Ocean acidification alters properties of the exoskeleton in adult Tanner crabs, Chionoecetes bairdi.

Ocean acidification can affect the ability of calcifying organisms to build and maintain mineralized tissue. In decapod crustaceans, the exoskeleton is a multilayered structure composed of chitin, protein and mineral, predominately magnesian calcite or amorphous calcium carbonate (ACC). We investigated the effects of acidification on the exoskeleton of mature (post-terminal-molt) female southern Tanner crabs, Chionoecetes bairdi Crabs were exposed to one of three pH levels - 8.1, 7.8 or 7.5 - for 2 years. Reduced pH led to a suite of body region-specific effects on the exoskeleton. Microhardness of the claw was 38% lower in crabs at pH 7.5 compared with those at pH 8.1, but carapace microhardness was unaffected by pH. In contrast, reduced pH altered elemental content in the carapace (reduced calcium, increased magnesium), but not the claw. Diminished structural integrity and thinning of the exoskeleton were observed at reduced pH in both body regions; internal erosion of the carapace was present in most crabs at pH 7.5, and the claws of these crabs showed substantial external erosion, with tooth-like denticles nearly or completely worn away. Using infrared spectroscopy, we observed a shift in the phase of calcium carbonate present in the carapace of pH 7.5 crabs: a mix of ACC and calcite was found in the carapace of crabs at pH 8.1, whereas the bulk of calcium carbonate had transformed to calcite in pH 7.5 crabs. With limited capacity for repair, the exoskeleton of long-lived crabs that undergo a terminal molt, such as C. bairdi, may be especially susceptible to ocean acidification.

Engineering Nitroxide Functional Surfaces Using Bioinspired Adhesion.

We pioneer a versatile surface modification strategy based on mussel-inspired oxidative catecholamine polymerization for the design of nitroxide-containing thin polymer films. A 3,4-dihydroxy-l-phenylalanine (l-DOPA) monomer equipped with a 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO)-derived oxidation-labile hydroxylamine functional group is employed as a universal coating agent to generate polymer scaffolds with persistent radical character. Various types of materials including silicon, titanium, ceramic alumina, and inert poly(tetrafluoroethylene) (PTFE) were successfully coated with poly(DOPA-TEMPO) thin films in a one-step dip-coating procedure under aerobic, slightly alkaline (pH 8.5) conditions. Steadily growing polymer films (∼1.1 nm h-1) were monitored by ellipsometry, and their thicknesses were critically compared with those obtained from atomic force microscopic cross-sectional profiles. The heterogeneous composition of surface-adherent nitroxide scaffolds examined by X-ray photoelectron spectroscopy was correlated to that examined by in-solution polymer analysis via high-resolution electrospray ionization mass spectrometry, revealing oligomeric structures with up to six repeating units, mainly composed of covalently linked dihydroxyindole along the polymer backbone. Critically, the reversible redox-active character of the nitroxide-containing polymer scaffolds was investigated by cyclic voltammetric measurements, revealing a convenient and facile access route to electrochemically active nitroxide polymer coatings with potential application in electronic devices such as organic radical batteries.

Liposomal drug delivery strategies to eradicate bacterial biofilms: Challenges, recent advances, and future perspectives.

Typical antibiotic treatments are often ineffectual against biofilm-related infections since bacteria residing within biofilms have developed various mechanisms to resist antibiotics. To overcome these limitations, antimicrobial-loaded liposomal nanoparticles are a promising anti-biofilm strategy as they have demonstrated improved antibiotic delivery and eradication of bacteria residing in biofilms. Antibiotic-loaded liposomal nanoparticles revealed remarkably higher antibacterial and anti-biofilm activities than free drugs in experimental settings. Moreover, liposomal nanoparticles can be used efficaciously for the combinational delivery of antibiotics and other antimicrobial compounds/peptide which facilitate, for instance, significant breakdown of the biofilm matrix, increased bacterial elimination from biofilms and depletion of metabolic activity of various pathogens. Drug-loaded liposomes have mitigated recurrent infections and are considered a promising tool to address challenges associated to antibiotic resistance. Furthermore, it has been demonstrated that surface charge and polyethylene glycol modification of liposomes have a notable impact on their antibacterial biofilm activity. Future investigations should tackle the persistent hurdles associated with development of safe and effective liposomes for clinical application and investigate novel antibacterial treatments, including CRISPR-Cas gene editing, natural compounds, phages, and nano-mediated approaches. Herein, we emphasize the significance of liposomes in inhibition and eradication of various bacterial biofilms, their challenges, recent advances, and future perspectives.

