Sanjukta Bose - Academia.edu (original) (raw)

Papers by Sanjukta Bose

Research paper thumbnail of Early Prediction of Multiple Organ Dysfunction in the Pediatric Intensive Care Unit

Frontiers in Pediatrics

Objective:The objective of the study is to build models for early prediction of risk for developi... more Objective:The objective of the study is to build models for early prediction of risk for developing multiple organ dysfunction (MOD) in pediatric intensive care unit (PICU) patients.Design:The design of the study is a retrospective observational cohort study.Setting:The setting of the study is at a single academic PICU at the Johns Hopkins Hospital, Baltimore, MD.Patients:The patients included in the study were <18 years of age admitted to the PICU between July 2014 and October 2015.Measurements and main results:Organ dysfunction labels were generated every minute from preceding 24-h time windows using the International Pediatric Sepsis Consensus Conference (IPSCC) and Proulx et al. MOD criteria. Early MOD prediction models were built using four machine learning methods: random forest, XGBoost, GLMBoost, and Lasso-GLM. An optimal threshold learned from training data was used to detect high-risk alert events (HRAs). The early prediction models from all methods achieved an area und...

Research paper thumbnail of Supporting data for: "Long lasting mucoadhesive membrane based on alginate and chitosan for intravaginal drug delivery

The document is a collection of supporting information for the manuscript titled: <strong>&... more The document is a collection of supporting information for the manuscript titled: <strong>"Long lasting mucoadhesive membrane based on alginate and chitosan for intravaginal drug delivery".</strong> The supporting information include: a) the stress-strain curves obtained from the compression studies of alginate, alginate/chitosan and alginate/chitosan + metronidazole after soaking in a simulated vaginal fluid for 10 minutes; b) a figure depicting an alginate/chitosan + metronidazole dry membrane before and after rupture during a tensile stress test; c) a figure showing a sample alginate/chitosan + metronidazole dry membrane being manually folded; d) the raw and processed data of the swelling studies in milliQ water and simulated vaginal fluid; e) the raw and processed data of the degradation studies in simulated vaginal fluid; f) the results of the antibacterial studies for both <em>Gardnerella vaginalis </em>and <em>Staphilococcus aureus <...

Research paper thumbnail of SWIFT: A Deep Learning Approach to Prediction of Hypoxemic Events in Critically-Ill Patients Using SpO2 Waveform Prediction

Hypoxemia is a significant driver of mortality and poor clinical outcomes in conditions such as b... more Hypoxemia is a significant driver of mortality and poor clinical outcomes in conditions such as brain injury and cardiac arrest in critically ill patients, including COVID-19 patients. Given the host of negative clinical outcomes attributed to hypoxemia, identifying patients likely to experience hypoxemia would offer valuable opportunities for early and thus more effective intervention. We present SWIFT (SpO2Waveform ICU Forecasting Technique), a deep learning model that predicts blood oxygen saturation (SpO2) waveforms 5 and 30 minutes in the future using only prior SpO2 values as inputs. When tested on novel data, SWIFT predicts more than 80% and 60% of hypoxemic events in critically ill and COVID-19 patients, respectively. SWIFT also predicts SpO2 waveforms with average MSE below .0007. SWIFT provides information on both occurrence and magnitude of potential hypoxemic events 30 minutes in advance, allowing it to be used to inform clinical interventions, patient triaging, and opti...

Research paper thumbnail of Degradation studies of spray coated polymer films using cantilever sensors

 Users may download and print one copy of any publication from the public portal for the purpose... more  Users may download and print one copy of any publication from the public portal for the purpose of private study or research.  You may not further distribute the material or use it for any profit-making activity or commercial gain  You may freely distribute the URL identifying the publication in the public portal If you believe that this document breaches copyright please contact us providing details, and we will remove access to the work immediately and investigate your claim.

