Bulk Mechanical Properties Research Articles

Phase decomposition behavior and its impact on mechanical properties in bulk nanostructured Cu-20 at.%Fe supersaturated solid solution

Extended solid solution of immiscible systems, achieved by extreme processing approaches, can be transformed into nanostructured composites via phase decomposition, which are drawing great research attention for their excellent thermal stability and high strength. Here we fabricated the supersaturated solid solution of Cu-20 at.%Fe, a typical immiscible alloy, in bulk state by high pressure torsion, which provides a great freedom over powders for studying the microstructure evolution and mechanical properties in the process of the phase decomposition in immiscible alloys. We found that in the Cu-Fe solid solution, spinodal decomposition of the Fe phases took place at the initial stage of annealing through volume diffusion. This process gives rise to: (1) metastable γ-Fe particles in the Cu grains with coherent Fe/Cu interface, and (2) the more stable α-Fe phase at the grain boundaries. This process was accompanied by moving boundary reaction which first proceeded in the pattern of spinodal decomposition and then changed into classical nucleation-growth mode with the depletion of Fe atoms in Cu. The resultant Cu-Fe nanocomposites were jointly strengthened by the ultrafine Cu and α-Fe grains according to the rule of mixture, including grain boundary strengthening and the hardening of nanoscale γ-Fe precipitates in the Cu grains. The effects of different strengthening mechanisms were scrutinized and their contributions to mechanical properties were quantitatively evaluated. This work sheds light onto the opportunity of designing and fabricating nanostructured composites via phase decomposition in immiscible systems.

Chondroitin sulfate, dermatan sulfate, and hyaluronic acid differentially modify the biophysical properties of collagen-based hydrogels

Fibrillar collagens and glycosaminoglycans (GAGs) are structural biomolecules that are natively abundant to the extracellular matrix (ECM). Prior studies have quantified the effects of GAGs on the bulk mechanical properties of the ECM. However, there remains a lack of experimental studies on how GAGs alter other biophysical properties of the ECM, including ones that operate at the length scales of individual cells such as mass transport efficiency and matrix microstructure. This study focuses on the GAG molecules chondroitin sulfate (CS), dermatan sulfate (DS), and hyaluronic acid (HA). CS and DS are stereoisomers while HA is the only non-sulfated GAG. We characterized and decoupled the effects of these GAG molecules on the stiffness, transport, and matrix microarchitecture properties of type I collagen hydrogels using mechanical indentation testing, microfluidics, and confocal reflectance imaging, respectively. We complement these biophysical measurements with turbidity assays to profile collagen aggregate formation. Surprisingly, only HA enhanced the ECM indentation modulus, while all three GAGs had no effect on hydraulic permeability. Strikingly, we show that CS, DS, and HA differentially regulate the matrix microarchitecture of hydrogels due to their alterations to the kinetics of collagen self-assembly. In addition to providing information on how GAGs define key physical properties of the ECM, this work shows new ways in which stiffness measurements, microfluidics, microscopy, and turbidity kinetics can be used complementarily to reveal details of collagen self-assembly and structure. Statement of SignificanceCollagen and glycosaminoglycans (GAGs) are integral to the structure, function, and bioactivity of the extracellular matrix (ECM). Despite widespread interest in collagen-GAG composite hydrogels, there is a lack of quantitative understanding of how different GAGs alter the biophysical properties of the ECM across tissue, cellular, and subcellular length scales. Here we show using mechanical, microfluidic, microscopy, and analytical methods and measurements that the GAG molecules chondroitin sulfate, dermatan sulfate, and hyaluronic acid differentially regulate the mechanical, transport, and microstructural properties of hydrogels due to their alterations to the kinetics of collagen self-assembly. As such, these results will inform improved design and utilization of collagen-based scaffolds of tailored composition, mechanical properties, molecular availability due to mass transport, and microarchitecture.

