Interfiber Distance Research Articles

Mesoscale mechanism of damage in fracture process zone of CFRP laminates simulated with triaxial stress state-dependent constitutive equation of matrix resin

The three-dimensional failure process experimentally observed by synchrotron radiation X-ray computed tomography (SR X-CT) regarding the influence of the interfiber distance is discussed on the basis of the results of numerical experiments. Triaxial stress states in the fracture process zone of carbon fiber reinforced polymers were analyzed on the mesoscale under mode I and mixed-mode (mode I + II) loading. Yield and damage models depending on stress triaxiality were used to accurately simulate three-dimensional stress states in the damage zone around the crack tip. Owing to the heterogeneity of composites, deviatoric stress is prominent in the thin resin region where the interfiber distance is small under mode I loading. On the other hand, matrix resin is triaxially stressed in the middle point between carbon fibers in the thick resin region where the interfiber distance is large. Under mode II loading, the shapes of fiber/matrix debonding depended on the interfiber distance. Areas with stress concentration were found owing to a large debonding area in the thick resin region resulting in a matrix cracking-prone stress state. These findings explain the damage and failure processes well observed by SR X-CT and provide a fundamental understanding of the damage mechanism at a mesoscale.

Design and Characterization of Porous Electrodes for Redox Flow Batteries

The commercialization of redox flow batteries as large-scale energy storage systems depends on lowering the capital and operating costs which depend on achieving maximum power density. Optimizing electrode design parameters and flow field-electrode combinations is critical to minimize losses and maximize active material utilization. Modeling the current drawn from an electrode offers a means to interpret electrode structure based on the electrolyte distribution driven by internal design. However, direct imaging methods (such as in-situ fluorescence microscopy and X-ray tomography) and numerical methods for current to potential prediction (3D Lattice Boltzmann modeling) are specific to individual electrode structures and possess limited predictable value to obtain an ideal electrode design. In this work, we present an electrode impedance spectroscopy (EIS)-based approach for determining electrode design parameters and devise a general method for determination of effective diffusion layer thickness. Using COMSOL modeling we verified the development of slug flow behavior in highly randomized porous electrode systems, indicating that the mass transport properties are dictated by inter-fiber distance. An analytical model to predict current as a function of applied overpotential is presented which allows us to vary structural parameters of the porous electrodes to study the influence of surface area, inter-fiber distances and diffusion layer thickness on the RFB performance. This model is a highly flexible tool applicable to any electrochemical system using a porous electrode and identifies critical variables affecting electrode design to characterize optimal electrode structure to minimize mass transport losses and optimize operational parameters.

Additive manufacturing of ultrahigh-resolution Poly(ε-caprolactone) scaffolds using melt electrowriting

Melt electrowriting (MEW) is an advanced additive manufacturing technology that produces high-resolution scaffolds for medical applications. Although there are many valuable parameter groups for MEW, the corresponding principles need to be clarified to improve the success of printing high-fidelity scaffolds. To this end, we investigate the print limit of MEW with respect to the minimum interfiber distance and the maximum print period based on a medical-grade poly(ε-caprolactone) material. The results indicate that relatively large turning loops and low turning speeds improve the print accuracy of the scaffolds; however, excessively large turning loops and low turning speeds result in fiber accumulation on the edge of the scaffolds, resulting in print failure. The turning loops with 500 μm in diameter and turning speeds of 0.625 × CTS (critical translation speed) can achieve well-defined MEW scaffolds with an interfiber distance down to 25 μm. For printing such high-resolution scaffolds, the constant printing process can last one week. Fiber placement gets random when the fiber diameter is larger than 2.5 μm, caused by the melt polymer degradation and shear thinning in the printing process. Additionally, we verify that the method of charge neutralization is not beneficial for improving the fiber overlay. This is a fundamental study clarifying the principles of printing high-resolution MEW scaffolds, being capable of extending the application of the MEW products.