Research paper thumbnail of Early identification of impending cardiac arrest in neonates and infants in the cardiovascular ICU: a statistical modelling approach using physiologic monitoring data

Cardiology in the Young, 2019

Objective:To develop a physiological data-driven model for early identification of impending card... more Objective:To develop a physiological data-driven model for early identification of impending cardiac arrest in neonates and infants with cardiac disease hospitalised in the cardiovascular ICU.Methods:We performed a single-institution retrospective cohort study (11 January 2013–16 September 2015) of patients ≤1 year old with cardiac disease who were hospitalised in the cardiovascular ICU at a tertiary care children’s hospital. Demographics and diagnostic codes of cardiac arrest were obtained via the electronic health record. Diagnosis of cardiac arrest was validated by expert clinician review. Minute-to-minute physiological monitoring data were recorded via bedside monitors. A generalized linear model was used to compute a minute by minute risk score. Training and test data sets both included data from patients who did and did not develop cardiac arrest. An optimal risk-score threshold was derived based on the model’s discriminatory capacity for impending arrest versus non-arrest. Mo...

Research paper thumbnail of An efficient energy-density-dependent undersampling approach for compressive sensing in spectral domain optical coherence tomography (Conference Presentation)

High-Speed Biomedical Imaging and Spectroscopy: Toward Big Data Instrumentation and Management II, 2017

Many prior studies performed in the area of compressive optical coherence tomography (OCT) have m... more Many prior studies performed in the area of compressive optical coherence tomography (OCT) have mostly dealt with the problem of compressive sensing and sparse recovery of processed OCT images. Unlike these studies, in this paper, we study the application of compressive sensing in terms of efficient data storage and generating OCT images from undersampled raw unprocessed spectral domain OCT data. High resolution spectral domain OCT requires acquisition of enormous amount of data at very high sampling rate but such a large amount of the raw data impedes fast and efficient data storage and communication. To solve the problem of storing a large amount of data, we propose a specific undersampling method guided by the energy density of the spectral domain data in order to facilitate sparse representation of the raw data in terms of its salient frequency domain samples. This method takes into account not just the higher amplitude spectral data, as suggested in some previous studies but samples data based on nearly uniform distribution of energy over all the sampling intervals in the entire spectrum. Finally, we apply some state of the art sparse recovery methods involving L1 minimization to recover our desired high resolution images from the undersampled spectral domain data. We demonstrate the performance of our proposed scheme by comparing it with the recovery accuracy of some recent energy-guided undersampling methods and the conventional compressive sensing with random undersampling. We also compare the performance of our method with the other methods in terms of data compression ratio with respect to the reconstruction error.

Research paper thumbnail of Blu-Ray-based micromechanical characterization platform for biopolymer degradation assessment

Sensors and Actuators B: Chemical, 2017

 Users may download and print one copy of any publication from the public portal for the purpose... more  Users may download and print one copy of any publication from the public portal for the purpose of private study or research.  You may not further distribute the material or use it for any profit-making activity or commercial gain  You may freely distribute the URL identifying the publication in the public portal If you believe that this document breaches copyright please contact us providing details, and we will remove access to the work immediately and investigate your claim.

Research paper thumbnail of Microcantilever sensors for fast analysis of enzymatic degradation of poly (d, l-lactide)

Polymer Degradation and Stability, 2015

 Users may download and print one copy of any publication from the public portal for the purpose... more  Users may download and print one copy of any publication from the public portal for the purpose of private study or research.  You may not further distribute the material or use it for any profit-making activity or commercial gain  You may freely distribute the URL identifying the publication in the public portal If you believe that this document breaches copyright please contact us providing details, and we will remove access to the work immediately and investigate your claim.

Research paper thumbnail of Micromechanical fast quasi-static detection of α and β relaxations with nanograms of polymer

Journal of Polymer Science Part B: Polymer Physics, 2015

 Users may download and print one copy of any publication from the public portal for the purpose... more  Users may download and print one copy of any publication from the public portal for the purpose of private study or research.  You may not further distribute the material or use it for any profit-making activity or commercial gain  You may freely distribute the URL identifying the publication in the public portal If you believe that this document breaches copyright please contact us providing details, and we will remove access to the work immediately and investigate your claim.

