Biomedical Engineering - Theses
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Surface Acoustic Wave Microfluidic Platform for Cell Mechanical Measurement
Cells are dynamic, living structures that remodel themselves in response to stimuli from environment or in relation to cellular processes such as cell growth, proliferation, differentiation, migration and death. The change of cell mechanical property can be a biophysical indicator in response to the abnormal alteration in cell functionality under pathological conditions. The advances in tool development for cell mechanical measurement have facilitated in-depth discussion of cell mechanics, but heavily limited by low throughput and high cost. The emerging lab-on-a-chip microfluidic methods provide a promising solution due to the miniaturisation, among which the acoustofluidic method (the fusion of acoustics and microfluidics) appears to be advantageous due to its tunability, biocompatibility and acousto-mechanical nature. In this dissertation, I explored the application of surface acoustic wave (SAW) microfluidics in the area of cell mechanics, including establishing SAW devices for cell mechanical measurement, comparing SAW-based measurement with the benchmark from a conventional method, investigating the impacts on cell mechanical characteristic, and extending the concept to a high-throughput cytometry comparable to the real-world need. The results show that the SAW microfluidic method can provide an effective measurement on cell mechanical characteristics and probe the impact of cellular interior structure or cellular phenotype. It is consistent with the conventional benchmark and can be a complement for some cellular structures of interest. At last, it can operate as a continuous-flow high-throughput cytometry, which could be exploited in future studies related to cell mechanics.
Effect of perturbations on the biomechanics of lower limb in relation to anterior cruciate ligament (ACL) injuries
The knee is the most injured joint in the body with injuries often caused by a tear in the anterior cruciate ligament (ACL). Over 70% of ACL injuries are non-contact, meaning that an excessive amount of force or moment is generated by the individuals themselves, which induces the tear. Non-contact ACL injuries most commonly occur following a perturbation. Perturbations make the athlete unbalanced or at loss of control, which ultimately alters their normal neuromuscular control and can lead to injury. In order to understand the effect of this unconscious neuromuscular response, this study aimed to induce unanticipated perturbations during walking in 10 male and 10 female athletes. Moreover, the effect of prophylactic knee braces was examined during these perturbations. Musculoskeletal modelling in OpenSim was used to calculate kinematics, kinetics, and muscle forces during these perturbations. Females portrayed muscle force patterns during perturbations, that are likely to increase the risk of ACL injury. Furthermore, females exhibited a larger difference in muscle forces between their dominant and non-dominant limbs. Finally, prophylactic knee braces significantly reduced peak quadriceps and soleus muscle forces during perturbations. Unlike planned movements in laboratory studies, unexpected perturbations provide with deeper insight in the mechanism of ACL injuries. Although ACL injuries do not typically occur during walking, potentially injurious movement patterns during a disturbance to natural balance while walking, could provide insight on what may be reproduced, on a higher scale, during high impact and high-speed athletic tasks that can effectively tear the ACL.
Mechanical behaviour of Subchondral Bone: Elastic Moduli and Energy Dissipation in Subchondral Bone under Impact and Repetitive Loads
The damage to osteochondral tissue can develop degenerative joint diseases such as subchondral bone necrosis, osteochondral fracture, and osteoarthritis. In the development of these joint diseases, the subchondral bone plays a crucial role due to several risk factors: obesity, hereditary, aging, gender, and intense mechanical loads. The intense mechanical loads include both trauma/impact and repetitive loads which occur during high-intensity training and have been identified as the primary risk factor in the development of joint diseases. In this dissertation, we utilized mechanical tests combined with digital image correlation and micro-computed tomography to study the mechanical behaviour (in particular, Elastic Modulus and Energy Dissipation) of subchondral bone under both trauma/impact and repetitive loads. Results suggest that the presence of severe cartilage lesion in osteochondral tissue reduces the stiffness of cartilage and increases the compressive strain in the subchondral bone under trauma/impact loads. Moreover, the application of simulated physiological repetitive loads on subchondral bone has demonstrated the importance of the highest speeds in the development of the joint disease, consistent with the observations made in equine athletes. The results also exhibit the influence of microstructural properties on the mechanical behaviour of subchondral bone under repetitive loads. The results and approach of simulating physiological loading may be useful in optimizing training protocol and prevent joint diseases.
