Mathematical modelling of magnesium corrosion for orthopaedic implants

Magnesium (Mg) has grasped the attention of biomaterial researchers due to its desirable properties for orthopaedic implants. It is a biodegradable, lightweight structured metal with mechanical properties more comparable to the human bone than frequently used implant materials like titanium and stainless steel. However, the element corrodes rapidly in aqueous environments, which prevents its direct use as an implant material. In this thesis, novel mathematical models are presented to address the problem of Mg corrosion. In aqueous environments, a Mg implant reacts to form magnesium hydroxide (\ce{Mg(OH)2}), which can react further with bicarbonate ions to form magnesium carbonate (\ce{MgCO3}); these reactions are considered in the corrosion models developed in this work, and this is the first study to consider \ce{MgCO3}. A simple mass action model was derived first, which predicted the amount of Mg and its corrosion products over time, where an exponential decay of Mg was perceived. The backbone of this thesis is a PDE model for Mg corrosion, which considers distinct porous layers of \ce{Mg(OH)2} and \ce{MgCO3} surrounding a block of Mg with the advection and diffusion of \ce{H2O} and \ce{CO2} through porous media; this porous media assumption is a novel feature in comparison to other metal corrosion models. The model was derived and analysed in one spatial dimension for Cartesian, radically symmetric spherical and cylindrical geometries. Singularities resulting from the model at small time were handled using asymptotic analysis. The effect of the model parameters on key timescales was investigated, whereby porosity of the layers and reaction rates of \ce{H2O} and Mg were shown to have a significant effect. Furthermore, the porous media assumption on the Mg compound layers led to the prediction of a slightly faster corrosion of the original Mg block compared to that with different rates of advection. In addition to the above, corrosion from inside a single Mg pore was considered using the same modelling approach. The timescale for pore closure and the size of Mg corrosion at pore closure were of particular interest, and were affected by changes in the parameters. The pore closure time was found to be rapid in comparison to the degradation time of the implant. The final model in this work is a physiologically based pharmacokinetic (PBPK) model, which is used to explore the effects of a corroding Mg implant on blood serum levels; a high amount of Mg in the blood can cause complications. Values for the implant release rate of Mg and urine excretion rates were refined in the model, where it was highlighted that an Mg implantation must be carefully considered for patients, particularly those with reduced renal function

Validación de contenido diagnóstico de enfermería, NANDA (00285) “Disposición para mejorar el duelo”

Recientemente la taxonomía NANDA ha incluido el diagnóstico “disposición para mejorar el duelo”, el cuál ha sido aprobado en el año 2020, con una evidencia de 2.1, el cual se compone de una etiqueta, definición, características definitorias, y factores relacionados o de riesgo y referencias bibliográficas. En el presente trabajo se explicará la elección del panel de expertos y técnica Delphi descrito por el método Fehring (1987), el cuál será necesario para la validación de dicho diagnóstico, recientemente añadido.Recently, the NANDA taxonomy has included the diagnosis "disposition to improve grief", which has been approved in 2020, with evidence of 2.1, which is made up of a label, definition, defining characteristics, and related or risk factors. and bibliographical references. In the present work, the choice of the panel of experts and the Delphi technique described by the Fehring method (1987) will be explained, which will be for the validation of said recently added diagnosis

OPTIMIZATION OF THE FORMULATION PARAMETERS OF A PARAPHARMACEUTICAL 100% BIO CREAM

The extraction of the aromatic fraction (hydrolat, essential oil) fresh aerial part of Lavandula vera was accomplished by steam distillation. The average yield of essential oil is 1-2%. The anti-inflammatory cream BIO obtained has interesting dermal properties. This cream is endowed with remarkable healing properties and anti-infectious. It leads to dermatological applications and opens the way eventually fruitful research. During this work we have formulated an anti-inflammatory cream 100% BIO whose active ingredient is the essential oil of lavender with these attractive properties. Optimization of formulation parameters made it possible to have a stable cream. Physicochemical analysis, sensory (with diagram properties evaluation) and comparative study with a reference cream (conventional) was able to show the qualities of our BIO cream

Selection and Characterization of a Lysine Yielding Mutant of Corynebacterium glutamicum - a Soil Isolate from Pakistan

L-lysine is the second limiting amino acid for poultry and supplemented in broiler feed for optimal performance. Lysine can be produced by inducing mutation in glutamate producing bacteria. The study was conducted to enhance lysine production from a local strain of Corynebacterium glutamicum. The bacterium was mutated by exposure to UV. Mutants resistant to s-2-aminoethyle L-cystein (AEC) and showing auxotrophy for L-homoserine were screened for lysine production qualitatively and quantitatively. A mutant showing highest production of lysine (8.2 mg/mL) was selected for optimization of physical and nutritional parameters for maximum production of lysine in shake flask. An initial pH 7.6, 30˚C temperature, 300 rpm and 60 h incubation time were the optimized values of physical requirements. Cane molasses and corn starch hydrolysate were required at 15% (w/v) in the fermentation media which provided around 9% total sugars to produce maximum lysine (17 to 18 mg/mL). When amonium sulphate was used at 3.5% (w/v) level in molasses or corn starch hydrolysate based fermentation media, production of lysine slightly increased above 18 mg/mL. It is concluded that industrial by products like cane molasses, corn steep liquor, and corn starch hydrolysate can be used as carbon and organic nitrogen sources in fermentation medium for scale up process of lysine production and this lysine enriched broth may be used in broiler feed later. However, more potent lysine producing mutant and additional in vivo trials would be required to commercialize this product

Common Organisms causing surgical site infection(SSI) in Postoperative patients in a tertiary care Hospital

