Adhesive Polymer Research Articles

Stability of Conducting Polymer-Coated Carbon Microfibers for Long-Term Electrical Stimulation of Injured Neural Tissue.

Electroactive microfiber-based scaffolds aid neural tissue repair. Carbon microfibers (CMFs) coated with the conducting polymer poly(3,4-ethylenedioxythiophene) doped with poly[(4-styrenesulfonic acid)-co-(maleic acid)] (PEDOT:PSS-co-MA) provide efficient support and guidance to regrowing axons across spinal cord lesions in rodents and pigs. We investigated the electrical and structural performance of PEDOT:PSS-co-MA-coated carbon MFs (PCMFs) for long-term, biphasic electrical stimulation (ES). Chronopotentiometry and electrochemical impedance spectroscopy (EIS) allowed the characterization of charge transfer in PCMFs during ES in vitro, and morphological changes were assessed by scanning electron microscopy (SEM). PCMFs that were 4 mm long withstood two-million-biphasic pulses without reaching cytotoxic voltages, with a 6 mm length producing optimal results. Although EIS and SEM unveiled some polymer deterioration in the 6 mm PCMFs, no significant changes in voltage excursions appeared. For the preliminary testing of the electrical performance of PCMFs in vivo, we used 12 mm long, 20-microfiber assemblies interconnected by metallic microwires. PCMFs-assemblies were implanted in two spinal cord-injured pigs and submitted to ES for 10 days. A cobalt-alloy interconnected assembly showed safe voltages for about 1.5 million-pulses and was electrically functional at 1-month post-implantation, suggesting its suitability for sub-chronic ES, as likely required for spinal cord repair. However, improving polymer adhesion to the carbon substrate is still needed to use PCMFs for prolonged ES.

Thermal Stability and Heat Transfer of Polyurethanes for Joints Applications of Wooden Structures.

Wood characterized by desired mechanical properties and wood joining material is essential for creating wooden structures. The polymer adhesives are suitable for such applications due to the possibility of energy dissipation from stresses generated by wooden structures and the elimination of thermal bridging, which are common problems in metal joining materials. This research focuses on the thermophysical properties of the laboratory-prepared flexible and rigid polyurethanes to select an appropriate polymer adhesive. Our results showed that the highest thermal stability was in the case of the new PSTF-S adhesive, which reached 230 °C, but the lowest mass loss in the air environment was around 54% for the PS material. The mean thermal expansion coefficient for F&R PU adhesives was 124-164∙10-6 K-1. The thermal diffusivity of examined adhesives varied between 0.100 and 0.180 mm2s-1. The thermal conductivity, depending on the type of polyurethane, was in the 0.13-0.29 W∙m-1∙K-1 range. The relative decrease in thermal diffusivity after heating the adhesives to 150 °C was from 2% for materials with the lowest diffusivity to 23% for the PU with the highest value of heat transfer. It was found that such data can be used to simulate wooden construction joints in future research.

Highly Adhesive, Ultrafast Self-Healing, and Conductive Dopamine-Based Polymer Hydrogels for Sensitive Human Motion Sensing

Highly Adhesive, Ultrafast Self-Healing, and Conductive Dopamine-Based Polymer Hydrogels for Sensitive Human Motion Sensing

Arthrobotrys oligospora (Fungi: Orbiliales) and its liquid culture filtrate myco-constituents kill Haemonchus contortus infective larvae (Nematoda: trichostrongylidae)

ABSTRACT Arthrobotrys oligospora is a nematode-trapping fungus belonging to the family Orbiliaceae and one of the main antagonists of nematodes in soil, including plant and animal parasitic nematodes and free-living nematodes. This species develops three-dimensional adhesive nets in which nematodes are trapped, destroyed and consumed by the fungus. It also possesses other strategies to immobilise, kill and degrade nematodes, i.e. nematode-attractant substances, cuticle adhesion polymers and a number of nematocidal metabolites. The objective of this study was to assess the in vitro nematocidal activity of a strain of A. oligospora through its predatory activity and its liquid culture filtrates (LCF) against the ruminant parasite Haemonchus contortus (HcL3) and to investigate the presence of myco-compounds with potential nematocidal activity. Predatory activity (PA) was assessed in agar plates; 200 HcL3 were placed on agar plates with the fungus and a control group and incubated for 10 days. The LCF confrontation with nematodes was performed in microtiter plates. Two media, Czapek-Dox Broth (Cz-DB) and potato dextrose broth, were assessed. Three concentrations (25, 50 and 100 mg/mL) were assessed at 48 and 72 h (n = 4, per concentration). The experiment was performed in triplicate. The results showed 73.6 ± 2.7% PA and the highest mortality (83%) with the LCF in Cz-DB after 72 h. Gas chromatography–mass spectrometry (GC–MS) analysis revealed that the A. oligospora ethyl acetate phase was composed of 1,2-benzenedicarboxylic acid, bis (2-methylpropyl) ester, (M) 1,4-benzenedicarboxylic acid, bis (2-methylpropyl) ester and (M) decanedioic acid (2-ethylexyl) ester. These compounds could be responsible for nematocidal activity.

