AFM-Based Mechanical Nanomanipulation

Advances in several research areas increase the need for more sophisticated fabrication techniques and better performing materials. Tackling this problem from a bottom-up perspective is currently an active field of research. The bottom-up fabrication procedure offers sub-nanometer accurate manipulation. At this time, candidates to achieve nanomanipulation include chemical (self-assembly), biotechnology methods (DNA-based), or using controllable physical forces (e.g. electrokinetic forces, mechanical forces). In this thesis, new methods and techniques for mechanical nanomanipulation using probe force interaction are developed. The considered probes are commonly used in Atomic Force Microscopes (AFMs) for high resolution imaging. AFM-based mechanical nanomanipulation will enable arranging nanoscale entities such as nanotubes and molecules in a precise and controlled manner to assemble and produce novel devices and systems at the nanoscale. The novelty of this research stems from the development of new modeling of the physics and mechanics of the tip interaction with nanoscale entities, coupled with the development of new smart cantilevers with multiple degrees of freedom. The gained knowledge from the conducted simulations and analysis is expected to enable true precision and repeatability of nanomanipulation tasks which is not feasible with existing methods and technologies

Thermally actuated mechanical systems

This thesis will discuss the generation of controlled sub-micron motions using novel micro actuators. Our research focuses on the development of an arm-type actuator and a free-motion locomotive walking device. Nano-science and nano-technology focuses on the creation of novel functional materials and also at the development of new fabrication techniques incorporating them. In the fields of novel fabrication techniques, manipulations of micron or sub-micron objects by micro actuators have been suggested in the science and engineering societies for mainly two reasons. From a scientific standpoint, new tools enable new prospective sciences, as is evident from the development of the atomic force microscope. From an engineering standpoint, the miniaturization of manipulation tools will require less material and less energy during a material's production. In spite of such importance, progress in the actuator miniaturization is in a primitive state, especially for the micro mobile devices. The thesis will be a key step in pursuit of this goal with an emphasis on generating motions. Our static actuator uses the excellent elastic properties of multiwall carbon nanotubes as a template for a bimorph system. Deflections in response to temperature variations are demonstrated. The mobile device itself is a bimorph system consisting of thin metal films. Control mechanisms for its velocity and steering are discussed. Finally, fundamental limits on the capabilities of the two devices in a more general sense are discussed under via laws of physics

Interfacial phenomena between bacterial or mammalian cells and orthopaedic biomaterials

Adhesion as a scientific phenomenon has been researched for the past 70 years, as the notion of two entities contacting effects a huge expanse of daily activities, from writing to sophisticated cellular and bacterial interactions essential for growth and survival. Inherently, a robust and adequate model of adhesion was acquired, one in which biological aspects were considered. Initially, the methodology required was optimised using the atomic force microscope (AFM) by testing a model bone substrate against ultra-high molecular weight polyethylene (UHMWPE), a material commonly found in the articulating acetabular cup. Once a force mapping technique was established experimentation continued to bacterial adhesion against model bone samples of various roughness, establishing that the adhesion phenomena occurs at a scale dependency due to the alterations in the topography of the surface at the micro to nano level. Aseptic loosening and osteolysis are major causes of failures in implanted biomedical devices at the hip. These issues are governed by the deterioration of the moving components, producing particles known as wear debris associated with the metals, bone cement, and UHMWPE materials initiating an immune response which is detrimental to the surrounding cells and tissues adjacent to the implant. The notion of mechanical aspects altering the health of mammalian cells has been ignored throughout the research of implantations and their effect on the cells by foreign bodies; the only concept studied to date is the viability and functionality post exposure. Therefore, this thesis aims at observing ii mesenchymal and osteoblast (both rodent and human) cells associated to wear debris (metal and polymeric particles of various sizes and compositions) exposure and the effect this has on cell nanomechanical and adhesive properties using the AFM techniques. The data obtained indicated that Cobalt nanoparticles were more damaging on all cell types than Titanium and polymeric particles

Effect of nonlinear friction on the motion of an object on solid surface induced by external vibration

