Anisotropic Deformation in a Polymer Slab Subjected to Fluid Adsorption.

Nanoporous adsorbents can mechanically swell or shrink once upon the accumulation of guest fluid molecules at their internal surfaces or in their cavities. Existing theories in this field attribute such sorption-induced swelling to a tensile force, while shrinkage is always associated with a contractive force. In this study, however, we propose that the sorption-induced deformation of a porous architecture is not solely dictated by the stress conditions but can also be largely influenced by its mechanical anisotropy. In more detail, the sorption-induced deformation of a polymeric slab is investigated using a hybrid molecular dynamics and Monte Carlo algorithm. When subjected to water loading, the slab is found to swell along its normal direction and display an overall positive volumetric strain. Moreover, the surface roughness is enhanced as a response to the surface energy decrease induced by the water covering the slab external surface. Unexpectedly, the in-plane deformation of the slab material seems to be highly constrained, so that it is far below its normal counterpart. This anisotropy is enhanced when the slab thickness decreases. With a thickness of around 1.35 nm, an in-plane shrinkage is observed throughout the entire hygroscopic range. A theoretical analysis based on a poromechanical model suggests that the anisotropic mechanical properties, which are common for a slab material, are the essence of the constrained in-plane swelling or even shrinkage under the isotropic sorption-induced tensile forces. This study, unveiling overlooked mechanisms of sorption-induced shrinkage in mechanically anisotropic materials, provides new insights into this field.

Sorption-Deformation Interplay in Hierarchical Porous Polymeric Structures Composed of a Slit Pore in an Amorphous Matrix.

Prevailing absorbents like wood-derived porous scaffolds or polymeric aerogels are normally featured with hierarchical porous structures. In former molecular simulation studies, sorption, deformation, and coupled sorption-deformation have been studied for single-scale materials, but scarcely for materials where micropores (<2 nm) and mesopores (2-50 nm) coexist. The present work, dealing with a mesoscopic slit pore between two slabs of microporous amorphous cellulose (AC), aims at modeling sorption-deformation interplay in hierarchical porous cellulosic structures inspired by polymeric modern adsorbents. Specifically, the atomic system is modeled by a hybrid workflow combining molecular dynamics (MD) and grand canonical Monte Carlo (GCMC) simulations. The results clarify the multiple sorption/deformation mechanisms in porous materials with different slit-pore sizes, including water filling in micropores, surface covering at the solid-air interface, and subsequent capillary condensation in mesopores. In particular, before the onset of capillary condensation, the sorption behavior of the AC matrix in the hybrid system is almost the same as that of bulk AC, in which sorption and deformation enhance each other through sorption-induced swelling and additional sorption in the newly created voids. Upon capillary condensation, the interaction between the micropores and the mesopore emerges. Water molecules in the mesopore exert a negative hydrostatic pressure perpendicular to the slab surface on the matrices, resulting in an increase in porosity and water content, a decrease in distance between the centers of mass (COMs) of the slabs, and thus a thinning of the slit pore. As described by Bangham's Law, the surface area of the rough slit-pore slab increases proportionally to the surface energy variation during surface covering. For a system composed of a compliant polymer like AC, however, the surface area enlargement does not result in an in-plane swelling as expected but instead in an in-plane shrinkage along with an increase in local roughness or irregularity (an accordion effect).

Sorption-Deformation-Percolation Model for Diffusion in Nanoporous Media.

Diffusion of molecules in porous media is a critical process that is fundamental to numerous chemical, physical, and biological applications. The prevailing theoretical frameworks are challenged when explaining the complex dynamics resulting from the highly tortuous host structure and strong guest-host interactions, especially when the pore size approximates the size of diffusing molecule. This study, using molecular dynamics, formulates a semiempirical model based on theoretical considerations and factorization that offer an alternative view of diffusion and its link with the structure and behavior (sorption and deformation) of material. By analyzing the intermittent dynamics of water, microscopic self-diffusion coefficients are predicted. The apparent tortuosity, defined as the ratio of the bulk to the confined self-diffusion coefficients, is found to depend quantitatively on a limited set of material parameters: heat of adsorption, elastic modulus, and percolation probability, all of which are experimentally accessible. The proposed sorption-deformation-percolation model provides guidance on the understanding and fine-tuning of diffusion.

ZipFix Versus Conventional Sternal Closure: One-Year Follow-Up.