Microscale strain concentrations in tissue-engineered osteochondral implants are dictated by local compositional thresholds and architecture

Tissue-engineered osteochondral implants manufactured from condensed mesenchymal stem cell bodies have shown promise for treating focal cartilage defects. Notably, such manufacturing techniques have shown to successfully recapture the bulk mechanical properties of native cartilage. However, the relationships among the architectural features, local composition, and micromechanical environment within tissue-engineered cartilage from cell-based aggregates remain unclear. Understanding such relationships is crucial for identifying critical parameters that can predict in vivo performance. Therefore, this study investigated the relationship among architectural features, composition, and micromechanical behavior of tissue-engineered osteochondral implants. We utilized fast-confocal microscopy combined with a strain mapping technique to analyze the micromechanical behavior under quasi-static loading, as well as Fourier Transform Infrared Spectroscopy to analyze the local compositions. More specifically, we investigated the architectural features and compositional distributions generated from tissue maturation, along with macro- and micro-level strain distributions. Our results showed that under compression, cell-based aggregates underwent deformation followed by body movement, generating high local strain around the boundaries, where local aggrecan concentration was low and local collagen concentration was high. By analyzing the micromechanics and composition at the single aggregate length scale, we identified a strong threshold relationship between local strain and compositions. Namely at the aggrecan concentration below 0.015 arbitrary unit (A.U.) and the collagen concentration above 0.15 A.U., the constructs experienced greater than threefold increase in compressive strain. Overall, this study suggests that local compositional features are the primary driver of the local mechanical environment in tissue-engineered cartilage constructs, providing insight into potential quality control parameters for manufacturing tissue-engineered constructs.

Measuring the surface cohesion of calcium silicate hydrate

Calcium silicate hydrate (C-S-H) is the main binding phase of Portland cement concrete. Though C-S-H is known to be assembled from nanoscale features, there is little experimental study on how C-S-H nano solids interact with each other at the interface, which may hold the key to explain its macroscale strength, creep, and shrinkage behaviour. This work attempts to experimentally quantify the interactions between C-S-H solid surfaces using atomic force microscopy (AFM). We took a new approach to measure the surface adhesion under different relative humidity (R.H.) and calculate the Hamaker constant using an algorithm that eliminates the influence of surface roughness. The effect of chemical composition (e.g. Ca/Si ratio) and RH on surface forces, e.g. the van der Waals and capillary force, were systematically explored and compared with molecular calculation results. Our work provides an insight into the nexus of C-S-H chemistry – adhesion force – bulk mechanical properties.

Unveiling the Role of Compositional Drifts on the Tack of Pressure‐Sensitive‐Adhesives

AbstractPressure‐sensitive‐adhesives (PSAs) are pervasive in electronic, automobile, packaging, and biomedical applications due to their ability to stick to numerous surfaces without undergoing chemical reactions. These materials are typically synthesized by the free radical copolymerization of alkyl acrylates and acrylic acid, leading to an ensemble of polymer chains with varying composition and molecular weight. Here, reversible addition−fragmentation chain‐transfer (RAFT) copolymerizations in a semi‐batch reactor are used to tailor the molecular architecture and bulk mechanical properties of acrylic copolymers. In the absence of cross‐links, the localization of acrylic acid toward the chain ends leads to microphase separation, creep resistance, and enhanced tack. However, in the presence of Al(acac)3 crosslinker, the creep resistance remains unchanged and mostly the large‐strain mechanical properties are affected. This behavior is attributed to microphase separation, but also to a change in the energy required to break physical associations, and untangle and elongate associative polymers to large deformations.