An integrated circuit towards improved management of epilepsy and other neurological conditions
Epilepsy is the second-most common neurological disorder, with an estimated prevalence of 1% worldwide. Antiepileptic drugs (AEDs) are the frontline treatment but, despite more than 25 agents available, there can be significant difficulties in finding a treatment plan that controls seizures without unacceptable side effects. Furthermore, approximately 30% of patients do not obtain full control of seizures with the available AEDs. Therefore, there exists a need for novel therapies. Therapeutic electrical stimulation of the brain and peripheral nervous system has shown great promise in treating those with refractory epilepsy, but still little is known about the mechanisms underlying this. Recent work looking at prolonged recordings of the brain has revealed a deep rhythmicity to seizures that may provide a method of developing patient-specific prediction algorithms that could be used to titrate electrical stimulation therapies. What is missing in research and in clinical practise is an implantable device which provides enough flexibility to explore new paradigms and adapt to suit the needs of the patient. Safety considerations of implantable devices necessarily precedes large-scale clinical evaluation, and this has prevented exploration of speculative higher density arrays, which come at a cost to power, complexity and mechanical reliability with no guarantee of improvement to efficacy. Rather than redesign the system from scratch, this PhD thesis asks, “how can existing implantable technology be leveraged to create flexible high-density brain recording and stimulation systems?” In response to this question, an integrated circuit called XPAND was designed to enable seamless expansions of electrode count for a wide variety of commercial stimulators. Comprising a 6 x 64 element high voltage crosspoint switch powered and configured entirely using biphasic stimulation pulses, XPAND was designed with clinical safety in mind. Fabricated in Austria Microsystems H35 high voltage CMOS process, key modules within the chip were characterised, and the crosspoint switch shown to simultaneously route high voltage stimulation and ECG signals.
Impact of multiple scale structural mechanisms on epithelium movement
Simple epithelial tissue is formed by individual cells connecting together to form a monolayer sheet. This sheet generates the complex structures of organs by undergoing both large and small scale morphogenic events. Columnar epithelial cells have a height greater than their width and are polarised with a ring of circumferential contractile fibres localised to their apical cell-cell junctions. There has been considerable investigation into the movement of this apical network, especially using lasers to sever individual apical cell edges. From these apical investigations, a variety of mechanical mechanisms have been suggested to control epithelium movement. However, these mechanisms are contrasting, and are often derived for specific experiments, rather than general apical epithelium movement. Recently, it has been recognised that in additional to the apical network, the entire three-dimensional cell shape impacts epithelium movement. Additionally, there has been growing interest in understanding how epithelium scale movement is controlled by smaller scaler structures, such as contractile fibres. This thesis utilises both computational and experimental approaches to investigate how the mechanics of underlying structures can drive epithelium scale movement, with a focus on the contribution of individual cells and contractile fibres to apical epithelium movement upon laser severing. These investigations demonstrate that studying the mechanisms of underlying cell and sub cell structures can provide new insights into the causal mechanics of general epithelium movement. It is also shown that inclusion of these mechanisms can lead to greater prediction of epithelium movement.