BACKGROUND: The present study aimed to compare postoperative complications commonly revealed after sternotomy closure by new sternal ZipFix™ (Synthes GmbH, Oberdorf, Switzerland) implant and conventional steel wire. METHODS: Among the initial 360 subjects, 326 patients enrolled in this randomised control trial who were candidates for cardiac surgery from April 2014 to March 2015. After the surgery, the sternal closure was randomly done with poly-ether-ether-ketone (PEEK) based sternal ZipFix (ZF) on the sternal body (n=168) or with conventional wires (CWs) (n=158). Patients were followed postoperatively as well as 1, 3, 6, and 12 months after discharge regarding postoperative complications such as pain severity, dehiscence, and infection including incisional infections (superficial or deep), and organ/space infection (mediastinitis or osteomyelitis). RESULTS: The mean age of the ZF and CW groups were 63.58±10.9 and 62.42±7.1years, respectively (p=0.262). In addition, there was no significant difference between the two groups' baseline characteristics (p>0.05). Our study showed higher mean pain severity score in the conventional closure group compared with ZipFix closure group at all study time points (p<0.001). Infection was seen in 2.76% of the overall participants with no significant difference of incisional and organ infection between the two groups throughout the study. After 1-month follow-up, five patients in the CW group had sternal dehiscence whereas no patients in ZF had dehiscence (p<0.001). CONCLUSIONS: Our trial demonstrates greater clinical advantages in terms of pain and sternal dehiscence post surgery by using sternal ZipFix compared to conventional steel wire.

A simple modified Bentall technique for surgical reconstruction of the aortic root - short and long term outcomes.

BACKGROUND: Since the first introduction of the Bentall technique, several modifications have been proposed to improve patient outcomes and decrease intra- and post-operative complications. We describe a simplified modification of the technique that tries to lessen the intra-operative time, improve homeostasis and miminize early and late complications. Our experience with the technique and short- and long-term patient outcomes are reported. METHODS: From August 1996 to October 2013, 110 consecutive patients underwent this modified technique. The procedure used Dacron composite graft with a mechanical valve (St. Jude Medical®) for aortic root replacement. To avoid intra-operative complications, no mobilization of coronary ostia was done. Additionally, the tubular aorta was kept minimally unchanged. RESULTS: Total bleeding after the operation was 450 ± 105 mL. The mean duration of intensive care unit and hospital stay were 2 ± 1 and 5 ± 2 days, respectively. Sixty-six patients (60 %) were discharged from the surgical intensive care unit on the first postoperative day, 34 patients (30.9 %) were discharged on the second day and ten patients (9.1 %) needed more time to stay in the intensive care unit due to haemodynamic or respiratory problems. At 5-years follow up, survival rate was 97 %. In the three deceased patients, causes of death were mediastinitis, sepsis and myocardial infarction. No operation-related complications such as anticoagulant-related hemorrhage, valve or graft thrombosis, or coronary pseudoaneurysm were occurred during follow-up. CONCLUSIONS: The proposed modification of the Bentall technique seems to minimize late intra-operative blood loss, improves homeostasis, shortens the operation time and is associated with excellent long-term outcomes in patients undergoing composite graft replacement of the aortic root.

A large saphenous vein graft aneurysm one year after coronary artery bypass graft surgery presenting as a left lung mass.

Aneurysm of a saphenous vein graft (SVG) is a rare but fatal complication of coronary artery bypass graft (CABG) surgery. The development of SVG aneurysms appears usually about 10-20 years after the operation at an estimated rate of <1%. A 68-year-old male was referred to the emergency department after frequent episodes of dyspnea, chest pain and hemoptysis. He previously had CABG surgery one year before. The physical examination was normal. Chest radiogram showed a left pulmonary midzone mass. CT-angiogram demonstrated a large aortic pseudoaneurysm (6.36 x 6.06 cm) in the middle part of the ascending aorta. After sternotomy, the ascending aorta above sinotubular junction near the origin of brachiocephalic artery was resected and replaced with a tube graft. The patient was transferred to ICU with stable hemodynamic status. SVG aneurysm should be considered while encountering mediastinal mass or undiagnosed cardiopulmonary symptoms in patients with a previous history of CABG because of its rarity and overlap of symptoms with other thoracic, pulmonary, and cardiac diseases. Surgery seems to be the treatment of choice to reduce the risk of rupture and embolism.