There are enumerable examples of natural processes which fall in the class of non-equilibrium stochastic dynamics. In the literature it is prescribed that such a process can be described completely using transition probability that satisfy the Fokker Planck equation. The analytical solutions of transition probability density function are difficult to obtain and are available for linear systems along with few first order nonlinear systems. We studied such nonlinear stochastic systems and tried to identify the important parameters associated with the dynamics and energy dissipative mechanism using statistical tools.We present experimental study of macroscopic systems driven away far from equilibrium with an applied bias and external mechanical noise. This includes sliding of small solid object, gliding of a liquid drop or a rolling of a rigid sphere. We demonstrated that the displacement statistics are non-Gaussian at short observation time, but they tend towards a Gaussian behavior at long time scale. We also found that, the drift velocity increases sub-linearly, but the diffusivity increases super-linearly with the strength of the noise. These observations reflect that the underlying non-linear friction controls the stochastic dynamics in each of these cases. We established a new statistical approach to determine the underlying friction law and identified the operating range of linear and nonlinear friction regime.In all these experiments source of the noise and the origin of the energy dissipation mechanism (i.e. friction) are decoupled. Naturaly question arises whether the stochastic dynamics of these athermal systems are amenable to Einstein\u27s Fluctuation dissipation theorem which is valid strictly for a closed thermodynamic system. We addressed these issues by comparing Einstein\u27s ratio of Diffusivity and mobility which are measurable quantities in our experimental systems. As all our experimental systems exhibit substantial negative fluctuations of displacement that diminishes with observation time scale, we used another approach of integrated fluctuation theorem to identify athermal temperature of the system by characterizing a persistence time of negative fluctuations in terms of the measurable quantity. Specific experiments have also been designed to study the crossing of a small object over a physical barrier assisted by an external noise and a bias force. These results mimic the classical Arrhenius behavior from which another effective temperature may be deduced. All these studies confer that the nonlinear system does not possess any unique temperature.Detachment of a solid sphere as well as a liquid drop from a structured rubber surface during subcritical motion in presence of external noise was examined in the light of Arrhenius\u27 activated rate equation. Drift velocity of small drops of water-glycerin solution behaves nonlinearly with viscosity which is reminiscence of Kramers\u27 turn over theory of activated rate. In a designed experiment of barrier crossing of liquid drops we satisfactorily verified the Kramers\u27 formalism of activated rate at the low friction limit

Characterising the force balance between active pharmaceutical ingredients for inhalation and its impact on deposition

