Multiscale Innovative Materials and Structures (MIMS).

Increasing attention is growing towards advanced multiscale metamaterials and nanostructures, due to recent developments in nanoscience and nanotechnology [...].

Tensegrity Modelling and the High Toughness of Spider Dragline Silk.

This work establishes a tensegrity model of spider dragline silk. Tensegrity systems are ubiquitous in nature, being able to capture the mechanics of biological shapes through simple and effective modes of deformation via extension and contraction. Guided by quantitative microstructural characterization via air plasma etching and low voltage scanning electron microscopy, we report that this model is able to capture experimentally observed phenomena such as the Poisson effect, tensile stress-strain response, and fibre toughness. This is achieved by accounting for spider silks' hierarchical organization into microfibrils with radially variable properties. Each fibril is described as a chain of polypeptide tensegrity units formed by crystalline granules operating under compression, which are connected to each other by amorphous links acting under tension. Our results demonstrate, for the first time, that a radial variability in the ductility of tensegrity chains is responsible for high fibre toughness, a defining and desirable feature of spider silk. Based on this model, a discussion about the use of graded tensegrity structures for the optimal design of next-generation biomimetic fibres is presented.

Design and Testing of Bistable Lattices with Tensegrity Architecture and Nanoscale Features Fabricated by Multiphoton Lithography.

A bistable response is an innate feature of tensegrity metamaterials, which is a conundrum to attain in other metamaterials, since it ushers unconventional static and dynamical mechanical behaviors. This paper investigates the design, modeling, fabrication and testing of bistable lattices with tensegrity architecture and nanoscale features. First, a method to design bistable lattices tessellating tensegrity units is formulated. The additive manufacturing of these structures is performed through multiphoton lithography, which enables the fabrication of microscale structures with nanoscale features and extremely high resolution. Different modular lattices, comprised of struts with 250 nm minimum radius, are tested under loading-unloading uniaxial compression nanoindentation tests. The compression tests confirmed the activation of the designed bistable twisting mechanism in the examined lattices, combined with a moderate viscoelastic response. The force-displacement plots of the 3D assemblies of bistable tensegrity prisms reveal a softening behavior during the loading from the primary stable configuration and a subsequent snapping event that drives the structure into a secondary stable configuration. The twisting mechanism that characterizes such a transition is preserved after unloading and during repeated loading-unloading cycles. The results of the present study elucidate that fabrication of multistable tensegrity lattices is highly feasible via multiphoton lithography and promulgates the fabrication of multi-cell tensegrity metamaterials with unprecedented static and dynamic responses.

High-Performance Nylon-6 Sustainable Filaments for Additive Manufacturing.

This study deals with the development of Nylon-6 fused deposition modeling (FDM) filaments for additive manufacturing, which couples high mechanical performances with eco-sustainability. These filaments were extruded from recycled Nylon-6 granulates through a dedicated twin-screw extrusion line, which processes either pure Nylon-6 grains, or mixtures of such a material with minor fractions of acrylonitrile butadiene styrene (ABS) and titanium dioxide (TiO2). The rheological and thermal properties of the investigated filaments are analyzed, including melt flow index, melting temperature, and decomposition temperature, which are of the utmost importance when avoiding the overheating and decomposition of the material. Such a study is conducted in both pre-extrusion and post-extrusion conditions. The tensile strength, the wear resistance, and the printability of the examined recycled Nylon-6 filaments are also studied by comparing the properties of such filaments with those exhibited by different nylon-based filaments for FDM that are available in the market. The given results show that the recycling of Nylon-6 through the "caprolactam" regeneration route enables the newly formed material to retain high physical and mechanical properties, such as tensile strength at yield in the interval 55.79-86.91 MPa. Referring to the basic composition of the filaments examined in the present study, this remarkably high-yield strength is accompanied by a Young modulus of 1.64 GPa, and wear resistance of 92 µm, under a 15 min/1 kg load pin-on-disk test carried at the sliding speed of 250 rpm.

Multi-Material Additive Manufacturing of Sustainable Innovative Materials and Structures.

This paper highlights the multi-material additive manufacturing (AM) route for manufacturing of innovative materials and structures. Three different recycled thermoplastics, namely acrylonitrile butadiene styrene (ABS), polylactic acid (PLA), and high impact polystyrene (HIPS) (with different Young's modulus, glass transition temperature, rheological properties), have been selected (as a case study) for multi-material AM. The functional prototypes have been printed on fused deposition modelling (FDM) setup as tensile specimens (as per ASTM D638 type-IV standard) with different combinations of top, middle, and bottom layers (of ABS/PLA/HIPS), at different printing speed and infill percentage density. The specimens were subjected to thermal (glass transition temperature and heat capacity) and mechanical testing (peak load, peak strength, peak elongation, percentage elongation at peak, and Young's modulus) to ascertain their suitability in load-bearing structures, and the fabrication of functional prototypes of mechanical meta-materials. The results have been supported by photomicrographs to observe the microstructure of the analyzed multi-materials.

Biomechanical features of bidirectional-barbed suture: a randomized laboratory analysis.