A Fully Biodegradable and Ultra‐Sensitive Crack‐Based Strain Sensor for Biomechanical Signal Monitoring

AbstractA fully biodegradable, ultra‐sensitive, and soft strain sensor is pivotal for temporary, real‐time monitoring of microdeformations, crucial in disease diagnosis, surgical precision, and prognosis of muscular, and vascular conditions. Nevertheless, the strain sensitivity of previous biodegradable sensors, denoted by gauge factor (GF) up to ≈100, falls short of requirements for complex biomedical monitoring scenarios, specifically monitoring cardio‐cerebrovascular diseases with microscale variations in vascular surface strain. Here, a fully biodegradable, ultra‐sensitive crack‐based flexible strain sensor is introduced achieving GF of 1355 at 1.5% strain through integration of molybdenum (Mo) film, molybdenum trioxide (MoO3) adhesion layer, and polycaprolactone (PCL) substrate. Analysis of crack morphology of biodegradable thin‐film metals, including Mo, tungsten (W), and magnesium (Mg), reveals material‐dependent sensitivity and repeatability of crack‐based strain sensors. The effect of the adhesion layer and polymer substrate is also investigated. Overall morphological studies on the sensor present a comprehensive understanding of metal film cracking behavior and corresponding performance characterization, showing significant potential for highly sensitive sensors. A hybrid membrane composed of candelilla wax (Cw), beeswax (Bw), and polybutylene adipate‐co‐terephthalate (PBAT) is introduced to provide hydrophobic, yet flexible encapsulation. In vivo, short‐term (≈3 days) monitoring of vascular pulsatility underscores the potential of the sensing tool for rapid, accurate, and temporal disease diagnosis and treatment.

Uncovering mussel foot protein (Mfp-3)'s binding secrets: Enhanced biomimetic adhesives via mass spectrometry and residue labeling

This study delves into the development of biomimetic adhesives, taking inspiration from the impressive underwater adhesion of mussels. In a departure from the traditional focus on DOPA, we explore a more comprehensive range of amino acids crucial for adhesion in wet environments. By utilizing amino acid labeling and mass spectrometry-based peptide mapping, we identify key peptide sequences within Mfp-3 responsible for effective aquatic adhesion. Of particular interest is the sequence YNRYARGY, which exhibits robust adhesion on both polar/acidic and hydrophobic surfaces, with an adsorption-free energy of approximately -4.5 kcal/mol (as determined by QCM). Incorporating this sequence (1% w/v), with tyrosine substitution for DOPA, into a standard PVA binder significantly enhances its adhesion capabilities. Lap-shear tests demonstrate a significant increase in PVA adhesion from 2.5 to 5 kPa on SiO2 and from 2.1 to 3.3 kPa on HDPE. These findings highlight the practical implications of our mass spectrometry approach with side chain modification in elucidating the mechanisms of mussel adhesion, thereby offering a promising strategy for advancing polymer adhesion technology.

A Novel Method of Self-Cross-Linking of Syringaldehyde with Activated Methoxy Groups via Cross-Coupling for Lignin-Based Wood Adhesives.

