Partial Deletion of Chromosome 8 β-defensin Cluster Confers Sperm Dysfunction and Infertility in Male Mice

β-defensin peptides are a family of antimicrobial peptides present at mucosal surfaces, with the main site of expression under normal conditions in the male reproductive tract. Although they kill microbes in vitro and interact with immune cells, the precise role of these genes in vivo remains uncertain. We show here that homozygous deletion of a cluster of nine β-defensin genes (DefbΔ9) in the mouse results in male sterility. The sperm derived from the mutants have reduced motility and increased fragility. Epididymal sperm isolated from the cauda should require capacitation to induce the acrosome reaction but sperm from the mutants demonstrate precocious capacitation and increased spontaneous acrosome reaction compared to wild-types but have reduced ability to bind the zona pellucida of oocytes. Ultrastructural examination reveals a defect in microtubule structure of the axoneme with increased disintegration in mutant derived sperm present in the epididymis cauda region, but not in caput region or testes. Consistent with premature acrosome reaction, sperm from mutant animals have significantly increased intracellular calcium content. Thus we demonstrate in vivo that β-defensins are essential for successful sperm maturation, and their disruption leads to alteration in intracellular calcium, inappropriate spontaneous acrosome reaction and profound male infertility

Mechanical force involved multiple fields switching of both local ferroelectric and magnetic domain in a Bi5Ti3FeO15 thin film

Multiferroics have received intense attention due to their great application potential in multi-state information storage devices and new types of sensors. Coupling among ferroic orders such as ferroelectricity, (anti-)ferromagnetism, ferroelasticity, etc. will enable dynamic interaction between these ordering parameters. Direct visualization of such coupling behaviour in single phase multiferroic materials is highly desirable for both applications and fundamental study. Manipulation of both ferroelectric and magnetic domains of Bi5Ti3FeO15 thin film using electric field and external mechanical force is reported, which confirms the magnetoelectric coupling in Bi5Ti3FeO15, indicates the electric and magnetic orders are coupled through ferroelasticity. Due to the anisotropic relaxation of ferroelastic strain, the back-switching of out-of-plane electric domains is not as obvious as in-plane. An inevitable destabilization of the coupling between elastic and magnetic ordering happens because of the elastic strain relaxation, which result in a subsequent decay of magnetic domain switching. Mechanical force applied on the surface of Bi5Ti3FeO15 film generates by an AFM tip will effectively drive a transition of the local ferroelastic strain state, reverse both the polarization and magnetization in a way similar to an electric field. Current work provides a framework for exploring cross-coupling among multiple orders and potential for developing novel nanoscale functional devices

Selective control of multiple ferroelectric switching pathways using a trailing flexoelectric field

Flexoelectricity is an electromechanical coupling between electrical polarization and a strain gradient(1) that enables mechanical manipulation of polarization without applying an electrical bias(2,3). Recently, flexoelectricity was directly demonstrated by mechanically switching the out-of-plane polarization of a uniaxial system with a scanning probe microscope tip(3,4). However, the successful application of flexoelectricity in low-symmetry multiaxial ferroelectrics and therefore active manipulation of multiple domains via flexoelectricity have not yet been achieved. Here, we demonstrate that the symmetry-breaking flexoelectricity offers a powerful route for the selective control of multiple domain switching pathways in multiaxial ferroelectric materials. Specifically, we use a trailing flexoelectric field that is created by the motion of a mechanically loaded scanning probe microscope tip. By controlling the SPM scan direction, we can deterministically select either stable 71 degrees ferroelastic switching or 180 degrees ferroelectric switching in a multiferroic magnetoelectric BiFeO3 thin film. Phase-field simulations reveal that the amplified in-plane trailing flexoelectric field is essential for this domain engineering. Moreover, we show that mechanically switched domains have a good retention property. This work opens a new avenue for the deterministic selection of nanoscale ferroelectric domains in low-symmetry materials for non-volatile magnetoelectric devices and multilevel data storag

Large polarization gradients and temperature-stable responses in compositionally-graded ferroelectrics

A range of modern applications require large and tunable dielectric, piezoelectric or pyroelectric response of ferroelectrics. Such effects are intimately connected to the nature of polarization and how it responds to externally applied stimuli. Ferroelectric susceptibilities are, in general, strongly temperature dependent, diminishing rapidly as one transitions away from the ferroelectric phase transition (TC). In turn, researchers seek new routes to manipulate polarization to simultaneously enhance susceptibilities and broaden operational temperature ranges. Here, we demonstrate such a capability by creating composition and strain gradients in Ba1-xSrxTiO3 films which result in spatial polarization gradients as large as 35 μC cm-2 across a 150 nm thick film. These polarization gradients allow for large dielectric permittivity with low loss (ɛr≈775, tan δ<0.05), negligible temperature-dependence (13% deviation over 500 °C) and high-dielectric tunability (greater than 70% across a 300 °C range). The role of space charges in stabilizing polarization gradients is also discussed