Red Blood Cell Passage through Narrow Capillaries: Sensitivity to Stiffness and Shape
Red blood cells (RBCs) squeeze through narrow capillaries as they transport oxygen to tissues and carbon dioxide to the lungs. The deformability of RBCs has been shown to depend on the viscoelasticity of the cell membrane and cytoplasm as well as the surface area to volume ratio (SA:V ratio) of the cell. In certain pathological diseases such as malaria, RBCs undergo restructuring of the membrane structure and modifications to the cell shape, which significantly reduce their deformability. Nonetheless, it is still unclear which factor has the greatest impact on the passage of RBCs through small capillaries. Here, we present a systematic analysis designed to identify the individual contributions of cell stiffness and SA:V ratio to the ability of RBCs to traverse narrow capillaries in a microfluidic device. We modified cellular rigidity using glutaraldehyde fixation, changed SA:V ratio by altering the buffer osmolarity and probed RBCs passage through microchannels. Our results showed that dramatic stiffening (~8 fold) had little effect (~6% retardation) on the ability of RBCs of the same geometry to traverse the channels. On the other hand, a moderate decrease (~13%) in the SA:V ratio affected the traversal of RBCs of similar stiffness more markedly (~19% decrease). We further studied RBCs infected by two different species of malaria parasites known to affect humans, Plasmodium falciparum and knowlesi. We found that P. falciparum rigidified the host RBC, but infected RBCs penetrated into microchannels with similar efficiency to uninfected RBCs. By contrast, P. knowlesi reduced the SA:V ratio of the host RBC resulting in restricted passage. We found that the earliest stage immature RBCs (reticulocytes) exhibited a similar SA:V ratio to mature RBCs and, despite being 30% larger, travelled into microchannels as efficiently as mature cells. Our finite element (FE) model provides a coherent rationale for our experimental observations, indicating that cell stiffness changes do not significantly affect RBC traversal in small capillaries due to the highly nonlinear mechanical behaviour of the cell membrane. Our numerical simulations predict that RBCs with low SA:V ratios are more prone to trapping in small capillaries (within the physiological size range) than RBCs with high membrane stiffness. Therefore, therapies targetting surface area to volume ratio of RBCs may be more effective than those that target cell stiffness.
Muscle and joint functions during walking in individuals with transfermoral amputation
Individuals with unilateral transfemoral amputation depend on compensatory muscle and joint function to generate motion of the lower limbs, which can produce gait asymmetry. Osseointegration is an alternative technique to socket-based prostheses that is used for reducing socket-skin contact problems. However, between-limb differences in joint kinematics and net joint moments may lead to abnormal hip joint contact behavior and muscle function. The aim of this dissertation is to investigate gait compensatory mechanism in individuals with transfemoral amputations fitted with socket (TFA) and bone-anchored prostheses using osseointegrated implants (BAP). In this study, two experimental and computational approaches were used to quantify the contributions of the intact and residual limb’s contralateral muscles to body center of mass acceleration and hip joint contact forces during walking. In the first approach, kinematics and kinetics data were collected from 6 TFAs and 4 BAPs performing over-ground self-selected walking task. In the second approach, a processing framework was employed using OpenSim software and MATLAB API scripting for developing three-dimensional musculoskeletal models and then to predict muscle forces and muscle contribution to waling and hip joint reaction forces. It was found that the intact limb hip muscles contributed more to body center of mass acceleration and hip contact forces than those in the residual limb. The results also suggest that osseointegrated amputees could quantify to decrease the asymmetries in the biomechanical measures between the intact and residual limbs than socket-based prosthesis amputees. The findings of this study would be useful in developing rehabilitation training programs and design of prostheses to improve gait symmetry and mitigate post-operative musculoskeletal pathology.
