Henk K. Versteeg

Use of ESPI in hemodynamics: a means of visualizing vessel blood flow

The successful development of total hip replacement as an effective surgical technique has been one of the most significant advances in modern orthopaedics. The method has superseded the traditional forms of treatment for hip fractures which involve extensive nailing across the site of the break. However, clinical experience has highlighted failures in both the implant and surrounding bone which have often been attributed to mechanical causes. The problem of optimizing the performance of an implant is very complex and includes a number of interrelated factors: fixation to the bone, strength of the prosthesis itself, wear of articulating surfaces, kinematic requirements, energy absorption, effect of implant position and bone structure in the surrounding area. This paper reports attempts to establish a test facility which can accurately model these parameters and monitor their effects with the intention of providing information for the orthopaedic field. Areas of interest that are intended to be examined include: the effect of bone preservation methods on the bones strength and weight-bearing characteristics, the effects of medical conditions on bone strength, such as osteoporosis, and the effect of the patients diet on bone character.

Design Optimisation of Novel Pharmaceutical Actuator Using Optical Diagnostics

Pharmaceutical metered dose inhalers (MDIs) are drug delivery devices that are designed to produce self-propelled aerosols for inhalation therapies. Conventional MDI actuators use configurations based on a “two-orifice-and-sump” design. This promotes partial expansion of the propellant as a pre-atomisation stage. The final aerosol contains large numbers of respirable particles (1–5μm), but the aerosol plume velocity tends to be very high (50–100m/s). The KOS Vortex Nozzle Assembly (VNA) is an innovative actuator concept, which enables a measure of control of plume velocity. The device utilises a combination of a vortex chamber and a Bernoulli horn to reduce the plume velocity whilst increasing the respirable fraction of drug particles. The aerosol generation process in all MDIs, including the KOS VNA, inevitably leads to a certain amount of internal and external drug deposition, which represents an inefficiency of the drug delivery technology that can threaten dose uniformity. This paper reports the findings of an experimental study using optical diagnostics to investigate the primary atomization mechanism and external drug deposition in the VNA. High-speed video imaging is used to document the developing aerosol plume in the near-orifice and mouthpiece regions as well as the flow regime inside the vortex chamber using transparent versions of the VNA manufactured by means of rapid prototyping. We consider how the improved understanding of the flow processes resulting from this study supports measurements of fine-particle fractions and mouthpiece deposition. We also discuss how this type of fundamental investigation using optical diagnostics can be used to drive design improvements to identify VNA geometries with improved aerosol properties and reduced external drug deposition.Copyright

An Optical Method for the Study of Aerosol Generation in Dry Powder Inhalers

Dry powder inhalers (DPIs) are portable, breath-actuated devices used for respiratory drug delivery. They have been the subject of intense research and development activity over the last 15 years, however, no systematic study of the effects of geometry on aerosol generation in DPIs has been reported in the literature. In particular, the first stage process — powder fluidisation — has hardly been studied in the context of DPI applications. The short time scales and the complexities of the air/powder interactions during the conversion of a powder bed into an aerosol present a challenging environment for experimental study. This paper reports an optical technique for the study of powder fluidisation inside a simplified, optically transparent DPI metering chamber geometry. We describe a system based on digital image analysis of high-speed video recordings of the transient powder-airflow interactions. Using diffuse backlighting we have generated black-on-white images of the interaction of frictional, cohesionless particles with an air jet flow. Image-processing techniques were subsequently applied to determine several aspects of the time-dependent properties that describe the development of the bed during the aeration of the powder. The paper concludes by pointing out how the proposed method could be used to improve understanding of the limitations associated with current DPI metering chamber configurations and help forward design of improved DPIs.Copyright

Design Analysis of the Volumatic: A CFD and Experimental Study

The aim of this paper has been to describe the novel approach adopted in studying the flow field within the Volumatic. In this study a combination of engineering tools such as Computational Fluid Dynamics (CFD), Laser Doppler Anemometry (LDA) and Flow visualization techniques have been employed. The initial part of the study involved the use of CFD in modelling the drug entering the Volumatic. The CFD model was then validated against measurements made using LDA. The agreement obtained was very good; this was particularly encouraging as the CFD analysis was carried out some six months prior to the experimental study.Copyright