Unlocking the print of poly(L-lactic acid) by melt electrowriting for medical application

Melt electrowriting (MEW) is an advanced 3D printing technology to process high-resolution scaffolds. Although MEW has printed many biodegradable polymers, most of them have low printability, including poly(L-lactic acid) (PLLA) discussed in this study. While the print of PLLA scaffolds by MEW is elementarily realized, the scaffolds' limited structural change and mechanical properties influence their application. This study aims at improving the printability and the mechanical properties of the PLLA. To this end, the printability of the PLLA regarding jet lag angle and critical translation speed is investigated; the print limitation of PLLA is discovered, and the uniaxial and cyclic tensile tests for the scaffolds in linear and nonlinear structures are carried out. The results suggest that drying the PLLA before printing can significantly restrain polymer degradation to extend the printing period to approximately one day; planar PLLA scaffolds are able to reach 25 layers, 100 µm interfiber distance, and 8 × 8 cm2 in dimension, and tubular PLLA scaffolds with 6 layers are successfully printed out; the mechanical properties of the PLLA scaffold reach the level of electrospun nonwoven fabrics. Thus, this study is a milestone work for the MEW technology to extend the printable materials.

Nano- and Microstructures of Collagen-Nanocellulose Hydrogels as Engineered Extracellular Matrices.

The extracellular matrix (ECM) is the fundamental acellular element of human tissues, providing their mechanical structure while delivering biomechanical and biochemical signals to cells. Three-dimensional (3D) tissue models commonly use hydrogels to recreate the ECM in vitro and support the growth of cells as organoids and spheroids. Collagen-nanocellulose (COL-NC) hydrogels rely on the blending of both polymers to design matrices with tailorable physical properties. Despite the promising application of these biomaterials in 3D tissue models, the architecture and network organization of COL-NC remain unclear. Here, we investigate the structural effects of incorporating NC fibers into COL hydrogels by small-angle neutron scattering (SANS) and ultra-SANS (USANS). The critical hierarchical structure parameters of fiber dimensions, interfiber distance, and coassembled open structures of NC and COL in the absence and presence of cells were determined. We found that NC expanded and increased the homogeneity in the COL network without affecting the inherent fiber properties of both polymers. Cells cultured as spheroids in COL-NC remodeled the hydrogel network without a significant impact on its architecture. Our study reveals the polymer organization of COL-NC hydrogels and demonstrates SANS and USANS as exceptional techniques to reveal nano- and micron-scale details on polymer organization, which leads to a better understanding of the structural properties of hydrogels to engineer novel ECMs.

Monitoring the skin structure during edema in vivo with spatially resolved diffuse reflectance spectroscopy.

Edema occurs in the course of various skin diseases. It manifests itself in changes in water concentrations in skin layers: dermis and hypodermis and their thicknesses. In medicine and cosmetology, objective tools are required to assess the skin's physiological parameters. The dynamics of edema and the skin of healthy volunteers were studied using spatially resolved diffuse reflectance spectroscopy (DRS) in conjunction with ultrasound (US). In this work, we have developed a method based on DRS with a spatial resolution (SR DRS), allowing us to simultaneously assess water content in the dermis, dermal thickness, and hypodermal thickness. An experimental investigation of histamine included edema using SR DRS under the control of US was conducted. An approach for skin parameter determination was studied and confirmed using Monte-Carlo simulation of diffuse reflectance spectra for a three-layered system with the varying dermis and hypodermis parameters. It was shown that an interfiber distance of 1mm yields a minimal relative error of water content determination in the dermis equal to 9.3%. The lowest error of hypodermal thickness estimation was achieved with the interfiber distance of 10mm. Dermal thickness for a group of volunteers (7 participants, 21 measurement sites) was determined using SR DRS technique with an 8.3% error using machine learning approaches, taking measurements at multiple interfiber distances into account. Hypodermis thickness was determined with root mean squared error of 0.56mm for the same group. This study demonstrates that measurement of the skin diffuse reflectance response at multiple distances makes it possible to determine the main parameters of the skin and will serve as the basis for the development and verification of an approach that works in a wide range of skin structure parameters.

