Characterising the mechanical properties of soft materials - such as gels and biological tissues - presents significant challenges compared to conventional, stiff engineering materials like ceramics, metals, and polymers. A major issue identified is the considerable variability in measured properties across different techniques, or even between different laboratories employing the same method. This comprehensive review addressed the need for a thorough examination of existing techniques, their limitations, and their drawbacks. Both laboratory-based and clinical methods were explored, including laboratory techniques such as tensile testing, compression test, indentation, atomic force microscopy, and rheometry, as well as clinical methods including ultrasound elastography and magnetic resonance elastography. The principles of operation and the theoretical foundations underlying the most widely employed modalities for material and tissue characterisation were presented. The limitations of these techniques were detailed, and numerous studies on the mechanical properties of soft tissues and tissue-mimicking phantoms were reported. The mechanical properties of various soft materials identified using these diverse techniques were compared and evaluated. The findings highlighted a clear need for the development of more reliable test apparatus and standardised procedures to accurately characterise these properties across nano, micro, and macro scales. These findings offer a valuable resource for researchers in the field, facilitating informed selection of characterisation methods and promoting greater accuracy and consistency in future work.
Despite significant advances in ceramic dental materials, the rehabilitation of anterior teeth remains challenging due to the complexity of optical and biomechanical properties. Although various esthetic approaches have been proposed, there is still a gap regarding to the mechanical behavior of bilayer crowns used in anterior restorations. To evaluate the biomechanical behavior of bilayer crowns with traditional and modified core designs using fatigue survival testing and finite element analysis (FEA), aiming a suitable rehabilitation for the anterior teeth area. Forty-five crowns were manufactured, according to the following groups: CC (conventional core), MCS (modified core/stratified veneer) and MCM (modified core/machined veneer). Cores were machined (lithium disilicate); veneers of CC and MCS groups were made through stratification (fluorapatite), and veneers of MCM group were also machined (leucite). Next, the crowns were cemented using resin cement (Variolink Esthetic LC) over full crown preparations made of epoxy resin and then subjected to cyclic fatigue test. After mechanical testing two events were considered: the presence of crack and/or chipping (event 1) and catastrophic failure of the crown (event 2). The average load to failure and number of cycles to failure in which events 1 and 2 occurred were used to perform the survival analysis according to Kaplan-Meier and Log-Rank (Mantel-Cox; 95%). Fracture marks and failure mode of the crowns were evaluated and classified by optical stereomicroscope and scanning electron microscope. Finally, FEA was performed to evaluate the stress distribution on the crowns. Fatigue test results showed that considering event 1 the groups with modified cores (MCS: 1020 N and MCM: 913 N) presented higher average loads and number of cycles to failure than the group CC (773 N). Considering event 2 all groups showed similar fatigue performance (∼1028 N). FEA results evidenced higher stress concentration at the load application area, with a slight stress at the cervical margin of the crowns regardless the group. Modified core designs improved resistance to initial veneer damage without compromising catastrophic failure performance. Stress distribution patterns supported the mechanical findings, indicating favorable biomechanical behavior.
The presence of surface tension forces associated with lung inflation are known to exist in vivo. In addition, lung tissue is subjected to pre-strain in situ at functional residual capacity. However, the contributions of these effects to the continuum-level mechanical response of lung tissue in deviatoric or non-volumetric deformations, important in human body models for safety, have not been quantified and are typically neglected in current lung models. In this study, an existing finite element micro-model of a representative alveolar cluster was enhanced with an explicit implementation of the surface tension membrane based on experimental data of surface tension forces in the lung. The micro-model was used to simulate, characterize, and quantify the effects of surface tension forces and alveolar pre-strains on the macroscopic mechanical response of lung parenchyma in uniaxial tension, compression, and pure shear. The results demonstrated that surface tension forces increase the stiffness of lung tissue in non-volumetric deformations, like how they increase the stiffness in volumetric deformations. The presence of tensile pre-strains in the alveolar wall that are present in vivo, further increase the stiffness of lung tissue in non-volumetric deformations relative to the stress-free lung condition. The combined effects of surface tension forces and alveolar pre-strains increased the model stiffness on the order of 10x in tension and 3x in compression and shear. The results presented herein indicate that the effects of alveolar pre-strain and surface tension are critical for continuum scale models of in vivo lungs to represent the mechanical properties of the lungs.