Objective: To investigate the types and frequency of organisms causing surgical site infections in postoperative patients and their association with other factors. Study Design: Cross-sectional Duration and Place of Study: Surgical Unit-II of –removed for blind review---and from 1st March 2021 – 31st July 2021. Patients and Methods: There were 391 surgeries in this study, but only 27 patients met the inclusion criteria. A diagnosis of SSI was based on specific parameters, including the detection of two or three cardinal signs of inflammation and the surgeon's confirmation of the diagnosis. This data was analyzed using IBM SPSS 23. Results: Among 391 patients, 242 had elective surgeries (male:female, 1.6:1), and 149 had emergency surgeries (male:female, 1:3.4). The mean length of stay for elective surgeries was 2.19 ± 1.8 days and 4.2 ± 3.7 days for emergency procedures. There were 98 abdominal procedures (65.77%) performed in emergency settings. Only 9 (3.71 %) elective procedures and 18 (12.08 %) emergency procedures reported surgical site infections. Escherichia coli was the most commonly isolated organism from SSI during the study. The rate of SSI in postoperative patients was 6.9%. There was a statistically significant association between SSI and type of surgery (p=0.002). The mean length of stay (LOS) was longer for patients with SSI (mean=12.5, p=.000).  Emergency cases had a longer LOS compared with elective cases (mean= 4.21 days vs 2.19 days, p=.000). Conclusion: According to our study, our unit's SSI were comparable to other developing countries. SSI are more frequent in emergency cases, men, and diabetics, and are the primary cause of longer hospital stays.  Keywords: Surgical Site Infection; E.Coli; Length of stay

Six-Minute Walk Test Performance in Healthy Adult Pakistani Volunteers

Objective: To determine the six-minute walking distance (6MWD) for healthy Pakistanis, identify factors affecting 6MWD, compare published equations with the local data and derive an equation. Study Design: Cross-sectional study. Place and Duration of Study: Two medical institutes of Karachi, from January to May 2011. Methodology: Subjects between 15 and 65 years were prospectively enrolled after screening. A standardized 6MWT was administered. SpO2, HR, BP and dyspnoea scores were determined pre- and post-test. Results: Two hundred and eleven (71%) men and 85 (29%) women participated. Mean 6MWD was 469.88 ± 101.24 m: men walked 502.35 ± 92.21 m and women walked 389.28 ± 74.29 m. On univariate analysis, gender, height, weight and age showed a significant relationship with the 6MWD. Gender and age were identified as independent factors in multiple regression analysis, and together explained 33% of the variance. The gender-specific prediction equations were: 6MWD (m) for men = 164.08 + (78.06*1) - (1.90*age in years) + (1.95*height in cms) 6MWD (m) for women = 164.08 - (1.90*age in years) + (1.95*height in cms). Conclusion: 6MWDs among the volunteer subjects were shorter than predicted by reference equations in literature. Height, gender and weight combined explained 33% of the variance. The moderate over-estimation of the 6MWD in Pakistani subject. The proposed equation gives predicted (mean) 6MWDs for adult Pakistani naïve to the test when employing standardized protocol

Use of pefloxacin as a surrogate marker to detect ciprofloxacin susceptibility in Salmonella enterica serotypes typhi and paratyphi A

Objective: To determine the use of pefloxacin as a surrogate marker to detect fluoroquinolone (ciprofloxacin) susceptibility against Salmonella enterica serotypes Typhi and Paratyphi A.Methods: The prospective, descriptive cross-sectional study was conducted at the Aga Khan University Hospital, Karachi, from September 2016 to March 2018, and comprised Salmonella Typhi and Paratyphi A isolates of blood cultures. Disk susceptibility tests and broth microdilution to test minimum inhibitory concentration were performed as per standard guidelines. Data was analysed using SPSS 21.Results: Of the 138 isolates, 91(66%) were intermediate resistant to ciprofloxacin but were resistant to pefloxacin, 42(30%) were resistant to both ciprofloxacin and pefloxacin, and 5(4%) were susceptible to both ciprofloxacin and pefloxacin. Of the isolates that were intermediate resistant to ciprofloxacin, 85(93%) had minimum inhibitory concentration range0.12-0.5mg\L, while 6(7%) had MIC\u3e1mg\L (p\u3c0.0001).Conclusions: Pefloxacin disk diffusion test was found to be reliable in detecting fluoroquinolone resistance among enteric fever causing Salmonella

Numerical modelling of effects of biphasic layers of corrosion products to the degradation of magnesium metal in vitro

© 2017 by the authors. Magnesium (Mg) is becoming increasingly popular for orthopaedic implant materials. Its mechanical properties are closer to bone than other implant materials, allowing for more natural healing under stresses experienced during recovery. Being biodegradable, it also eliminates the requirement of further surgery to remove the hardware. However, Mg rapidly corrodes in clinically relevant aqueous environments, compromising its use. This problem can be addressed by alloying the Mg, but challenges remain at optimising the properties of the material for clinical use. In this paper, we present a mathematical model to provide a systematic means of quantitatively predicting Mg corrosion in aqueous environments, providing a means of informing standardisation of in vitro investigation of Mg alloy corrosion to determine implant design parameters. The model describes corrosion through reactions with water, to produce magnesium hydroxide Mg(OH) 2 , and subsequently with carbon dioxide to form magnesium carbonate MgCO 3 . The corrosion products produce distinct protective layers around the magnesium block that are modelled as porous media. The resulting model of advection-diffusion equations with multiple moving boundaries was solved numerically using asymptotic expansions to deal with singular cases. The model has few free parameters, and it is shown that these can be tuned to predict a full range of corrosion rates, reflecting differences between pure magnesium or magnesium alloys. Data from practicable in vitro experiments can be used to calibrate the model's free parameters, from which model simulations using in vivo relevant geometries provide a cheap first step in optimising Mg-based implant materials