Superhydrophobic silicone/graphene oxide-silver-titania nanocomposites as eco-friendly and durable maritime antifouling coatings

In this work, a novel ecofriendly series of polydimethylsiloxane-polymethylmethacrylate (PDMS-PMMA) blend filled with silver nanospheres and titanium dioxide nanorods grafted on the graphene oxide surface (Ag–TiO2@GO) were produced by the catalytic hydrosilation method as outstanding marine antifouling coatings. Innovative Ag–TiO2@GO hybrid nanofillers, that would release fouling and confer surface robustness, were developed by a single-phase procedure. Ag nanospheres with 20 nm mean diameter were prepared by a controlled solvothermal method, while anatase TiO2 nanorods with 10 nm average diameter were grown by a hydrothermal technique. The solution casting method was used to distribute various Ag–TiO2@GO filler percentages throughout the silicone matrix. Atomic force microscopy, surface free energy, and water contact angle (WCA) were employed to examine the superhydrophobicity and roughness of the coatings. The mechanical durability and antifouling characteristics of the PDMS-PMMA nanocomposites filled with Ag–TiO2@GO composites were also investigated. Several microorganisms were employed to examine the fouling resistance of the coated specimens for 30 days. Trichogaster lalius fish and the bivalve Brachidontes variabilis species were used to examine the nanocomposites’ toxicity. Well-dispersion of Ag–TiO2@GO nanofillers in the PDMS-PMMA resin until 2.5 wt% exhibited the highest WCA (160° ± 2°), the lowest surface free energy (22.9 mN/m), rough topology, and improved bulk mechanical properties. Furthermore, the well-dispersed PDMSPMMA/Ag–TiO2@GO (2.5 wt%) nanocomposite presented the lowest biodegradability percentages and optical density against various gram-positive and gram-negative bacterial strains. Furthermore, it displayed non-toxicity against the tested species of fish and bivalve. The developed non-toxic and non-stick nanocoating exhibited various merits, including superhydrophobicity, mechanical robustness, and fouling retardancy, for using as maritime ship hull coatings.

Importance of geometric parameters in modeling of porous materials – a finite element study

AbstractPorous materials consist of interconnected skeletal structure around a porous space. The skeletal structure is usually formed of a solid phase and the pores are typically filled with a fluid (liquid or gas). Porous materials are characterized by two essential geometric properties: porosity and pore size distribution (PSD), which influence their bulk mechanical properties. Porosity, which is defined in terms of the ratio between the envelope and the skeletal densities, is sufficient to describe the elastic bulk properties of porous materials. Gibson and Ashby developed a power scaling law expressing the linear relation between the elastic modulus and the relative density. The PSD describes the spatial variation of the pore sizes and has recently been shown to influence the mechanical properties of porous materials. In addition to porosity and PSD, the pore characteristics, namely pore size and shape, and pore‐wall size and shape, also determine the geometric properties that influence the bulk response of these materials. In this study, the importance of the above‐mentioned geometric parameters in the modeling of the porous materials is studied using a computational framework. The bulk mechanical response under large deformation of various porous structures with PSD based on different probability density functions (PDF) and different combinations of other geometric properties under uniaxial compression is investigated. The sensitivity of mechanical response to these geometric parameters is studied. Interdependent parameters which are significantly influential are identified. By controlling these parameters, the synthesis of porous materials can be guided and optimized.

Alternations of hardness and tensile properties of the ultrasound-assisted aging treatments on the Al-Mg-Si alloy

Lightweight metals with appropriate strength are crucial materials among the critical future technologies and sustainable issues. The Al-Mg-Si alloys, which are processed by aging treatments, are considered promising candidates. Hence, the pseudo-binary Al-Mg2Si alloy with an excess Si addition was chosen in this study. In addition, to further manipulate the alloys, besides to the often-controlled two factors of aging temperature and aging time, ultrasound was introduced into the aging system as an additional third factor to further control the aging behaviors. One-step and two-step aging treatments were both conducted to verify the effect of the introduction of ultrasound. It was found that certain alternations of mechanical properties, such as micro Vickers hardness, which is a surface property, were obviously imposed. On the other hand, the tensile strength and fracture strain, which are bulk mechanical properties, showed limited changes between the ultrasound-applied and ultrasound-free specimens. Many possibilities have been proposed and discussed for the observed phenomenon. The cavitation would be the greatest factor in the alternation of the micro Vickers hardness. Microstructures observed by bright-field images were in good accordance with that of the observed mechanical properties.