Interparticulate interactions play a significant role in determining the downstream behaviours of all pharmaceutical formulations and are therefore essential considerations when approaching formulation design. Inhalation product formulation in particular is inherently bound to an understanding of these forces. Delivery of drugs to the lower airways to treat conditions like asthma and COPD requires a particle size of below 5 micron. This implicitly demands micronization of the active pharmaceutical ingredients (APls) and this process renders many particles of large surface area with high surface energies and an auto-adhesive tendency. There is therefore a concurrent reduction in the flowability and dispersion properties of these systems. The interactive character predisposes agglomeration, flocculation or device retention and will compromise manufacture, stability, device function, and the aerosolization behavior of a formulation. Ultimately the ability of any aerosolized API to reach the deep airways is dependent upon adhesion force dynamics. As such, an appreciation of the forces of attraction and scale of particulate interactions within inhaler technology is critical if a successful drug delivery device is to be realized. The advancement of the atomic force microscope (AFM) as a force probing apparatus, has meant that it is now possible to measure the force of adhesion between two particles of interest. However these measurements could not easily be compared, because there is no simple means to account for differences in the contact regime (geometrics) between measurements. However, the development of the cohesive adhesive balance (CAB) approach by Begat, Morton, Stainforth and Price in 2004 has offered a means to negate this limitation. Using a colloidal probe microscopy (CPM) derived technique a particle of a selected material of interest (API, carrier molecule etc.) is attached to an AFM cantilever and ramped onto and off the surface of another material of interest (adhesion measurement), and to a surface of the same material as the tip (cohesion measurement). By graphically plotting the adhesive force values of a series of tips, as a function of the cohesive force values of the same tips, a representation of the relative particle interaction can be obtained. Quantitative information regarding the adhesive/cohesive nature of the interaction can then be extracted from the graph and a description of the interaction formulated that can be compared to other material combinations. The CAB work carried out to date has used recrystallized model substrates. These molecularly flat surfaces ensured there would be no difference between the contact geometry of a functionalised AFM probe and the adhesive and cohesive surfaces of the study respectively. In this fashion the only variable between the two measurements would be the chemical interactivity, and not the interactive surface area. However while using such methodology guarantees the validity of the approach, it is not necessarily a true representation of the materials 'in-situ' and requires more complex sample preparation and complex experimental design. For a variety of reasons this can be misleading in its own right. This thesis details the .investigation into the application of an adapted CAB approach in characterizing the force balance between APls for inhalation in their real state. In so doing, the aim was to see whether such a CAB would offer a quicker and simpler, yet relevant and informative assessment of a drug system force balance. It was hoped that said force balance could in turn be associated with a measurable impact upon the formulation performance of the characterised ingredients as measured 'in-vitro'. This interest was particularly directed at the lesser characterized pressurized metered dose inhaler (pMOI) systems. While these formulations are solvent based, it was of interest to identify whether a simple API to API challenge could infer a descriptive balance that could link to 'in-vitro' performance. Furthermore there was interest in evaluating the use of a range of surface specific imaging techniques to analyse the deposition dynamics of the combination formulations. It was hoped that by doing so, the localisation of the individual components within the binary deposits could again be associated back to the force balance of that system, and that an appreciation of the capability of the techniques involved would be gained. The work that follows therefore commences with the evaluation and description of the capacity for the CAB approach to be adapted to measure force relationships between real beclomethasone dipropionate (BOP) particles and pMDI component surfaces. From this assessment it was found that even with relatively smooth substrates, the combination of bulky functional particles and the inherent substrate roughness caused a critical failure in the CAB model. The parity between cohesive and adhesive geometries of contact was excessively stretched, leading to a loss of force normalisation which was reflected in uncorrelated CAB plots. As a consequence little could be confidently gleaned from the force data acquired, although there was the suggestion that the use of a fluorinated ethylene proplylene (FEP) coating reduced the adhesive interaction between the APls and the pMDI canister wall. This was then followed by an attempt to find a compromise between the model crystal substrates of a pure CAB process and the real particle morphologies that had caused the CAB model to fail. Using a compression process to form API powder compacts, in conjunction with small and discreet functional particles, a confident CAB was achieved for two combinations of APls selected on the basis of surface energy and physical stability analysis. Salbutamol sulphate was characterised with beclomethasone dipropionate, and salmeterol xinafoate with fluticasone propionate. Both combinations showed CAB plots with a sufficiently strong linear regression analysis to suggest a broad accuracy of force balance assessment. Both beta2-agonists showed cohesively dominated relationships with respect to the paired glucocortiocoids, while in reverse both glucocorticoids showed adhesively dominated relationships with the beta2-agonists. There was concern raised over the compression process of the powder discs, and its impact on the physicochemical state of the APls, with some thermodynamic evidence of polymorphic changes that required further work. The next chapter looks at the 'in-vitro' deposition performance of the two API combinations from a HFA134a pMDI system by analysis in an Andersen Cascade Impactor (ACI). The coformulation of salmeterol with fluticasone induced an improvement in the fine particle performance of fluticasone, with a concurrent decrease in the fine particle performance of salmeterol. This impact was hypothesised to be related to alterations in the structure and strength of particle-particle agglomerates. The impact on deposition performance of coformulating beclomethasone and salbutamol was unclear, as a critical unexplained loss of beclomethasone by total recovered mass was seen from all beclomethasone containing formulations. This instability of beclomethasone within the HFA134a system, precluded an accurate assessment of a direct impact on salbutamol deposition. The final chapter, compared a range of surface specific imaging techniques, including scanning electron microscopy (SEM), desorption electrospray ionization mass spectrometry (DESI), Raman spectrometry and time-of-flight secondary ion mass spectrometry (ToF-SIMS) in assessing the extent and nature of 'in-vitro' co-deposition from the salmeterol and fluticasone pMDI formulations. It was apparent that the deposition of the two APls on ACI plates was not likely to be directly comparable assessment of the incidence of particle co-deposition 'in-vivo' due to the forced nature of nozzle directed impaction. However the combination of techniques employed produced a wealth of physical and chemical data that did suggest that the two APls showed extensive co-ordination 'in-vitro'. Raman spectroscopy was able to identify individual particle character and showed frequent salmeterol and fluticasone particle combinations, but suffered from exceptionally long run times and anomalies from photoreactive surface elements. The use of a multivariate approach to ToF-SIMs analysis defined the strong co-association of the two APls, although could not differentiate particle to particle deposition. Multivariate curve resolution (MeR) was used and produced distinct components that segregated ions from both APIS from the background plate but not from each other. SEM imaging was able to define the morphologies of the deposited particles, but was unable to differentiate the two. DES I imaging showed the presence of the two APls together within several drug spots, but could not be used to investigate individual drug spots, and the distribution within, due to inadequate spatial resolution and differences in desorption efficacy. While the co-association of the two APls was observed, the lack of a comparator in another combination of APls made the link between deposition performance and force balance purely descriptive. It was unclear as to whether the force balance of the system lends itself to a particular increase in co-deposition behaviour. However it was apparent that the analytical techniques employed all had respective strengths and weaknesses as mapping tools, and with further work with other formulations could be used to provide a tailored formulation screening process, if subsequent links to force balances could be made. To conclude, the work in this thesis details the successful process of adapting an AFM technique in characterising the broad force balance of combinations of APls. In so doing a force balance has been linked to the alteration in deposition behaviour of two APls when co-formulated in a HFA134 formulation. The subsequent co-deposition of the two APls was then analysed by a series of surface analytical techniques. This highlighted a general co-deposition trend, but the collective results were unable to definitively link to the force balance of the system. The information obtained forms the beginnings of what could be utilised as a fast and facile broad predictor of pMDI formulation performance, and an indication of appropriate analytical techniques for investigating particle association 'in-vitro'

