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Vitamin E (VE) is currently an approved antioxidant to improve the oxidation stability of highly crosslinked ultrahigh molecular weight polyethylene (UHMWPE) insert used commercially in total joint arthroplasty. However, the decrease in crosslink density caused by VE reduces wear resistance of UHMWPE, showing an uncoordinated challenge. In this work, we hypothesized that D-sorbitol (DS) as a secondary antioxidant can improve the antioxidant efficacy of VE on chemically crosslinked UHMWPE. The combined effect of VE and DS on oxidation stability of UHMWPE was investigated at a set of controlled hybrid antioxidant content. The hybrid antioxidant strategy showed significantly synergistic enhancement on the oxidation stability of chemically crosslinked UHMWPE compared with the single VE strategy. More strikingly, the crosslink density of the blends with hybrid antioxidants stayed at a high level since DS is not sensitive to crosslinking. The relationships between oxidation stability, mechanical properties, crosslink density, and crystallinity were investigated, by which the clinically relevant overall performance of UHMWPE was optimized. This work provides a leading-edge design mean for the development of joint bearings.

Bisphenol-A polycarbonate (PC) is an intrinsically crystallizable polymer. Its industrial parts, however, invariably remain in an amorphous state due to its extremely slow crystallization kinetics....

Although artificial polymeric scaffolds act as vital characters in bone repair, their application is limited due to their inferior bioactivity. Herein, osteoinductive poly(ε-caprolactone) (PCL) composite scaffolds were prepared by synchronously enlisting bioactive nanohydroxyapatite (nHA), bioglass (BG), and bone morphogenetic protein-2 (BMP-2), which was bound up with polydopamine (pDA). It was found that pDA deposition not only significantly enhanced hydrophilicity and cell affinity of composite scaffolds but also endowed steady immobilization of BMP-2 with long-term yet sustained release. Compared to pure PCL and PCL/nHA/BG (PHB) scaffolds, the designed PHB-pDA-BMP-2 scaffolds significantly induced the differentiation of bone marrow stromal cells toward an osteogenic lineage. Meanwhile

Oxidative degradation of ultrahigh molecular weight polyethylene (UHMWPE) bearings is one of the main factors that deteriorates their mechanical properties and abrasive wear resistance, which further results in the failure of total joint replacements. Absorption and diffusion of synovial fluids have been considered as causes of the oxidation of UHMWPE bearings. However, the role of synovial fluids in oxidation of UHMWPE remains elusive. In this work, we aimed to reveal the oxidation mechanism of UHMWPE joints with respect to squalene (a representative component of the synovial fluid). The UHMWPE doped in squalene showed slight oxidation, while severe oxidation was observed when squalene doped UHMWPE was exposed to oxygen atmosphere. Squalene manifested lipid peroxidation with notable oxidation products and oxygen-derived free radicals during thermo-oxidative aging. Lipid peroxidation was deduced to follow two routes including autoxidation and thermal oxidation. The aggressive free radicals of squalene abstracted hydrogen atoms from the UHMWPE chains, initiating the oxidation of UHMWPE artificial joints. These findings not only provide evidence for comprehending the process of squalene-induced UHMWPE oxidation but also are instructive to develop highly oxidative-resistant UHMWPE.

Three-dimensional (3D)-printed scaffolds have great advantages for bone repair, and the combination of physical and chemical modifications of the surface can improve deficient biological properties to promote bone regeneration. In this study, a nanotopological morphology and an amino group were introduced into scaffold surfaces in sequence by alkaline solution and amination, respectively. The surface properties and the ability for osteogenic induction were investigated. The nanotopological morphology of the surface slightly enhanced the hydrophilic property of the material, while amination obviously increased the hydrophilicity of the surface. The aminated surface improved cell adhesion and proliferation, while the nanotopological morphology was able to facilitate the spread of stem cells, pseudopod extension, and osteogenic differentiation by changing the cell skeleton. The study confirmed that a nanotopological morphology and an amino group can play synergistic roles in improving the osteogenic efficiency and hydrophilicity, which was also confirmed in vivo by showing that effective surface modification of polylactic acid scaffolds enhanced high-quality bone formation, thus demonstrating great potential for clinical applications. The results indicate that scaffolds with the synergy of a nanotopological morphology and amino modification improve the osteogenic induction ability of scaffolds.