Ultraviolet Light Treatment of Titanium Microfiber Scaffolds Enhances Osteoblast Recruitment and Osteoconductivity in a Vertical Bone Augmentation Model: 3D UV Photofunctionalization

Vertical bone augmentation to create host bone prior to implant placement is one of the most challenging regenerative procedures. The objective of this study is to evaluate the capacity of a UV-photofunctionalized titanium microfiber scaffold to recruit osteoblasts, generate intra-scaffold bone, and integrate with host bone in a vertical augmentation model with unidirectional, limited blood supply. Scaffolds were fabricated by molding and sintering grade 1 commercially pure titanium microfibers (20 μm diameter) and treated with UVC light (200-280 nm wavelength) emitted from a low-pressure mercury lamp for 20 min immediately before experiments. The scaffolds had an even and dense fiber network with 87% porosity and 20-50 mm inter-fiber distance. Surface carbon reduced from 30% on untreated scaffold to 10% after UV treatment, which corresponded to hydro-repellent to superhydrophilic conversion. Vertical infiltration testing revealed that UV-treated scaffolds absorbed 4-, 14-, and 15-times more blood, water, and glycerol than untreated scaffolds, respectively. In vitro, four-times more osteoblasts attached to UV-treated scaffolds than untreated scaffolds three hours after seeding. On day 2, there were 70% more osteoblasts on UV-treated scaffolds. Fluorescent microscopy visualized confluent osteoblasts on UV-treated microfibers two days after seeding but sparse and separated cells on untreated microfibers. Alkaline phosphatase activity and osteocalcin gene expression were significantly greater in osteoblasts grown on UV-treated microfiber scaffolds. In an in vivo model of vertical augmentation on rat femoral cortical bone, the interfacial strength between innate cortical bone and UV-treated microfiber scaffold after two weeks of healing was double that observed between bone and untreated scaffold. Morphological and chemical analysis confirmed seamless integration of the innate cortical and regenerated bone within microfiber networks for UV-treated scaffolds. These results indicate synergy between titanium microfiber scaffolds and UV photofunctionalization to provide a novel and effective strategy for vertical bone augmentation.

Effects of scaffold design parameters on the printing accuracy for melt electrowriting

Melt electrowriting (MEW), a high-resolution additive manufacturing technique, has been used to fabricate high-fidelity fibrous scaffolds. However, the printing accuracy of MEW is deteriorated by the occurrence of fiber deviation phenomena during the scaffold-fabrication process, which limits a broader application of this technique. Herein, an efficient universal index (Ip), along with an evaluation protocol is advanced to evaluate the printing accuracy of MEW. Then, experimental results show that key scaffold design parameters (fiber diameter (df), inter-fiber distance (Sf), and layer number (N)) can affect the value of Ip significantly. In general, the increase of df and N and the decrease of Sf can lead to inferior printing accuracy, accompanied by a decrement in Ip values. Moreover, the interplay between df and Sf on the printing accuracy is further analyzed based on a variable k (Sf over df). The variables k and N are subsequently identified as the two fundamental scaffold design parameters that affect the printing accuracy. Lastly, residual charge densities entrapped in the scaffolds are measured, thereby furnishing mechanistic insights into the effects of charge on the printing accuracy.

Silanization of 3D-Printed Silica Fibers and Monoliths.

Surface functionalization of complex three-dimensional (3D) porous architectures has not been widely investigated despite their potential in different application domains. In this work, silanization was performed in silica 3D-printed porous structures, and the homogeneity of functional groups within the architecture was investigated by comparing the extent of the functionalization in the walls and core of the monolith. A silica ink was used for direct ink writing (DIW) to shape fibers and monoliths with different architectures and stacking designs. The surfaces of the fibers and monoliths were functionalized with 3-aminopropyl(triethoxysilane) (APTES) using different reaction conditions. The nature of the functional groups on the surface and the presence of RSiO1.5 bonds were identified by solid-state 13C-NMR, 29Si-NMR, and by ξ-potential measurements. Elemental analysis was used to quantify the concentration of bonded APTES in the core and walls of the monolith. The availability and hydrolytic stability of the introduced amine group on fibers were evaluated using the adsorption of PdCl42- ions within the pH range of 2-5. The study found that geometries with interfiber distances above 250 μm are homogeneously functionalized with amine groups. As the interfiber distance of the monolith decreases, a significantly lower density of amine groups is detected in the core of the monolith. The determination of the homogeneity of 3D-printed monoliths makes this work relevant as it provides the limits of functionalization carried out in stirred batch reactors for geometrically defined structures produced from a 3D-printing process.