Characterising the force balance between active pharmaceutical ingredients for inhalation and its impact on deposition

Interparticulate interactions play a significant role in determining the downstream behaviours of all pharmaceutical formulations and are therefore essential considerations when approaching formulation design. Inhalation product formulation in particular is inherently bound to an understanding of these forces. Delivery of drugs to the lower airways to treat conditions like asthma and COPD requires a particle size of below 5 micron. This implicitly demands micronization of the active pharmaceutical ingredients (APls) and this process renders many particles of large surface area with high surface energies and an auto-adhesive tendency. There is therefore a concurrent reduction in the flowability and dispersion properties of these systems. The interactive character predisposes agglomeration, flocculation or device retention and will compromise manufacture, stability, device function, and the aerosolization behavior of a formulation. Ultimately the ability of any aerosolized API to reach the deep airways is dependent upon adhesion force dynamics. As such, an appreciation of the forces of attraction and scale of particulate interactions within inhaler technology is critical if a successful drug delivery device is to be realized. The advancement of the atomic force microscope (AFM) as a force probing apparatus, has meant that it is now possible to measure the force of adhesion between two particles of interest. However these measurements could not easily be compared, because there is no simple means to account for differences in the contact regime (geometrics) between measurements. However, the development of the cohesive adhesive balance (CAB) approach by Begat, Morton, Stainforth and Price in 2004 has offered a means to negate this limitation. Using a colloidal probe microscopy (CPM) derived technique a particle of a selected material of interest (API, carrier molecule etc.) is attached to an AFM cantilever and ramped onto and off the surface of another material of interest (adhesion measurement), and to a surface of the same material as the tip (cohesion measurement). By graphically plotting the adhesive force values of a series of tips, as a function of the cohesive force values of the same tips, a representation of the relative particle interaction can be obtained. Quantitative information regarding the adhesive/cohesive nature of the interaction can then be extracted from the graph and a description of the interaction formulated that can be compared to other material combinations. The CAB work carried out to date has used recrystallized model substrates. These molecularly flat surfaces ensured there would be no difference between the contact geometry of a functionalised AFM probe and the adhesive and cohesive surfaces of the study respectively. In this fashion the only variable between the two measurements would be the chemical interactivity, and not the interactive surface area. However while using such methodology guarantees the validity of the approach, it is not necessarily a true representation of the materials 'in-situ' and requires more complex sample preparation and complex experimental design. For a variety of reasons this can be misleading in its own right. This thesis details the .investigation into the application of an adapted CAB approach in characterizing the force balance between APls for inhalation in their real state. In so doing, the aim was to see whether such a CAB would offer a quicker and simpler, yet relevant and informative assessment of a drug system force balance. It was hoped that said force balance could in turn be associated with a measurable impact upon the formulation performance of the characterised ingredients as measured 'in-vitro'. This interest was particularly directed at the lesser characterized pressurized metered dose inhaler (pMOI) systems. While these formulations are solvent based, it was of interest to identify whether a simple API to API challenge could infer a descriptive balance that could link to 'in-vitro' performance. Furthermore there was interest in evaluating the use of a range of surface specific imaging techniques to analyse the deposition dynamics of the combination formulations. It was hoped that by doing so, the localisation of the individual components within the binary deposits could again be associated back to the force balance of that system, and that an appreciation of the capability of the techniques involved would be gained. The work that follows therefore commences with the evaluation and description of the capacity for the CAB approach to be adapted to measure force relationships between real beclomethasone dipropionate (BOP) particles and pMDI component surfaces. From this assessment it was found that even with relatively smooth substrates, the combination of bulky functional particles and the inherent substrate roughness caused a critical failure in the CAB model. The parity between cohesive and adhesive geometries of contact was excessively stretched, leading to a loss of force normalisation which was reflected in uncorrelated CAB plots. As a consequence little could be confidently gleaned from the force data acquired, although