As steric hindrance, methoxy groups are limiting the valorization of hardwood lignin. This paper reports a novel method of self-cross-linking of the syringaldehyde with activated methoxy groups (-OCH3) via cross-coupling reaction to obtain thermosetting polymers for lignin-based wood adhesives. The methoxy groups of syringaldehyde have been activated via cross-coupling reaction by substituting Ar-OCH3 with Ar-CH2-SiMe3, and dichloromethane, leading to cross-linking via methylene bridges to build a thermosetting polymer. FTIR spectra showed a decrease in the intensity of a -CH3 and -OH group, owing to the substitution of the methoxy group. 13C NMR spectra also supported these results with the -SiMe3 signal that disappeared after the cross-linking reaction. Furthermore, cross-linking between the activated methoxy groups was confirmed with a strong exothermic peak at 130 °C, resulting in an increase in the adhesion strength as hot-pressing temperature increased from 160 to 180 °C. These results suggest that the cross-linking between the activated methoxy groups of syringaldehyde is an important understanding of valorizing hardwood lignin via building thermosetting polymers for lignin-based adhesives.

The super-fast synthesis of high-strength epoxy adhesives by UV-initiated frontal polymerization at room temperature

The synthesis and processing of most polymer adhesives rely on energy-inefficient and environmentally burdensome manufacturing approaches. In this paper, a novel synthesis strategy, UV-initiated frontal polymerization (FP) for the fast synthesis of high-strength, self-propagating epoxy adhesives at room temperature, was presented, in which the self-propagating rate reached 71.4 mm min−1. CuCl2 was used as a catalyst to decrease the onset temperature of polymerization and ensure sufficient polymerization on the surface of the material to be bonded. Mild steel, glass, ceramic, wood, PMAA, and concrete were successfully bonded within several minutes at room temperature. In the same material system, the adhesive strength with the FP curing approach was greater than that of thermal curing, and the former had a better pore structure, as determined by MIP analysis. This paper provides a promising idea for the in-situ fast synthesis of high-strength epoxy adhesives at room temperature.

Enhancing the Delamination Efficiency of Polyimide-Copper Bilayers with UV/Heat-Activated Foamable Adhesive: Insights and Applications.

This study explores the adhesive properties of copolymers comprising glycidyl methacrylate (GMA) and 3-(trimethoxysilyl)propyl methacrylate (MPTMS), focusing on their suitability for adhesive applications. Peel resistance measurements revealed a substantial impact of the GMA/MPTMS ratio on adhesion capabilities, identifying an optimal ratio of 30/70 for copolymerization with tert-butyl acrylate (tBA) to improve foaming performance. tBA, a foaming monomer activated by a photoacid generator and heat, enhances the copolymerized adhesive's adhesion strength and foamability for postuse delamination. Chemical structure analysis through Nuclear magnetic resonance (NMR) and Fourier-transform infrared spectroscopy (FTIR) confirmed successful polymerization, while rheological properties indicated decreased complex viscosity and adhesive strength with an increasing tBA content. The deprotection of the t-butyl group facilitated foam formation, supported by morphology analysis. These findings provide insights into foamable adhesive development with potential applications in delamination processes and implications for further exploration in polymer adhesion.

Photocontrolled polymer adhesives facilitate the assembly of hydrogels for soft robotics

Photocontrolled polymer adhesives facilitate the assembly of hydrogels for soft robotics

A highly flexible and adhesive polymer electrolyte with fast ion conduction prepared via UV-induced in-situ polymerization for lithium metal batteries

Cathode–electrolyte integration via in-situ polymerization is an effective strategy to reduce interfacial resistance in solid-state/quasi-solid-state lithium batteries; however, ion conduction in the fraction of polymer electrolyte is still to be enhanced. Herein, we demonstrate a separator-free cathode–electrolyte integrated structure employing a novel poly(di(ethylene glycol) ethyl ether acrylate)-based quasi-solid polymer electrolyte (LiTFSI-poly(DEGA)-FEC QSPE, denoted as PDEGA-QSPE), prepared via UV-assisted in-situ polymerization. Poly(DEGA) as a linear polymer contains abundant ethylene oxide (EO) segments in its branched chain, exhibiting excellent flexibility and high adhesion. Benefited from the flexible molecular structure, PDEGA-QSPE exhibits a glass transition temperature (Tg) as low as around −68 °C and a good room-temperature ionic conductivity of 2.3 × 10−4 S cm−1, and it also shows an oxidative potential up to 4.7 V. The LiFePO4|PDEGA-QSPE|Li battery possesses an initial capacity of 149.2 mAh g−1 and a capacity retention of 92.5 % after 300 cycles at 0.2C under room temperature, and poly(DEGA)-based QSPE also has the potential to be applied to the high-voltage NCM811||Li battery. Compared with widely-employed monomers for in-situ polymerization such as poly(ethylene glycol) diacrylate (PEGDA), poly(DEGA) possesses remarkably improved flexibility and ion conduction capability, exhibiting broad research and application prospects.

