Northeast- or southwest-dipping subduction in the Cretaceous Caribbean gateway?

Most of the Caribbean plate, which currently lies between the American continents, represents a mantle plume-derived 8–20 km thick Cretaceous oceanic plateau that was formed in the Pacific region and moved eastwards. The northern islands of the Caribbean are largely made up of a dismembered island arc that was located along the western entrance to the inter-American region (termed the Great Arc of the Caribbean) in the mid-late Cretaceous. Importantly, the timing of Caribbean lithospheric movement into the inter-American region is controversial, with one hypothesis advocating that it happened in the Hauterivian-Albian (132.9–100.5 Ma), and a second hypothesis proposing the Turonian-Campanian (93.9–72.1 Ma). In order to investigate this problem, island arc rocks are studied on St. John, U.S. Virgin Islands, which are Barremian (127 Ma) to Santonian (83.6 Ma) in age. Immobile trace element and Ndsingle bondHf radiogenic isotope ratios demonstrate that the arc rocks are derived from the partial melting of an Atlantic MORB-like mantle source region that has been variably contaminated with slab-derived fluids composed of continental detritus and slow sediment clay components. We argue that the lack of a mantle plume geochemical signature in the rocks supports the idea that the movement of Caribbean lithosphere into the inter-American region occurred in the late Cretaceous (post-Santonian) due to a subduction polarity reversal caused by collision of the Caribbean oceanic plateau with the Great Arc of the Caribbean

A genetic algorithm optimization framework for the characterization of hyper-viscoelastic materials:application to human articular cartilage

This study aims to develop an automated framework for the characterization of materials which are both hyper-elastic and viscoelastic. This has been evaluated using human articular cartilage (AC). AC (26 tissue samples from 5 femoral heads) underwent dynamic mechanical analysis with a frequency sweep from 1 to 90 Hz. The conversion from a frequency- to time-domain hyper-viscoelastic material model was approximated using a modular framework design where finite element analysis was automated, and a genetic algorithm and interior point technique were employed to solve and optimize the material approximations. Three orders of approximation for the Prony series were evaluated at N = 1, 3 and 5 for 20 and 50 iterations of a genetic cycle. This was repeated for 30 simulations of six combinations of the above all with randomly generated initialization points. There was a difference between N = 1 and N = 3/5 of approximately ~5% in terms of the error estimated. During unloading the opposite was seen with a 10% error difference between N = 5 and 1. A reduction of ~1% parameter error was found when the number of generations increased from 20 to 50. In conclusion, the framework has proved effective in characterizing human AC

The role of extracellular vesicles in biomineralisation:current perspective and application in regenerative medicine

Extracellular vesicles comprise a heterogenous population of exosomes and microvesicles that have critical roles in intercellular signalling and tissue development. These complex particles have been implicated as mediators of the therapeutic effects of stem cells via the transfer of an assorted cargo of proteins and nucleic acids, which can modulate inflammation and enhance endogenous regeneration in a range of tissues. In addition, extracellular vesicles have the capacity to be loaded with therapeutic molecules for targeted delivery of pharmaceuticals. The versatility, biostability and biocompatibility of extracellular vesicles make them appealing for regenerative medicine and may endow considerable advantages over single molecule approaches. Furthermore, since production can be optimised and assessed ex vivo, extracellular vesicles present a decreased risk of neoplastic transformation when compared with cell-based methods. To date, the contribution of vesicles to tissue development has perhaps been most comprehensively defined within hard tissues, such as endochondral bone, where they were first identified in 1969 and henceforth referred to as matrix vesicles. Within developing bone, vesicles function as vehicles for the delivery of pro-osteogenic factors and initiate early nucleational events necessary for matrix mineralisation. However, advancement in our understanding of the biogenesis and characterisation of matrix vesicles has occurred largely in parallel to associated developments in wider extracellular vesicle biology. As such, there is a requirement to align current understanding of matrix vesicle–mediated mineralisation within the context of an evolving literature surrounding exosomes and microvesicles. In this review, we present an overview of current progress and opinion surrounding the application of vesicles in regenerative medicine with a primary focus on their potential as an acellular approach for enhancing hard tissue regeneration. This is balanced with an assessment of areas where further development is required to maximise their application for regenerative medicine

Achieving ultra-high strength and ductility in Mg–9Al–1Zn–0.5Mn alloy via selective laser melting

Fabrication of the Mg–9Al–1Zn–0.5Mn alloy with excellent mechanical performance using selective laser melting (SLM) technology is quite difficult owing to the poor weldability and low boiling point. To address these challenges and seek the optimal processing parameters, response surface methodology was systematically utilized to determine the appropriate SLM parameter combinations. Mg–9Al–1Zn–0.5Mn sample with high relative density (99.5 ​± ​0.28%) and favorable mechanical properties (microhardness ​= ​95.6 ​± ​5.28 HV0.1, UTS ​= ​370.2 ​MPa, and At ​= ​10.4%) was achieved using optimized SLM parameters (P ​= ​120 ​W, v ​= ​500 ​mm/s, and h ​= ​45 ​μm). Sample ​is dominated by a random texture and microstructure is primarily constituted by quantities of fine equiaxed grains (α-Mg phase), a small amount of β-Al12Mg17 structures (4.96 ​vol%, including spherical: [21¯1¯0]α// [111]β and long lath-like: [21¯1¯0]α// [11¯5]β or [1¯011]α// [32¯1¯]β), and some short rod-shaped Al8Mn5 nanoparticles. Benefiting from grain boundary strengthening, solid solution strengthening, and precipitation hardening of various nanoparticles (β-Al12Mg17 and Al8Mn5), high-performance Mg–9Al–1Zn–0.5Mn alloy biomedical implants can be fabricated. Precipitation hardening dominates the strengthening mechanism of the SLM Mg–9Al–1Zn–0.5Mn alloy.</p

Annexin-enriched osteoblast-derived vesicles act as an extracellular site of mineral nucleation within developing stem cell cultures

The application of extracellular vesicles (EVs) as natural delivery vehicles capable of enhancing tissue regeneration could represent an exciting new phase in medicine. We sought to define the capacity of EVs derived from mineralising osteoblasts (MO-EVs) to induce mineralisation in mesenchymal stem cell (MSC) cultures and delineate the underlying biochemical mechanisms involved. Strikingly, we show that the addition of MO-EVs to MSC cultures significantly (P < 0.05) enhanced the expression of alkaline phosphatase, as well as the rate and volume of mineralisation beyond the current gold-standard, BMP-2. Intriguingly, these effects were only observed in the presence of an exogenous phosphate source. EVs derived from non-mineralising osteoblasts (NMO-EVs) were not found to enhance mineralisation beyond the control. Comparative label-free LC-MS/MS profiling of EVs indicated that enhanced mineralisation could be attributed to the delivery of bridging collagens, primarily associated with osteoblast communication, and other non-collagenous proteins to the developing extracellular matrix. In particular, EV-associated annexin calcium channelling proteins, which form a nucleational core with the phospholipid-rich membrane and support the formation of a pre-apatitic mineral phase, which was identified using infrared spectroscopy. These findings support the role of EVs as early sites of mineral nucleation and demonstrate their value for promoting hard tissue regeneration