There is a growing recognition that we cannot afford the provision of all new health care technologies, even those that are proven to be beneficial. This is increasingly true in the US, where health care spending is on an unsustainable upward trajectory. US health care spending is greatly in excess of that of other countries; however, with respect to key health metrics, the US health care system performs relatively poorly. Despite this, unlike many other developed countries economic evaluation, and more specifically cost effectiveness evidence, is used sparingly in the US health care system. Notably, the Centers for Medicare and Medicaid Services (CMS), administrators of the Medicare programme, state that cost-effectiveness evidence is not relevant to coverage decisions for medical technology and interventions evaluated as part of National Coverage Determinations (NCDs). The empirical aspect of this thesis evaluates the current use and potential value of using cost-effectiveness evidence in CMS NCDs. A database was built using data obtained from NCD decision memoranda, the medical literature, a Medicare claims database, and Medicare reimbursement information. The findings of the empirical work show that, CMS’s stated position notwithstanding, cost-effectiveness evidence has been cited or discussed in a number of coverage decisions, and there is a statistically significant difference between positive and non-coverage decisions with respect to cost effectiveness. When controlling for factors likely to have an effect on coverage decisions, the availability of cost-effectiveness evidence is a statistically significant predictor of coverage. In addition, the quality of the supporting clinical evidence, the availability of alternative interventions, and the recency of the decision are statistically significant variables. Further, when hypothetically reallocating resources in accordance with cost-effectiveness substantial gains in aggregate health are estimated. It is shown that using cost-effectiveness to guide resource allocation has an effect on resource allocation across patient populations and types of technology.

Fully-realised three-dimensional patterning strategies enable the development of heterogeneous constructs which can recreate tissue architecture and cellular microenvironments over a large range of length scales. This in turn allows the development of more effective tissue models and tissue engineering therapies. The work presented in this thesis was designed to address the development of patterning methodologies and compatible biomaterial formulations. Poly(lactic-co-glycolic acid)-based (PLGA-based) microspheres were utilised for temporally-controlled protein delivery. Robust protocols were developed for the production of microspheres with two different mean sizes to provide distinct release kinetics which could be further tailored by the addition of a PLGA-poly(ethylene glycol)-PLGA (PLGA-PEG-PLGA) triblock copolymer. A semi-automated microinjection/micromanipulation (MM) system was used to precisely position individual microspheres into cell culture substrates. This approach has the potential to replicate complex interacting signal environments as seen in developmental and repair processes. Demineralised bovine bone, processed with or without a decellularisation step, was enzymatically digested to form solutions capable of gelation under physiological conditions. The resulting hydrogels outperformed collagen as in vitro culture substrates for bone-derived cells and are promising injectable scaffold materials. They were also formed into beads which could encapsulate exogenous proteins and which may be utilised in MM-based patterning strategies. Bioplotting was used to produce alginate hydrogel constructs containing highly viable cell populations. This technique was also used to deposit a PLGA-PEG microparticulate material which could be sintered under physiological conditions to achieve bone appropriate mechanical properties. PLGA-PEG/alginate dual material constructs could also be produced incorporating independent patterns of these two materials and of two cell populations and two protein signals. Bioplotting could therefore be used to produce sophisticated tissue engineering constructs for the repair of large, complex defects. Though this work focused on osteochondral applications much of the data is also more widely-applicable.

Bioresorbable implants are an attractive alternative to metallic bone fixation devices and offer potential to eliminate some of the clinical challenges with the latter. This work explores the manufacturing of fully bioresorbable fibre-reinforced composite rods and screws for such applications. Poly lactic acid (PLA) and phosphate glass fibres (PGF) were combined to provide mechanical reinforcement and biocompatibility characteristics. Aligned and randomly reinforced PLA/PGF composites were prepared by compression moulding prior to thermomechanical deformation into rod and screw forms. In vitro degradation and mechanical properties retention were investigated in phosphate buffered saline (PBS) at 37°C. The composite rods and screws exceeded published data for bioresorbable implants in their virgin state and were towards the upper range of cortical bone properties. The properties reduced rapidly in an aqueous medium and this was attributed to matrix plasticisation and fibre/matrix disbonding. The degraded samples maintained strength and stiffness close to the lower limits of the cortical bone. Water uptake and mass loss for composites exceeded equivalent values for PLA alone due to water wicking at the fibre/matrix interface. Ion release tests correlated linearly with mass loss profiles confirming that the dominant degradation mechanism was fibre dissolution. The PLA/PGF composites also exhibited good biocompatibility to human osteosarcoma and human mesenchymal stem cells.