Cerebral perfusion markers in full-term neonates as a measure of Hypoxic-Ischemic Encephalopathy during and immediately following Hypothermia Treatment
Hypoxic-Ischaemic Encephalopathy (HIE) is a leading cause of neonatal mortality and morbidity. Therapeutic Hypothermia (TH) is the only treatment for HIE, which has reduced the rate of mortality and morbidity although still around fifty per cent of infants affected die or have a neurodevelopmental disability, such as cerebral palsy. Every infant with HIE receives the same TH protocol: 72 hours at 33.5 degrees Celsius, before being rewarmed slowly over 12 hours. The infants with moderate-severe HIE are at the highest risk of disability or death. Should it be possible to identify those infants at greatest risk during the TH, they could be targeted for modified TH treatment or for additional adjuvant treatments such as allopurinol, melatonin or ethyropeitin. The severity of the HIE, and prognosis on outcome, is challenging while the infant is cooled, as the cooling itself reduces the prognostic power of many of the previously accepted assessment methods. MRI (Magnetic Resonance Imaging) is the gold standard, but moving infants to an MRI whilst cooled is problematic, and the HIE injury to the brain may not be evident for several days. The objective of this research study was to find a clinical parameter which would identify those infants at highest risk of a poor outcome. HIE is characterised by hyper-perfusion, cerebral blood flow (CBF) exceeding metabolic demand, consequent from a physiological response preferentially redirecting blood flow to the brain during a hypoxic episode. Thus, a marker of cerebral perfusion that could classify HIE infants by the degree of hyper-perfusion was sought. Initially the Resisitive Index (RI), as determined by measuring the Cerebral Blood Flow Velocities (CBFV’s) using Doppler Ultrasound (DUS), was investigated as a possible cerebral perfusion marker. The RI is an accepted measure of the resistance of the cerebral arteries and an RI < 0.55 is considered to be indicative of a previous hypoxic event. In the first part of this study, the RI was evaluated in 80 healthy and 18 HIE infants and found to be unreliable; some infants with HIE and a poor outcome did not have an RI < 0.55, whereas some infants without HIE did. Moreover, DUS is not continuous; it is a one-off measurement requiring a skilled operator. A pursuit for another cerebral perfusion marker ensued. Frequency-Domain Near Infrared Spectroscopy (FD-NIRS) promised absolute measurements of oxy- and deoxy-Haemoglobin (HbO and HbR) in the brain tissue. Increased CBF was expected to result in a higher than normal concentration of blood and therefore Haemoglobin in the brain tissue. The results from the second part of this research study of 40 healthy and 6 HIE infants suggest that hyper-perfusion is expressed in the concentration of HbO in the brain tissue, and that this is most related to poor outcome. The limited HIE population in this study prevents generalisation from this finding, though suggests that there is justification for further research using FD-NIRS to monitor infants with HIE.
Dynamic stability and variability of perturbed walking in young adults
Falls are the third major cause of inadvertent injury in young Australian adults aged between 18-35 years. The inability of an individual to respond to external perturbations due to walking on an inclined surface, or internal perturbations such as dual-task walking, are known to be associated with significantly higher risk of balance loss. Significant factors known to increase risk of balance loss during walking include performing an additional task requiring high motor-cognitive, sensory or cognitive load (internal perturbations), and walking on uneven surfaces such as sloped terrain (external perturbations). At present, however, dynamic balance of the entire body and the risk of balance loss during walking under such perturbations is not well understood. The objective of this study was to investigate dynamic stability and variability of the human body during walking, and assess the influence of external, motor-cognitive, sensory and cognitive perturbations on dynamic balance, including surface inclination, use of a cell phone, auditory and visual stimulation, and mental calculation. Nineteen healthy young adult males were recruited. Three-dimensional joint kinematics were obtained using an optical motion capturing system as subjects walked at their self-selected speed on an instrumented treadmill. Dual-tasking was simulated by subjecting participants to motor-cognitive, visual, cognitive and auditory perturbations during walking including cell phone usage (talking, texting and reading), watching a video clip, listening to music, and performing numeric calculations mentally. External perturbations were also applied through alteration of surface inclination. Variability analysis was performed on spatiotemporal gait parameters using Detrended Fluctuation Analysis (DFA) and Standard Deviation. Dynamic stability was subsequently estimated for the entire body as well as the head, trunk and lower extremity joints using linear and nonlinear measures including Margin of Stability (MoS), Lyapunov Exponent (LyE) and Maximum Floquet Multipliers (MaxFM). A novel method was devised to assess stability using Margin of Stability at heel contact (HC) and minimum foot clearance (MFC), gait events associated with backward and forward balance loss, respectively. Slip and trip propensity estimated using Required Coefficient