Hallux rigidus is a degenerative condition of the first metatarsophalangeal joint (MTPJ) characterized by progressive cartilage loss, pain, and restricted motion. Conventional surgical treatments such as arthrodesis eliminate joint mobility, while existing metallic, ceramic, and polymeric implants often fail to replicate the compliant, viscoelastic response of native cartilage. This mechanical mismatch increases interfacial stress and accelerates degeneration of the opposing cartilage. Synthetic cartilage implants aim to preserve motion, but their long-term performance remains inconsistent, with complications such as subsidence, migration, and persistent pain. Liquid crystal elastomers (LCEs) are a promising class of soft, tunable polymers that combine elastomeric elasticity with liquid-crystalline order. Their molecular architecture enables cartilage-level stiffness, reversible deformation, and energy dissipation through stress-induced mesogen reorientation. This study investigates an LCE-based hemiarthroplasty implant designed to mimic the mechanical behavior of articular cartilage. An anatomically simplified numerical model of the MTPJ incorporating the implant was developed, and experimentally derived, rate-dependent mechanical parameters were assigned to the LCE cap. Finite element simulations were conducted to evaluate stress distribution within the joint under loading conditions representative of the push-off phase of gait. The performance of the LCE implant was compared with cobalt-chromium and ultra-high-molecular-weight polyethylene materials. Results show that the LCE implant undergoes adaptive deformation under load, increasing effective contact area and reducing localized stress concentrations at the cartilage-implant interface. This promotes more uniform load transfer across the joint and suggests that LCE-based implants may mitigate long-term cartilage degeneration and improve functional outcomes compared with rigid implant materials.
To investigate the effect of resin-based cements, thermocycling and dynamic loading on the marginal and internal fit of inlays made from two different monolithic zirconia materials. Sixty-four caries-free extracted maxillary premolar teeth were embedded in acrylic resin molds and prepared for mesial occlusal distal inlays by one operator. They were randomly divided into two groups based on inlay material; Zolid Gen-X (n = 32) and IPS e.max ZirCAD Prime (n = 32). Each group was subdivided into two subgroups according to cement type: RelyX Unicem (n = 16) and Panavia F 2.0 (n = 16). Half of the specimens were incubated at 37 °C for 24hr while the other half underwent a thermomechanical aging protocol consisting of 1,200,000 dynamic loading cycles at 5 and 55 °C. Occlusal and proximal marginal fit were measured at 20 locations using a stereomicroscope at 20x magnification. Internal fit was assessed at seven locations using scanning electron microscopy (SEM) at 200x. Data were analyzed using three-way ANOVA and multivariate tests at a significance level of P < 0.05but comprom. The marginal gap of the monolithic zirconia inlays remained within clinically acceptable ranges (50-120 μm) regardless of the type of zirconia material. However, the choice of resin cement had a significant effect as RelyX cement produced smaller gaps compared to Panavia at both occlusal and proximal surfaces (P < 0.05). Simulated aging, including thermocycling and dynamic loading, significantly increased marginal gaps (P < 0.05), indicating its impact on long-term performance. In contrast, internal fit values ranged from 111.95 to 163.16 μm and showed no statistically significant differences between zirconia material, resin cement, or aging conditions (P > 0.05). These findings highlight the importance of selecting appropriate cement systems and considering aging effects to optimize the marginal integrity of zirconia inlays while confirming the stability of their internal fit. This study found no significant difference in marginal fit between Zolid Gen-X (4Y-TZP) and IPS e.max ZirCAD Prime (3Y-TZP/5Y-TZP gradient) under tested conditions. Both materials achieved clinically acceptable fit. However, RelyX cement provided significantly better marginal integrity than Panavia, and aging significantly increased marginal gaps. Internal fit was unaffected by material, cement, or aging, but exceeded ideal values. Cement choice and aging are crucial factors for marginal seal longevity.