Mechanical Properties of Al–Mg–Si Alloys (6xxx Series): A DFT-Based Study

Al–Mg–Si alloys are used in aircraft, train, and car manufacturing industries due to their advantages, which include non-corrosivity, low density, relatively low cost, high thermal and electrical conductivity, formability, and weldability. This study investigates the bulk mechanical properties of Al–Mg–Si alloys and the influence of the Si/Mg ratio on these properties. The Al cell was used as the starting structure, and then nine structures were modeled with varying percentages of aluminium, magnesium, and silicon. Elastic constant calculations were conducted using the stress–strain method as implemented in the quantum espresso code. This study found that the optimum properties obtained were a density of 2.762 g/cm3, a bulk modulus of 83.3 GPa, a shear modulus of 34.4 GPa, a Vickers hardness of 2.79 GPa, a Poisson’s ratio of 0.413, a Pugh’s ratio of 5.42, and a yield strength of 8.38 GPa. The optimum Si/Mg ratio was found to be 4.5 for most of the mechanical properties. The study successfully established that the Si/Mg ratio is a critical factor when dealing with the mechanical properties of the Al–Mg–Si alloys. The alloys with the optimum Si/Mg ratio can be used for industrial applications such as plane skins and mining equipment where these properties are required.

The Cold Angular Rolling Process of Copper Sheets: Unraveling Plastic Deformation Behavior and Unveiling Microstructural Transformations

The cold angular rolling process (CARP) is being developed as a continuous severe plastic deformation technique, which can process metal sheets without any length limitations at room temperature. CARP contains cold rolling and equal‐channel angular process components. The sheet thickness is kept consistent before and after CARP, allowing multiple passes of the sheet. The desired microstructure and mechanical properties can be achieved in the processed metallic sheets. The current study is aimed to evaluate the capability of CARP by processing copper sheets with different sheet widths for repetitive passes. The CARP‐treated sheets are examined by lab‐scale X‐ray and high‐energy synchrotron X‐ray diffraction to investigate the evolution in dislocation density, texture, and strain anisotropy, and by tensile testing to identify the bulk mechanical properties. The digital image correlation method is applied to tensile testing so that strain localization within the sample gauge is visualized and deformation behavior is evaluated after yielding till postnecking by estimating the hardening exponent and strain hardening rate of the CARP‐treated sheet. Comparing the reported continuous and multiple‐step processes on Cu and its alloys, the present study confirms that the CARP is potentially a useful sheet process for strengthening ductile metals.

Analysis of Acid Diffusion Effects on Physical Properties of Polymer Composites: A Combined Study of Mechanical and Electrical Characterization

In this study, we examined the impact of carbon nanotube (CNT) concentration on the mechanical properties of epoxy/CNT composites under acid exposure. Samples with varying CNT concentrations (0% to 5%) were fabricated and characterized using dynamic mechanical analysis (DMA) and nanoindentation. Beyond the percolation threshold, the composites experienced decreased bulk mechanical properties due to CNT agglomeration. Acid exposure for one week and one month revealed a gradient of properties from the sample’s skin to its core. Overall, the composites exhibited modified physical properties, with degradation influenced by the CNT concentration. Higher concentrations acted as barriers but also created pathways for acid diffusion through pores surrounding CNT agglomerates. The agreement between nanoindentation and vector network analyzer (VNA) measurements further supported our findings. This convergence of mechanical and electromagnetic characterization techniques holds promise for wireless structural health monitoring (SHM) applications. Our study enhances the understanding of epoxy/CNT composites for SHM applications. The relationship between CNT concentration, acid exposure, and mechanical properties guides material selection and the development of real-time damage-detection techniques. Integrating multiple measurement techniques, as demonstrated by the agreement between nanoindentation and VNA data, provides a comprehensive understanding of structural behavior, improving SHM practices.

NOVEL HIGH-STRENGTH POLYESTER COMPOSITE SCAFFOLDS FOR BONE REGENERATION.

