Umar Ansari

Review of Mechanics and Applications of Auxetic Structures

One of the important mechanical properties of materials is Poisson’s ratio, which is positive for most of the materials. However, certain materials exhibit “auxetic” properties; that is, they have a negative Poisson’s ratio. Thus auxetic and non-auxetic materials exhibit different deformation mechanisms. A specific microscopic structure in the auxetic materials is important for maintaining a negative Poisson’s ratio. Based on their distinct nature auxetic materials execute certain unique properties in contrast to other materials, which are reviewed in this paper. Thus auxetic materials have important applications in the biomedical field which are also a part of this review article. Many auxetic materials have been discovered, fabricated, and synthesized which differ on the basis of structure, scale and deformation mechanism. The different types of auxetic materials such as auxetic cellular solids, microscopic auxetic polymers, molecular auxetic materials, and auxetic composites have been reviewed comprehensively in this paper. Modeling of auxetic structures is of considerable importance and needs appropriate stress strain configurations; thus different aspects of auxetic modeling have also been reviewed. Packing parameters and relative densities are of prime importance in this regard. This review would thus help the researchers in determining and deciding the various aspects of auxetic nature for their products.

Industrial automation using embedded systems and machine-to-machine, man-to-machine (M2M) connectivity for improved overall equipment effectiveness (OEE)

Embedded systems in general and microcontrollers in particular are playing a key role in todays industrial automation and remote monitoring era for enhanced productivity and reduced costs. The aim of this paper is to report research at e-Monitoring and e-Management Research Centre (eM2RC) at College of E&ME (NUST) on distributed e-Monitoring and e-Management (eM2) using Man-to-Machine, Machine-to Machine (M2M) connectivity for industrial automation. The reported system has successfully been developed, tested and implemented in the local Liquefied Petroleum Gas (LPG) industry to improve Overall Equipment Effectiveness (OEE) resulting in an increased overall system efficiency. The research is based on a combination of hardware and software logic in which the hardware implementation emphasizes the role of embedded systems and M2M connectivity for e-Monitoring and e-Management applications. The e-Information is sent to central server and related technicians/managers/executives for immediate decision making to reduce downtimes and improve quality.

Real-time wound management through integrated pH sensors: a review

Purpose – Real-time monitoring of wound or injured tissues is critical for speedy recovery, and the onset of a cascade of biochemical reactions provides potential biomarkers that facilitate the process of wound monitoring, e.g. pH, temperature, moisture level, bacterial load, cytokines, interleukins, etc. Among all the biomarkers, pH has been known to have a profound impact on the wound healing process, and is used to determine the incidence of bacterial infection of the wound (persistently elevated alkaline pH), proteolytic activity at the site of injury, take rate in skin grafting, wound healing stage and preparation for wound debridement. Design/methodology/approach – This review highlights the significance of pH in determination of clinical parameters and for selection of an appropriate treatment regime, and it presents an in-depth analysis of the designs and fabrication methods that use integrated pH sensors, which have been reported to date for the real-time monitoring of wound healing. Findings – F...

Macro-scale model study of a tunable drug dispensation mechanism for controlled drug delivery in potential wound-healing applications

Background Auxetic materials tend to exhibit stretching in the direction of the applied load as well as in the perpendicular direction. This may be an inherent property of the material, or it might be a particular structural characteristic that confers it with auxetic properties. In this study, the auxetic properties of a rotating squares auxetic design were utilized in tandem with a stretching mechanism to manufacture a device that offers the advantages of adjustable pore size and hence tunable drug delivery characteristics. Methods An auxetic polyurethane film was fabricated through the polymer casting technique. An acrylonitrile-butadiene-styrene (ABS) plastic mold for polymer casting was made through additive manufacturing. Stereolithography was used for fabrication of the mechanism that controlled pore size of the polymeric auxetic film. A laminate arrangement of the film and the mechanism was devised, through which movement of the mechanism controlled stretching of the auxetic film underneath. Results Results were analyzed through image processing. It was observed that a 2-dimensional increase (in length and width) of the auxetic film took place that corresponded to an increase in pore size of the film. Several mathematical correlations were drawn up. Conclusions It may be concluded that the first factor controlling drug release kinetics is the pore size of the film. This study explored a prototype mechanism that has the potential for being used in devices for controlled drug delivery or in smart bandage systems that may enhance wound healing in chronic wound treatment.

New Biofunctional Loading of Natural Antimicrobial Agent in Biodegradable Polymeric Films for Biomedical Applications.

The study focuses on the development of novel Aloe vera based polymeric composite films and antimicrobial suture coatings. Polyvinyl alcohol (PVA), a synthetic biocompatible and biodegradable polymer, was combined with Aloe vera, a natural herb used for soothing burning effects and cosmetic purposes. The properties of these two materials were combined together to get additional benefits such as wound healing and prevention of surgical site infections. PVA and Aloe vera were mixed in a fixed quantity to produce polymer based films. The films were screened for antibacterial and antifungal activity against bacterial (E. coli, P. aeruginosa) and fungal strains (Aspergillus flavus and Aspergillus tubingensis) screened. Aloe vera based PVA films showed antimicrobial activity against all the strains; the lowest Aloe vera concentration (5%) showed the highest activity against all the strains. In vitro degradation and release profile of these films was also evaluated. The coating for sutures was prepared, in vitro antibacterial tests of these coated sutures were carried out, and later on in vivo studies of these coated sutures were also performed. The results showed that sutures coated with Aloe vera/PVA coating solution have antibacterial effects and thus have the potential to be used in the prevention of surgical site infections and Aloe vera/PVA based films have the potential to be used for wound healing purposes.