The mechanical interactions between virus-like particles and host cells may offer targets for new viral treatments and vaccines with modes of action that are independent of the immune system. The physical properties of structures involved govern the particle-cell interactions. While the mechanical properties of virions and mammalian cells have been widely studied, data on virus-like particles are limited. This study aimed to determine the mechanical and morphological properties of HIV-1 virus-like particles with different envelopes. Three HIV-like particles, i.e. Gagᴹ + gp150, Gagᴹ + gp140HA2tr, and Gagᴹ + gp120HA2, were produced by combining the same Gag protein shell with different trimeric glycoprotein envelopes. The particles' spring constant, breaking force, and dimensions were determined using atomic force microscopy, and the elastic modulus was quantified using finite element analysis. Spring constant, elastic modulus, and breaking force were higher for Gagᴹ + gp140HA2tr and Gagᴹ + gp120HA2 than for Gagᴹ + gp150. The particle height was smaller for Gagᴹ + gp120HA2 than for Gagᴹ + gp150 and Gagᴹ + gp140HA2tr. Possible mechanisms underlying the increase of the particles' stiffness and mechanical strength are the inclusion of the influenza virus HA transmembrane domain in the HIV Env protein, and the lower expression and packing density of Env in Gagᴹ + gp140HA2tr and Gagᴹ + gp120HA2 compared to Gagᴹ + gp150 found previously. Upon confirmation, the proposed mechanisms offer potential to tailor the mechanics of HIV virus-like particles and guide mechanical interactions between VLPs and host cells towards improving vaccines.
The long-term clinical performance of conventional soft denture liners is limited by microbial colonization, poor adhesion, and plasticizer leaching. This study developed a polyurethane-acrylate soft denture liner enabling moldless fabrication through digital photolithography-based 3D printing. Two urethane-acrylate oligomers with different molecular weights (1K: 12900 g/mol, 2K: 18500 g/mol) were synthesized and mixed in five different ratios to investigate compositional effects on mechanical and viscoelastic behavior. Increasing the proportion of the 2K oligomer enhanced tensile strength and elongation, with compositions ≥1:1 (GR-C) showing mechanical performance comparable to conventional silicone-based soft liners. Dynamic mechanical analysis showed storage modulus values (0.50-0.65 MPa) within the oral mucosal elastic range (0.37-5.93 MPa), indicating damping capacity. Shore A hardness of all compositions remained within the extra-soft range after 30 days, satisfying ISO 10139-2. Under compressive loading, higher 1K content increased resistance to deformation, while GR-C demonstrated intermediate compressive stress at 10-30% strain. In terms of dimensional accuracy, GR-A and GR-D showed greater deviations than the other groups, with higher deviations along the x- and y-axes compared to the z-axis, and group- and axis-dependent patterns were observed. Optical rheometry revealed that increasing the 2K oligomer content reduced the storage modulus while increasing the loss modulus and loss tangent, indicating enhanced viscous behavior. Water sorption (13.1-14.9 μg/mm3) was within previously reported ranges, whereas solubility (12.3-16.2 μg/mm3) was comparatively higher. Near-surface degree of conversion approached 100% after post-polymerization. GR-C was selected as the optimized formulation and showed no cytotoxicity in an L929 cell assay. In the printability assessment using a novel digital workflow, GR-C exhibited a root-mean square (RMS) deviation of 0.619 mm. These results demonstrate that controlled oligomer composition enables tunable tensile, compressive, and viscoelastic properties in 3D-printable polyurethane-acrylate soft denture liners.
Orthopaedic and dental implants, the majority of which are made from titanium alloys, face the crucial challenge of both inducing osteogenesis whilst inhibiting bacterial biofilm formation in an economical manner over the life of the implant. This study introduces an innovative strategy combining cost-effective alloying elements, selected due to their reported biological benefits, for developing new titanium alloys that achieve a tailorable mechanical, corrosion, and biological response. The combination of alloying and manufacturing results in homogeneous materials characterised by a lamellar microstructure. The developed low-cost Ti alloys have a maximum ultimate compression strength of 659 MPa, maximum tensile yield stress of 606 MPa, and maximum elongation of 8.3% without failing catastrophically. The alloys do not degrade as abiotic corrosion is significantly hampered by their intrinsic passivation behaviour (maximum corrosion rate of 8.9 μm/year), and have adjustable surface wettability with contact angles in the 60-81° range. Consequently, stomal cell attachment, cytotoxicity and cytokine production (IL-6 and TGF-β1), and antibacterial rate on S. aureus are consistent and comparable to those of current implnat materials. Based on these characteristics, the low-cost Ti alloys are promising materials for load-bearing biomedical devices.