Research paper thumbnail of Micromechanical resonators as a tool for polymer characterization

The aim of this Ph.D. project was the evaluation of micromechanical resonators like cantilevers a... more The aim of this Ph.D. project was the evaluation of micromechanical resonators like cantilevers and strings as analytical tools for characterization of polymers. Spray coating was used as the technique to coat one side of the micromechanical resonators with polymer. Process optimization of different spray coating parameters was carried out with two polymer-solvent systems to obtain homogeneous films with uniform thickness and low roughness. Full factorial experimental design was employed to identify the most important parameter among the crucial parameters of spray coating such as nozzle-substrate distance, the temperature of the substrate and the speed of the spraying nozzle. Micromechanical string resonators were successfully developed as an analytical tool for sensitive and fast thermal characterization of polymers with only a few nanograms of sample. Both the glass transition (T g) and sub-T g transition of different polymers were detected and confirmed by conventional thermal polymer characterization techniques. An analytical model was derived to validate the resonance frequency response of the polymer coated microstrings during heating cycles. The resonance frequency change provided the quasi-static T g of polymers while the quality factor change provided the frequency dependent shift of T g to higher temperature. Microcantilevers were successfully employed as a platform for fast estimation of polymer degradation rate with minute amount of sample compared to conventional techniques. A detailed investigation of enzymatic degradation of poly (D, L-lactide) was done in buffered proteinase K solution. The influence of concentration of the enzyme solution, pre-hydration in buffer, surface morphology and adsorption time of enzymes on the rate of degradation was studied. The bulk degradation rate estimated from the experimental results and model simulation of multilayered cantilever structures matched well with values reported in literature. The basic understanding of the spray coating process and the newly developed approaches of microstrings and microcantilevers as analytical tools show promising potential for investigation of different polymers and pharmaceutical systems. viii Danske Resumé Formålet med dette phd-projekt er at evaluere mikromekaniske resonatorer-bjaelker og strengesom analytiske vaerktøjer til karakterisering af polymerer. Sprøjtebelaegning (spray coating) blev anvendt til at deponere polymer på den ene side af de mikromekaniske resonatorer. For at opnå en homogen film, med ensartet tykkelse og lav ruhed, blev der udført procesoptimeringer af forskellige sprøjtebelaegnings parametre, med to forskellige polymer/opløsningsmiddel systemer. Blandt de vigtigste parametre for sprøjtebelaegning, så som dyse-substrat afstand, substrat temperatur og sprøjtedysehastighed, blev den mest betydende parameter identificeret ved hjaelp af en total faktoranalyse af det eksperimentelle design. De mikromekaniske streng resonatorer er med stor succes blevet udviklet til et følsomt analytisk redskab til hurtig termisk karakterisering af nanogram-prøver af polymer. Både den formelle glasovergangstemperatur (T g), samt den underliggende T g overgang, blev påvist i forskellige polymerer og bekraeftet ved konventionelle teknikker til termisk karakterisering af polymerer. En analytisk model blev udledt til at validere aendringer i resonansfrekvensen af de polymerbelagte mikrostrenge under opvarmningscykler. AEndringen i resonansfrekvensen giver en kvasi-statisk T g bestemmelse for polymerer mens aendringer i kvalitetsfaktoren (Q faktorer) giver det frekvensafhaengige skift af T g til højere temperatur. Ydermere er det lykkedes at bruge mikrobjaelker som en platform til hurtig estimering af nedbrydningshastigheder i polymerer, og med anvendelse af minimal prøvemaengde sammenlignet med konventionelle teknikker. En detaljeret undersøgelse blev gennemført af den enzymatiske nedbrydning af poly (D, L-lactid) i bufferet proteinase K-opløsning. Indflydelsen på nedbrydningshastigheden blev undersøgt ved hjaelp af: koncentrationen af enzymopløsningen, prehydrering i buffer, overflademorfologi og enzymadsorptionstid,. Ud fra de eksperimentelle resultater, samt en modelsimulering af flerlags bjaelkestrukturer, blev nedbrydningstiden estimeret, og viste sig at have god overensstemmelse med vaerdier tidligere rapporteret i litteraturen. Den grundlaeggende forståelse af sprøjtebelaegningsprocessen, samt de nyudviklede tilgange til brug af mikrobjaelker og-strenge som analytiske vaerktøjer, har meget lovende potentiale indenfor undersøgelse af forskellige polymerer og farmaceutiske systemer.

