Establishing superfine nanofibrils for robust polyelectrolyte artificial spider silk and powerful artificial muscles.

Spider silk exhibits an excellent combination of high strength and toughness, which originates from the hierarchical self-assembled structure of spidroin during fiber spinning. In this work, superfine nanofibrils are established in polyelectrolyte artificial spider silk by optimizing the flexibility of polymer chains, which exhibits combination of breaking strength and toughness ranging from 1.83 GPa and 238 MJ m-3 to 0.53 GPa and 700 MJ m-3, respectively. This is achieved by introducing ions to control the dissociation of polymer chains and evaporation-induced self-assembly under external stress. In addition, the artificial spider silk possesses thermally-driven supercontraction ability. This work provides inspiration for the design of high-performance fiber materials.

Morphology modulation of artificial muscles by thermodynamic-twist coupling.

Human muscles can grow and change their length with body development; therefore, artificial muscles that modulate their morphology according to changing needs are needed. In this paper, we report a strategy to transform an artificial muscle into a new muscle with a different morphology by thermodynamic-twist coupling, and illustrate its structural evolution during actuation. The muscle length can be continuously modulated over a large temperature range, and actuation occurs by continuously changing the temperature. This strategy is applicable to different actuation modes, including tensile elongation, tensile contraction and torsional rotation. This is realized by twist insertion into a fibre to produce torsional stress. Fibre annealing causes partial thermodynamic relaxation of the spiral molecular chains, which serves as internal tethering and inhibits fibre twist release, thus producing a self-supporting artificial muscle that actuates under heating. At a sufficiently high temperature, further relaxation of the spiral molecular chains occurs, resulting in a new muscle with a different length. A structural study provides an understanding of the thermodynamic-twist coupling. This work provides a new design strategy for intelligent materials.

Spider Silk-Inspired Artificial Fibers.

Spider silk is a natural polymeric fiber with high tensile strength, toughness, and has distinct thermal, optical, and biocompatible properties. The mechanical properties of spider silk are ascribed to its hierarchical structure, including primary and secondary structures of the spidroins (spider silk proteins), the nanofibril, the "core-shell", and the "nano-fishnet" structures. In addition, spider silk also exhibits remarkable properties regarding humidity/water response, water collection, light transmission, thermal conductance, and shape-memory effect. This motivates researchers to prepare artificial functional fibers mimicking spider silk. In this review, the authors summarize the study of the structure and properties of natural spider silk, and the biomimetic preparation of artificial fibers from different types of molecules and polymers by taking some examples of artificial fibers exhibiting these interesting properties. In conclusion, biomimetic studies have yielded several noteworthy findings in artificial fibers with different functions, and this review aims to provide indications for biomimetic studies of functional fibers that approach and exceed the properties of natural spider silk.

Safety culture implications on safe work practices and work place exposure incidents in Operation Theater.

BACKGROUND & OBJECTIVES: The study was undertaken to estimate the prevalence of body and blood fluid exposure incidents such as needle stick injuries, direct contact, splashes, and cuts among health care personnel (HCP) in operation theaters (OTs). The study objective was to investigate perception of safety culture and potential challenges faced by HCP in Pakistani context. METHODS: An analytical cross-sectional survey was conducted in four tertiary care hospitals of Rawalpindi and Islamabad that were Akbar Niazi Teaching Hospital (ANTH), Fauji Foundation Hospital (FFH), Benazir Bhutto Hospital (BBH) and Holy Family Hospital (HFH) during March, 2019 to June, 2019. The data of the current study was collected from surgical staff in OTs at four tertiary care teaching hospitals including nurses, house officers, post graduate trainees, registrars, consultants, and technicians in the twin cities i.e., Rawalpindi and Islamabad. RESULTS: In our findings (N=367) there was a high prevalence of exposure incidents in past six months, 45% had had got a needle injury, 36% have got a splash, 28.8% had direct contact and 35.6% had a cut once respectively in past six months, the occurrence of exposure incidents twice, thrice and more is also enormous. CONCLUSION: The study reflected a dire need of trainings at hospitals so that very strategically the importance of safety being a priority and value of HCP is inculcated on daily basis.

Bifurcations and hybrid control in a 3×3 discrete-time predator-prey model.