Osteosynthesis systems are widely used in the bony skeleton, such as in post-oncologic or traumatic reconstruction and orthognathic surgery. Silk protein-based biomaterials are novel alternatives to metal fixation systems, with studies showing degradability, good biocompatibility, nonsensitivity to temperature, and minimized stress-shielding. Mechanical properties of three generations of silk-based hardware were studied and compared to conventional metal and resorbable systems. Silk plates and screws were prepared using three techniques: (1) hexafluoro-2-propanol-derived (HFIP)-based approach, (2) aqueous-derived approach and (3) thermally molded silks formed by direct fusing amorphous silk nanomaterials ASN (ASN, diameters from 30 nm to 1 μm), at high pressure. Three-point bending, tensile, compression, and double lap shear tests were performed. Mechanical properties of thermal silk plates varied depending on the hydration condition. Dry thermally processed silk plates had a higher flexural modulus (2.4 -7.8 GPa) than both dry HFIP-derived (1.7 - 4.4 GPa) and aqueous-derived silk plated (2.7 GPa), suggesting superiority in flexural load bearing without permanent deformation. Hydrated thermal silk plates had excellent tensile toughness (0.9-10.5 MJ ·m-3) compared to current resorbables (0.1-5 MJ ·m-3). Silk pins performed similarly to current resorbables in terms of maximum shear strength. Silk bulk materials exhibited mechanical tolerance above trabecular bone and approached that of cortical bone. The closely matched elastic moduli reduce stress shielding. Thermally processed silk is a promising biomaterial with favorable properties compared to current metal systems, resorbables, and earlier iterations of silk fabrication techniques. Hydration status allows further refinement of mechanical properties of silk osteofixation systems.
The objective of this work was to develop a finite element model of the thoracolumbar spine to assess the effects of passive structures, rib cage, intervertebral disc (IVD), iliolumbar ligament (ILL), and facet cartilage-capsular ligament (FC-FCL), on segmental range of motion (RoM) and thoracolumbar curvature. The model included the vertebrae, rib cage, IVDs, and pelvis, with ligaments and the FC modeled as tension-only and compression-only spring elements, respectively. The model was subjected to 60° of flexion and 55° of extension. A simulated follower load of 1175 N was applied, increasing by 2.4% at each segmental level. Changes in lumbar intervertebral rotations (IVR), lumbar and thoracic RoM and lumbar lordotic (LLA) and thoracic kyphotic angles (TKA) were analyzed for cases involving removal of the ILL and rib cage and removing the L4-L5 and L5-S1 FC-FCL and increasing the elastic moduli of the L4-L5 and L5-S1 IVD, independently. Removing the L5-S1 FC-FCL increased segmental motion (21.7°) in extension with compensatory reductions at L4-L5 (5.5°). Increases in lumbar lordosis (7°) were proportional to increases in thoracic kyphosis (7°). Similar yet smaller effects were observed when removing the rib cage and ILL, with the inverse observed following increasing IVD stiffness. Removal of the rib cage and ligaments or changes in the stiffness of the IVD influence segmental mobility and drives compensatory adjustments in adjacent segments to maintain congruency. Understanding how these tissues affect spinal alignment may inform surgical strategies aimed at preserving or restoring tissue function to maintain spinal stability.
This study evaluated the effect of the material thickness on the fatigue behavior of a polycrystalline and a glass-ceramic used for occlusal veneers. Disc-shaped specimens of 4 mol% yttria-stabilized zirconia (4YSZ, IPS e.max ZirCAD MT) and lithium disilicate (LD, IPS e.max CAD) were fabricated in three thicknesses (0.5, 1.0 and 1.5 mm; n = 15) and adhesively cemented to fiberglass-reinforced epoxy resin discs to reach a total height of 3.5 mm. Cyclic fatigue testing was performed at 20 Hz with an initial load of 300 N, increasing by 50 N every 10,000 cycles up to 600 N, and then by 100 N every 10,000 cycles until failure, detected by transillumination (defined as the presence of cracks or structural discontinuities identified by light transmission). Fatigue failure load (FFL) and cycles for fatigue failure (CFF) were recorded. Fractographic and degree of conversion analyses were performed. Data was analyzed with Kaplan-Meier and analysis of variance tests. The results showed that 4YSZ exhibited superior FFL and CFF compared to LD, except for the 1 mm thick specimens. For LD, increasing thickness from 0.5 mm to 1.0 mm and 1.5 mm improved fatigue resistance, though no difference occurred between 1.0 mm and 1.5 mm. For 4YSZ, no difference was found between 0.5 mm and 1.0 mm, but 1.5 mm showed superior performance. All fractures originated from the cementation surface, and resin cement degree of conversion was unaffected by ceramic type or thickness. These findings support the clinical feasibility of minimally invasive zirconia occlusal veneers (≥0.5 mm), whereas lithium disilicate requires at least 1.0 mm thickness for reliable mechanical performance.