Research paper thumbnail of Micromechanical String Resonators: Analytical Tool for Thermal Characterization of Polymers

ACS Macro Letters, 2014

Resonant microstrings show promise as a new analytical tool for thermal characterization of polym... more Resonant microstrings show promise as a new analytical tool for thermal characterization of polymers with only few nanograms of sample. The detection of the glass transition temperature (T g) of an amorphous poly(D,L-lactide) (PDLLA) and a semicrystalline poly(L-lactide) (PLLA) is investigated. The polymers are spray coated on one side of the resonating microstrings. The resonance frequency and quality factor (Q) are measured simultaneously as a function of temperature. Change in the resonance frequency reflects a change in static tensile stress, which yields information about the Young's modulus of the polymer, and a change in Q reflects the change in damping of the polymer-coated string. The frequency response of the microstring is validated with an analytical model. From the frequency independent tensile stress change, static T g values of 40.6 and 57.6°C were measured for PDLLA and PLLA, respectively. The frequency-dependent damping from Q indicates higher T g values of 62.6 and 88.8°C for PDLLA and PLLA, respectively, at ∼10 5 Hz. Resonant microstrings facilitate thermal analysis of nanogram polymer samples measuring the static and a dynamic glass transition temperature simultaneously.

Research paper thumbnail of Dynamic rheology and morphology of HDPE-fumed silica composites: Effect of interface modification

Polymer Engineering & Science, 2012

In the present study, high density polyethylene (HDPE)based composites containing different amoun... more In the present study, high density polyethylene (HDPE)based composites containing different amounts of fumed silica (FS) were prepared by melt compounding in a corotating twin screw extruder. Polyethylene-gmaleic anhydride copolymer (PE-g-MA) containing 1 wt% maleic anhydride was used for interface modification between filler and polymer. The interaction between the surface hydroxyl groups of fumed silica nanoparticles with maleic anhydride groups of PEg -MA led to a finer dispersion of the filler in the HDPE matrix. The terminal complex viscosity and terminal storage modulus were highest at 1 wt% filler loading due to widely spread network formation by FS nanoparticles. This filler network plausibly got disturbed at higher filler content and/or interface modification which was reflected in their stress relaxation behavior also. The dynamic rheological behavior of the composites was explained in terms of morphological observations.

Research paper thumbnail of Process Optimization of Ultrasonic Spray Coating of Polymer Films

Research paper thumbnail of Effect of maleic anhydride grafted polyethylene on engineering properties and morphology of fumed silica filled polyethylene blown films

Journal of Plastic Film & Sheeting, 2012

Blown films of high-density polyethylene (HDPE)/fumed silica (FS) composites were prepared by mel... more Blown films of high-density polyethylene (HDPE)/fumed silica (FS) composites were prepared by melt-mixing in twin-screw extruder. Maleic anhydride grafted polyethylene (PE-g-MA) was introduced to improve the state of filler dispersion during melt processing. The blown films were tested for thermal, mechanical, morphological, barrier, and optical properties. The Fourier Transform Infrared Spectroscopy-Attenuated Total Reflectance (FTIR-ATR) study indicated that interaction between FS and HDPE was slightly enhanced by PE-g-MA. No change in percent crystallinity was observed but mechanical properties improved after modification. Morphological analyses showed large FS clusters at higher loading which decreased after modification. Both oxygen and water vapor transmission rates of the films increased in composites as compared to HDPE, plausibly due to formation of nanogaps in blown film and/or increased solubility of penetrant molecules at filler–matrix interface.