Mucosa is a protective and lubricating barrier in biological tissue, which has a great clinical inspiration because of its slippery, soft, and hydrophilic surface. However, mimicking mucosal traits on complex surface remains an enormous challenge. Herein, a novel approach to create mucosa-like conformal hydrogel coating is developed. A thin conformal hydrogel layer mimicking the epithelial layer is obtained by first absorbing micelles, followed by forming covalent interlinks with the polymer substrate via interface-initiated hydrogel polymerization. The resulting coating exhibits uniform thickness (≈15 µm), mucosa-matched compliance (Young's modulus = 1.1 ± 0.1 kPa) and lubrication (coefficients of friction = 0.018 ± 0.003), robust interfacial bonding against peeling (peeling strength = 1218.0 ± 187.9 J m

The correlation between aggregates and bound rubber structures in silicone rubbers (S(phr)) with various silica fractions (ΦSi) has been investigated by contrast matching small-angle neutron scattering (SANS), swelling kinetics, and low-field nuclear magnetic resonance (NMR). Mixed solvents with deuterated cyclohexane fractions of 4.9% and 53.7% were chosen to match the scattering length densities of the matrix (SMP(phr)) and the filler (SMS(phr)), respectively. All the data consistently suggest that: (i) There is a critical threshold ΦSic between 10 and 30 phr; below Φsic, the isolated aggregates are dominant, while beyond Φsic, some rubber fraction is trapped among the agglomerate; (ii) Φsr-independent thicknesses around 7.5 nm (NMR) and 8.6 nm (SANS) suggest that the bound rubber formation is determined by inherent properties of the components, and the power-law around 4.2 suggests an exponential changed gradient density of the bound rubber; (iii) SMS(80) presents a bicontinuous bound rubber with three characteristic lengths of 41, 100, and 234 nm. The expanded correlation length, a 20 nm smaller aggregate sizes suggest that such existent bicontinuous network in dry samples with less ΦSi is kind of impacted by swelling. With the obtained bound rubber models, the reinforcing mechanism of filled silicone rubber is elucidated.

With the world’s focus on environmental and sustainability problems, bio-based polymer porous materials have achieved tremendous attention. Here, light weight and biodegradable cellulose/polylactic acid (PLA) porous biocomposites with outstanding mechanical and heat resistance properties are fabricated based on a novel template-directed strategy. The cellulose/PLA porous biocomposites exhibit densities as low as 0.09 g/cm3 and specific moduli as high as 288.9 MPa g−1 cm3. More importantly, the biocomposites possess a high service temperature of 221.3 °C after a thermal treatment, ascribing to the exclusive formation of stereocomplex crystals (SCs) in PLA with a high crystallinity of 0.5. In situ wide-angle X-ray diffraction observations reveal that cellulose templates significantly accelerate the nucleation of SCs without suppressing the growth, and thus greatly facilitate SC crystallization. The stimulation of SC nucleation lies in the interfacial hydrogen bonding interactions between cellulose templates and PLA molecules, which promote the formation of precursor racemic helical pairs. The current work provides further inspiration on fabricating bio-based polymer porous materials in a greener and more sustainable way.

We report a facile means to engineer oriented surface topology of poly(e-caprolactone) (PCL) via homoepitaxial crystallization. It involved uniaxially stretching the PCL substrate, immersing the un...

Manipulation of the conductive network is essential for the electromagnetic interference (EMI) shielding performance of conductive polymer composites, which have broad application prospects to address the concerns of electromagnetic pollution emitted by modern electronics. In this work, the oriented segregated structure was achieved in carbon nanotube (CNT)/ultrahigh molecular weight polyethylene (UHMWPE) composites via solid-phase stretching and the orientation of segregated network was controlled by adopting different draw ratios. Benefiting from the unique oriented segregated structure, the composites delivered prominent EMI shielding performance with intriguing frequency selectivity, which did not occur in conventional segregated composites. Moreover, remarkable mechanical reinforcement was obtained in the oriented segregated composites, which was attributed to the interfacial crystallization along segregated pathways and the formation of highly oriented lamellae. At a draw ratio of 6, the oriented segregated composite with 2 wt% CNTs showed the maximum EMI shielding effectiveness of 33.5 dB and tensile strength of 216.1 MPa, which surpassed the conventional segregated composite by 69.2% and 455.5%, respectively. This effort demonstrates a simple, feasible, and effective approach for the design and fabrication of mechanically robust, bandwidth-selective EMI shielding composites.