The human amniotic membrane (hAM) is a collagen-rich tissue increasingly used as a natural scaffold in tissue engineering. A key step in these applications is decellularization, which extracts the extracellular matrix (ECM) as a biomaterial. In this study, native hAM was processed using two different protocols: peptide bond hydrolysis with EDTA-assisted trypsin (En) and cell membrane disruption using a nonionic detergent combined with reversible alkaline swelling (SD), along with nuclease activity. The effects of each protocol on the composition, structure, and tensile behavior of the processed hAM were evaluated. Additionally, the repopulation efficiency of epithelial cells on both surfaces of the decellularized hAM was assessed. Comparisons between decellularized and digested hAM and native tissue revealed residual DNA contents ranging from 0.14 to 30% for the En method and from 1.7 to 10% for the SD method. Meanwhile, sulfated glycosaminoglycans (sGAG) content varied from 1.5 to 30% and from 1 to 18%, respectively. The En method substantially reduces fibronectin levels, while the SD method reduces lumican in the leached components of decellularized hAM. En-treated specimens exhibit altered elastic and rupture properties, negatively impacting their mechanical behavior. The hAM-derived ECM materials were repopulated by human vaginal epithelial cells, adopting morphologies that depend on the surface characteristics provided by the anatomical portion of the native tissue. Overall, these results suggest that native tissue variability influences the final composition of hAM-derived materials, that tensile properties are influenced by the used decellularization method, and that surface characteristics play a critical role in epithelial cell repopulation.
Traumatic brain injury (TBI) induced by rotational loading is a major contributor to neurological dysfunction, yet the biomechanical mechanisms underlying these injuries remain poorly understood. In this study, a high-resolution, anatomically accurate three-dimensional finite element model of the mouse brain (FEM-MB) was developed. The FEM-MB was validated against previously published experimental data, showing good agreement in both the timing and magnitude of strain responses. The FEM-MB was then subjected to unidirectional and multidirectional rotational loading scenarios at low (100 rad/s), moderate (150 rad/s), and high (200 rad/s) peak angular velocities to investigate the mouse brain's response to multidirectional rotational loading. The FEM-MB results consistently revealed that deep brain regions, particularly the thalamic-hippocampal region, hypothalamus, and brainstem, experienced the highest maximum principal strains. These results highlight that not only the magnitude, but also the direction and temporal asymmetry of rotational loading, significantly affect the strain distribution across brain regions. In particular, the thalamic-hippocampal and brainstem regions had the highest strains under coronal and axial plane rotations, aligning with known injury patterns. These findings underscore the critical role of rotation direction and loading profile on strain magnitude and distribution in the mouse brain under dynamic rotational loading. Overall, the FEM-MB provides a robust in silico platform to investigate the effects of dynamic rotation loading in preclinical models of TBI.
Extruded Mg-Zn-Zr alloys are promising materials for orthopedic applications due to their bio-safe alloying elements and high strength. However, their rapid corrosion remains a major limitation. Surface treatment using hydroxyapatite (HAp) coatings is an effective approach to enhance both corrosion resistance and biocompatibility of the alloys. However, understanding about formation of the HAp coating on different extrusion directions, and its resulting corrosion and mechanical behavior, is limited. In this study, a HAp coating was formed on both cross-sectional and longitudinal direction of a commercially extruded Mg-Zn-Zr alloy via a chemical conversion method. The cross-sectional surface exhibited various regions of poor coating coverage above coarse second-phase particles, whereas the longitudinal surface showed easily detachable coating regions formed over the elongated former Mg grains. These defective sites then promoted severe pitting corrosion. The coating reduced the corrosion rate of the alloy by up to 36.39% by day 14; however, its protective effect diminished quickly thereafter. Regardless of coating presence, the strength reduction rate doubled during the period from day 14 to 28 due to sudden fracture when pit depth exceeded 0.6-0.8 mm, indicating a critical threshold for mechanical integrity. After immersion, both uncoated and coated samples remained at about 70% of their initial strength, approximately twice that of human cortical bones, highlighting a strong potential for load-bearing implants.