The aim of the current prospective study was to evaluate the biomechanical stability of barbed suture vs. conventional suture. Biomechanical stability of a 14x14-cm PDO/polydioxanone, with a half circle and 36-mm needle, bidirectional barbed 0-Quill suture (Angiotech, Vancouver, British Columbia, Canada) vs. 1-Poliglecaprone 25 (Monocryl, Ethicon, Inc, Somerville, NJ) suture was evaluated on biological specimens. The 1-Monocryl suture was chosen because it is widely used by gynecological surgeons in the repair either of the vaginal cuff or the uterine wall defects. Forty specimens of aponeurotic muscle, obtained from abdominal wall of a lamb, were prepared, and randomly assigned to 1 of 2 repair groups: Group A (n = 20) classic repair with 1-Monocryl suture; Group B (n = 20) 0-Quill barbed suture. Each specimen was transected at the midpoint and then repaired. Biomechanical stability of the repaired specimen was verified on a CMT6000 electromechanical universal testing machine (SANS, MTS SYSTEMS, China Co., Ltd., Shenzhen, China), with a 1kN cell. Biomechanical tests showed that maximum force was similar for 1-Monocryl and 0-Quill respectively (p = non-significant). This randomized laboratory study shows that biomechanical stability of the sutures is comparable.

Bidirectional barbed suture in laparoscopic myomectomy: clinical features.

OBJECTIVE: To compare bidirectional knotless barbed suture versus standard sutures, with either extracorporeal or intracorporeal knots, and to assess the feasibility, safety, and rapidity in repairing a uterine wall defect after laparoscopic myomectomy. SUBJECTS AND METHODS: This was a randomized clinical study having a Canadian Task Force Classification of I. In tertiary-care university-based teaching hospitals, 117 women who underwent laparoscopic myomectomy were enrolled. In accord with randomization, uterine wall defects were closed with either extracorporeal (poliglecaprone 25; Monocryl™-1; Ethicon Inc., Somerville, NJ) or intracorporeal (polyglactin 910; Vicryl™-1; Ethicon Inc.) knots or a bidirectional knotless barbed suture (Quill™-0; Angiotech Pharmaceuticals, Inc., Vancouver, BC, Canada). RESULTS: Time required to suture was significantly lower in the group operated on with a bidirectional suture than in groups with traditional sutures (P<.001). No significant difference was observed in operative time among the study groups. The degree of surgical difficulty was significantly lower in the Quill group than in the other groups. CONCLUSIONS: Use of barbed sutures reduces the time required to repair a uterine wall defect during laparoscopic myomectomy. In a follow-up of patients carried out at 3 months, 6 months, and 1 year after the surgery, there were no wound dehiscence, no bleeding, and no other potential major complications.

Bidirectional barbed suture in total laparoscopic hysterectomy and lymph node dissection for endometrial cancer: technical evaluation and 1-year follow-up of 61 patients.

OBJECTIVE: This randomized clinical study compared the feasibility and safety of the shortest suture for bidirectional knotless barbed versus standard sutures, with either extracorporeal or intracorporeal knots, for vaginal cuff closure following total laparoscopic hysterectomy (TLH) and lymph node dissection for early endometrial cancer. SUBJECTS AND METHODS: The study design was Canadian Task Force Classification I. In tertiary-care university-based teaching hospitals, 61 women underwent TLH and lymph node dissection. In accord with randomization, the vaginal cuff in TLH was closed with either extracorporeal or intracorporeal knots (1-Monocryl(®); Ethicon Inc., Somerville, NJ) and a bidirectional knotless barbed suture (0-Quill™; Angiotech Pharmaceuticals, Inc., Vancouver, BC, Canada). All patients were evaluated at 3-month, 6-month, and 1-year follow-up. RESULTS: Time required to suture was significantly lower in the group treated with bidirectional suture than in groups with traditional sutures (P<.001). No significant difference was observed in the operative time between the study groups. The degree of surgical difficulty was significantly lower in the bidirectional barbed suture group than in the other groups. At 1-year follow-up all patients presented no wound dehiscence, no bleeding, dyspareunia, and other potential major complications such as ureteric, bladder, or bowel injury. CONCLUSIONS: Use of a barbed suture reduces the time required to repair the vaginal cuff during TLH. At follow-up of patients, carried out 3 months, 6 months, and 1 year after the surgery, no wound dehiscence, no bleeding, or no other potential major surgical complications had occurred.

A variational constitutive model for soft biological tissues.

In this paper, a fully variational constitutive model of soft biological tissues is formulated in the finite strain regime. The model includes Ogden-type hyperelasticity, finite viscosity, deviatoric and volumetric plasticity, rate and microinertia effects. Variational updates are obtained via time discretization and pre-minimization of a suitable objective function with respect to internal variables. Genetic algorithms are used for model parameter identification due to their suitability for non-convex, high dimensional optimization problems. The material behavior predicted by the model is compared to available tests on swine and human brain tissue. The ability of the model to predict a wide range of experimentally observed behavior, including hysteresis, cyclic softening, rate effects, and plastic deformation is demonstrated.