine of the future.Het correct functioneren van ons lichaam wordt bepaald door het mechanisch gedrag van onze organen. Een verbeterd inzicht in het biomechanisch functioneren van deze zachte weefsels is daarom van cruciale waarde voor de keuze voor, en ontwikkeling van, efficiënte klinische behandelingsstrategieën gefocust op de patiënt-specifieke pathofysiologie. Deze doctoraatsthesis brengt het passieve en actieve biomechanisch gedrag van gastro-intestinaal en cardiovasculair weefsel, zowel op korte als lange termijn, in kaart via computermodellen die een brug vormen tussen cel-, weefsel- en orgaanniveau. Aan de hand van histologische karakterisering, mechanische testen en medische beeldvormingstechnieken worden virtuele slokdarm- en hartmodellen ontwikkeld die het patiënt-specifieke orgaangedrag zo accuraat mogelijk simuleren. Naast de diagnostische waarde van deze modellen, laat de ontwikkelde modelleringstechnologie ook toe om het effect van verschillende behandelingstechnieken, via medicatie, chirurgie en/of medische apparatuur bijvoorbeeld, acuut en chronisch te voorspellen. Bijgevolg biedt deze doctoraatsthesis inzichten die een onmiskenbare impact zullen hebben op de gepersonaliseerde geneeskunde van de toekomst

Amniotic membrane as a battlefield dressing for the ocular surface

The use of amniotic membrane (AM) as a dressing for ocular surface injuries has attracted the interest of the military ophthalmological community. First applied in the 1930s, the tissue is widely used today, although clinical indications for treatment are incompletely defined. While AM is most commonly stored frozen and thawed before use, dried AM is preferred for logistical reasons. Optimal preservation of the tissue is necessary to preserve its quality. The effect of drying on the physical and biological properties of the tissue are unknown. A systematic review of the evidence of AM treatment of acute chemical injuries was conducted. A framework was proposed for optimising the dried tissue through thermal, moisture sorption and surface analytical techniques. The physical properties of AM preparations were compared by mechanical testing and mathematical modelling, and an attempt was made to cross-link the AM collagen. Inflammatory aspects of the tissue were assessed by immunological techniques, zymography and macrophage assays. There is a lack of high quality evidence to support the clinical application of AM for acute burns. Complex interactions were demonstrated between the dried tissue, its excipients and moisture, suggesting novel ways of optimising the product. The mechanical properties of the dried membrane indicated that the process adversely affected the tissue, and artificial cross-linking could not be achieved. While the presence of antimicrobial peptides was not clearly established, the elution of collagenolytic enzymes was shown in therapeutic preparations of AM. The production of tumour necrosis factor by macrophages, which adhere to the spongy layer of AM, was suppressed. This project makes original contributions relevant to the use of dried AM as a biomaterial in ophthalmic surgery. Further refinements of this work, animal model experimentation and clinical trials may support its future acceptance as a clinical application

Strain induced remodeling of urinary bladder smooth muscle

Numerous pathologies that affect the urinary bladder, such as spinal cord injury (SCI), bladder outlet obstruction, or diabetes, cause bladder wall remodeling. Bladder remodeling is marked by changes in the extracellular matrix (ECM) proteins collagen and elastin as well as alterations in bladder smooth muscle cell (BSMC) hypertrophy and phenotype. Previous work has examined the bladder following SCI and found an early increase in elastin and hypertrophy followed by longer term fibrosis. These studies indicated that the mediating factor in bladder remodeling in response to early stage SCI and other pathologies such as obstruction and diabetes is strain. In the SCI bladder, the strain history is changed from normal filling and voiding to over distension and intermittent smooth muscle cell contraction. The goals of this study were to utilize an ex vivo organ culture model to examine the effects of strain on bladder smooth muscle remodeling, examine the effects of TGF-ß1, found to be up regulated in the SCI bladder, and to utilize a tissue engineering methodology to examine the effects of strain in cell-seeded biologic scaffolds. The first aim from this study showed that abnormal strain frequency profoundly induces elastogenesis in the ex vivo bladder. Further examination with the addition of TGF-ß1 with and without mechanical stimulation showed that mechanical stretch of the ex vivo bladder mimics the early stage SCI bladder in remodeling and cell phenotype, and the addition of TGF-ß1 alters this phenotype. Additionally, it was found that TGF-ß1 added to culture of BSMC on collagen gels decreases gel contraction but increases collagen organization of the gels. Finally, in a tissue engineered construct it was found that the growth factors VEGF and FGF-2 promote penetration of BSMC into small intestinal submucosa and that strain frequency alters the ECM proteins that the BSMC produce with a frequency of 0.1 Hz promoting elastogenesis and a frequency of 0.5 Hz promoting collagen production. The information gained in this study gives further insight into the role of strain in pathological remodeling of the bladder, and it provides a basis for tissue engineering constructs with controlled BSMC penetration and ECM composition

Aerospace Medicine and Biology: A cumulative index to the 1982 issues

This publication is a cumulative index to the abstracts contained in the Supplements 229 through 240 of Aerospace Medicine and Biology: A continuing Bibliography. It includes three indexes: subject, personal author, and corporate source