Repair of critical sized bone defects, particularly in load-bearing areas, is a major clinical problem that requires surgical intervention and implantation of biological or engineered grafts. For load-bearing sites, it is essential to use engineered grafts that have both sufficient mechanical strength and appropriate pore properties to support bone repair and tissue regeneration. Unfortunately, the mechanical properties of such grafts are often compromised due to the creation of pores required to facilitate tissue ingrowth following implantation. To overcome the limitations associated with porous scaffolds and their reduced mechanical strength, we have developed a methodology for creating a solid structure that retains its bulk mechanical properties while also evolving into a porous structure in a biological environment through degradation and erosion. In this study, we utilized polyesters that have been approved by the FDA, including poly (lactic acid) (PLA), poly(glycolic acid) (PGA), their copolymer PLGA (PLGA, with a ratio of 85:15 and 50:50 of PLA:PGA), and poly(caprolactone) (PCL). These polymers and their ceramic composites with tricalcium phosphate (TCP) were compression molded into solid forms, which exhibited mechanical properties with compressive modulus as high as 2745 ± 364 MPa within the range of human trabecular bone and in the lower range of human cortical bone. The use of fast-degrading PLGA (50:50) and PGA as porogens allowed the formation of pores within the solid structures due to their degradation, and the TCP acts as a buffering agent to neutralize their acidic degradation byproducts. These scaffolds facilitated the growth of new blood vessels and tissue ingrowth in a subcutaneous implantation model. In addition, in a rat critical-sized mandibular bone defects these scaffolds supported bone growth with 70% of new bone volume fraction. Furthermore, the extent of bone regeneration was found to be higher for the scaffolds with bone morphogenic proteins (BMP2), indicating their suitability for bone repair and regeneration.

Structure and energetics of hydroxyl‐terminated polybutadiene via density functional theory

AbstractHydroxyl‐terminated polybutadiene (HTPB) is a commonly used binding polymer in industry to produce polyurethanes. HTPB synthesis via allylic radical propagation leads to varied compositions and conformations that govern the bulk physical and mechanical properties of this polymer. While HTPB is incredibly well studied, its enthalpy of formation is still an open question and is critical to understanding the energetic contributions of the binding polymer in propellant formulations. This study investigates a series of HTPB polymers of experimentally relevant size and composition to understand the effects of conformations and monomer compositions on enthalpies of formation. The distribution of component monomer species comprising HTPB polymers is shown to have a significant effect on the condensed phase enthalpy of formation. The present study provides a best estimate of 331.2±50.3 kJ/mol or 150.7±22.9 kJ/kg for the condensed phase enthalpy of formation for commercially available HTPB formulations. The effects of the polymer folding motifs are smaller but distinct, with more highly folded structures exhibiting lower enthalpies of formation.

Thermochemical modelling and mechanical property of the Al-7.6Si-xZr alloy

This study utilised the gravity casting method to modify hypoeutectic Al-7.6Si alloys with Zr at varying weight percentages (0.1%, 0.2%, and 0.3%). The unmodified alloy typically consists of a needle or platelike eutectic silicon within the dendritic α-Al phase. The addition of Zr increases the liquidus temperature of the alloy and results in the formation of ZrSi and ZrSi2 compounds, which act as nucleation sites for both the eutectic Si and α-Al grains. As a result, the needle or platelike eutectic silicon transforms into a fibrous structure with a more uniform distribution, and the α-Al phase becomes finer and globular. These microstructural changes lead to improved bulk hardness, ductility, and mechanical properties of the alloy.

Morphological induced improvements in the bulk mechanical properties of chemically etched additively manufactured Ti-6Al-4V micro-struts

Morphological induced improvements in the bulk mechanical properties of chemically etched additively manufactured Ti-6Al-4V micro-struts

The Importance of Effective Ligand Concentration to Direct Epithelial Cell Polarity in Dynamic Hydrogels.