In vitro modelling offers the potential of recapitulating human degenerate tissue for physiological studies and pharmacological screening. Yet, few systems have been developed to date, primarily due to the lack of vascularisation in engineered tissue. Here, the development of an in vitro pump is addressed. This will be the first component of a long term strategy to build internal circulatory systems for in vitro engineered tissue. Firstly, mechanical characterisation and surface biocompatibility of spin coated poly(dimethylsiloxane) (PDMS) elastomeric membranes was investigated to assess whether PDMS could be used as a structural constituent. Results showed that spin coating speed defines both film thickness and specific mechanical properties since tensile testing revealed that PDMS membranes exhibit thickness-dependent mechanical properties. Plasma polymerisation of allylamine was used to surface engineer the hydrophobic PDMS surface to promote cell adhesion and proliferation. Surface characterisation revealed that PDMS surfaces became hydrophilic and nitrogen enriched as a result of plasma polymerised allylamine (ppAAm) deposition. Additionally, a thick ppAAm deposition (92 nm) is required to minimise hydrophobic recovery of PDMS. Cell culture studies showed that cells readily attached to ppAAm (92 nm) deposited PDMS and that these surfaces were best suited to cultivating cells compared to other surface treatments. Secondly, a method was developed to control cell positioning on the PDMS surface, since cell alignment is required to generate directional and contractile force. The deposition of ppAAm (92 nm) and airbrushing of extracellular matrix (ECM) aerosols can be spatially restricted using a micro-stencil. Individual and multiple cell line patterns were achieved that remained faithful for ≤ 10 days. Importantly, this technique micropatterned cells at high resolution over macro scales. External mechanical stimulation was used to influence cell alignment and cytoskeletal organisation on ppAAm (92 nm)/ Fibronectln (Fn) micropatterned PDMS. Results showed that incorporating substrate strain with surface micropatterning can be used to control site- and alignment- specific cell attachment.

This thesis discusses the development of the multiple-breat h-helium washout (MBHW) measurement for lung-function study. Multiple-breath washout (MBW) has been regarded as a sensitive technique to study the ventilation inhomogeneity in conducting or acinar airways. The tracer gas washed out from the lungs breath by breath is monitored. By analysing the concentration of the tracer gas versus the expired tidal volumes, the washout results provide two indices Scond and Sacin which reflect the degree of ventilation inhomogeneity. Scond is the increasing rate of the noramlised phase III slopes breath by breath while the Sacin is the normalised phase III slope from the first breath with the subtraction of Scond. The higher Scond value the greater ventilation inhomogeneity in the conductive airways while the higher Sacin value the greater ventilation inhomogeneity in the acinar airways. Traditionally, nitrogen is used as the tracer gas, washed out by the pure oxygen in a multiple-breath-nitrogen washout (MBNW) measurement. It is usually chosen because it is the gas we normally breathe and has no direct influence on physiology unlike oxygen. In this study,4He gas is used as the tracer gas instead. Since helium is less dense and has higher diffusivity than nitrogen, it is believed that it will be able to reach deeper into our lungs in a given time. Therefore, helium washout may provide more ventilation information especially in the small airways. In our MBHW system, a quartz tuning fork with a resonant frequency 32768Hz is used as the gas density sensor. The resonant frequency of the tuning fork is linearly related to the surrounding gas density. The helium concentr ation is given by eliminating all other gas components and calculating it from the tuning fork signal. Considering other components of our expiration, the carbon dioxide is detected by the infrared sensor, and the water is filtered out by a trap. We have performed the washout measurements on 11 volunteers, three of them have been diagnosed having mild lung diseases (asthma), two are smokers, and the other five are normal healthy people. The peak expiratory flow is also measured for each subject. The single breath MBHW curves from asthmatic people have higher normalised phase III slopes and higher Scond or Sacin values. This shows a greater conductive or acinar ventilation inhomogeneity in asthmatics’ lungs. The lung clearance washout curves are fitted with a summation of two exponential curves which represent two compartments with different ventilation rates. The compartment with higher decay rate represents the better-ventilated compartment and the other one is the poorly-ventilated compartment. Subjects with larger proportion of poorly-ventilated compartments have a lower peak expiratory flow rate compared to the predicted values. A 2.2-litre lung model has been built. A loud speaker has been used to simulate the movement of the diaphragm. MBHW measurements have been performed on the lung model which has a 0- to 4-generation dichromatic structure. The washout results from the lung models is compared to the results from the real lungs.