of Friction (RCoF) and MFC height, respectively. Finally, the most destabilizing additional task while walking was determined using deviation of MoS and trip propensity values during dual-task trials from the corresponding values during baseline walking. The results showed that dual-tasking during walking adversely affects balance in a direction specific-manner. Specifically, cell phone texting and reading while walking reduces balance in the mediolateral direction, while cell phone talking increases the risk of tripping in the anteroposterior direction. Upslope terrain increased the risk of balance loss in the anteroposterior and vertical directions and did not affect gait balance in the mediolateral direction, while walking down was associated with greater stability in the anteroposterior direction. Cognitive and sensory perturbations affected gait balance mostly in the anteroposterior and vertical directions rather than the mediolateral direction. Analysis of trip propensity showed that motor-cognitive dual-tasking due to cell phone usage while walking, cognitive and sensory perturbations due to performing additional auditory and visual tasks while walking are associated with greater risk of tripping, as measured by a lower MFC height. Particularly, talking while walking, and cognitive and sensory dual-tasking while walking may ultimately lead to an increase in risk of tripping in young adults. However, the risk of tripping in young individuals is not sensitive to external perturbations caused by sloped terrains. Participants mostly changed their step length and step time during walking under perturbations. Among the various measures used to determine the most destabilizing secondary task while walking, MFC height was more sensitive to the applied perturbations. Talking while walking was associated with the largest deviation from baseline condition. The findings of this investigation confirmed that head stabilization during ambulation has higher priority compared to other segments, and individuals try to adopt different strategies to attenuate perturbations from the lower body to the head. The current data highlighted the importance of arm swing in balance maintenance during walking under perturbations, and demonstrated that individuals try to compensate restricted arm swing during walking by modulating step width. With respect to gait adaptations, the results of this research support the idea that individual’s response to applied perturbations through dual-tasking while walking depend on the magnitude of the applied perturbation. The evidence from this study suggests that talking while walking is the most challenging secondary task during locomotion among the applied perturbations in this study, and additional sensory tasks are the least challenging one. These findings have significant implications for development of a gait training protocol for more frail people to successfully address common perturbations arising from daily living activities during everyday life. These data also suggest that MFC height analysis and local stability analysis of the lower body should be performed to gain better understanding on the effect of additional concurrent task while walking on the risk of tripping and gait stability, respectively. The analysis of MoS presented extends knowledge of step-to-step balance changes during walking at different gait events associated with common fall patterns occurring at HC and MFC. Further work needs to be done to analyse the influence of similar attention-demanding secondary tasks or ‘distractions’ in more vulnerable populations, including the elderly, fallers, and individuals with sensory or motor impairments that affect locomotor control.
Localisation of the Epileptogenic Zone from Interictal State MEG Data of Focal Epilepsy Patients
Over twenty million people in the world have drug refractory epilepsy. Their seizures cannot be adequately controlled by medication. Epilepsy surgery can remove or alter abnormal brain areas where seizures start, which is the only way to cure epilepsy and can be an effective treatment for drug refractory epilepsy patients. Accurate localisation of the epileptogenic zone (EZ) is crucially important to achieve seizure freedom after surgery. Magnetoencephalography (MEG) is a non-invasive brain functional imaging technique with superb temporal resolution. Clinically, neurophysiologists visually annotate interictal spikes in MEG recordings and apply localisation methods using averaged spikes. The manual annotation of spikes can be very time consuming for neurophysiologists. The aim of this thesis is to develop automatic methods to localise the epileptogenic zone using interictal state MEG recording for focal epilepsy patients. This thesis comprises three research objectives to achieve this goal. First, investigate localisation performance of kurtosis beamforming with various source selection approaches; the use of a 1 second sliding window for calculating kurtosis is shown to deliver the best performance relative to the other measures considered. Second, develop a method to detect interictal spikes automatically on virtual sensors (VSs) that are reconstructed using beamforming; the method based on feature extraction and machine learning delivers similar performance to labels by expert raters. Third, explore spatial distribution of interictal spikes across VSs and associate spike frequencies with EZs and surgical outcomes; the method is promising for localising the EZ at the lobe level. Potential future research is discussed based on these outcomes.