Nanoscale geometry determines mechanical biocompatibility of vertically aligned nanofibers

Vertically aligned carbon nanofibers (VACNFs) are promising material candidates for neural biosensors due to their ability to detect neurotransmitters in physiological concentrations. However, the expected high rigidity of CNFs could induce mechanical mismatch with the brain tissue, eliciting formation of a glial scar around the electrode and thus loss of functionality. We have evaluated mechanical biocompatibility of VACNFs by growing nickel-catalyzed carbon nanofibers of different lengths and inter-fiber distances. Long nanofibers with large inter-fiber distance prevented maturation of focal adhesions, thus constraining cells from obtaining a highly spread morphology that is observed when astrocytes are being contacted with stiff materials commonly used in neural implants. A silicon nanopillar array with 500 nm inter-pillar distance was used to reveal that this inhibition of focal adhesion maturation occurs due to the surface nanoscale geometry, more precisely the inter-fiber distance. Live cell atomic force microscopy was used to confirm astrocytes being significantly softer on the long Ni-CNFs compared to other surfaces, including a soft gelatin hydrogel. We also observed hippocampal neurons to mature and form synaptic contacts when being cultured on both long and short carbon nanofibers, without having to use any adhesive proteins or a glial monoculture, indicating high cytocompatibility of the material also with neuronal population. In contrast, neurons cultured on a planar tetrahedral amorphous carbon sample showed immature neurites and indications of early-stage apoptosis. Our results demonstrate that mechanical biocompatibility of biomaterials is greatly affected by their nanoscale surface geometry, which provides means for controlling how the materials and their mechanical properties are perceived by the cells. Statement of significanceOur research article shows, how nanoscale surface geometry determines mechanical biocompatibility of apparently stiff materials. Specifically, astrocytes were prevented from obtaining highly spread morphology when their adhesion site maturation was inhibited, showing similar morphology on nominally stiff vertically aligned carbon fiber (VACNF) substrates as when being cultured on ultrasoft surfaces. Furthermore, hippocampal neurons matured well and formed synapses on these carbon nanofibers, indicating high biocompatibility of the materials. Interestingly, the same VACNF materials that were used in this study have earlier also been proven to be capable for electrophysiological recordings and sensing neurotransmitters at physiological concentrations with ultra-high sensitivity and selectivity, thus providing a platform for future neural probes or smart culturing surfaces with superior sensing performance and biocompatibility.

Synthesis of carbon nanotube arrays on quartz-based fibrous materials and their morphological characterization

Carbon nanotubes (CNTs) were synthesized on quartz-based fibrous materials via chemical vapor deposition using camphor. Quartz wool with two different fiber diameters, and quartz filter paper were used as the substrate materials for the synthesis. Quartz wool produced a high yield of CNTs, and the arrays on the fibers had characteristic plate-shaped aligned structures. In addition, CNTs were grown on the quartz filter paper fibers; however, most of these CNTs were not aligned. The effects of the fiber diameter and interfiber distance of the substrate materials on the yield and morphology of the resulting CNTs are discussed.

A 3D Platform to Investigate Dynamic Cell-to-Cell Interactions Between Tumor Cells and Mesenchymal Progenitors.

