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We stabilize nematic droplets with handles against surface tension-driven instabilities, using a yield-stress material as outer fluid, and study the complex nematic textures and defect structures that result from the competition between topological constraints and the elasticity of the nematic liquid crystal. We uncover a surprisingly persistent twisted configuration of the nematic director inside the droplets when tangential anchoring is established at their boundaries, which we explain after considering the influence of saddle splay on the elastic free energy. For toroidal droplets, we find that the saddle-splay energy screens the twisting energy, resulting in a spontaneous breaking of mirror symmetry; the chiral twisted state persists for aspect ratios as large as ∼20. For droplets with additional handles, we observe in experiments and computer simulations that there are two additional −1 surface defects per handle; these are located in regions with local saddle geometry to minimize the nematic distortions and hence the corresponding elastic free energy.geometric frustration | topology | torus | double twist | boojum T he liquid crystal in a common display is twisted due to the orientation of the molecules at the confining glass plates. By manipulating this twist using electric fields, an image can be generated. More exotic structures can emerge when the liquid crystal is confined by curved rather than flat surfaces. The topology and geometry of the bounding surface can drive the system into structures that would not be achieved without the presence of external fields. In this sense, the shape of the surface plays a role akin to that of an external field. Thus, under confinement by curved surfaces, the molecules can self-assemble into complex hierarchical structures with emergent macroscopic properties not observed for flat liquid crystal cells. However, the design principles and properties of structures generated by this geometric route are still largely unknown.The lowest energy state of an ordered material, such as a liquid crystal or a simple crystal, is typically defect-free because any disruption of the order will raise the elastic energy. However, the situation can be very different if the material is encapsulated within a confining volume and there is strong alignment of the molecules at the bounding surfaces. In this case, the preferred local order cannot be maintained throughout space. Such a material will be geometrically frustrated and its ground state could contain topological defects, which are spatial regions where the characteristic order of the material is lost. For nematic liquid crystals, the molecules tend to align along a common director, n. The presence of defects at the boundaries, which we characterize with their topological charge, s, giving the amount of n-rotation at the boundary as we encircle the defect, raises the energy of the system. Thus, the formation of defects is normally disfavored due to this increase in energy. However, when an orientationally ordered material is confine...

The unremitting coronavirus disease 2019 (COVID-19) pandemic caused by the novel severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) marked a year-long phase of public health adversaries and has severely compromised healthcare globally. Early evidence of COVID-19 noted its impact on the pulmonary and cardiovascular functions, while multiple studies in recent time shed light on its substantial neurological complications, though a comprehensive understanding of the cause(s), the mechanism(s), and their neuropathological outcomes is scarce. In the present review, we conferred evidence of neurological complications in COVID-19 patients and shed light on the SARS-CoV-2 infection routes including the hematogenous, direct/neuronal, lymphatic tissue or cerebrospinal fluid, or infiltration through infected immune cells, while the underlying mechanism of SARS-CoV-2 invasion to the central nervous system (CNS) was also discussed. In an up-to-date manner, we further reviewed the impact of COVID-19 in developing diverse neurologic manifestations associated with CNS, peripheral nervous system (PNS), skeletal muscle, and also pre-existing neurological diseases, including Alzheimer's disease, Parkinson's disease, multiple sclerosis, epilepsy, and myasthenia gravis. Furthermore, we discussed the involvement of key factors including age, sex, comorbidity, and disease severity in exacerbating the neurologic manifestations in COVID-19 patients. An outlook of present therapeutic strategies and state of existing challenges in COVID-19 management was also accessed. Conclusively, the present report provides a comprehensive review of COVID-19-related neurological complications and emphasizes the need for their early clinical management in the ongoing COVID-19 pandemic. Keywords COVID-19 • SARS-CoV-2 • CNS • PNS • Neuroinvasion • COVID-19 pandemic • Neurological complications Highlights• Coronavirus disease 2019 (COVID-19)-associated complications involve substantial neurological manifestations.• SARS-CoV-2 infection routes include the hematogenous, neuronal, lymphatic tissue/cerebrospinal fluid, or infiltration through infected immune cells.• COVID-19 promotes neurologic manifestations associated with the central and peripheral nervous system and exacerbates the pre-existing neurological and neurodegenerative conditions. • Patient's age, sex, comorbidity, and severity of the infection are key factors that determine the extent of neurologic manifestations in COVID-19 patients.

The novel Coronavirus disease of 2019 (nCOV-19) is a viral outbreak noted first in Wuhan, China. This disease is caused by Severe Acute Respiratory Syndrome (SARS) Coronavirus (CoV)-2. In the past, other members of the coronavirus family, such as SARS and Middle East Respiratory Syndrome (MERS), have made an impact in China and the Arabian peninsula respectively. Both SARS and COVID-19 share similar symptoms such as fever, cough, and difficulty in breathing that can become fatal in later stages. However, SARS and MERS infections were epidemic diseases constrained to limited regions. By March 2020 the SARS-CoV-2 had spread across the globe and on March 11th, 2020 the World Health Organization (WHO) declared COVID-19 as pandemic disease. In severe SARS-CoV-2 infection, many patients succumbed to pneumonia. Higher rates of deaths were seen in older patients who had co-morbidities such as diabetes mellitus, hypertension, cardiovascular disease (CVD), and dementia. In this review paper, we discuss the effect of SARS-CoV-2 on CNS diseases, such as Alzheimer's-like dementia, and diabetes mellitus. We also focus on the virus genome, pathophysiology, theranostics, and autophagy mechanisms. We will assess the multiorgan failure reported in advanced stages of SARS-CoV-2 infection. Our paper will provide mechanistic clues and therapeutic targets for physicians and investigators to combat COVID-19.

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