Epithelial cysts and organoids are multicellular hollow structures formed by correctly polarized epithelial cells. Important in steering these cysts from single cells is the dynamic regulation of extracellular matrix presented ligands, and matrix dynamics. Here, control over the effective ligand concentration is introduced, decoupled from bulk and local mechanical properties, in synthetic dynamic supramolecular hydrogels formed through noncovalent crosslinking of supramolecular fibers. Control over the effective ligand concentration is realized by 1) keeping the ligand concentration constant, but changing the concentration of nonfunctionalized molecules or by 2) varying the ligand concentration, while keeping the concentration of non-functionalized molecules constant. Theresults show that in 2D, the effective ligand concentration within thesupramolecular fibers rather than gel stiffness (from 0.1 to 8kPa) regulates epithelial polarity. In 3D, increasing the effective ligand concentration from 0.5 × 10-3 to 2 × 10-3 m strengthens the effect of increased gel stiffness from 0.1 to 2kPa, to synergistically yield more correctly polarized cysts. Through integrin manipulation, it isshown that epithelial polarity is regulated by tension-based homeostasis between cells and matrix. Theresults reveal the effective ligand concentration as influential factor in regulating epithelial polarity and provide insights on engineering of synthetic biomaterials for cell and organoid culture.

DFT based investigation of bulk mechanical, thermophysical and optoelectronic properties of PbTaSe2 topological semimetal

PbTaSe2 is a non-centrosymmetric topological semimetal. In this work we have explored the structural, elastic, mechanical, bonding, electronic, acoustic, thermal, and optical properties of PbTaSe2. The electronic bond structure calculations confirm semi-metallic character. Fermi surface topology shows both electron and hole sheets. The single crystal elastic constants reveal that PbTaSe2 is elastically stable. The compound is soft, ductile, and highly machinable at the same time. It also possesses very high level of dry lubricity. Various anisotropy indicators suggest that PbTaSe2 is elastically anisotropic. The structure has layered character. The phonon dynamics has been investigated. Phonon dispersion plot shows that the compound is dynamically stable with a clear frequency gap between the acoustic and optical branches. The Debye temperature, phonon thermal conductivity, and melting temperature of PbTaSe2 is low. The compound has medium Grüneisen parameter. The bonding character is mainly dominated by ionic bonding with some metallic contribution. The optical parameters have been studied in detail. The optical spectra reveal metallic features. The compound reflects visible light very efficiently (reflectance above 60%). It is also an efficient absorber of the ultraviolet light. The compound exhibits significant optical anisotropy with respect to the polarization directions of the incident electric field.

Recycling of wheat straw aggregates of end-of-life vegetal concrete: Experimental investigation to develop a new building insulation material

The recycling of end-of-life bio-composite materials contributes to reducing the environmental and economic costs of the building sector. The current research is about studying the feasibility of reusing wheat straw aggregates from crushed vegetal blocks after deconstruction, manufactured three years ago. These recycled materials are composed of wheat straw aggregates and interparticles of old lime. These aggregates are also partially covered by a gangue of old lime (called “surrounded lime). The objective is to investigate the possibility of incorporating recycled wheat straw a second time in a new biocomposite formulation with recycled wheat straw aggregates (RWSA). For the first time, RWSA is physically characterized (grain size distribution, densities, water absorption) to establish a comparison with the natural wheat straw. A second time, two formulation groups are defined and performed by varying the water/binder ratio (W/B = 1.1; 0.8) and considering the presence of old-lime inter-particles (equal to 55% per unit of particle mass). For each group, the quantity of RWSA in the formulations increases in mass proportion (0, 30, 50, 70, 100%). The physical bulk density, thermal (conductivity), and mechanical (compression strength) properties of the new recycled concrete are identified, with the valuation of the influence of the curing time (28 and 90 days) and formulation parameters on these properties. A third group with different straw/binder ratios (S/B ratios) is considered with formulations where the aggregates were entirely recycled without considering the presence of the old-lime inter-particles. The influences of curing time, W/B ratio, and different percentages of RWSA on the thermal and mechanical properties were highlighted. Through microstructural analysis, it can be observed that increasing the proportion of RWSA in biocomposites increases the carbonation rate and hence the strength of such compounds. The carbonation rate increased from 42.58% in biocomposites containing 100% normal straw to 81.8% in those containing 100% recycled straw due to the presence of old-lime inter-particles. This confirms the findings in terms of the increase in thermal conductivity and mechanical strengths with the substitution rate of RWSA.