TPU-assisted adhesive PDMS film for dry or underwater environments

Adhesive polymer films with anisotropic properties on either side have attracted tremendous interest for biomedical and engineering applications. However, developing an innovative solution that provides effective adhesion under both dry and wet conditions remains a considerable challenge. In this study, we devised a novel process for creating adhesive films by casting polydimethylsiloxane (PDMS) onto a thermoplastic polyurethane (TPU) substrate. During the curing process, the PDMS layer in contact with the TPU was lightly cross-linked, which significantly increased adhesion. The catalytic reaction used for polymerization was regulated by the TPU, which is known to adsorb metal ions. This adhesive PDMS film (APF) demonstrated outstanding adhesion on various substrates under dry and underwater conditions and maintained adhesion even after repeated use. In practical applications, the APF proved to be an effective waterproof patch by adhering to the surfaces of objects submerged in water.

Tensile, flexural, and mode-I cracking behavior of interpenetrating phase composites (IPC), developed using additively manufactured PLA-based structures with different infill densities and epoxy resin polymer as matrix

Interpenetrating phase composites (IPC) materials are designed to combine the advantages of made-from materials or develop an intended behavior. Recently, the use of 3D printed structures has received attention due to advantages, such as the rapid and cheap prototyping techniques of complex structures. However, most materials, such as polylactic acid (PLA) used for conventional 3D printing, have low strength and insignificant durability. To overcome these issues, the excellent characteristics of polymer adhesives, such as epoxy resin, can be used to increase their strength and durability. In this paper, PLA-based 3D printed samples and epoxy resin adhesive were merged to develop an interpenetrating phase composite. The samples were printed with 25, 50, 75, and 100 infill percentages and tested in direct tensile, bending, and mode-I fracture. From the results, it can be seen that reducing the infill percentage to 75, 50, and 25 % reduces the tensile strength to 16, 9, and 3 MPa (−40 %, −66 %, and −90 % compared to the sample with 100 % infill with 26 MPa strength), adding epoxy resin to develop an IPC, results in 24, 29 and 32 MPa tensile strength. Compared to 3D-printed parts with the same infill percentages, the IPCs have 150, 320, and 1140 % higher tensile strengths, respectively. Also, the failed samples were reviewed by scanning electron microscope.

Control of Pore Sizes in Epoxy Monoliths and Applications as Sheet-Type Adhesives in Combination with Conventional Epoxy and Acrylic Adhesives.

Materials with monolithic structures, such as epoxy monoliths, are used for a variety of applications, such as for column fillers in gas chromatography and HPLC, for separators in lithium-ion batteries, and for precursor polymers for monolith adhesion. In this study, we investigated the fabrication of epoxy monoliths using 1,3-bis(N,N-diglycidylaminomethyl)cyclohexane (TETRAD-C) as the tetrafunctional epoxy and 4,4'-methylenebis(cyclohexylamine) (BACM) as the amine curing agent to control pore diameters using polyethylene glycols (PEGs) of differing molecular weights as the porogenic agents. We fabricated an epoxy monolith with micron-order pores and high strength levels, and which is suitable for the precursors of composite materials in cases where smaller PEGs are used. We discussed the effects of the porous structures of monoliths on their physical properties, such as tensile strength, elongation, elastic modulus, and glass transition temperatures. For example, epoxy monoliths prepared in the presence of PEGs exhibited an elastic modulus less than 1 GPa at room temperature and Tg values of 175-187 °C, while the epoxy bulk thermoset produced without any porogenic solvent showed a high elastic modulus as 1.8 GPa, which was maintained at high temperatures, and a high Tg of 223 °C. In addition, the unique adhesion characteristics of epoxy monolith sheets are revealed as a result of the combinations made with commercial epoxy and acrylic adhesives. Epoxy monoliths that are combined with conventional adhesives can function as sheet-type adhesives purposed with avoiding problems when only liquid-type adhesives are used.