Biomaterials play an important role in tissue engineering, where they are used as scaffolds for the 3D culture of cells, to help the generation of neo tissues in-vitro and achieve superior tissue engraftment and regeneration in-vivo. The work presented in this thesis describes how thermoresponsive particle gels, a class of materials not previously investigated for tissue engineering applications, can find important applications in this field. The main gels developed and studied were the aqueous thermoresponsive particle gels prepared from poly(poly(ethylene glycol) methacrylate ethyl ether) (polyPEGMA246-EE) together with polycaprolactone (PCL) microparticles. The thermoresponsive polymer polyPEGMA246-EE, synthesised by free radical polymerisation, was employed as an adsorbing steric stabiliser for polycaprolactone microparticles prepared by the single emulsion solvent evaporation method. The resulting suspensions exhibited reversible temperature induced gelation based on incipient flocculation, where they switched from being free flowing at temperatures below 19°C to form space filling gels at body temperature (37°C) over periods of ~1 minute. On cooling, the suspensions returned to a fluid state. The viscoelastic properties of the particle gels could be controlled by varying the temperature and composition, enabling these gels to be tailored for specific applications. Using NIH3T3 as a model cell line, PCL/polyPEGMA246-EE particle gels exhibited key characteristics advantageous for the 3D culture of cells. These were mainly the ability to assemble around the cells at temperatures, above the LCST of polyPEGMA246-EE, and the provision of a supportive scaffold with appropriate mechanical properties for growth, along with good cytocompatibility enabling cell spreading and proliferation over extended culture times, as well as the rapid return to a flowable state on cooling allowing for suspension transfer, for cell subculture and harvesting, without the need for enzymes. The latter property would also allow for the injectable delivery of the in-vitro conditioned cell-gel constructs for therapeutic applications. Another variant of thermoresponsive particle gels has also been presented in this thesis. Thermoresponsive magnetic-particle gels were developed from the combination of magnetic polystyrene microparticles and the thermoresponsive polymer polyPEGMA246-EE. These exhibited reversible thermogelling behaviour which allowed for cell encapsulation, while their magnetic sensitivity allowed for cell recovery through simple magnetic particle separation. The novel concept of scaffold deconstruction by temperature, and cell recovery through magnetic-particles separation is significant for applications where a scaffold-free outcome would be desired such as the commercial expansion of therapeutic cells. In this thesis, the preparation and application of first generation biocompatible thermoresponsive particle gels is described. The combination of ease of preparation, the potential for scale-up and positive cell response make thermoresponsive particle gels promising as a new class of materials for applications in cell culture, as supports for tissue growth and in cell delivery systems. The materials developed and studied in this thesis are believed to represent a significant contribution to the fields of biomaterials, drug delivery and tissue engineering.

An injectable scaffold system for the delivery of cells and growth factors was developed in this project to enhance healing of bone fractures. The project was focused to meet the clinical need for an off-the-shelf synthetic biodegradable bone graft material. The concept required the injection of a paste to fill defects then rapidly solidify to a mechanically supportive macroporous structure. The injectable paste was developed from a two-component biodegradable microparticle scaffold based on poly(lactic-co-glycolic acid) (PLGA) and comprised of a versatile temperature insensitive (type 1) carrier and an adhesive (type 2) component made temperature sensitive with the addition of poly(ethylene glycol) (PEG) as a plasticizer. The plasticized adhesive type 2 component achieved wet compressive strengths up to 18 MPa at 37 °C after 24 hours. The sintering strategy utilised the changes in viscoelastic and mechanical properties that occur in the glass transition region of amorphous polymers. The specific mechanism devised in this thesis exploited the biocompatibility and diffusivity of PEG to increase polymer glass transition temperature in the wet sintering process. The solidification speed was demonstrated by rheological assessment of storage modulus and wet compressive strengths up to 2 MPa after 15 minutes at 37 °C. Restricting particle size distribution to narrow 100 µm bands controlled porosity between 35-65%. The interconnectivity of the macroporous structures was demonstrated by the invasion of 3T3 cells seeded on the outer surface of the scaffold and evaluated by microcomputed tomography. The innocuous nature of the solidification process was demonstrated by the survival and proliferation of in situ seeded primary human fibroblasts, osteoblasts and murine C2C12 cells. The multifunctional type 1 component acted as a porous spacer, protein delivery vehicle and cell carrier when modified with polyethylenimin. The potential use of the scaffold as a controlled delivery system for recombinant human bone morphogenetic protein-2 (rhBMP-2) was demonstrated by the sustained differentiation of murine C2C12 myoblast to osteogenic alkaline phosphatase positive cells over 28 days. In this thesis a novel sintering mechanism has been developed that facilitates control of pore size and porosity of injectable scaffolds. The benign nature of the process facilitates the potential use of this injectable system as a delivery vehicle for cell and growth factor therapy.