New insights on conservation of marble artworks from computational chemistry

Architectural elements made of marble are subject to deterioration when exposed outdoors. A promising route to prevent deterioration is treating marble with an aqueous solution of diammonium hydrogen phosphate (DAP) to form hydroxyapatite (HAP). In this way, dissolution of marble can be prevented (as the solubility of HAP is orders of magnitude lower than calcite’s solubility) and cracks can be sealed (as HAP creates new bridges between calcite grains). To improve the treatment performance, the addition of alcohol to the DAP solution has recently been investigated with encouraging results. Here, we combined computational chemistry and experimental tests to identify alternative organic solvents that can further increase the treatment efficacy. First, we used density functional theory and molecular dynamics to screen alternative solvents (water, ethanol, isopropanol, and acetone), comparing their binding affinity and competitive adsorption behaviour onto calcite. Then, we treated marble specimens with DAP solutions with the additives and characterized the resulting performance. The results of the study indicate that acetone binds to calcite less strongly than the other solvents and does not completely displace water from the surface, which is expected to be beneficial. Nonetheless, the coating formed using acetone showed similar composition, thickness, and protective ability as the coatings formed with the other solvents. In terms of consolidation, all solvents were effective in improving surface and bulk mechanical properties. Overall, the extent of interaction with the calcite surface does not seem to be a critical factor. This can be explained by considering that, in addition to the different binding affinity to the calcite surface, the solvents may weaken the hydration shell of the phosphate ions in the DAP solution, thus facilitating the formation of HAP. Based on our results, this latter aspect seems to be predominant. Additional computational studies are in progress to elucidate this aspect.

Nanotextured porous titanium scaffolds by argon ion irradiation: Toward conformal nanopatterning and improved implant osseointegration.

Stress shielding and osseointegration are two main challenges in bone regeneration, which have been targeted successfully by chemical and physical surface modification methods. Direct irradiation synthesis (DIS) is an energetic ion irradiation method that generates self-organized nanopatterns conformal to the surface of materials with complex geometries (e.g., pores on a material surface). This work exposes porous titanium samples to energetic argon ions generating nanopatterning between and inside pores. The unique porous architected titanium (Ti) structure is achieved by mixing Ti powder with given amounts of spacer NaCl particles (vol % equal to 30%, 40%, 50%, 60%, and 70%), compacted and sintered, and combined with DIS to generate a porous Ti with bone-like mechanical properties and hierarchical topography to enhance Ti osseointegration. The porosity percentages range between 25% and 30% using 30 vol % NaCl space-holder (SH) volume percentages to porosity rates of 63%-68% with SH volume of 70 vol % NaCl. Stable and reproducible nanopatterning on the flat surface between pores, inside pits, and along the internal pore walls are achieved, for the first time on any porous biomaterial. Nanoscale features were observed in the form of nanowalls and nanopeaks of lengths between 100 and 500 nm, thicknesses of 35-nm and heights between 100 and 200 nm on average. Bulk mechanical properties that mimic bone-like structures were observed along with increased wettability (by reducing contact values). Nano features were cell biocompatible and enhanced in vitro pre-osteoblast differentiation and mineralization. Higher alkaline phosphatase levels and increased calcium deposits were observed on irradiated 50 vol % NaCl samples at 7 and 14 days. After 24 h, nanopatterned porous samples decreased the number of attached macrophages and the formation of foreign body giant cells, confirming nanoscale tunability of M1-M2 immuno-activation with enhanced osseointegration.