Research paper thumbnail of Process optimization for spray coating of poly (D, L-lactic acid) films

 Users may download and print one copy of any publication from the public portal for the purpose... more  Users may download and print one copy of any publication from the public portal for the purpose of private study or research.  You may not further distribute the material or use it for any profit-making activity or commercial gain  You may freely distribute the URL identifying the publication in the public portal If you believe that this document breaches copyright please contact us providing details, and we will remove access to the work immediately and investigate your claim.

Research paper thumbnail of Early Prediction of Multiple Organ Dysfunction in the Pediatric Intensive Care Unit

Frontiers in Pediatrics

Objective:The objective of the study is to build models for early prediction of risk for developi... more Objective:The objective of the study is to build models for early prediction of risk for developing multiple organ dysfunction (MOD) in pediatric intensive care unit (PICU) patients.Design:The design of the study is a retrospective observational cohort study.Setting:The setting of the study is at a single academic PICU at the Johns Hopkins Hospital, Baltimore, MD.Patients:The patients included in the study were <18 years of age admitted to the PICU between July 2014 and October 2015.Measurements and main results:Organ dysfunction labels were generated every minute from preceding 24-h time windows using the International Pediatric Sepsis Consensus Conference (IPSCC) and Proulx et al. MOD criteria. Early MOD prediction models were built using four machine learning methods: random forest, XGBoost, GLMBoost, and Lasso-GLM. An optimal threshold learned from training data was used to detect high-risk alert events (HRAs). The early prediction models from all methods achieved an area und...

Research paper thumbnail of Supporting data for: "Long lasting mucoadhesive membrane based on alginate and chitosan for intravaginal drug delivery

The document is a collection of supporting information for the manuscript titled: <strong>&... more The document is a collection of supporting information for the manuscript titled: <strong>"Long lasting mucoadhesive membrane based on alginate and chitosan for intravaginal drug delivery".</strong> The supporting information include: a) the stress-strain curves obtained from the compression studies of alginate, alginate/chitosan and alginate/chitosan + metronidazole after soaking in a simulated vaginal fluid for 10 minutes; b) a figure depicting an alginate/chitosan + metronidazole dry membrane before and after rupture during a tensile stress test; c) a figure showing a sample alginate/chitosan + metronidazole dry membrane being manually folded; d) the raw and processed data of the swelling studies in milliQ water and simulated vaginal fluid; e) the raw and processed data of the degradation studies in simulated vaginal fluid; f) the results of the antibacterial studies for both <em>Gardnerella vaginalis </em>and <em>Staphilococcus aureus <...

Research paper thumbnail of SWIFT: A Deep Learning Approach to Prediction of Hypoxemic Events in Critically-Ill Patients Using SpO2 Waveform Prediction

Hypoxemia is a significant driver of mortality and poor clinical outcomes in conditions such as b... more Hypoxemia is a significant driver of mortality and poor clinical outcomes in conditions such as brain injury and cardiac arrest in critically ill patients, including COVID-19 patients. Given the host of negative clinical outcomes attributed to hypoxemia, identifying patients likely to experience hypoxemia would offer valuable opportunities for early and thus more effective intervention. We present SWIFT (SpO2Waveform ICU Forecasting Technique), a deep learning model that predicts blood oxygen saturation (SpO2) waveforms 5 and 30 minutes in the future using only prior SpO2 values as inputs. When tested on novel data, SWIFT predicts more than 80% and 60% of hypoxemic events in critically ill and COVID-19 patients, respectively. SWIFT also predicts SpO2 waveforms with average MSE below .0007. SWIFT provides information on both occurrence and magnitude of potential hypoxemic events 30 minutes in advance, allowing it to be used to inform clinical interventions, patient triaging, and opti...

Research paper thumbnail of Degradation studies of spray coated polymer films using cantilever sensors

 Users may download and print one copy of any publication from the public portal for the purpose... more  Users may download and print one copy of any publication from the public portal for the purpose of private study or research.  You may not further distribute the material or use it for any profit-making activity or commercial gain  You may freely distribute the URL identifying the publication in the public portal If you believe that this document breaches copyright please contact us providing details, and we will remove access to the work immediately and investigate your claim.