A biocompatible, highly adhesive zwitterionic polymer hydrogel with high ionic conductivity, anti-freezing and moisturizing for wearable strain sensor

Although wearable sensors based on polymer hydrogels have great progress, achieving biocompatibility, long-term stability, and being used in harsh environments for polymer hydrogels remains a significant challenge. In this work, a new simple tactic is proposed to prepare biocompatible zwitterionic polymer hydrogels (PDM) by copolymerization of dopamine acrylamide (DAA) and 2-methacryloyloxyethyl phosphorylcholine (MPC). The synergistic effects of the Hofmeister and electrostatic interaction effect based on a series of inorganic salts on PDM hydrogels are studied. The PD3M7/4 M Zn(ClO4)2 hydrogel presents a high ionic conductivity of 13.58 S m−1 at 25 °C. The re-prepared hydrogel demonstrates outstanding anti-freezing properties, even at −45 °C, the hydrogel exhibits transparency and flexibility, and the ionic conductivity is up to 1.81 S m−1. Moreover, the hydrogel has excellent adhesive strength (34.7 kPa), and anti-dehydration (94.4 % after 30 days). The freeze-dried PD3M7/4 M Zn(ClO4)2 gel can recover up to 89.5 % of the original water content after 96 h at 20 % RH and 25 °C. Importantly, the wearable strain sensor based on PD3M7/4 M Zn(ClO4)2 hydrogel shows high sensitivity (7.43 kPa−1 at 25 °C and 4.83 kPa−1 at −45 °C), ultra-low detection limit (30 Pa), outstanding cycle stability (10000 cycles), and quickly responds to human movement detection at 25 °C and −45 °C. This work provides an effective strategy to prepare the hydrogel which will be more appropriate to apply in wearable sensors and biological tissue engineering.

Decoding the influence of low temperature on biofilm development: The hidden roles of c-di-GMP

Biofilms are widely used and play important roles in biological processes. Low temperature of wastewater inhibits the development of biofilms derived from wastewater activated sludge. However, the specific mechanism of temperature on biofilm development is still unclear. This study explored the mechanism of temperature on biofilm development and found a feasible method to enhance biofilm development at low temperature. The amount of biofilm development decreased by approximately 66 % and 55 % at 4 °C and 15 °C, respectively, as compared to 28 °C. The cyclic dimeric guanosine monophosphate (c-di-GMP) concentration also decreased at low temperature and was positively correlated with extracellular polymeric substance (EPS) content, formation, and adhesion strength. Microbial community results showed that low temperature inhibited the normal survival of most microorganisms, but promoted the growth of some psychrophile bacteria like Sporosarcina, Caldilineaceae, Gemmataceae, Anaerolineaceae and Acidobacteriota. Further analysis of functional genes demonstrated that the abundance of functional genes related to the synthesis of c-di-GMP (K18968, K18967 and K13590) decreased at low temperature. Subsequently, the addition of exogenous spermidine increased the level of intracellular c-di-GMP and alleviated the inhibition effect of low temperature on biofilm development. Therefore, the possible mechanism of low temperature on biofilm development could be the inhibition of the microorganism activity and reduction of the communication level between cells, which is the closely related to the EPS content, formation, and adhesion strength. The enhancement of c-di-GMP level through the exogenous addition of spermidine provides an alternative strategy to enhance biofilm development at low temperatures. The results of this study enhance the understanding of the influence of temperature on biofilm development and provide possible strategies for enhancing biofilm development at low temperatures.

Formulation and evaluation of hydrocortisone micro beads

The current study aimed to develop hydrocortisone mucoadhesive microbeads to prolong the drug's action in the gastrointestinal system, targeting Crohn's disease treatment. Hydrocortisone, known for its anti-inflammatory and anti-rheumatic effects, was utilized in bead form to enhance therapeutic efficacy, extend residence time, and reduce dosage frequency. Using sodium alginate, HPMC, and Eudragit L-100 as adhesive polymers, and calcium chloride and aluminium chloride as cross-linking agents, the study crafted microbeads with an entrapment efficiency between 57.23% and 91.69%. Evaluations focused on in vitro drug release, particle size, surface characteristics, entrapment efficiency, and the role of cross-linking ions. Of the formulations, HCS-8 (with sodium alginate and Eudragit L-100 using aluminium chloride as the gelling solution) and HCS-2 showed optimal drug release profiles. Notably, HCS-8 achieved a 12-hour drug release delay, attributed to aluminium chloride's cross-linking action. Drug release kinetics revealed a zero-order linearity (R2=0.99), suggesting super case 2 transport as the primary release mechanism.