Auxetic Polymeric Bone Stent for Tubular Fractures: Design, Fabrication and Structural Analysis

Fracture fixation techniques, fracture management, and orthopedic trauma care have evolved, and various advancements have been made in the last 50 years. Minimally invasive biological osteosynthetic devices have the potential of transforming the prospects of orthopedic treatment. Internal fixation techniques offer tremendous advantages in the management of bone fractures. The main objective of this study was to fabricate a novel auxetic polymeric bone stent with potential applications in internal fixation procedures. A new “connected stars” geometry has been used for the fabrication of this device. After fabrication, the mechanical characterization of the auxetic bone stent was also carried out to study its properties and deformation behavior. The research work undertaken also assesses the potential for auxetic behavior of these tubular structures. GRAPHICAL ABSTRACT

Auxetic coronary stent endoprosthesis: fabrication and structural analysis

Background Cardiovascular heart disease is one of the leading health issues in the present era and requires considerable health care resources to prevent it. The present study was focused on the development of a new coronary stent based on novel auxetic geometry which enables the stent to exhibit a negative Poissons ratio. Commercially available coronary stents have isotropic properties, whereas the vascular system of the body shows anisotropic characteristics. This results in a mismatch between anisotropic–isotropic properties of the stent and arterial wall, and this in turn is not favorable for mechanical adhesion of the commercially available coronary stents with the arterial wall. It is believed that an auxetic coronary stent with inherent anisotropic mechanical properties and negative Poissons ratio will have good mechanical adhesion with the arterial wall. Methods The auxetic design was obtained via laser cutting, and surface treatment was performed with acid pickling and electropolishing, followed by an annealing process. In vitro mechanical analysis was performed to analyze the mechanical performance of the auxetic coronary stent. Scanning electronic microscopy (SEM) was used to determine the effects of fabrication processes on the topography of the auxetic stent. Results and Conclusions The elastic recoil (3.3%) of the in vitro mechanical analysis showed that the auxetic stent design effectively maintained the luminal patency of the coronary artery. Also, the auxetic coronary stent showed no foreshortening, therefore it avoids the problem of stent migration, by expanding in both the radial and longitudinal directions. By virtue of its synclastic behavior, the auxetic stent bulges outward when it is radially expanded through an inflated balloon.

A biaxial strain–based expansion mechanism for auxetic stent deployment

Background Auxetics, a special class of materials, tend to expand both in the radial and longitudinal directions when a unidirectional tensile force is applied. Recently, studies have come up with new designs for auxetic vascular and nonvascular stents which are deployed with commercial balloon catheters. There are some inherent limitations associated with a unidirectional application of expansion force in the effective deployment of stents. This work proposed a solution to some of these limitations through the use of a biaxial mode of a predetermined strain-based expansion mechanism. Method The design incorporated a pressure-activated crank-slider mechanism. Fabrication of a prototype for experimental verification was carried out through milling and high-speed lathe machining. The testing of the device employed the use of auxetic stents, fabricated from a biocompatible polymer. A finite element study is presented to extrapolate experimental results to a broader range of operation and working conditions. Results and Conclusions The expansion mechanism is similar in operation to the opening of an umbrella. The length of the connected auxetic stent increases when internal hydraulic pressure is applied. The degree of linear expansion in 1 direction influences the expansion of auxetic stent in the lateral direction. As the device exerts pressure longitudinally, a larger amount of the force is distributed on the unit cells/hinges which ultimately results in an increased expansion of the stent.

Audio signal's test in designing a cost-effective hearing aid device using a microcontroller

A large number of hearing impaired people in rural sector of Pakistan cannot afford the high prices of digital hearing aids. Moreover, since the analogue devices amplify the speech and noise signals equally, they are not much flexible and have functional limitations. These problems can be solved with digital devices which are generally costly. In this research work, a microcontroller based cost-effective and portable hearing aid is designed and tested. The main components include sound detection circuit, microcontroller and a digital to analogue (DAC) convertor. Device is aimed to process human voice frequencies with an adjustable gain of up to 80 dB. It is tested with an input audio signal and it showed satisfactory results for low frequency signals up to 3.5 kHz which caters for the frequency range of most human voices. The system is now being developed for more effective noise suppression and broader frequency range.

Structure and motility of the esophagus from a mechanical perspective

AbstractEsophagus is an important part of the alimentary canal that performs various functions, most important of which is the transfer of bolus from the pharynx to the stomach. This involves active contraction of both the circular and longitudinal esophageal muscles. Esophageal anatomical features are harmonized with the functional and physiological demands of esophagus. However, impairment of esophageal functions may occur resulting in symptoms like dysphagia, gastroesophageal reflux or esophageal pain. This review covers broadly the anatomical and physiological details of esophagus, mechanical function of esophagus and its motility. In particular, the mechanical characteristics of the esophageal tissue and its motile function have been scrutinized. An overlay of the diagnostic technologies tapping these metrics is also covered.