Research paper thumbnail of Early identification of impending cardiac arrest in neonates and infants in the cardiovascular ICU: a statistical modelling approach using physiologic monitoring data

Cardiology in the Young, 2019

Objective:To develop a physiological data-driven model for early identification of impending card... more Objective:To develop a physiological data-driven model for early identification of impending cardiac arrest in neonates and infants with cardiac disease hospitalised in the cardiovascular ICU.Methods:We performed a single-institution retrospective cohort study (11 January 2013–16 September 2015) of patients ≤1 year old with cardiac disease who were hospitalised in the cardiovascular ICU at a tertiary care children’s hospital. Demographics and diagnostic codes of cardiac arrest were obtained via the electronic health record. Diagnosis of cardiac arrest was validated by expert clinician review. Minute-to-minute physiological monitoring data were recorded via bedside monitors. A generalized linear model was used to compute a minute by minute risk score. Training and test data sets both included data from patients who did and did not develop cardiac arrest. An optimal risk-score threshold was derived based on the model’s discriminatory capacity for impending arrest versus non-arrest. Mo...

Research paper thumbnail of An efficient energy-density-dependent undersampling approach for compressive sensing in spectral domain optical coherence tomography (Conference Presentation)

High-Speed Biomedical Imaging and Spectroscopy: Toward Big Data Instrumentation and Management II, 2017

Many prior studies performed in the area of compressive optical coherence tomography (OCT) have m... more Many prior studies performed in the area of compressive optical coherence tomography (OCT) have mostly dealt with the problem of compressive sensing and sparse recovery of processed OCT images. Unlike these studies, in this paper, we study the application of compressive sensing in terms of efficient data storage and generating OCT images from undersampled raw unprocessed spectral domain OCT data. High resolution spectral domain OCT requires acquisition of enormous amount of data at very high sampling rate but such a large amount of the raw data impedes fast and efficient data storage and communication. To solve the problem of storing a large amount of data, we propose a specific undersampling method guided by the energy density of the spectral domain data in order to facilitate sparse representation of the raw data in terms of its salient frequency domain samples. This method takes into account not just the higher amplitude spectral data, as suggested in some previous studies but samples data based on nearly uniform distribution of energy over all the sampling intervals in the entire spectrum. Finally, we apply some state of the art sparse recovery methods involving L1 minimization to recover our desired high resolution images from the undersampled spectral domain data. We demonstrate the performance of our proposed scheme by comparing it with the recovery accuracy of some recent energy-guided undersampling methods and the conventional compressive sensing with random undersampling. We also compare the performance of our method with the other methods in terms of data compression ratio with respect to the reconstruction error.

Research paper thumbnail of Blu-Ray-based micromechanical characterization platform for biopolymer degradation assessment

Sensors and Actuators B: Chemical, 2017

 Users may download and print one copy of any publication from the public portal for the purpose... more  Users may download and print one copy of any publication from the public portal for the purpose of private study or research.  You may not further distribute the material or use it for any profit-making activity or commercial gain  You may freely distribute the URL identifying the publication in the public portal If you believe that this document breaches copyright please contact us providing details, and we will remove access to the work immediately and investigate your claim.

Research paper thumbnail of Microcantilever sensors for fast analysis of enzymatic degradation of poly (d, l-lactide)

Polymer Degradation and Stability, 2015

 Users may download and print one copy of any publication from the public portal for the purpose... more  Users may download and print one copy of any publication from the public portal for the purpose of private study or research.  You may not further distribute the material or use it for any profit-making activity or commercial gain  You may freely distribute the URL identifying the publication in the public portal If you believe that this document breaches copyright please contact us providing details, and we will remove access to the work immediately and investigate your claim.

Research paper thumbnail of Micromechanical fast quasi-static detection of α and β relaxations with nanograms of polymer

Journal of Polymer Science Part B: Polymer Physics, 2015

 Users may download and print one copy of any publication from the public portal for the purpose... more  Users may download and print one copy of any publication from the public portal for the purpose of private study or research.  You may not further distribute the material or use it for any profit-making activity or commercial gain  You may freely distribute the URL identifying the publication in the public portal If you believe that this document breaches copyright please contact us providing details, and we will remove access to the work immediately and investigate your claim.