there was the suggestion that the use of a fluorinated ethylene proplylene (FEP) coating reduced the adhesive interaction between the APls and the pMDI canister wall. This was then followed by an attempt to find a compromise between the model crystal substrates of a pure CAB process and the real particle morphologies that had caused the CAB model to fail. Using a compression process to form API powder compacts, in conjunction with small and discreet functional particles, a confident CAB was achieved for two combinations of APls selected on the basis of surface energy and physical stability analysis. Salbutamol sulphate was characterised with beclomethasone dipropionate, and salmeterol xinafoate with fluticasone propionate. Both combinations showed CAB plots with a sufficiently strong linear regression analysis to suggest a broad accuracy of force balance assessment. Both beta2-agonists showed cohesively dominated relationships with respect to the paired glucocortiocoids, while in reverse both glucocorticoids showed adhesively dominated relationships with the beta2-agonists. There was concern raised over the compression process of the powder discs, and its impact on the physicochemical state of the APls, with some thermodynamic evidence of polymorphic changes that required further work. The next chapter looks at the 'in-vitro' deposition performance of the two API combinations from a HFA134a pMDI system by analysis in an Andersen Cascade Impactor (ACI). The coformulation of salmeterol with fluticasone induced an improvement in the fine particle performance of fluticasone, with a concurrent decrease in the fine particle performance of salmeterol. This impact was hypothesised to be related to alterations in the structure and strength of particle-particle agglomerates. The impact on deposition performance of coformulating beclomethasone and salbutamol was unclear, as a critical unexplained loss of beclomethasone by total recovered mass was seen from all beclomethasone containing formulations. This instability of beclomethasone within the HFA134a system, precluded an accurate assessment of a direct impact on salbutamol deposition. The final chapter, compared a range of surface specific imaging techniques, including scanning electron microscopy (SEM), desorption electrospray ionization mass spectrometry (DESI), Raman spectrometry and time-of-flight secondary ion mass spectrometry (ToF-SIMS) in assessing the extent and nature of 'in-vitro' co-deposition from the salmeterol and fluticasone pMDI formulations. It was apparent that the deposition of the two APls on ACI plates was not likely to be directly comparable assessment of the incidence of particle co-deposition 'in-vivo' due to the forced nature of nozzle directed impaction. However the combination of techniques employed produced a wealth of physical and chemical data that did suggest that the two APls showed extensive co-ordination 'in-vitro'. Raman spectroscopy was able to identify individual particle character and showed frequent salmeterol and fluticasone particle combinations, but suffered from exceptionally long run times and anomalies from photoreactive surface elements. The use of a multivariate approach to ToF-SIMs analysis defined the strong co-association of the two APls, although could not differentiate particle to particle deposition. Multivariate curve resolution (MeR) was used and produced distinct components that segregated ions from both APIS from the background plate but not from each other. SEM imaging was able to define the morphologies of the deposited particles, but was unable to differentiate the two. DES I imaging showed the presence of the two APls together within several drug spots, but could not be used to investigate individual drug spots, and the distribution within, due to inadequate spatial resolution and differences in desorption efficacy. While the co-association of the two APls was observed, the lack of a comparator in another combination of APls made the link between deposition performance and force balance purely descriptive. It was unclear as to whether the force balance of the system lends itself to a particular increase in co-deposition behaviour. However it was apparent that the analytical techniques employed all had respective strengths and weaknesses as mapping tools, and with further work with other formulations could be used to provide a tailored formulation screening process, if subsequent links to force balances could be made. To conclude, the work in this thesis details the successful process of adapting an AFM technique in characterising the broad force balance of combinations of APls. In so doing a force balance has been linked to the alteration in deposition behaviour of two APls when co-formulated in a HFA134 formulation. The subsequent co-deposition of the two APls was then analysed by a series of surface analytical techniques. This highlighted a general co-deposition trend, but the collective results were unable to definitively link to the force balance of the system. The information obtained forms the beginnings of what could be utilised as a fast and facile broad predictor of pMDI formulation performance, and an indication of appropriate analytical techniques for investigating particle association 'in-vitro'