Development of next generation biodegradable drug-eluting coronary artery stents
Cardiovascular diseases are a leading cause of mortality globally, causing approximately 17 million deaths annually. Additionally, this number is predicted to rise to 23 million by 2030. The most common type of cardiovascular disease is coronary heart disease, a disease of coronary arteries that supply oxygen rich blood to the heart. Coronary artery disease is the build-up of a waxy substance called a plaque inside the coronary artery which leads to its narrowing and blockage. In current medical practice, coronary heart disease is commonly treated through balloon angioplasty and stenting to open the artery. Current stents are drug- eluting, metallic, and permanent, and recipients require prolonged anti-platelet therapy. Permanent stenting is not required. The diseased vessel can heal within 6 months to 1 year after intervention. As such, the concept of biodegradable stents has emerged as the alternative to conventional stenting, in which the stent degrades away leaving behind only the healed vessel. The first generation of biodegradable stents has been linked to higher rates of late stage thrombosis, and it has been suggested that this is due to increased strut thicknesses that cause disturbance to the laminar blood flow and result in activation of thrombogenic pathways. The aim of this thesis is to develop customizable, biodegradable, multi drug eluting coronary artery stents by using polymer chemistry, materials science, and additive manufacturing. The novel materials developed in this work are to be blood-compatible, biodegradable, have sufficient mechanical properties, promote endothelialisation, have multi-drug eluting properties, and be processable through additive manufacturing techniques. To achieve this, we used the following approaches: (1) Design and additive manufacturing of custom-made biodegradable nanocomposite based coronary artery stents (2) Design and synthesis of biocompatible and biodegradable core-cross linked star-brush polymers for antithrombotic drugs (3) Development of multi-drug eluting biodegradable nanocomposite-star polymer materials for application as coronary artery stents utilizing additive manufacturing.
Selenium nanoparticles as antibacterial agents for potential application in chronic wound healing
Chronic wounds have become a global problem. The importance of microbial colonies in delaying chronic wound healing has been highlighted recently. Keeping the wound free of infection plays a vital role in fast and successful wound healing. The rapid development of antibiotic resistance and the inability of antibiotics to penetrate biofilms seriously limit the efficacy of antibiotics. Therefore, new effective antimicrobial treatments are urgently needed to realize rapid and successful chronic wound healing. One promising candidate to address this requirement is selenium nanoparticles (Se NPs) which have antimicrobial activity. In this thesis, we were working on developing new antibacterial Se NPs, and adopting 3D printing technology to fabricate latticed wound dressings with a controlled release of Se NPs. First, the influence of size on the antibacterial activity and cytotoxicity of Se NPs was investigated. In Chapter 3, spherical Se NPs ranging from 43 to 205 nm in diameter were fabricated, and their mammalian cytotoxicity and antibacterial activity as a function of their size were systematically studied. The antibacterial activity of the Se NPs was shown to be strongly size dependent, with 81 nm Se NPs showing the maximal growth inhibition and killing effect of methicillin-sensitive and methicillin-resistant Staphylococcus aureus (MSSA and MRSA). The Se NPs were shown to have multi-modal mechanisms of action that depended on their size, including depleting internal adenosine triphosphate (ATP), inducing reactive oxygen species (ROS) production, and disrupting membrane potential. All the Se NPs were non-toxic towards mammalian cells up to 25 microgram/mL. Furthermore, the minimum inhibitory concentration (MIC) for the 81 nm particles produced in this research against MSSA is 16 +/- 7 microgram/mL, significantly lower than previously reported MIC values for