Characterising the effects of power ultrasonic devices on surrogate tissue materials

Power ultrasonic surgical devices operating at low ultrasonic frequencies (20-100 kHz) have been shown to provide some advantages over reciprocating or manual devices in removal of tissue. Despite opportunities for widespread applications in orthopaedic, dental, ophthalmic and general surgical procedures, the mechanisms of interaction between high power ultrasound and human tissue is not well understood and little is known about the effects and safety implications for power ultrasonics in human tissue. Therefore, the effects of power ultrasonic devices on human tissue are investigated in this thesis. From the limited literature on this topic, the basic effects caused by high power ultrasound on human tissue can be summarized into three main categories: mechanical response, thermal effects and acoustic cavitation. However, the relative contribution of each of these remains unclear. Thus, this study aims to analyse these responses and effects of tissue mimic materials subject to power ultrasonic excitation and hence investigate the potential to quantitively characterise the power ultrasonic damage on tissue. Due to the complexity of the interaction between cutting surface with tissue, the damage caused by cutting process was not covered. But the investigation of the damage by accumulated ultrasound energy in tissue was the main research topic in this thesis. To substitute for human tissue, representative materials such as E-glass filled epoxy resin (ER), polyurethane foam (PUF) and transparent silicone elastomer (SE) were used in experimental studies to simulate the behaviour of cortical bone, cancellous bone and soft tissue respectively. Their mechanical properties were characterised using uni-axial compression and tensile tests to measure elastic modulus and dynamic mechanical analysis (DMA) to study the viscoelastic behaviour. Frequency and temperature dependent behaviour of tissue surrogates under power ultrasonic excitation were determined using the DMA data based on the time/frequency temperature superposition principle (TTS). The parameters relevant to thermal properties, including thermal conductivity and specific heat capacity were measured using the heat flow method and differential scanning calorimetry (DSC). Ultrasonic horns were designed using the finite element (FE) method. The performance of the power ultrasonic system was then examined using experimental modal analysis (EMA) with a laser Doppler vibrometer (LDV) to ensure the system met the experimental requirements. To characterise the responses and effects of tissue mimics subject to power ultrasonic excitation, non-invasive field measurements have been developed for the fast and reproducible experimental assessment of ultrasonic displacement, strain, stress and temperature fields. An ultra-high speed camera and an infrared (IR) camera were used simultaneously for ER and PUF plate samples to obtain the imaging data which provided the displacement and strain fields with digital image correlation (DIC) technique and the steady-state temperature distribution with thermal imaging. The stress field in a transparent rectangular cubiod SE sample during power ultrasonic loading was mapped using a laser interferometer with acousto-optic effects. Due to the absorption of IR light by transparent SE, the temperature distribution of SE was not recorded by IR camera. Numerical and analytical models were developed to simulate the ultrasonic wave propagation using ABAQUS FE software package and Mathematica respectively. These models incorporated frequency dependent mechanical properties of the mimic materials to verify experimental results. The results of the models matched well with the experimental findings of ultrasonic displacement, strain and stress fields. To assess the thermal effects of power ultrasound on the viscoelastic tissue mimics, thermo-mechanical FE models were created using the PZFlex FE software package. Furthermore, FE models for thermal analysis were parameterized in terms of dynamic modulus and acoustic damping coefficient with frequency and temperature dependency for determination of the heat generation and thermal conductivity and specific heat capacity for characterisation of the heat transfer. The FE results have close correlation with measurement results by an IR camera. Based on the experimental and numerical studies, the damage of tissue mimicking materials under power ultrasonic excitation is related to accumulations of cyclic deformation and heating. Non-invasive full-field surface displacement, strain, stress and temperature measurements have the potential to be used to predict the damage of tissue samples interacting with the power ultrasonic devices. This study has provided confidence that the methodology can be applied to study tissue samples subject to excitations typical of ultrasonic surgical devices, including those for orthopaedic bone cutting