In this paper, we explore the bifurcations and hybrid control in a $3\times3$ discrete-time predator-prey model in the interior of $\mathbb{R}_+^3$. It is proved that $3\times3$ model has four boundary fixed points: $P_{000}(0,0,0)$, $P_{0y0}\left(0,\frac{r-1}{r},0\right)$, $P_{0yz}\left(0,\frac{d}{f},\frac{rf-f-dr}{cf}\right)$, $P_{x0z}\left(\frac{d}{e},0,\frac{a}{b}\right)$, and the unique positive fixed point: $P^+_{xyz}\left(\frac{br(d-f)+f(b+ac)}{ber},\frac{br-b-ac}{br},\frac{a}{b}\right)$ under certain restrictions to the involved parameters. By utilizing method of Linearization, local dynamics along with topological classifications about fixed points have been investigated. Existence of prime period and periodic points of the model are also investigated. Further for $3\times3$ model, we have explored the occurrence of possible bifurcations about each fixed point, that gives more insight about the under consideration model. It is proved that the model cannot undergo any bifurcation about $P_{000}(0,0,0)$ and $P_{x0z}\left(\frac{d}{e},0,\frac{a}{b}\right)$, but the model undergo P-D and N-S bifurcations respectively about $P_{0y0}\left(0,\frac{r-1}{r},0\right)$ and $P_{0yz}\left(0,\frac{d}{f},\frac{rf-f-dr}{cf}\right)$. For the unique positive fixed point: $P^+_{xyz}\left(\frac{br(d-f)+f(b+ac)}{ber},\frac{br-b-ac}{br},\frac{a}{b}\right)$, we have proved the N-S as well as P-D bifurcations by explicit criterion. Further, theoretical results are verified by numerical simulations. We have also presented the bifurcation diagrams and corresponding maximum Lyapunov exponents for the $3\times3$ model. The computation of the maximum Lyapunov exponents ratify the appearance of chaotic behavior in the under consideration model. Finally, the hybrid control strategy is applied to control N-S as well as P-D bifurcations in the discrete-time model.

Analysis Of Level Of Satisfaction Of Postgraduate Trainees On Surgical Floor.

BACKGROUND: Organizations flourish with a satisfied workforce. There is little known information on demographic characteristics and motivators for job satisfaction among Pakistani postgraduate trainees in surgery. Job satisfaction is predicted by intrinsic motivators (personal growth and perceived ability to work) and extrinsic motivators (perceived social support). Work family interference/enhancement and job stressors (workload and long working hours) also impacts job satisfaction; predicting overall life satisfaction. This study aims at examining life satisfaction predicted by personal and professional characteristics.. METHODS: The postgraduate trainees in the public and private hospitals of Rawalpindi and Islamabad were surveyed using validated measures of life satisfaction, personal growth, perceived social support, perceived ability to work, work family interference/enhancement, job stressors, co-workers support, supervisors support, and job satisfaction from September 15 to December 28, 2017. RESULTS: Personal growth, perceived ability to work, availability of social support, and work family enhancement positively correlate to job and life satisfaction. Work life interference and job stressors negatively relate to job and life satisfaction. Job satisfaction is also partially mediated by intrinsic and extrinsic motivators on life satisfaction, whereas job stressors weakened the relationship between job satisfaction and life satisfaction. Long working hours is negatively related to job satisfaction and life satisfaction. CONCLUSIONS: Life satisfaction is predicted by job satisfaction that is characterized intrinsic and extrinsic motivators. Healthcare organizations face challenge of providing reduced working hours, increased salaries, supportive working environment, and increased supervision to enhance the job satisfaction of employees and to improve the functioning of the healthcare environment.

Global dynamics and bifurcation analysis of a host-parasitoid model with strong Allee effect.

In this paper, we study the global dynamics and bifurcations of a two-dimensional discrete time host-parasitoid model with strong Allee effect. The existence of fixed points and their stability are analysed in all allowed parametric region. The bifurcation analysis shows that the model can undergo fold bifurcation and Neimark-Sacker bifurcation. As the parameters vary in a small neighbourhood of the Neimark-Sacker bifurcation condition, the unique positive fixed point changes its stability and an invariant closed circle bifurcates from the positive fixed point. From the viewpoint of biology, the invariant closed curve corresponds to the periodic or quasi-periodic oscillations between host and parasitoid populations. Furthermore, it is proved that all solutions of this model are bounded, and there exist some values of the parameters such that the model has a global attractor. These theoretical results reveal the complex dynamics of the present model.

Coronary artery bypass surgery in old age group: is age itself a barrier?

OBJECTIVE: To analyse the data retrospectively and identify risk factors that may adversely affect mortality in patients aged seventy years and older with coronary artery bypass graft (CABG). METHODS: From Jan 2003 to Oct 2007, 63 consecutive patients of 70 years or older underwent primary isolated CABG on cardiopulmonary bypass (CPB) in Department of Surgery, Liaquat National Hospital. Forty one (65%) were male. The mean age was 72.7 +/- 3 years (range 70 to 81 years). Preoperatively 83% were in New York Heart Association (NYHA) class III or IV. Left main stem (LMS) lesion (> 70%) was present in 20 (32%). Renal impairment (RI) with creatinine more then 2 mg/dl was present in 9 (14%) patients. History of prior stroke was present in 7 (11%). Emergency surgery (within 48 hours after Myocardial Infarct (MI)) was performed in 33 (52%) patients. RESULTS: The overall hospital mortality (30 days) was 9.5%. The mean Parsonet score was 23 +/- 3, and 10 +/- 3 in those who died or survived respectively. Mean intensive care unit stay was 2.3 +/- 0.7 days, mean ward stay was 6 +/- 3 days. Preoperative LMS lesion or MI less then 48 hours, poor left ventriculal function, prolonged CPB time and post operative stroke were the significant independent predictors of operative morality. CONCLUSION: CABG can be performed in a selected elderly population. Careful attention to risk factors associated with high mortality can be helpful in improving post-operative morality. Age in itself may not be responsible for high morality.