The mechanical integrity and failure mechanisms of human hair fibers are critically dependent on the hierarchical structure of the cuticle, which serves as a durable record of biological and environmental history. In this study, we employed a multi-parametric approach to quantify the nanomechanical evolution of hair degradation, establishing a correlation between surface physicochemistry and local tribological properties. We combined Atomic Force Microscopy in Quantitative Nanomechanical Mapping (QNM) mode with Power Spectral Density (PSD) analysis, Scanning Electron Microscopy (SEM), and Energy-Dispersive X-ray Spectroscopy (EDS). QNM revealed distinct nanomechanical signatures: bleached fibers exhibited elevated adhesion domains and markedly increased heterogeneity compared to virgin counterparts. These tribological behaviors were consistent with trends observed in EDS analysis regarding chemically adsorbed sodium and oxidative residues, although morphological changes remained the primary indicator of damage. While natural aging in distal regions induced surface deterioration, the magnitude of damage was significantly more pronounced in fibers subjected to combined bleaching and UV irradiation. This suggests a synergistic degradation pathway where chemical pre-treatment amplifies the susceptibility to UV-induced defects. This study demonstrates that chemical adsorption and weathering can co-occur, yet manifest along statistically distinct chemical and structural dimensions that jointly compromise the cuticle barrier function. These findings highlight the potential utility of nanoscale multiparametric mapping not only for assessing cosmetic treatments, but also for informing forensic and clinical contexts, where such tribological descriptors may support diagnostic profiling of structural and chemical anomalies.
Stents are essential medical devices for treating peripheral artery disease, but the outcomes of design testing depend strongly on the mechanical environment in which they are deployed. During stent development, surrogate arterial models are commonly used to reproduce the pulsatile behaviour and geometry of human arteries, according to standards requirements. However, these surrogates differ from the mechanical properties of living human arteries. This study compared eight materials commonly used in vascular devices development with fresh human arteries as reference. The tested materials were frozen human femoral artery, preserved human femoral artery, fresh and frozen sheep carotid artery, fresh and frozen pig abdominal aorta, basic silicon and technical silicon. Samples were tested on a planar bi-axial testing machine to quantify their mechanical properties. Stress and strain data were analyzed in the longitudinal and circumferential directions under nine different strain rate ratios. Bi-linear and constitutive model fitting were applied to describe and compare mechanical responses. Histological analysis characterized the structure and composition of each biological material, and constitutive parameters inferred from histology were numerically fitted. Frozen human femoral arteries and fresh pig abdominal aortas were identified as the closest models to human femoral arteries when comparing toe, high stress stiffness, diameter and thickness (utility score values of 9.44 and 8.38 respectively). No material fully matched the stiffness for both slopes and transition strain thresholds. Further research is needed to design surrogate materials that more accurately reproduce the mechanical behaviour of living arteries and support reproducible and physiologically relevant vascular testing.
The mechanical reliability of self-expanding stents critically depends on the ability of their constituent beam elements to sustain large bending deformation without instability. While NiTi alloys are widely used, their processing complexity and transformation-related uncertainties motivate the exploration of alternative metallic systems. Zr-based metallic glasses (MGs), which combine high elastic recoverability with structural homogeneity, offer a compelling but insufficiently understood option under bending-dominated loading. In this study, the bending deformation behavior of a 0.25 mm-thick Zr61Ti2Cu25Al12 (ZT1) high-toughness MG beam is investigated under conditions relevant to miniaturized stent architectures. Emphasis is placed on precisely capturing the onset of yielding under bending, unraveling the two-stage evolution and underlying mechanisms of shear-band-mediated plasticity, and clarifying the size-dependent nature of plastic deformation stability in MG beams. The results reveal a distinct bending-specific deformation response that differs fundamentally from uniaxial loading, characterized by thickness-sensitive shear-band organization and enhanced resistance to shear localization. By linking these observations to fracture-mechanics considerations, this study provides a mechanistic framework for understanding why thin MG beams can accommodate large bending strains without catastrophic failure. The insights gained establish a foundation for the rational design of MG components in bending-dominated biomedical devices.