Biomimetic modification of hydroxyapatite on a polymer surface is a potent strategy for activating biological functions in bone tissue engineering applications. However, the polymer surface is bioinert, and it is difficult to introduce a uniform calcium phosphate (CaP) layer. To overcome this limitation, we constructed a specific nano-topographical structure onto a poly(e-caprolactone) substrate via surface-directed epitaxial crystallization. Formation of the CaP layer on the nano-topological surface was enhanced by 2.34-fold compared to that on a smooth surface. This effect was attributed to the abundant crystallization sites for CaP deposition because of the increased surface area and roughness. Bone marrow mesenchymal stromal cells (BMSCs) were used to examine the biological effect of biomineralized surfaces. We clearly demonstrated that BMSCs responded to surface biomineralization. Osteogenic differentiation and proliferation of BMSCs were significantly promoted on the biomineralized nano-topological surface. The expression of alkaline phosphatase and osteogenic-related genes as well as extracellular matrix mineralization was significantly enhanced. The proposed strategy shows potential for designing bone repair scaffolds.

The biology of immediate post-extraction implant osseointegration is mediated by a coordinated cascade of osteoblast-osteoclast interactions. The aim of this study was to develop a dual-delivery system that allowed sequential release of substance P (SP) to promote bone regeneration and alendronate (ALN) to reduce bone resorption, which will improve the implant osseointegration. We used coaxial electrospinning to fabricate the core-shell poly lactic-co-glycolic acid (PLGA)/gelatin nanofibers, which consists of SP in the shell and ALN in the core. This programmed delivery system was shown to release SP and ALN sequentially to match the spatio-temporal specificity of bone healing. The migration assay demonstrated that the SP-ALN dual-delivery system increased bone marrow mesenchymal stem cells (BMSCs) transmigration. Besides, the expression of osteogenic/osteoclastic markers, Alizarin Red staining, tartrate-resistant acid phosphatase (TRAP) staining, F-actin staining and bone resorption experiment showed that the dual-delivery system can render a microenvironment favorable for osteogenic differentiation and adverse to osteoclastogenesis. Using a rat immediate implant model, we validated the promoted osteogenic property and osseointegration around the implants of SP-ALN dual-delivery system by micro-computed tomography (micro-CT) and histological analysis. These findings suggest that the dual-delivery system with time-controlled release of SP and ALN by core-shell nanofibers provides a promising strategy to facilitate immediate implant osseointegration through favorable osteogenesis. STATEMENT OF SIGNIFICANCE: Immediate implant placement is potentially challenged by the difficulties in achieving primary implant stability and early osteogenesis. Initial period of osteointegration is regulated by osteoblastic/osteoclastic cells resulting in a coordinated healing process. To have an efficient bone regeneration, the coaxial electrospinning was used to fabricate a programmed dual-delivery system. The SP released rapidly and favored for BMSCs migration and osteogenic differentiation, while the sustained release of ALN can reduce the bone resorption. The rat immediate implant model indicated that the SP-ALN dual-delivery system could present the promoted peri‑implant osteogenic property and osseointegration through modulating the osteogenesis-osteoclastogenesis balance. This work highlights the sequential dual delivery of SP and ALN has a promising potential of achieving enhanced osseointegration for immediate implant placement.

Unique banded cylindrites of polyoxymethylene/poly(butylene succinate) blends were induced by the intense interfacial shear, which was applied by pulling a single glass fiber (GF) with non-nucleation ability. The crystalline morphology and structure of banded cylindrites were quantitively correlated with the shear rates to provide revealing insights in shear-induced nucleation and lamellar assembly. Densely packed row-nuclei emerged on the surface of pulled GF and the nucleation density increased dramatically with the shear rate. The subsequent lamellar extension and twisting were restricted perpendicularly to the GF axis, resulting in the formation of banded cylindrites. As the shear rate increased, the band spacing showed a linear decrease and the eccentricity of elliptical bands showed a linear increase. It was attributed to the augment of unbalanced surface stress caused by steric hindrance of serried nuclei. While the growth rate of banded cylindrites remained constant regardless of the shear rate, s...