We here investigated the dynamic cell-to-cell interactions between tumor and mesenchymal stromal/stem cells (MSCs) by the novel VITVOⓇ 3D bioreactor that was customized to develop in vivo-like metastatic nodules of Ewing’s sarcoma (ES). MSCs are known to contribute to tumor microenvironment as cancer associated fibroblast (CAF) precursors and, for this reason, they have also been used as anti-cancer tools. Using dynamic conditions, the process of tissue colonization and formation of metastatic niches was recreated through tumor cell migration aiming to mimic ES development in patients. ES is an aggressive tumor representing the second most common malignant bone cancer in children and young adults. An urgent and unmet need exists for the development of novel treatment strategies to improve the outcomes of metastatic ES. The tumor-tropic ability of MSCs offers an alternative approach, in which these cells can be used as vehicles for the delivery of antitumor molecules, such as the proapoptotic TNF-related apoptosis inducing ligand (TRAIL). However, the therapeutic targeting of metastases remains challenging and the interaction occurring between tumor cells and MSCs has not yet been deeply investigated. Setting up in vitro and in vivo models to study this interaction is a prerequisite for novel approaches where MSCs affinity for tumor is optimized to ultimately increase their therapeutic efficacy. Here, VITVOⓇ integrating a customized scaffold with an increased inter-fiber distance (VITVO50) was used to develop a dynamic model where MSCs and tumor nodules were evaluated under flow conditions. Colonization and interaction between cell populations were explored by droplet digital PCR (ddPCR). VITVO50 findings were then applied in vivo. An ES metastatic model was established in NSG mice and biodistribution of TRAIL-expressing MSCs in mice organs affected by metastases was investigated using a 4-plex ddPCR assay. VITVOⓇ proved to be an easy handling and versatile bioreactor to develop in vivo-like tumor nodules and investigate dynamic cell-to-cell interactions with MSCs. The proposed fluidic system promises to facilitate the understanding of tumor-stroma interaction for the development of novel tumor targeting strategies, simplifying the analysis of in vivo data, and ultimately accelerating the progress towards the early clinical phase.

Finite element modeling of glass particle reinforced epoxy composites under uniaxial compression and sliding wear

Abstract In this study, the failure mechanism of glass particle epoxy composites was investigated under compression and sliding wear. Random fiber distribution with minimum interfiber distance was modeled by representative volume elements (RVEs). Spherical and platelet type glass particles were used for the reinforcements. A numerical simulation of the elastic properties of composites was performed for a perfectly bonded interface, and the results were compared using the Mori Tanaka mean field approach. The elastic stiffness results indicated that the platelet reinforced composites bore more load than spherical ones because of the aspect ratio effects. The separation distance based cohesive zone model was applied to modeling the failure zone at the particle matrix interfaces to establish sliding wear. The effect of the perfectly bonded interface and the cohesive zone interface on overall stiffness and elasto-plastic behavior were discussed. The cohesive zone interface was found to be effective at the interface in terms of the strength and debonding characteristics of the composites. The results were compared with the sliding wear test results of glass particle reinforced composites. The numerical and sliding wear experimental results indicated that matrix yield stress, plastic strain, particle penetration at the contact interface and particle stress are found to be effective parameters for the debonding mechanism.

Quantitative micro-computed tomography analysis and rheological investigation of Nitrile rubber/Rockwool composites

This study reports the reinforcement degree investigation of two types of rockwool fibers (F1 and F2), in nitrile rubber composites. The micro-computed tomography (micro-CT) 3D images showed that both fibers were well-dispersed in the NBR matrix, without a preferential orientation. The micro-CT analysis also allowed quantifying volume fraction, inter-fiber distance, and aspect ratio. Those morphometric parameters were used for supporting the composites rheological behavior assessment. Changes in the elastic modulus and phase angle followed the same trend of the inter-fiber distance values, regardless the type of fiber. Both volume fraction and aspect ratio data from the micro-CT analysis were used to predict theoretical values of elastic modulus using the Guth-Gold and modified Guth-Gold equations, and the results obtained were compared to the rheological experimental data. This analysis was helpful to better understand the rockwool fibers reinforcement degree differences in the production of the nitrile rubber composites.

Accuracy of homogeneous models for photon diffusion in estimating neonatal cerebral hemodynamics by TD-NIRS.

We assessed the accuracy of homogenous (semi-infinite, spherical) photon diffusion models in estimating absolute hemodynamic parameters of the neonatal brain in realistic scenarios (ischemia, hyperoxygenation, and hypoventilation) from 1.5 cm interfiber distance TD NIRS measurements. Time-point-spread-functions in 29- and 44-weeks postmenstrual age head meshes were simulated by the Monte Carlo method, convoluted with a real instrument response function, and then fitted with photon diffusion models. The results show good accuracy in retrieving brain oxygen saturation, and severe underestimation of total cerebral hemoglobin, suggesting the need for more complex models of analysis or of larger interfiber distances to precisely monitor all hemodynamic parameters.