Osseointegrated Oral implants

In the past, osseointegration was regarded to be a mode of implant anchorage that simulated a simple wound healing phenomenon. Today, we have evidence that osseointegration is, in fact, a foreign body reaction that involves an immunologically derived bony demarcation of an implant to shield it off from the tissues. Marginal bone resorption around an oral implant cannot be properly understood without realizing the foreign body nature of the implant itself. Whereas the immunological response as such is positive for implant longevity, adverse immunological reactions may cause marginal bone loss in combination with combined factors. Combined factors include the hardware, clinical handling as well as patient characteristics that, even if each one of these factors only produce subliminal trauma, when acting together they may result in loss of marginal bone. The role of bacteria in the process of marginal bone loss is smaller than previously believed due to combined defense mechanisms of inflammation and immunological reactions, but if the defense is failing we may see bacterially induced marginal bone loss as well. However, problems with loss of marginal bone threatening implant survival remains relatively uncommon; we have today 10 years of clinical documentation of five different types of implant displaying a failure rate in the range of only 1 to 4 %

Osteoarthritis

Osteoarthritis is one of the most debilitating diseases affecting millions of people worldwide. However, there is no FDA approved disease modifying drug specifically for OA. Surgery remains an effective last resort to restore the function of the joints. As the aging populations increase worldwide, the number of OA patients increases dramatically in recent years and is expected to increase in many years to come. This is a book that summarizes recent advance in OA diagnosis, treatment, and surgery. It includes wide ranging topics from the cutting edge gene therapy to alternative medicine. Such multifaceted approaches are necessary to develop novel and effective therapy to cure OA in the future. In this book, different surgical methods are described to restore the function of the joints. In addition, various treatment options are presented, mainly to reduce the pain and enhance the life quality of the OA patients

Kilohertz ultrasound as a potential therapy for dental repair

Biological effects are known to occur with ultrasound energy at kilohertz frequencies. This has led to research into its use as a non-invasive tool for tissue healing and repair. The aim of this research is to investigate the in vitro application of kilohertz ultrasound and to measure the biological responses using models of dental pulp cells which play an important role in dental repair. Ultrasound emitted from a longwave therapy instrument (DuoSon, SRA Developments Ltd) was characterised and measured identifying the range and intensity of the field. These measurements, coupled with biological data, identified the difficulties when conducting research with kilohertz ultrasound in vitro and indicated that the use of multi-well culture plates is not appropriate when investigating the effects of kilohertz ultrasound in cell culture. An improved method for in vitro kilohertz ultrasound application was devised enabling the investigation of non-thermal ultrasound effects on primary human dental cells. Cell proliferation, viability and gene expression, including the dental-related and biomechanically-responsive gene, dentine matrix protein-1, responded in a dose-dependent manner with respect to the duration of ultrasound application. These findings highlight the complexity of the biophysical interaction of kilohertz ultrasound with cells and demonstrate the need for further clarification of specific ultrasound settings for optimal therapeutic application. This study has demonstrated a positive effect of kilohertz ultrasound on human dental pulp cells and has identified methods to improve in vitro cell culture models to capture robust data to develop a novel therapy for dental repair

Modelling, Simulation and Data Analysis in Acoustical Problems

Modelling and simulation in acoustics is currently gaining importance. In fact, with the development and improvement of innovative computational techniques and with the growing need for predictive models, an impressive boost has been observed in several research and application areas, such as noise control, indoor acoustics, and industrial applications. This led us to the proposal of a special issue about “Modelling, Simulation and Data Analysis in Acoustical Problems”, as we believe in the importance of these topics in modern acoustics’ studies. In total, 81 papers were submitted and 33 of them were published, with an acceptance rate of 37.5%. According to the number of papers submitted, it can be affirmed that this is a trending topic in the scientific and academic community and this special issue will try to provide a future reference for the research that will be developed in coming years