Experimental Analysis and Numerical Modelling of the Mechanical Behavior of a Sisal-Fiber-Reinforced Geopolymer

The present paper is devoted to the proposal of appropriate numerical modelling able to provide a suitable description of the mechanical behavior of a composite geopolymer. Reference is made to a natural sisal-fiber-reinforced geopolymer. The study is based on the results of appropriate experimental investigations for compressive, flexural and splitting loadings, taking into account different weight percentages of fibers to evidence their role in the mechanical behavior. The main objective of the paper is to calibrate the microplane constitutive model, available in ANSYS software version 18.1, where the numerical analyses are performed. Therefore, the present study is structured in two different steps. Firstly, the mechanical behavior of geopolymers reinforced with sisal fibers is experimentally investigated, and subsequently, the gathered test data are interpreted and utilized to calibrate the relevant constitutive model to be used in the numerical stage. The obtained results are compared with experimental data, yielding good correlations. The paper's results supply the parameters required to obtain an affordable numerical model of the reinforced geopolymer for different percentages of fibers to be adopted for material design with assigned mechanical properties

Topology in full QCD at high temperature: a multicanonical approach

We investigate the topological properties of $N_f = 2+1$ QCD with physical quark masses, at temperatures around 500 MeV. With the aim of obtaining a reliable sampling of topological modes in a regime where the fluctuations of the topological charge $Q$ are very rare, we adopt a multicanonical approach, adding a bias potential to the action which enhances the probability of suppressed topological sectors. This method permits to gain up to three orders of magnitude in computational power in the explored temperature regime. Results at different lattice spacings and physical spatial volumes reveal no significant finite size effects and the presence, instead, of large finite cut-off effects, with the topological susceptibility which decreases by 3-4 orders of magnitude while moving from $a \simeq 0.06$ fm towards the continuum limit. The continuum extrapolation is in agreeement with previous lattice determinations with smaller uncertainties but obtained based on ansatzes justified by several theoretical assumptions. The parameter $b_2$, related to the fourth order coefficient in the Taylor expansion of the free energy density $f(\theta)$, has instead a smooth continuum extrapolation which is in agreement with the dilute instanton gas approximation (DIGA); moreover, a direct measurement of the relative weights of the different topological sectors gives an even stronger support to the validity of DIGA.Comment: 23 pages, 13 figure

APPROCCIO CLINICO E RIABILITATIVO AL PAZIENTE PROTESIZZATO D'ARTO INFERIORE

Nella chirurgia sostitutiva protesica, ripercorrendo le tappe riabilitative e analizzandone le modalità e le tecniche, si evince che è possibile permettere al paziente il riapprendimento della corretta deambulazione con la riorganizzazione di tutte le fasi e della gestualità corrente per il reinserimento efficace nel contesto sociale di appartenenza. Oltre che dal punto di vista puramente motorio, il soggetto deve essere seguito anche sotto l’aspetto della psicomotricità e nel rispetto di importanti esigenze psicologiche. Viene sorretto, incoraggiato, ma soprattutto responsabilizzato sul fatto che per la ripresa completa si rende indispensabile la sua partecipazione attiva e la costanza dell’impegno. I riflessi pratici di una guarigione efficace e completa sono quindi estremamente proficui per il soggetto, il quale avverte in sé la capacità di ottemperare all’impegno del proprio recupero; seppur con stati d’ansia che insidiano il suo equilibrio, egli tenderà a proiettarsi nel suo futuro che quindi non apparirà denso di incognite. Non vi sarà commiserazione né emarginazione, ma voglia di vivere in una società che, anche se disumanizza i rapporti fra le differenti fasce di età, offre interessi e spazi per quanti sappiano organizzare la propria esistenza senza frustrazioni, remore e tentennamenti. La riabilitazione del protesizzato è un processo complesso perché non riguarda solamente il recupero della funzionalità della singola articolazione ma è rivolto a un riaddestramento globale del soggetto a una nuova modalità di vita relazionale. Il programma riabilitativo, quindi, deve essere personalizzato sul singolo e deve proporsi obiettivi differenti in base alle condizioni generali (anche cognitive). È necessario rendere possibile il raggiungimento di un livello di autosufficienza e autonomia motoria tale da permettere il ritorno alle normali attività di vita quotidiana

Effect of suturing the femoral portion of a four-strand graft during an ACL reconstruction.

Purpose A suture passed along the part of the graft that will be inserted into the femoral tunnel is widely used by surgeons, because it could prevent the graft sliding on the femoral fixation device during pulling from the tibial side. The aim of this study was to evaluate the biomechanical effects of suturing the intratunnel femoral part of the graft during an anterior cruciate ligament (ACL) reconstruction. Methods Bovine digital extensor tendons and tibias were harvested from 20 fresh-frozen mature bovine knees ranging in age from 18 to 24 months. Quadruple-strand bovine tendons were passed through the tibial tunnel and secured distally with a bioabsorbable interference screw. In one half of all grafts (N = 10), the looped-over part of the graft was sutured in a whipstitch technique over a distance of 30 mm (Group 1). In one half of all grafts (N = 10), the looped-over part was left free from any suture (Group 2). The grafts were preconditioned at 50 N for 10 min, fol- lowed by cyclic loading at 1 Hz between 50 N and 250 N for 1,000 cycles. Load-to-failure test was then carried out at a rate of 1 mm/s. Results There was no statistically significant difference between mean stiffness at pullout and yield load between the two groups. In all specimens on Group 1, failure occurred following to partial breaking and then slipping of the tendons between the screw and the tunnel. Concerning Group 2, in six cases failure occurred as described for Group 1 specimens. In the remaining four cases, failure occurred entirely through the ligament mid-substance. Conclusions Suturing in a whipstitch fashion the femoral portion of the graft doesn’t affect the mechanical proprie- ties of the ACL graft. When suspension fixation device is used, suturing the looped-over part of the graft could be helpful in order to provide equal tension in all of the strands of the graft at time of tibial fixation

Does the 5-strand-graft have superior biomechanical behaviour than 4-strand-graft during acl reconstruction?