Research paper thumbnail of Micromechanical resonators as a tool for polymer characterization

The aim of this Ph.D. project was the evaluation of micromechanical resonators like cantilevers a... more The aim of this Ph.D. project was the evaluation of micromechanical resonators like cantilevers and strings as analytical tools for characterization of polymers. Spray coating was used as the technique to coat one side of the micromechanical resonators with polymer. Process optimization of different spray coating parameters was carried out with two polymer-solvent systems to obtain homogeneous films with uniform thickness and low roughness. Full factorial experimental design was employed to identify the most important parameter among the crucial parameters of spray coating such as nozzle-substrate distance, the temperature of the substrate and the speed of the spraying nozzle. Micromechanical string resonators were successfully developed as an analytical tool for sensitive and fast thermal characterization of polymers with only a few nanograms of sample. Both the glass transition (T g) and sub-T g transition of different polymers were detected and confirmed by conventional thermal polymer characterization techniques. An analytical model was derived to validate the resonance frequency response of the polymer coated microstrings during heating cycles. The resonance frequency change provided the quasi-static T g of polymers while the quality factor change provided the frequency dependent shift of T g to higher temperature. Microcantilevers were successfully employed as a platform for fast estimation of polymer degradation rate with minute amount of sample compared to conventional techniques. A detailed investigation of enzymatic degradation of poly (D, L-lactide) was done in buffered proteinase K solution. The influence of concentration of the enzyme solution, pre-hydration in buffer, surface morphology and adsorption time of enzymes on the rate of degradation was studied. The bulk degradation rate estimated from the experimental results and model simulation of multilayered cantilever structures matched well with values reported in literature. The basic understanding of the spray coating process and the newly developed approaches of microstrings and microcantilevers as analytical tools show promising potential for investigation of different polymers and pharmaceutical systems. viii Danske Resumé Formålet med dette phd-projekt er at evaluere mikromekaniske resonatorer-bjaelker og strengesom analytiske vaerktøjer til karakterisering af polymerer. Sprøjtebelaegning (spray coating) blev anvendt til at deponere polymer på den ene side af de mikromekaniske resonatorer. For at opnå en homogen film, med ensartet tykkelse og lav ruhed, blev der udført procesoptimeringer af forskellige sprøjtebelaegnings parametre, med to forskellige polymer/opløsningsmiddel systemer. Blandt de vigtigste parametre for sprøjtebelaegning, så som dyse-substrat afstand, substrat temperatur og sprøjtedysehastighed, blev den mest betydende parameter identificeret ved hjaelp af en total faktoranalyse af det eksperimentelle design. De mikromekaniske streng resonatorer er med stor succes blevet udviklet til et følsomt analytisk redskab til hurtig termisk karakterisering af nanogram-prøver af polymer. Både den formelle glasovergangstemperatur (T g), samt den underliggende T g overgang, blev påvist i forskellige polymerer og bekraeftet ved konventionelle teknikker til termisk karakterisering af polymerer. En analytisk model blev udledt til at validere aendringer i resonansfrekvensen af de polymerbelagte mikrostrenge under opvarmningscykler. AEndringen i resonansfrekvensen giver en kvasi-statisk T g bestemmelse for polymerer mens aendringer i kvalitetsfaktoren (Q faktorer) giver det frekvensafhaengige skift af T g til højere temperatur. Ydermere er det lykkedes at bruge mikrobjaelker som en platform til hurtig estimering af nedbrydningshastigheder i polymerer, og med anvendelse af minimal prøvemaengde sammenlignet med konventionelle teknikker. En detaljeret undersøgelse blev gennemført af den enzymatiske nedbrydning af poly (D, L-lactid) i bufferet proteinase K-opløsning. Indflydelsen på nedbrydningshastigheden blev undersøgt ved hjaelp af: koncentrationen af enzymopløsningen, prehydrering i buffer, overflademorfologi og enzymadsorptionstid,. Ud fra de eksperimentelle resultater, samt en modelsimulering af flerlags bjaelkestrukturer, blev nedbrydningstiden estimeret, og viste sig at have god overensstemmelse med vaerdier tidligere rapporteret i litteraturen. Den grundlaeggende forståelse af sprøjtebelaegningsprocessen, samt de nyudviklede tilgange til brug af mikrobjaelker og-strenge som analytiske vaerktøjer, har meget lovende potentiale indenfor undersøgelse af forskellige polymerer og farmaceutiske systemer.

