Advanced material modelling in numerical simulation of primary acetabular press-fit cup stability

Primary stability of artificial acetabular cups, used for total hip arthroplasty, is required for the subsequent osteointegration and good long-term clinical results of the implant. Although closed-cell polymer foams represent an adequate bone substitute in experimental studies investigating primary stability, correct numerical modelling of this material depends on the parameter selection. Material parameters necessary for crushable foam plasticity behaviour were originated from numerical simulations matched with experimental tests of the polymethacrylimide raw material. Experimental primary stability tests of acetabular press-fit cups consisting of static shell assembly with consecutively pull-out and lever-out testing were subsequently simulated using finite element analysis. Identified and optimised parameters allowed the accurate numerical reproduction of the raw material tests. Correlation between experimental tests and the numerical simulation of primary implant stability depended on the value of interference fit. However, the validated material model provides the opportunity for subsequent parametric numerical studies.     

Synergistic influence of phosphorylation and metal ions on tau oligomer formation and coaggregation with alpha-synuclein at the single molecule level

ABSTRACT: BACKGROUND: Fibrillar amyloid-like deposits and co-deposits of tau and alpha-synuclein are found in several common neurodegenerative diseases. Recent evidence indicates that small oligomers are the most relevant toxic aggregate species. While tau fibril formation is well-characterized, factors influencing tau oligomerization and molecular interactions of tau and alpha-synuclein are not well understood. RESULTS: We used a novel approach applying confocal single-particle fluorescence to investigate the influence of tau phosphorylation and metal ions on tau oligomer formation and its coaggregation with alpha-synuclein at the level of individual oligomers. We show that Al3+ at physiologically relevant concentrations and tau phosphorylation by GSK-3beta exert synergistic effects on the formation of a distinct SDS-resistant tau oligomer species even at nanomolar protein concentration. Moreover, tau phosphorylation and Al3+ as well as Fe3+ enhanced both formation of mixed oligomers and recruitment of alpha-synuclein in pre-formed tau oligomers. CONCLUSIONS: Our findings provide a new perspective on interactions of tau phosphorylation, metal ions, and the formation of potentially toxic oligomer species, and elucidate molecular crosstalks between different aggregation pathways involved in neurodegeneration.     

Therapeutic vaccination with simian immunodeficiency virus (SIV)-DNA + IL-12 or IL-15 induces distinct CD8 memory subsets in SIV-infected macaques

DNA vaccination is an invaluable approach for immune therapy in that it lacks vector interference and thus permits repeated vaccination boosts. However, by themselves, DNA-based vaccines are typically poor inducers of Ag-specific immunity in humans and non-human primates. Cytokines, such as IL-12 and IL-15, have been shown to be potent adjuvants for the induction and maintenance of cellular immune responses, in particular during HIV infection. In this study, we examined the ability of therapeutic vaccination with SIV-DNA+IL-12 or IL-15 as molecular adjuvants to improve DNA vaccine potency and to enhance memory immune responses in SIV-infected macaques. Our results demonstrate that incorporating IL-12 into the vaccine induces SIV-specific CD8 effector memory T cell (T(EM)) functional responses and enhances the capacity of IFN-gamma-producing CD8 T(EM) cells to produce TNF. Lower levels of PD-1 were expressed on T cells acquiring dual function upon vaccination as compared with mono-functional CD8 T(EM) cells. Finally, a boost with SIV-DNA+IL-15 triggered most T cell memory subsets in macaques primed with either DNA-SIV or placebo but only CD8 T(EM) in macaques primed with SIV-DNA+IL-12. These results indicate that plasmid IL-12 and IL-15 cytokines represent a significant addition to enhance the ability of therapeutic DNA vaccines to induce better immunity.     

Strain-time cell-death threshold for skeletal muscle in a tissue-engineered model system for deep tissue injury

Deep tissue injury (DTI) is a severe pressure ulcer that results from sustained deformation of muscle tissue overlying bony prominences. In order to understand the etiology of DTI, it is essential to determine the tolerance of muscle cells to large mechanical strains. In this study, a new experimental method of determining the time-dependent critical compressive strains for necrotic cell death (E(zz)(c)(t)) in a planar tissue-engineered construct under static loading was developed. A half-spherical indentor is used to induce a non-uniform, concentric distribution of strains in the construct, and E(zz)(c)(t) is calculated from the radius of the damage region in the construct versus time. The method was employed to obtain E(zz)(c)(t) for bio-artificial muscles (BAMs) cultured from C2C12 murine cells, as a model system for DTI. Specifically, propidium iodine was used to fluorescently stain the development of necrosis in BAMs subjected to strains up to 80%. Two groups of BAMs were tested at an extracellular pH of 7.4 (n=10) and pH 6.5 (n=5). The lowest strain levels causing cell death in the BAMs were determined every 15min, during 285-min-long trials, from confocal microscopy fluorescent images of the size of the damage regions. The experimental E(zz)(c)(t) data fitted a decreasing single-step sigmoid of the Boltzmann type. Analysis of the parameters of this sigmoid function indicated a 95% likelihood that cells could tolerate engineering strains below 65% for 1h, whereas the cells could endure strains below 40% over a 285min trial period. The decrease in endurance of the cells to compressive strains occurred between 1-3h post-loading. The method developed in this paper is generic and suitable for studying E(zz)(c)(t) in virtually any planar tissue-engineered construct. The specific E(zz)(c)(t) curve obtained herein is necessary for extrapolating biological damage from muscle-strain data in biomechanical studies of pressure ulcers and DTI.     