Purpose. This study aimed to compare the biomechanical proprieties of 4 and 5-strand- grafts. Methods. For the present study, fresh-frozen bovine common digital extensor tendons were used. Tendon grafts were prepared and sized to have a length of almost 27 cm and a cylinder 4 strand diameter of 8 mm. In half of all samples (Group A, n=12,), the graft was formed by 2 bundles duplicated around a metallic rod creating a 4-strand-tendon construct. In the other half of samples (Group B, n= 12,) 5-strand-tendon construct was created duplicating a single tendon around the rod, and tripling the other one. The grafts were preconditioned at 50 N for 10 min, followed by 1,000 cyclic loading between 50 and 250 N. Load-to-failure test was then carried out at a rate of 1 mm/s. Results. No statistically significant differences were found between two groups concern- ing cyclic elongation at the 500th cycle and at the final cycle. An increased stiffness was observed in the Group B during cyclic loads and at pull-out (p<0.05). Significant differ- ences were noted at the ultimate load-to-failure between Group A (1533 ± 454 N) and Group B (1139 ± 276 N) (p< 0.05). Conclusion. This study showed that both graft construct appears to be biomechanical- ly effective in a bovine tendon model. 5-strand-graft showed an increased stiffness and a decreased ultimate load-to-failure comparing to the 4-strand-graft construct. Biomechan- ically, no real benefit could be observed in the clinical setting increasing the numbers of strands used for the ACL reconstructive surgery

Clinical biomarkers in brain injury: a lesson from cardiac arrest.

Cardiac arrest (CA) is the primary cause of death in industrialized countries. Successful resuscitation rate is estimated of about 40%, but a good neurological outcome remains difficult to achieve. The majority of resuscitated victims suffers of a pathophysiological entity termed as "post resuscitation disease". Today's efforts are mainly pointed to the chain of survival, often devoting less attention to post-resuscitation care. Resuscitated patients are often victims of nihilistic therapeutic approach, with clinicians failing to promptly institute strategies that mitigate the ischemia-reperfusion injury to vital organs. Only after 72 hours prognostication can be realistically attempted. Neurological evaluation relies on a combination of clinical, instrumental and laboratoristic parameters, since no one alone holds a specificity of 100%. Biochemical markers, such as neuron specific enolase and S-100b, may contribute to predict prognosis after CA. To the contrary, when used individually the necessary precision remains poorly characterized. Biochemical studies suffer from substantial methodological differences hampering attempts to summarize their findings. We review the information available on biochemical markers of brain damage for neurological prognostication after CA

HEAT SHOCK PROTEINS AND AUTOIMMUNE SYSTEM ACTIVATION IN IBD: ARTICULAR MANIFESTATIONS AND THE EPIDEMIOLOGICAL FREQUENCY IN ORTHPEDICS

clinical evidence suggest that arthritis is one of the complications of inflammatori bowel disease (IBD) of which the etiological causes are still not completely understood. Among the possible explanations the most probable theory is poor regulation of the intestinal immune system, which causes a cross-like immune reactivity against the resident micro flora. Arthritis is these subjects involves different joints and is asymmetric, with greater involvement of the large joints of the lower limbs. Joints may also be involved with the spinal forms of sacroileitis and ankilosing spondylitis. This clinical evidence explains the existence of Lesnioski-Crohn's disease, a variant of IBD in which patients have bone joint problems that may also be the primary manifestations of the disease

INFLAMMATORY BOWEL DISEASE AND PERIPHERAL ATRHITIS: MESALAZINA AND PROBIOTICS

The inflammaotory bowel disease (IBD) are a group of inflammatory pathologies of the digestive line with chronicity and recurrent characteristic. The IBDs mostly recognized are the ulcerative colitis and Crohn's disease; they are more frequent in the industrialized countries and among the caucasian populations that among those africans or oriental. The secondary artropaties to IBD recognize a multifactorial genesis in subjects predisposed as a result genetically or environmental factors; a fundamental role of the intestinal dysbiosis they are hypothesized

Polybutylene succinate artificial scaffold for peripheral nerve regeneration

Regeneration and recovery of nerve tissues are a great challenge for medicine, and positively affect the quality of life of patients. The development of tissue engineering offers a new approach to the problem with the creation of multifunctional artificial scaffolds that act on various levels in the damaged tissue, providing physical and biochemical support for the growth of nerve cells. In this study, the effects of the use of a tubular scaffold made of polybutylene succinate (PBS), surgically positioned at the level of a sciatic nerve injured in rat, between the proximal stump and the distal one, was investigated. Scaffolds characterization was carried out by scanning electron microscopy and X-ray microcomputed tomography and magnetic resonance imaging, in vivo. The demonstration of the nerve regeneration was based on the evaluation of electroneurography, measuring the weight of gastrocnemius and tibialis anterior muscles, histological examination of regenerated nerves and observing the recovery of the locomotor activity of animals. The PBS tubular scaffold minimized iatrogenic trauma on the nerve, acting as a directional guide for the regenerating fibers by conveying them toward the distal stump. In this context, neurotrophic and neurotropic factors may accumulate and perform their functions, while invasion by macrophages and scar tissue is hampered