Research paper thumbnail of Micromechanical String Resonators: Analytical Tool for Thermal Characterization of Polymers

ACS Macro Letters, 2014

Resonant microstrings show promise as a new analytical tool for thermal characterization of polym... more Resonant microstrings show promise as a new analytical tool for thermal characterization of polymers with only few nanograms of sample. The detection of the glass transition temperature (T g) of an amorphous poly(D,L-lactide) (PDLLA) and a semicrystalline poly(L-lactide) (PLLA) is investigated. The polymers are spray coated on one side of the resonating microstrings. The resonance frequency and quality factor (Q) are measured simultaneously as a function of temperature. Change in the resonance frequency reflects a change in static tensile stress, which yields information about the Young's modulus of the polymer, and a change in Q reflects the change in damping of the polymer-coated string. The frequency response of the microstring is validated with an analytical model. From the frequency independent tensile stress change, static T g values of 40.6 and 57.6°C were measured for PDLLA and PLLA, respectively. The frequency-dependent damping from Q indicates higher T g values of 62.6 and 88.8°C for PDLLA and PLLA, respectively, at ∼10 5 Hz. Resonant microstrings facilitate thermal analysis of nanogram polymer samples measuring the static and a dynamic glass transition temperature simultaneously.

Research paper thumbnail of Dynamic rheology and morphology of HDPE-fumed silica composites: Effect of interface modification

Polymer Engineering & Science, 2012

In the present study, high density polyethylene (HDPE)based composites containing different amoun... more In the present study, high density polyethylene (HDPE)based composites containing different amounts of fumed silica (FS) were prepared by melt compounding in a corotating twin screw extruder. Polyethylene-gmaleic anhydride copolymer (PE-g-MA) containing 1 wt% maleic anhydride was used for interface modification between filler and polymer. The interaction between the surface hydroxyl groups of fumed silica nanoparticles with maleic anhydride groups of PEg -MA led to a finer dispersion of the filler in the HDPE matrix. The terminal complex viscosity and terminal storage modulus were highest at 1 wt% filler loading due to widely spread network formation by FS nanoparticles. This filler network plausibly got disturbed at higher filler content and/or interface modification which was reflected in their stress relaxation behavior also. The dynamic rheological behavior of the composites was explained in terms of morphological observations.

Research paper thumbnail of Process Optimization of Ultrasonic Spray Coating of Polymer Films

Research paper thumbnail of Effect of maleic anhydride grafted polyethylene on engineering properties and morphology of fumed silica filled polyethylene blown films

Journal of Plastic Film & Sheeting, 2012

Blown films of high-density polyethylene (HDPE)/fumed silica (FS) composites were prepared by mel... more Blown films of high-density polyethylene (HDPE)/fumed silica (FS) composites were prepared by melt-mixing in twin-screw extruder. Maleic anhydride grafted polyethylene (PE-g-MA) was introduced to improve the state of filler dispersion during melt processing. The blown films were tested for thermal, mechanical, morphological, barrier, and optical properties. The Fourier Transform Infrared Spectroscopy-Attenuated Total Reflectance (FTIR-ATR) study indicated that interaction between FS and HDPE was slightly enhanced by PE-g-MA. No change in percent crystallinity was observed but mechanical properties improved after modification. Morphological analyses showed large FS clusters at higher loading which decreased after modification. Both oxygen and water vapor transmission rates of the films increased in composites as compared to HDPE, plausibly due to formation of nanogaps in blown film and/or increased solubility of penetrant molecules at filler–matrix interface.

Research paper thumbnail of Process optimization for spray coating of poly (D, L-lactic acid) films

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