216 research outputs found
Biology of Human Malaria Plasmodia Including Plasmodium Knowlesi
Malaria is a vector-borne infection caused by unicellular parasite of the genus Plasmodium. Plasmodia are obligate intracellular parasites that are able to infect and replicate within the erythrocytes after a clinically silent replication phase in the liver. Four species (P.falciparum, P.malariae, P.ovale and P.vivax) are traditionally recognized as responsible of natural infection in human beings but the recent upsurge of P.knowlesi malaria in South-East Asia has led clinicians to consider it as the fifth human malaria parasite. Recent studies in wild-living apes in Africa have revealed that P.falciparum, the most deadly form of human malaria, is not only human-host restricted as previously believed and its phylogenetic lineage is much more complex with new species identified in gorilla, bonobo and chimpanzee. Although less impressive, new data on biology of P.malariae, P.ovale and P.vivax are also emerging and will be briefly discussed in this review
Mechanics of mineralized collagen fibrils upon transient loads
Collagen is a key structural protein in the human body, which undergoes
mineralization during the formation of hard tissues. Earlier studies have
described the mechanical behavior of bone at different scales highlighting
material features across hierarchical structures. Here we present a study that
aims to understand the mechanical properties of mineralized collagen fibrils
upon tensile/compressive transient loads, investigating how the kinetic energy
propagates and it is dissipated at the molecular scale, thus filling a gap of
knowledge in this area. These specific features are the mechanisms that Nature
has developed to passively dissipate stress and prevent structural failures. In
addition to the mechanical properties of the mineralized fibrils, we observe
distinct nanomechanical behaviors for the two regions (i.e., overlap and gap)
of the D-period to highlight the effect of the mineralization. We notice
decreasing trends for both wave speeds and Young s moduli over input velocity
with a marked strengthening effect in the gap region due to the accumulation of
the hydroxyapatite. In contrast, the dissipative behavior is not affected by
either loading conditions or the mineral percentage, showing a stronger
dampening effect upon faster inputs compatible to the bone behavior at the
macroscale. Our results improve the understanding of mineralized collagen
composites unveiling the energy dissipative behavior of such materials. This
impacts, besides the physiology, the design and characterization of new
bioinspired composites for replacement devices (e.g., prostheses for sound
transmission or conduction) and for optimized structures able to bear transient
loads, e.g., impact, fatigue, in structural applications
strongly balanced 4 kite designs nested into oq systems
In this paper we determine the spectrum for octagon quadrangle systems [OQS] which can be partitioned into two strongly balanced 4-kitedesigns
Molecular origin of viscoelasticity in mineralized collagen fibrils
Bone is mineralized tissue constituting the skeletal system, supporting and
protecting body organs and tissues. At the molecular level, mineralized
collagen fibril is the basic building block of bone tissue, and hence,
understanding bone properties down to fundamental tissue structures enables to
better identify the mechanisms of structural failures and damages. While
efforts have focused on the study of the micro- and macro-scale viscoelasticity
related to bone damage and healing based on creep, mineralized collagen has not
been explored on a molecular level. We report a study that aims at
systematically exploring the viscoelasticity of collagenous fibrils with
different mineralization levels. We investigate the dynamic mechanical response
upon cyclic and impulsive loads to observe the viscoelastic phenomena from
either shear or extensional strains via molecular dynamics. We perform a
sensitivity analysis with several key benchmarks: intrafibrillar mineralization
percentage, hydration state, and external load amplitude. Our results show a
growth of the dynamic moduli with an increase of mineral percentage, pronounced
at low strains. When intrafibrillar water is present, the material softens the
elastic component but considerably increases its viscosity, especially at high
frequencies. This behaviour is confirmed from the material response upon
impulsive loads, in which water drastically reduces the relaxation times
throughout the input velocity range by one order of magnitude, with respect to
the dehydrated counterparts. We find that upon transient loads, water has a
major impact on the mechanics of mineralized fibrillar collagen, being able to
improve the capability of the tissue to passively and effectively dissipate
energy, especially after fast and high-amplitude external loads
Tympanic Membrane Collagen Expression by Dynamically Cultured Human Mesenchymal Stromal Cell/Star-Branched Poly(Δ-Caprolactone) Nonwoven Constructs
The tympanic membrane (TM) primes the sound transmission mechanism due to special
ïŹbrous layers mainly of collagens II, III, and IV as a product of TM ïŹbroblasts, while type I is less
represented. In this study, human mesenchymal stromal cells (hMSCs) were cultured on star-branched
poly("-caprolactone) (*PCL)-based nonwovens using a TM bioreactor and proper dierentiating
factors to induce the expression of the TM collagen types. The cell cultures were carried out for
one week under static and dynamic conditions. Reverse transcriptase-polymerase chain reaction
(RT-PCR) and immunohistochemistry (IHC) were used to assess collagen expression. A Finite
Element Model was applied to calculate the stress distribution on the scaolds under dynamic
culture. Nanohydroxyapatite (HA) was used as a ïŹller to change density and tensile strength of *PCL
scaolds. In dynamically cultured *PCL constructs, ïŹbroblast surface marker was overexpressed, and
collagen type II was revealed via IHC. Collagen types I, III and IV were also detected. Von Mises
stress maps showed that during the bioreactor motion, the maximum stress in *PCL was double
that in HA/*PCL scaolds. By using a *PCL nonwoven scaold, with suitable physico-mechanical
properties, an oscillatory culture, and proper dierentiative factors, hMSCs were committed into
ïŹbroblast lineage-producing TM-like collagens
Piezoelectric energy harvesting solutions
This paper reviews the state of the art in piezoelectric energy harvesting. It presents the basics of piezoelectricity and discusses materials choice. The work places emphasis on material operating modes and device configurations, from resonant to non-resonant devices and also to rotational solutions. The reviewed literature is compared based on power density and bandwidth. Lastly, the question of power conversion is addressed by reviewing various circuit solutions
Piezoelectric Signals in Vascularized Bone Regeneration
The demand for bone substitutes is increasing in Western countries. Bone graft substitutes aim to provide reconstructive surgeons with off-the-shelf alternatives to the natural bone taken from humans or animal species. Under the tissue engineering paradigm, biomaterial scaffolds can be designed by incorporating bone stem cells to decrease the disadvantages of traditional tissue grafts. However, the effective clinical application of tissue-engineered bone is limited by insufficient neovascularization. As bone is a highly vascularized tissue, new strategies to promote both osteogenesis and vasculogenesis within the scaffolds need to be considered for a successful regeneration. It has been demonstrated that bone and blood vases are piezoelectric, namely, electric signals are locally produced upon mechanical stimulation of these tissues. The specific effects of electric charge generation on different cells are not fully understood, but a substantial amount of evidence has suggested their functional and physiological roles. This review summarizes the special contribution of piezoelectricity as a stimulatory signal for bone and vascular tissue regeneration, including osteogenesis, angiogenesis, vascular repair, and tissue engineering, by considering different stem cell sources entailed with osteogenic and angiogenic potential, aimed at collecting the key findings that may enable the development of successful vascularized bone replacements useful in orthopedic and otologic surgery
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