Microscale viscoplastic analysis of unidirectional CFRP composites under the influence of curing process

Cure-induced residual stresses have a great impact on the mechanical behavior of carbon fiber reinforced polymer (CFRP) composites. This paper develops an integrated analytical framework to study the effect of the cure-induced residual stresses on the mechanical behavior of unidirectional IM7/8552 composites. During the curing process, evolution of the material properties of the resin matrix is captured using the cure hardening instantaneous linear elastic (CHILE) model. In addition to the mechanical strain, thermal and chemical shrinkage strains of the resin are taken into account in the determination of the residual stresses. By introduction of the predicted residual stresses into the representative volume element (RVE), the quasi-static and dynamic compression analyses are performed to demonstrate the local viscoplastic deformation of the matrix and the homogenized stress–strain response of the composites. Simulation results are in good agreement with the experimental data. The comparative analysis indicates that the cure-induced residual stresses lead to an earlier nonlinearity and lower compressive strength. Furthermore, to investigate the effect of the fiber distribution on the residual stresses and compressive response of the composites, a parametric analysis is performed, in which two parameters are considered, i.e., minimal inter-fiber distance and fiber volume fraction.

Fiber Bridging during Melt Electrowriting of Poly(ε‐Caprolactone) and the Influence of Fiber Diameter and Wall Height

AbstractMelt electrowriting (MEW) is a direct‐writing technology for small diameter fibers; however, due to electrostatic attraction, the technique is restricted in how close these microfibers can be positioned on the collector. Here, the minimum interfiber distance between parallel poly(ε‐caprolactone) MEW microfibers is determined for different fiber diameters and number of layers on noncoated and star‐shaped poly(ethylene oxide‐stat‐propylene oxide) (sP(EO‐stat‐PO))‐coated glass coverslips. The effect of the fiber diameter, the number of fiber layers, and shape of turning loops affect precision and the minimum interfiber distance. Single fibers with diameter of 5, 10, and 15 µm have a minimum interfiber distance without fiber bridging of 33 ± 2.7, 54 ± 2.2, and 62 ± 2.7 µm, respectively. Increasing the number of layers to ten increases this minimum interfiber distance approximately twofold to 60 ± 3.5, 97 ± 4.5, and 102 ± 2.7 µm for the increasing fiber diameters. The sP(EO‐stat‐PO) slightly increases the minimum interfiber distance for the 15 µm diameter group only, with spacing for the 5 and 10 µm fibers unaffected by the coating. Identifying and determining the fabrication limits for MEW is highly instructional for users working and designing scaffolds with this technology.

Prediction of the cohesive strength for simulating composite delamination by a micro-mechanical model based on random RVE

A three-dimensional micro-mechanical model based on the random RVE is developed to predict the cohesive strengths of all the three delamination modes in unidirectional laminates. The interface RVE with two layers of randomly distributed fibers is established to represent the cohesive layer. Two types of random microstructure corresponding to the square and hexagonal periodic packing are defined. Delamination is assumed to be induced by matrix yield and cracking. The extended linear Drucker–Prager yield criterion and a paraboloidal yield criterion are used to predict the crack initiation in the matrix and compared with the major principal stress criterion. The predicted results show that the cohesive strengths are largely dependent on the type of random microstructure and the random microstructure morphology described by the minimum inter-fiber distance and the fiber alignment angle. Global sensitivity analysis based on a polynomial chaos expansion surrogate model is done to quantify the influence of the geometrical parameters on the variance of the cohesive strengths. Moreover, the predicted cohesive strengths are found to be unequal.