Polylactide (PLA) films with an excellent balance of toughness and stiffness were realized by extensional stress efficiently. For the relatively low extensional stress, gauche–gauche conformers tha...

Simultaneous existence of topographic and chemical cues on the polymeric surface was demonstrated to be a valid route to accelerate osteoblast differentiation. Herein, nanotopographical pattern and bioactive components were sequentially introduced onto the poly( l -lactic acid) (PLLA) surface via etching treatment followed by mussel-inspired polydopamine (PDA) coating. The PLLA nanolamellae were formed on nanotopographical surface with the roughness of 62.0 nm by extracting the amorphous phase of annealed PLLA. Subsequently, uniform PDA decoration was obtained on the etched surface without changing the surface roughness via dopamine self-polymerization. In vitro cell culture revealed that the combination of nanolamellae and PDA decoration showed more significant promotion of cell viability, alkaline phosphatase activity, osteopontin, and collagen type I expression than only using nanolamellae or PDA decoration. The enhanced osteoblast differentiation was mediated by the integrin β1 signaling pathway. Our proposed approach opens a simple, universal, and promising gateway to construct polymeric surface with comprehensive cues for enhancing osteogenic differentiation.

Surface function has an importance for the bioactivity of porous polymeric scaffolds. The goal of the present study is to immobilize highly bioactive chitosan (CS) onto the surface of porous composite scaffolds to accelerate bone regeneration. Porous poly(ε-caprolactone) (PCL)/bioactive glass (BG) composite scaffolds with strong anchor of CS were fabricated via mussel-inspired polydopamine (PDA) coating as a bridging layer. In vitro cell culture showed that firm immobilization of CS onto the composite scaffolds significantly enhanced protein adsorption, cell adhesion, and osteogenic differentiation compared to CS-decorated scaffolds via physical adsorption. In vivo assessments demonstrated that covalent immobilization of CS onto the surface of scaffolds obviously promoted cranial bone regeneration in comparison with the counterparts with physical adsorption of CS. The proposed method offers a feasible and effective means to fabricate artificial bioactive scaffolds for bone tissue engineering application.

BACKGROUND: Synovial fluid components, especially lipids, can trigger oxidation of ultrahigh-molecular-weight polyethylene (UHMWPE) artificial joint components in vivo. The use of antioxidants such as vitamin E effectively diminishes the oxidative cascade by capturing free radicals and reducing the oxidation potential of UHMWPE implants. Using a thermo-oxidative aging method, we recently found that tea polyphenols can enhance the oxidation resistance of irradiated UHMWPE in comparison with commercial vitamin E. However, it is yet unknown whether tea polyphenols can reduce lipid-induced oxidation. QUESTIONS/PURPOSES: We explored whether tea polyphenol-stabilized UHMWPE would exhibit (1) lower squalene absorption; (2) stronger oxidation resistance; and (3) lower content of free radicals than vitamin E-stabilized UHMWPE under a physiologically-motivated in vitro accelerated-aging model. METHODS: Tea polyphenol (lipid-soluble epigallocatechin gallate [lsEGCG]) and vitamin E were blended with UHMWPE powders followed by compression molding and electron beam irradiation at 100 and 150 kGy. Small cubes (n = 3, 60 mg, 4 × 4 × 4 mm(3)) cut from the blocks were doped in squalene at 60°, 80°, 100°, and 120° C for 2 hours. Gravimetric change of the cubes after squalene immersion was measured to assess absorption. Thin films (n = 3, ∼60 μm) were also microtomed from the blocks and were doped at 120° C for 24 hours. Oxidation induction time (n = 3, 5 mg of material from the cubes) and incipient oxidation temperature (n = 3, thin films) were obtained to determine the oxidation stability. Signal intensity of the free radicals, obtained by electron spin resonance spectroscopy, was used to qualitatively rank the antioxidant ability of vitamin E and lsEGCG. RESULTS: Squalene absorption was comparable between lsEGCG/UHMWPE and vitamin E/UHMWPE at a given temperature and radiation dose. The oxidation induction time of 100 kGy-irradiated UHMWPE was increased with lsEGCG compared with vitamin E except at 120° C. For example, the oxidation induction time value of 100 kGy-irradiated lsEGCG/UHMWPE immersed at 60(o) C was 25.3 minutes (24.2–27.8 minutes), which was 8.3 minutes longer than that of 100 kGy-irradiated vitamin E/UHMWPE which was 17.0 minutes (15.0–17.1 minutes) (p = 0.040). After squalene immersion at 120° C, the incipient oxidation temperature of 100 and 150 kGy irradiated lsEGCG/UHMWPE was 234° C (227–240° C) and 227° C (225–229° C), which was higher than vitamin E-stabilized counterparts with value of 217° C (214–229° C; p = 0.095) and 216° C (207–218° C; p = 0.040), respectively. The electron spin resonance signal of 150 kGy irradiated lsEGCG/UHMWPE was qualitatively weaker than that of 150 kGy irradiated vitamin E/UHMWPE. CONCLUSIONS: lsEGCG-stabilized UHMWPE demonstrated higher oxidation resistance than vitamin E-stabilized UHMWPE after squalene immersion, likely because lsEGCG donates more protons to eliminate macroradicals than vitamin E. CLINICAL RELEVANCE: Our in vitro findings provide support that lsEGCG may be effective in protecting against oxidation that may be associated with synovial fluid-associated oxidation of highly crosslinked UHMWPE joint replacement components.