Ultrasonic welding of CF/PA6 composite to 6061Al alloy utilizing an interfacial coating as energy director

This study investigates ultrasonic plastic welding to join the carbon fiber-reinforced thermoplastics and 6061Al alloy in a lap-type joint configuration. An interfacial polymer coating through a fluidized bed on aluminum alloy was considered an energy director, as it was essential for concentrating heat at the interface during welding. The significant ultrasonic process setting (weld pressure: 0.5 MPa, weld time: 600 ms, hold time: 1000 ms) was statistically realized for a maximum lap shear strength of the joint that showed the interlaminar shear (first-layer ply) failure of the composite, while the welding interface morphology revealed interdiffusion of thermoplastics with the load-bearing carbon fibers attached to the composite-coating resin mixtures, whereas the coating interface offered a strong adhesion of polymer on the aluminum surface asperities through mechanical interlocking. An efficient multi-material joint was obtained within 1.6 s in comparison to the adhesive bonding technology that required at least 20 min. Additionally, the interfacial coating serves as an insulator, avoiding galvanic corrosion in joints as well as fretting damage. The encouraging findings of this research provide deeper insight into joining thermoplastic composites to metals by ultrasonic plastic welding without the use of a separate energy director, which simplifies the process of industrialization.

A new strategy for structural color fabrics: Transfer of photonic crystal coatings from slides to fabrics

The construction of three-dimensional photonic crystals on textile surfaces has emerged as a highly effective method to create fabrics with structural color, generating significant interest among researchers. However, the strict requirements of the substrate fabrics and the challenges associated with patterning coatings for bright structural colors have hindered the widespread application of photonic crystal materials in the textile industry. In this study, we present a strategy for obtaining patterned structural color coatings on fabrics made of different materials. Pre-crystallized poly(styrene-methyl methacrylate-acrylic acid) (P(St-MMA-AA)) liquid photonic crystals (LPCs) are used as raw material for the rapid preparation of solid photonic crystals (SPCs). These SPCs with structural colors are used as templates and transferred to various fabrics through transfer printing techniques. Importantly, the SPCs maintain an ordered face-centered cubic structure both before and after transfer. Such a feature ensures that the processed structural color fabrics exhibit vibrant and iridescent structural colors. This result is achieved by modification of the substrate fabric with viscous polymer and the intact retention of SPCs. The sandwich structure formed by the adhesive polymer on the base fabric and the encapsulation of the film-forming material on the SPCs imparts good stability to the structural color fabric. It is worth noting that patterned photonic crystal coatings can be easily obtained on the fabrics made of different materials (cotton, linen, wool, and silk fabrics) by manipulating the shape of the viscous polymer. Additionally, a wide range of common materials, such as paper, wood, steel, and others, can be used as target substrates. This novel dyeing strategy not only offers new ideas for preparing patterned structural color fabrics but also further promotes the application of photonic crystal materials in textile printing or display.

Mode I/II cracking behavior of additively manufactured interpenetrating phase composites (IPC), an experimental and theoretical study

An interpenetrating phase composite (IPC) material combines the advantages of being made from materials for an intended behavior. 3D-printed parts have received attention for rapid prototyping of complex structures; however, their porous inherent makes them susceptible to cracking. Polymer adhesives can be used to overcome these issues to increase their strength and durability. In this paper, IPCs were developed using 3D-printed scaffolds and epoxy resin matrix, and their fracture behavior was examined. The samples were printed with 25, 50, 75, and 100 infill percentages and tested in the full range of mode I-II fracture. From the results, the promising behavior of IPCs can be seen. Where the 3d printed samples with 100, 75, 50, and 25 infills show 2.4, 1.8, 0.8, and 0.3 MPa√m mode-I fracture toughness, IPCs made from samples with 75, 50, and 25 infills, show 2.0, 2.2 and 2.7 MPa√m, respectively. The same trends are also seen in the full range of mode I-II fractures. The generalized maximum tangential stress (GMTS) criterion accurately predicted KIIc/KIc ratios among the investigated mixed-mode fracture criteria. The evaluations indicated that the discrepancy between the measurements is mainly due to the sign and magnitude of the T-stress parameter.