Postinfarct sympathetic hyperactivity differentially stimulates expression of tyrosine hydroxylase and norepinephrine transporter

The balance between norepinephrine (NE) synthesis, release, and reuptake is disrupted after acute myocardial infarction, resulting in elevated extracellular NE. Stimulation of sympathetic neurons in vitro increases NE synthesis and the synthetic enzyme tyrosine hydroxylase (TH) to a greater extent than it increases NE reuptake and the NE transporter (NET), which removes NE from the extracellular space. We used TGR(ASrAOGEN) transgenic rats, which lack postinfarct sympathetic hyperactivity, to test the hypothesis that increased cardiac sympathetic nerve activity accounts for the imbalance in TH and NET expression in these neurons after myocardial infarction. TH and NET mRNA levels were identical in the stellate ganglia of unoperated TGR(ASrAOGEN) rats compared with Sprague Dawley (SD) controls, but the threefold increase in TH and twofold increase in NET mRNA seen in the stellate ganglia of SD rats 1 wk after ischemia-reperfusion was absent in TGR(ASrAOGEN) rats. Similarly, the increase in TH and NET protein observed in the base of the SD ventricle was absent in the base of the TGR (ASrAOGEN) ventricle. Neuronal TH content was depleted in the left ventricle of both genotypes, whereas NET was unchanged. Basal heart rate and cardiac function were similar in both genotypes, but TGR(ASrAOGEN) hearts were more sensitive to the beta-agonist dobutamine. Tyramine-induced release of endogenous NE generated similar changes in ventricular pressure and contractility in both genotypes, but postinfarct relaxation was enhanced in TGR(ASrAOGEN) hearts. These data support the hypothesis that postinfarct sympathetic hyperactivity is the major stimulus increasing TH and NET expression in cardiac neurons.     

Blood pressure response to chronic episodic hypoxia: the renin-angiotensin system.

By using an inspired oxygen fraction that produces oxyhemoglobin desaturation equivalent to that seen in human sleep apnea, we have demonstrated that 35 days of recurrent episodic hypoxia (every 30 s for 7 h/day) results in an 8-13 mmHg persistent increase in diurnal systemic mean arterial blood pressure (MAP) in rats. Blockade of angiotensin II receptors (AT(1a)) eliminates this response. Separate groups of male Sprague-Dawley rats were fed high-salt (8%), ad libitum-salt, or low-salt (0.1%) diets for 7 wk: 2 wk of wash-in for baseline blood pressure measurement and 5 wk of experimental conditions. Rats in each salt group were subjected to episodic hypoxia whereas controls remained unhandled under normoxic conditions. MAP remained at basal levels in all nonepisodic hypoxia controls as well as high-salt-diet episodic hypoxia-exposed rats. Ad lib and low-salt episodic hypoxia rats showed an increase in MAP from 106 and 104 mmHg at baseline to 112 and 113 mmHg, respectively (P < 0.05). Whole kidney renin mRNA was suppressed in high-salt controls and episodic hypoxia rats, whereas kidney AT(1a) mRNA showed opposite changes. Suppression of the renin-angiotensin system with a high-salt diet blocks the increase in MAP in episodic hypoxia-challenged rats, in part by suppressing local tissue renin levels. Upregulation of the tissue angiotensin II system appears to be necessary for the chronic blood pressure changes that occur from episodic hypoxia.     

Autoradiographic and electron microscopic studies of minced cardiac muscle regeneration in the adult newt, notophthalmus viridescens.

The regenerative response of minced cardiac muscle grafts in the adult newt was studied using autoradiography and electron microscopy. One-sixteenth to one-eighth of the newt ventricle was amputated, minced, and returned to the wounded ventricle. At five days after grafting, no reorganization of graft msucle pieces was apparent and there was degeneration of much of the muscle graft. Another, smaller population of 5-day myocytes had euchromatic nuclei and intact sarcolemmae. In 10- and 16-day grafts, continuity between ventricular and graft lumina was established and coalescence of graft pieces was apparent. Ultrastructurally, 10- and 16-day graft myocytes appeared to have fewer myofibrillae and increased amounts of rough endoplasmic reticulum, polyribosomes, Golig complexes, and dense bodies when compared to uninjured ventricular myocytes. The peak of proliferative activity of graft cells was observed at 16 days. Electron microscopic autoradiography revealed breadkdown of myofibrillar structure in labeled myocytes, whereas in myocytes in the later stages of mitosis only scattered myofilaments and no Z bands were present. By 30 days, grafts appeared as an integrated structure composed primarily of cardiac muscle. Myocytes of 30-day grafts were observed in various stages of myofibrillogenesis and contained numberous 10-nm filaments. Seventy-day graft mycoytes had numberous well organized myofibrillae and intercellular junctions similar to those seen in uninjured ventricular myocytes.