Adolescents have been identified as users of medical devices who are currently overlooked in the design and development of these products. This research presents a set of studies that investigate the non-clinical user requirements of adolescent medical device users. Interviews with a range of healthcare professionals provided guidance into chronic conditions and devices which are relevant to adolescent populations. Workshops involving healthy adolescents in schools were carried out to elicit adolescent perspectives of current medical device design. The results of this study showed that the range of medical devices presented did not satisfy adolescent user requirements and provided insight into factors which are important to this specific user group. The workshop also identified the acapella® physiotherapy device, used for chest and airway clearance in the treatment of cystic fibrosis, as a suitable case study for further evaluation with real adolescent users. Case study interviews were carried out with adolescents with cystic fibrosis: the users of the acapella®. The interviews identified a range of unmet requirements and expanded on the results from the workshops. In addition to the more general design factors, users of the acapella® highlighted the effect of device use on clinical effectiveness. The data from the workshops and case study interviews was used in a co-design project with an adolescent user of the device. A design specification was interpreted from the data to produce a visual representation of the adolescent requirements. The research has produced two outputs. The first is the development of a prototype tool for eliciting adolescent design priorities for medical devices - The Adolescent Medical Device Assessment Tool (AMDAT) The second deliverable is a set of guidelines which detail the specific requirements and goals of adolescent users of medical devices - Adolescent Medical Device Requirements. This guidance aims to facilitate the consideration of adolescent user requirements in the design and development of new medical devices. The research investigation has contributed new understanding to the fields of human factors and adolescent healthcare. The findings from these studies demonstrate how adolescent populations can be successfully engaged in research tasks. This research investigation has shown that adolescents have specific needs of medical devices and that meeting these needs through user-centred methods may lead to better adherence of use and improved health outcomes.

The current advances of nanotechnology in medicine and biology open new horizons towards the development of novel tools (nanosensors) for the detection of several biological compounds, disease biomarkers and cellular molecules. Fluorescent nanosensors are utilised as efficient, rapid and sensitive probes in many analytical and biological applications. The small size of nanosensors enables their insertion into live cells, with minimal cellular disturbance, to detect a specific target within the intracellular environment in real-time. The work described within this thesis outlines the development of fluorescent nanosensors for the detection of cellular and biological markers. Chapter one illustrates a brief introduction for the different types of nanosensors and the methods that are utilised for nanosensor characterisation. Chapter Two describes the development, fabrication and characterisation of size-tuneable ratiometric fluorescent pH nanosensors. The nanosensors were able to detect the pH, one of the most important biological markers, over an extended dynamic range from pH 3.5 to 7.5, encompassing the pH of many biological systems. Chapter Three demonstrates the utilisation of the developed pH nanosensors for the real-time measurement of the intracellular pH of yeast cells, as a model eukaryotic cell, during glucose metabolism. Chapter Four details the study of the process of fluorescence quenching using size controlled core-shell silica nanoparticles. The study showed interesting results for enhanced distance-dependent fluorescence quenching assay using silica nanoparticles. In Chapter Five, aptamer-based fluorescent nanosensors have been developed for the quantitative assay of DNA hybridisation and interferon gamma, a model cytokine.

Tissue engineering (TE) is a rapidly evolving interdisciplinary field that joins together materials science, biomedical engineering and cellular biology, in a quest to reconstruct living tissues upon injury or loss. For this reason TE has the potential to have a large impact in clinical implantations, expanding tissue supply for transplantation therapies. The scaffold is a centrepiece in TE, since it aims to mimic the extracellular matrix (ECM) that is found in natural tissue. Nonetheless, a major constraint in achieving larger constructs has been the lack of means to transport oxygen and waste produced by the cells. The construction of complex structures with an integrated vasculature, with high spatial resolution, is now a reality that opens the door for more complex and larger engineered tissues and organs. This thesis presents the results of a study on the impact on oxygen diffusion and cell viability in stem cell seeded constructs, after biomaterial (hydrogel) mechanical reinforcement with a laponite clay, considered to be of great potential for regenerative medicine. The impact on oxygen and nutrient diffusion and cell viability in stem cell seeded constructs after hydrogel mechanical reinforcement through polymer concentration is also presented and discussed. The impact on oxygen diffusion and cell viability after the creation of a microchannel network inside stem cell constructs, through a bioprinting technique, was quantified and constitutes the last part of the present work.