Mechanical Resistance in Decapod Claw Denticles: Contribution of Structure and Composition.

The decapod crustacean exoskeleton is a multi-layered structure composed of chitin-protein fibers embedded with calcium salts. Decapod claws display tooth-like denticles, which come into direct contact with predators and prey. They are subjected to more regular and intense mechanical stress than other parts of the exoskeleton and therefore must be especially resistant to wear and abrasion. Here, we characterized denticle properties in five decapod species. Dactyls from three brachyuran crabs (Cancer borealis, Callinectes sapidus, and Chionoecetes opilio) and two anomuran crabs (Paralomis birsteini and Paralithodes camtschaticus) were sectioned normal to the contact surface of the denticle, revealing the interior of the denticle and the bulk endocuticle in which it is embedded. Microhardness, micro- and ultrastructure, and elemental composition were assessed along a transect running the width of the cuticle using microindentation hardness testing, optical and scanning electron microscopy (SEM), and energy dispersive X-ray spectroscopy (EDS), respectively. In all species tested, hardness was dramatically higher-up to ten times-in the denticle than in the bulk endocuticle. Likewise, in all species there was an increase in packing density of mineralized chitin-protein fibers, a decrease in width of the pore canals that run through the cuticle, and a decrease in phosphorous content from endocuticle to denticle. The changes in hardness across the cuticle, and the relationship between hardness, calcium, and magnesium content, however, varied among species. Although mechanical resistance of the denticles was exceptionally high in all species, the basis for resistance appears to differ among species. STATEMENT OF SIGNIFICANCE: Understanding the diverse mechanisms by which animals attain exceptionally high mechanical resistance may enable development of novel, biologically inspired materials. Decapod crustacean claws, and particularly the tooth-like denticles that these claws display, are of interest in this regard, as they must be especially resistant to wear. We assessed mechanical, elemental, and structural properties of the claw cuticle in five decapod species. Without exception, microhardness was dramatically higher in the denticle than in the bulk endocuticle. Multivariant statistical analyses, however, showed that the relationships among microhardness, elemental content, and structural variables differed among species. Such patterns likely result from strong evolutionary pressure on feeding and defensive structures and a trade-off between mechanical properties and energetic cost of exoskeleton formation.

The sea urchin Paracentrotus lividus as a bioeroder of plastic.

It is increasingly recognised that plastic pollution of the marine environment is highly dynamic in nature. Larger plastic items are fragmented or eroded into smaller and smaller pieces as its moves through marine ecosystems and small particles can be fouled or flocculate into larger aggregates. Whilst physical processes play a major part in photo- and oxidative degradation of plastic debris, biological process may also contribute to the breakdown of larger plastic items into smaller particulates, yet this has not been studied well to date. Here, we demonstrate the potential for the sea urchin Paracentrotus lividus to act as bioeroders of macroplastics. We found that urchins readily graze on a plastic surface, with this grazing activity generating microplastics, when held in experimental systems together. On average each urchin produced 91.7 (±33.8 pieces) smaller plastic pieces (118-15,797 µm) from one macroplastic item over a ten day period. This plastic fragmentation by the urchins grazing activity was strongly influenced by the additional availability of natural food and by the presence of fouling of the macroplastic surface. Fragmentation of macroplastic by urchins dropped by 97% when urchins were exposed to virgin plastic in the presence of natural food (kelp). However, when macroplastic was biofouled urchins acted to fragment this plastic irrespective of the presence of additional food. The majority of fragments produced were negatively buoyant due to both the biofouling process and indeed the fouling by faecal matter, sinking to the bottom of the exposure systems. This smaller size range of plastic would then bioavailable to a much wider suite of species than the original macroplastic item; hence this bioerosion process has the potential to contribute to the transfer plastic fragments through benthic food webs.

Compressive cyclic ratcheting and fatigue of synthetic, soft biomedical polymers in solution.