It is an effective strategy to improve the heat resistance of polylactide (PLA) via forming stereocomplex crystals (SCs) in poly( l -lactide) (PLLA)/poly( d -lactide) (PDLA) blend. In this work, pentearythritol (PENTA), which is an environment-friendly polyhydroxy compound for food packaging, is selected to facilitate the SC crystallization and suppress the HC crystallization for HMW PLLA/PDLA blend. Impressively, only 3 wt% PENTA is added, the exclusive SCs with high content (Xc,SC = 50%) can be obtained, which exhibits a high promotion efficiency of crystallization of SCs. Interestingly, with PENTA content ascending, the crystallinity of SCs increases drastically first and then in a relatively slow manner. Furthermore, Miscibility with high content of PENTA leads to a relatively looser packing of SC lamella in the blend confirmed by scanning electron microscope (SEM) due to intercalation of PENTA between crystal lamella. The mechanism of how PENTA facilitates the formation of SCs at molecular level is also proposed in this work.

Despite being currently state-of-the-art to prevent the oxidation of irradiated ultrahigh molecular weight polyethylene (UHMWPE) bearings, vitamin E (VE) poses concerns in the loss of cross-linking efficiency and is limited to be used at very low concentrations. It thus emphasizes the urgent demand for more efficient stabilizers. In this study, oxidation stability of highly cross-linked UHMWPE was demonstrated to be enhanced by tea polyphenols, such as lipid-soluble tea polyphenols (lsPPT), epigallocatechin gallate (EGCG), and lipid-soluble epigallocatechin gallate (lsEGCG). These antioxidants were blended with UHMWPE granules and consolidated by compression molding prior to E-beam irradiation. The presence of tea polyphenols substantially prolonged oxidation induction time of the irradiated UHMWPE before and after accelerated aging. Especially, lsEGCG was significantly superior to VE in terms of stabilizing capacity. Explained by the hydrogen donation mechanism, tea polyphenols with multiple phenolic hydroxyls could scavenge more radiation-induced free radicals than VE with only one phenolic hydroxyl, which was verified by the electron spin resonance spectra. Intriguingly, tea polyphenols showed less inhibitive effect on the cross-link density of irradiated UHMWPE than VE. Besides, there is no significant difference in crystallinity, mechanical performance as well as in vitro biocompatibility between the irradiated UHMWPE stabilized by tea polyphenols and VE. These findings highlight tea polyphenols, especially lsEGCG, are promising alternatives to extend the life span of UHMWPE implants.