Human hair is a hierarchical composite, primarily composed of α-keratin, in which the cortex contributes to tensile strength through keratin intermediate filaments, while the cuticle ensures surface protection, chemical resistance, and water regulation due to its multilayered architecture. Although the tensile properties of the cortex have been extensively studied, the mechanical response of the cuticle under stress remains less understood. In this work, we investigate cuticular mechanics by correlating morphological deformation with molecular-level responses using Raman spectroscopy. A human hair was subjected to uniaxial strain up to 32%, and the spacing between cuticular scale edges was monitored. A 1:1 correlation was observed between cuticular strain and applied elongation in the range 3-26%, indicating that scale deformation follows the macroscopic fiber extension. Raman analysis revealed strain-induced alterations in disulfide (-Cα-CH2-S-S-CH2-Cα-) crosslinks, with portion of disulfide bridges undergoing a gauche-to-trans conformational change, predominantly within the sulfur-rich A-layer and exocuticle. Although a slight reduction in hydrogen-bond strength was observed, no α-helix to β-sheet transition was detected. The structural stability of the cuticle under stress is attributed to its high content of keratin-associated proteins and dense crosslinking via disulfide and isopeptide bonds. Furthermore, the experimental results concerning the relaxation under macroscopic strain are compatible with thinning of lipid layers and gliding of cuticular scales. These findings collectively demonstrate that the cuticular Cell Membrane Complex (CMC) facilitates scale gliding while preserving structural integrity, highlighting its critical role in hair mechanics and resistance to external stresses.
While titanium dioxide (TiO2) nanotubes are widely recognized for enhancing the osseointegration of dental implants, their clinical translation is severely hindered by poor mechanical stability, often leading to coating detachment during surgical insertion. Addressing this critical limitation, this study aimed to optimize the adhesion of TiO2 nanotubes through annealing and to evaluate the protective role of substrate topography during simulated implantation. Nanotubes were grown via anodization on both machined and Sandblasted, Large-grit, Acid-etched (SLA) titanium substrates, followed by annealing from 300 °C to 700 °C. Results indicated that annealing at 500 °C provided the optimal balance of anatase crystallinity and adhesion stability, yielding the highest adhesion strength. However, simulated insertion tests revealed that high adhesion alone is insufficient; nanotubes on smooth machined surfaces suffered extensive delamination due to shear forces. In contrast, the SLA substrate demonstrated a unique mechanical shielding effect, where intrinsic micro-cavities effectively protected the nanotubes from abrasive friction. The study concludes that combining SLA surface topography with 500 °C annealing creates a synergistic defense, preserving the bioactive coating's integrity against insertion torques and overcoming the primary mechanical barrier to the clinical application of nanostructured implants.
Lattice structures are increasingly being adopted for orthopaedic implant designs; however, questions remain about the long-term strength and risk of fatigue failure of porous titanium (Ti) and Ti-alloy structures. To provide a deeper understanding of this issue, this study conducted a comprehensive review of fatigue performance of latticed Ti/Ti-alloy parts, printed via laser powder bed fusion (PBF-LB), for orthopaedic applications, spanning studies over the past decade. Key lattice parameters were collected, including porosity, pore size, feature thickness, and lattice type, and their corresponding effect on fatigue performance of the end part. This review found that many Ti/Ti-alloy lattice structures can achieve comparable mechanical properties to trabecular bone (E of 0.01-3 GPa, fatigue strength of 0.3-3 MPa) while only one reviewed sample matched both the Young's modulus and fatigue strength of cortical bone (E of 15-20 GPa, fatigue strength 40-60 MPa). This review addresses the gap in having consolidated data describing the effects of various properties of Ti/Ti-alloy lattices on their compressive fatigue strengths, providing guidance on design considerations of such lattice structures for orthopaedic applications. Data provided in this review further highlights the need for continued development of implant latticing strategies and design parameter development to better mimic human cortical bone in orthopaedic implants.