The use of soft, synthetic materials for the replacement of soft, load-bearing tissues has been largely unsuccessful due to a lack of materials with sufficient fatigue and wear properties, as well as a lack of fundamental understanding on the relationship between material structure and behavior under cyclic loads. In this study, we investigated the response of several soft, biomedical polymers to cyclic compressive stresses under aqueous conditions and utilized dynamic mechanical analysis and differential scanning calorimetry to evaluate the role of thermo-mechanical transitions on such behavior. Studied materials include: polycarbonate urethane, polydimethylsiloxane, four acrylate copolymers with systematically varied thermo-mechanical transitions, as well as bovine meniscal tissue for comparison. Materials showed compressive moduli between 2.3 and 1900MPa, with polycarbonate urethane (27.3MPa) matching closest to meniscal tissue (37.0MPa), and also demonstrated a variety of thermo-mechanical transition behaviors. Cyclic testing resulted in distinct fatigue-life curves, with failure defined as either classic fatigue fracture or a defined increased in maximum strain due to ratcheting. Our study found that polymers with sufficient dissipation mechanisms at the testing temperature, as evidenced by tan delta values, were generally tougher than those with less dissipation and exhibited ratcheting rather than fatigue fracture much like meniscal tissue. Strain recovery tests indicated that, for some toughened polymers, the residual strain following our cyclic loading protocol could be fully recovered. The similarity in ratcheting behavior, and lack of fatigue fracture, between the meniscal tissue and toughened polymers indicates that such polymers may have potential as artificial soft tissue.

Anterior cruciate ligament fixation: is radial force a predictor of the pullout strength of soft-tissue interference devices?

BACKGROUND: In anterior cruciate ligament (ACL) reconstruction, an interference device achieves soft-tissue graft fixation by radially compressing the graft against the bone. PURPOSE: The objective of this study was to measure the radial force generated by different interference devices and evaluate the effect of this radial force on the pullout strength of graft-device constructs. STUDY DESIGN: Controlled laboratory study. METHODS: A resultant force (F(R)) was used as a representative measure of the total radial force generated. Bovine tendons were fixated in either synthetic bone or porcine tibia using one of following devices: (1) RCI titanium screw, (2) PEEK screw, (3) IntraFix sheath-and-screw device, and (4) ExoShape sheath-and-insert device. F(R) was measured while each device was inserted into synthetic bone mounted on a test machine (n=5 for each device). In a subsequent test series, graft-device constructs were loaded to failure at 50mm/min. The pullout strength was measured as the ultimate load before failure (n=10 for each device). RESULTS: The F(R) values generated during insertion into synthetic bone were 777 ± 86N, 865 ± 140N, 1313 ± 198N, and 1780 ± 255N for the RCI screw, PEEK screw, IntraFix, and ExoShape, respectively. The pullout strengths in synthetic bone for the RCI screw, PEEK screw, IntraFix and ExoShape were 883 ± 125N, 716 ± 249N, 1147 ± 142N, and 1233 ± 190N, respectively. CONCLUSIONS: These results suggest that the F(R) generated during interference fixation affects the pullout strength with sheath-based devices providing superior F(R) compared with interference screws. The use of synthetic bone was validated by comparing the pullout strengths to those when tested in porcine tibia. CLINICAL RELEVANCE: These results could be valuable to a surgeon when determining the best fixation device to use in the clinical setting.

The dependence of MG63 osteoblast responses to (meth)acrylate-based networks on chemical structure and stiffness.

The cell response to an implant is regulated by the implant's surface properties including topography and chemistry, but less is known about how the mechanical properties affect cell behavior. The objective of this study was to evaluate how the surface stiffness and chemistry of acrylate-based copolymer networks affect the in vitro response of human MG63 pre-osteoblast cells. Networks comprised of poly(ethylene glycol) dimethacrylate (PEGDMA; Mn approximately 750) and diethylene glycol dimethacrylate (DEGDMA) were photopolymerized at different concentrations to produce three compositions with moduli ranging from 850 to 60 MPa. To further decouple chemistry and stiffness, three networks comprised of 2-hydroxyethyl methacrylate (2HEMA) and PEGDMA or DEGDMA were also designed that exhibited a range of moduli similar to the PEGDMA-DEGDMA networks. MG63 cells were cultured on each surface and tissue culture polystyrene (TCPS), and the effect of copolymer composition on cell number, osteogenic markers (alkaline phosphatase specific activity and osteocalcin), and local growth factor production (OPG, TGF-beta1, and VEGF-A) were assessed. Cells exhibited a more differentiated phenotype on the PEGDMA-DEGDMA copolymers compared to the 2HEMA-PEGDMA copolymers. On the PEGDMA-DEGDMA system, cells exhibited a more differentiated phenotype on the stiffest surface indicated by elevated osteocalcin compared with TCPS. Conversely, cells on 2HEMA-PEGDMA copolymers became more differentiated on the less stiff 2HEMA surface. Growth factors were regulated in a differential manner. These results indicate that copolymer chemistry is the primary regulator of osteoblast differentiation, and the effect of stiffness is secondary to the surface chemistry.