Comparison of 2 single incision slings on the vagina in an ovine model

Stress urinary incontinence carries a significant healthcare burden for women worldwide. Single incision slings are minimally invasive mesh devices designed to treat stress urinary incontinence. For prolapse repair, meshes with higher porosity and lower structural stiffness have been associated with improved outcomes. In this study, we compared the higher stiffness, lower porosity Altis sling with the lower stiffness, higher porosity Solyx sling in an ovine model. We hypothesized that SIS-B would have a negative impact on the host response. A total of Altis and Solyx single incision slings were implanted suburethrally into sheep according to the manufacturer's instructions on minimal tension. The mesh-urethral-vaginal complex and adjacent ungrafted vagina (no mesh control) were harvested en bloc at 3 months. Masson's trichrome and picrosirius red staining of 6 μm thin sections was performed to measure interfiber distance and tissue integration. Smooth muscle contractility to a 120 mM KCl stimulus was performed in an organ bath to measure myofiber-driven contractions. Standard biochemical assays were used to quantify glycosaminoglycan, total collagen, and elastin content, and collagen subtypes. Bending stiffness was performed in response to a uniaxial force to define susceptibility to folding/buckling. Statistical analysis was performed using Mann-Whitney, Gabriel's pairwise post hoc, Wilcoxon matched-pairs, and chi-square tests. The animals had similar ages (3-5 years), parity (multiparous), and weights (45-72 kg). Trichrome cross sections showed that the Altis sling buckled in a "C" or "S" shape in most samples (8 of 11), whereas buckling after Solyx sling implantation was observed in only a single sample (1 of 13; P=.004). Tissue integration, as measured by the presence of collagen or smooth muscle between the mesh fibers on trichrome 4× imaging, was increased in samples implanted with the Solyx sling compared with the Altis sling (P<.05). Total collagen content decreased significantly with both products when compared with the ungrafted vagina consistent with stress shielding. There was no difference in the 2 groups with regard to glycosaminoglycan or elastin content. The Altis sling mesh tissue complex demonstrated significantly higher amounts of both collagen types I and III than the Solyx sling-implanted tissue and the ungrafted control. Smooth muscle contractility in response to 120 mM KCl was decreased after implantation of both slings compared with the sham (P=.011 and P<.01), with no difference between mesh types (P=.099). Bending stiffness in the Altis sling was more than 4 times lower than in the Solyx, indicating an increased propensity to buckle (0.0186 vs 0.0883). The structurally stiffer Altis sling had decreased tissue integration and increased propensity to buckle after implantation. Increased collagen types I and III after the implantation of this device suggests that these changes may be associated with a fibrotic response. In contrast, the Solyx sling largely maintained a flat configuration and had improved tissue integration. The deformation of the Altis sling is not an intended effect and is likely caused by its lower bending stiffness. Both meshes induced a decrease in collagen content and smooth muscle contractility similar to previous findings for prolapse meshes and consistent with stress shielding. The long-term impact of buckling warrants further investigation.

Hierarchical fibrous guiding cues at different scales influence linear neurite extension

Surface topographies at micro- and nanoscales can influence different cellular behavior, such as their growth rate and directionality. While different techniques have been established to fabricate 2-dimensional flat substrates with nano- and microscale topographies, most of them are prone to high costs and long preparation times. The 2.5-dimensional fiber platform presented here provides knowledge on the effect of the combination of fiber alignment, inter-fiber distance (IFD), and fiber surface topography on contact guidance to direct neurite behavior from dorsal root ganglia (DRGs) or dissociated primary neurons. For the first time, the interplay of the micro-/nanoscale topography and IFD is studied to induce linear nerve growth, while controlling branching. The results demonstrate that grooved fibers promote a higher percentage of aligned neurite extension, compensating the adverse effect of increased IFD. Accordingly, maximum neurite extension from primary neurons is achieved on grooved fibers separated by an IFD of 30 μm, with a higher percentage of aligned neurons on grooved fibers at a large IFD compared to porous fibers with the smallest IFD of 10 µm. We further demonstrate that the neurite “decision-making” behavior on whether to cross a fiber or grow along it is not only dependent on the IFD but also on the fiber surface topography. In addition, axons growing in between the fibers seem to have a memory after leaving grooved fibers, resulting in higher linear growth and higher IFDs lead to more branching. Such information is of great importance for new material development for several tissue engineering applications. Statement of SignificanceOne of the key aspects of tissue engineering is controlling cell behavior using hierarchical structures. Compared to 2D surfaces, fibers are an important class of materials, which can emulate the native ECM architecture of tissues. Despite the importance of both fiber surface topography and alignment to direct growing neurons, the current state of the art did not yet study the synergy between both scales of guidance. To achieve this, we established a solvent assisted spinning process to combine these two crucial features and control neuron growth, alignment, and branching. Rational design of new platforms for various tissue engineering and drug discovery applications can benefit from such information as it allows for fabrication of functional materials, which selectively influence neurite behavior.