Personal cooling technologies (PCTs) locally control the temperature of an individual instead of a whole building and are thus energy saving. However, most PCTs still consume energy and are heavy in weight, restricting their application among human beings. To achieve personal thermal comfort and no energy consumption on hot summer days, we designed a bilayer structure fabric with high thermal comfort by increasing the dissipation of human thermal radiation and reducing solar energy absorption simultaneously. The fabric consisted of two layers, including a polyethylene film with nanopores (100-1000 nm in pore size) and a film made of nylon 6 nanofibers (ca. 100 nm in diameter) with beads (ca. 230 nm in diameter), which could increase the visible light reflectance but not affect the infrared wave radiation. Therefore, the designed fabric showed a high heat dissipation power, which was 14.13, 17.93, and 17.93 W/m2 higher than that of the selected traditional textiles of cotton, linen, and odile, respectively, suggesting good cooling capability. Its cooling performance was better than those reported by the previous research works even at a higher ambient temperature. Meanwhile, the moisture penetrability and hygroscopic property results indicated that the wearing comfort of the designed fabric reached the levels of the selected traditional textiles.

For the first time, the influences of two inevitable processing fields (pressure and flow fields) on the crystallization of a semirigid molecular chain polymer, that is, poly(l-lactic acid) (PLLA), were explored using a homemade pressuring and shearing device. The results reveal that the shear rate facilitated the generation of precursor because it induced oriented segment formation. It was found that the most sensitive shear temperature for the generation of PLLA precursor under 100 MPa was 180 °C. When the shear temperature was higher (e.g., 190 °C), the relaxation of shear-induced oriented segments was too quick to induce the generation of PLLA precursor. Oppositely, at a lower shear temperature (170 °C), the oriented segments were hard to relax within the whole shear rate range (3.1-31.4 s-1). Annealing treatment was infaust to the PLLA precursor formation because it promoted the relaxation of oriented segments. Different from the shear and annealing, pressure played a more complicated role in the formation of PLLA precursor. Pressure decreased the free volume between PLLA molecular chains and meantime increased the supercooling of PLLA melt. In addition, PLLA chains tended to form locally oriented segment bundles to adapt to the pressurized state, which facilitated the formation of PLLA precursor and the following crystallization process. These two factors lowered the movability of PLLA chains and suppressed the relaxation of chain, so shear-induced orientation facilitated PLLA precursor formation under pressure. In that case, pressure and shear flow showed a synergetic promoting effect on the generation of PLLA precursor and the following crystallization process. These meaningful results could be helpful for comprehending the relationship between crystallization conditions and the crystallization behavior of PLLA and thus would provide guidance to fabricating the final products through controlling the crystallization process of PLLA.

Thermal conductivity of drawn polyethylene (PE) fibers has been extensively studied, while thermal conductivity for the stretched PE sheets still remains unknown. In addition, no consensus conclusions have been reached on the thermal conduction mechanisms for drawn PE. In this work, melt processed PE sheets are subjected to uniaxial stretching under different stretch ratios. The in-plane and out-of-plane thermal conductivity of stretched PE has been measured and the crystalline structure has been analyzed through 2-dimensional wide-angle X-ray diffraction (2D-WAXD) and scanning electron microscopy (SEM). Results show that both in-plane and out-of-plane thermal conductivities of stretched PE increase with increasing stretch ratios. The enhancement of thermal conductivity has been ascribed to the formation of interlocking shish-kebab superstructures induced by the stretching process. A new model is proposed to demonstrate the thermal conductivity improvement seen for the uniaxial-stretched PE. To the best of our knowledge, it is the first time that the mechanisms of thermal conductive enhancement were revealed for uniaxially stretched semi-crystalline PE sheet along with the understanding of the associated process-structure-property relationship. This work may provide key information towards design and manufacturing of polymer-based materials for thermal management applications.

Conductive polymer composites (CPCs) with segregated structure exhibit outstanding electromagnetic interference (EMI) shielding performance at low filler loadings. However, the mechanical performance is compromised due to poor interfacial adhesion resulting from the selective distribution of conductive fillers. Herein, a simple and effective approach, i.e. solid-phase extrusion (SPE), was proposed to fabricate segregated carbon nanotube (CNT)/poly(vinylidene fluoride) composites with high mechanical performance. Morphology examination revealed that both the matrix and segregated conductive network were highly oriented along the extrusion direction under the forceful flow field of SPE. The resultant SPE composites showed an excellent electrical conductivity of 74.5 S/m and a high EMI shielding effectiveness of 36.8 dB with only 4 wt% CNTs. More notably, simultaneous enhancement of the strength and fracture toughness was achieved. Compared to the counterparts with conventional segregated structure, tensile strength and elongation at break of SPE composites were significantly increased by ∼100% and ∼900%, reaching 120–140 MPa and 60%, respectively. This work demonstrates a valuable approach to prepare high-performance CPCs for EMI shielding applications.

Piezoelectric polymers hold great potential for various electromechanical applications, but only show low performance, with |d33 | < 30 pC/N. We prepare a highly piezoelectric polymer (d33 = −62 pC/N) based on a biaxially oriented poly(vinylidene fluoride) (BOPVDF, crystallinity = 0.52). After unidirectional poling, macroscopically aligned samples with pure β crystals are achieved, which show a high spontaneous polarization (Ps) of 140 mC/m2. Given the theoretical limit of Ps,β = 188 mC/m2 for the neat β crystal, the high Ps cannot be explained by the crystalline-amorphous two-phase model (i.e., Ps,β = 270 mC/m2). Instead, we deduce that a significant amount (at least 0.25) of an oriented amorphous fraction (OAF) must be present between these two phases. Experimental data suggest that the mobile OAF resulted in the negative and high d33 for the poled BOPVDF. The plausibility of this conclusion is supported by molecular dynamics simulations., Piezoelectric polymers usually have rather low piezoelectric coefficients less than 30 pC/N. Here, the authors achieve a highly piezoelectric polymer (d33 = −62 pC/N) based on a poled biaxially oriented poly(vinylidene fluoride) with a pure β phase due to the mobile oriented amorphous fraction.

An ideal bone substitute requires not only high bioactivity but also sufficient mechanical performance, which is however inaccessible due to the lack of rational structure and composition design. Here, bioactive glass (BG)/hydroxyapatite (HA)/polyethylene (PE) composites with bone-like structure were prepared via a structuring injection molding. The strong and reciprocating shear field offered by the modified injection molding induced plenty of interlocked shish kebabs, mimicking the aligned collagen fibers in the natural bone. Such a bone-like structure enhanced the strength and toughness of the BG/HA/PE composites simultaneously, compensating the mechanical loss caused by the presence of BG. In vitro cell culture assays demonstrated that the combination of BG and HA significantly promoted cell attachment, proliferation, and alkaline phosphatase activity compared to the use of HA alone. It was attributed to upregulated expression of β-catenin stimulated by BG. The mineralization in simulated body fluid r...

Highly crosslinked ultrahigh-molecular-weight polyethylene (UHMWPE) bearings are wear-resistant to reduce aseptic loosening but are susceptible to oxidize in vivo/in vitro, as reported in clinical studies. Despite widespread acceptance of antioxidants in preventing oxidation, the crosslinking efficiency of UHMWPE is severely impacted by antioxidants, the use of which was trapped in a trace amount. Herein, we proposed a new strategy of polyphenol-assisted chemical crosslinking to facilitate the formation of a crosslinking network in high-loaded tea polyphenol/UHMWPE blends. Epigallocatechin gallate (EGCG), a representative of tea polyphenol, was mixed with UHMWPE and peroxide. Multiple reactive phenolic hydroxyl groups of tea polyphenol coupled with the nearby free radicals to form extra crosslinking sites. The crosslinking efficiency was remarkably enhanced with increasing tea polyphenol content, even at a concentration of 8 wt %. Given by the hydrogen donation principle, the high-loaded tea polyphenol also enhanced the oxidation stability of the crosslinked UHMWPE. The antioxidative performance was preserved even after tea polyphenol elution. Moreover, superior antibacterial performance was achieved by the in situ tea polyphenol release from the interconnected pathways in the present design. The strategy of polyphenol-assisted chemical crosslinking is applicable for producing highly crosslinked, antioxidative, and antibacterial UHMWPE, which has promising prospects in clinical applications.

Oxidative stability of radiation crosslinked ultrahigh molecular weight polyethylene (UHMWPE) artificial joints is significantly improved by vitamin E (VE), but there is a dilemma that VE hinders crosslinking and thus jeopardizes the wear of UHMWPE. In this effort, we proposed an efficient strategy to stabilize UHMWPE under limited antioxidant contents, where VE and D-sorbitol (DS) were used as the primary antioxidant and the secondary antioxidant respectively. For non-irradiated blends with fixed antioxidant contents, oxidative stability accessed by oxidation induction time (OIT) of VE/DS/UHMWPE blends was superior to that of VE/UHMWPE blends, while DS/UHMWPE blends showed no increase in OIT. The cooperation between DS and VE exhibited a synergistic effect on enhancing the oxidative stability of UHMWPE. Interestingly, the irradiated VE/DS/UHMWPE blends showed comparable OIT but a significantly higher crosslink density than the irradiated VE/UHMWPE blends. The crystallinity, melting point, and in vitro biocompatibility of the blends were not affected by VE and DS. The quantitative relationships of mechanical properties, oxidation stability, crystallinity and crosslink density were established to unveil the correlation of these key factors. The overall properties of VE/UHMWPE and VE/DS/UHMWPE blends were compared to elucidate the superiority of the antioxidant compounding strategy. These findings provide a paradigm to break the trade-off between oxidative stability, crosslink density and mechanical properties, which is constructive to develop UHMWPE bearings with upgraded performance for total joint replacements. STATEMENT OF SIGNIFICANCE: VE-stabilized UHMWPE is the most commonly used material in total joint replacements at present. However, oxidation and wear resistance of VE/UHMWPE implants cannot be unified since VE reduces the efficiency of radiation crosslinking. It limits the use of VE. Herein, we proposed a compounding stabilization by the synergy between VE and DS. The antioxidation capability of VE was revived by DS, thus enhancing the oxidation stability of unirradiated UHMWPE. The irradiated VE/DS/UHMWPE exhibited similar oxidation stability but higher crosslink density than irradiated VE/UHMWPE, which is beneficial to combat wear of UHMWPE and to inhibit the occurrence of osteolysis. This synergistic antioxidation strategy endows the UHMWPE joint material with good overall performance, which is of clinical significance.

Periprosthetic joint infection (PJI) is one of the main causes for the failure of joint arthroplasty. In view of the limited clinical effect of oral/injectable antibiotics and the drug resistance problem, there is a pressing need to develop antibacterial implants with therapeutic antimicrobial properties. In this work, we prepared a highly antibacterial ultrahigh molecular weight polyethylene (UHMWPE) implant by incorporating tea polyphenols. The presence of tea polyphenols not only improved the oxidation stability of irradiated UHMWPE, but also gave it the desirable antibacterial property. The potent antibacterial activity was attributed to the tea polyphenols that produced excess intracellular reactive oxygen species and destroyed the bacterial membrane structure. The tea polyphenol-blended UHMWPE had no biological toxicity to human adipose-derived stem cells and effectively reduced bacteria-induced inflammation in vivo. These results indicate that tea polyphenol-blended UHMWPE is promising for joint replacement prostheses with multifunctionality to meet patient satisfaction.

Endotracheal intubation is a crucial procedure for mechanical ventilation and respiratory support therapy. However, friction mismatch between the tube material and tissues often causes complications, such as laryngopharyngeal airway mucosa injury, tracheal granuloma, and inflammatory reaction. In this work, a highly lubricated coating was designed and applied on the tracheal tube. Hyaluronic acid (HA) and triblock copolymer (Pluronic F127) were co-deposited on the surface-activated tube to form a hydration layer through intermolecular interaction. The coating exhibited high artificial saliva adsorption ratio and water-retention rate, providing excellent lubrication to the tube. The friction coefficient of the coated tube in artificial saliva was 77% less than that observed for the original tube. The efficacy of the lubricated coating on endotracheal intubation was assessed in vivo by using a cynomolgus monkey model. The coating was demonstrated to be effective to alleviate the injury caused by endotracheal intubation.