Se NPs. This data illustrates that Se NP size is a facile yet critical and previously underappreciated parameter that can be tailored for maximal antimicrobial efficacy. We have identified that using Se NPs with a size of 81 nm and concentration of 10 microgram/mL shows promise as a safe and efficient way to kill S. aureus without damaging mammalian cells. Second, the effect of charge on the antibacterial activity of Se NPs was researched. It has been shown previously that Se NPs with a net negative surface charge have good antibacterial activity against Gram-positive bacteria but are less effective against Gram-negative bacteria. Gram-negative bacteria have been observed to be more sensitive to positively charged nanoparticles because the surface charge of Gram-negative bacteria is generally more negative than that of Gram-positive bacteria. Therefore, in Chapter 4, Se NPs were capped with a positively charged protein – recombinant spider silk protein eADF4 (kappa 16) – to give them a net positive charge. Compared to the negatively charged polyvinyl alcohol (PVA) capped Se NPs, the positively charged eADF4 (kappa 16) coated Se NPs demonstrated a much higher bactericidal efficacy against the Gram-negative bacteria E. coli in water. Particularly, the minimum bactericidal concentration (MBC) of 46 nm eADF4 (kappa 16) capped Se NPs (8 +/- 1 microgram/mL) was approximately 50 times lower than the 46 nm PVA capped Se NPs (405 +/- 80 microgram/mL). Scanning electron microscopy (SEM) images showed that the PVA capped Se NPs were repelled by the E. coli cells, while the eADF4 (kappa 16) capped Se NPs attached to or even coated the E. coli cells. In addition, antibacterial films were created by immobilising the eADF4 (kappa 16) capped Se NPs on positively charged spider silk and these were shown to retain good bactericidal efficacy and overcome the issue of low particle stability in culture broth. It was found that these Se NPs needed to be released from the film surface in order to exert their antibacterial effects and this can be achieved by regulating the surface charge of the film. Overall, eADF4 (kappa 16) coated Se NPs are promising new antibacterial agents against life-threatening bacteria. Third, the optimal size of Se NPs combined with positive surface charge was fabricated to realize a high antibacterial efficacy. In Chapter 5, 81 nm Se NPs combined with epsilon-poly-L-lysine (Se NP-epsilon-PL) were fabricated and their antibacterial activity and cytotoxicity were investigated. Se NP-epsilon-PL exhibited effective antibacterial activities against all tested 8 different species of bacteria including both Gram-positive and Gram-negative bacteria, and some of them are drug-resistant bacteria types. Bacteria were found to be very difficult to develop resistance to Se NP-epsilon-PL comparing to the conventional antibiotic kanamycin. S. aureus and E. coli started to develop resistance to kanamycin from 44 and 52 generations, respectively. By contrast, S. aureus started to develop resistance to Se NP-epsilon-PL after 132 generations, and E. coli failed to develop resistance to Se NP-epsilon-PL during the whole tested 312 generations. On the other hand, Se NP-epsilon-PL showed low cytotoxicity to human dermal fibroblasts. Based on its efficient and wide-spectrum antibacterial activity, the difficulty to develop resistance in bacteria and its low cytotoxicity, Se NP-epsilon-PL might become a promising member of the new generation of antibacterial agents. Finally, in Chapter 6, alginate dressings with pH-responsive release of Se NPs were fabricated using 3D printing technology. Although the antibacterial activity of Se NPs has been proved, relatively high concentrations of Se NPs are toxic to the mammalian cells. It has been reported that the pH of body fluid in bacteria infected wounds is higher than that in normal skin. To enable faster release of Se NPs at a relatively high pH to perform higher bactericidal efficacy and slower release of Se NPs at a relatively low pH to protect the normal cells, alginate wound dressings with pH-responsive release of Se NPs were 3D printed using a Bioplotter. Calcium phosphate nanoparticles (CaP NPs) were introduced into alginate dressings to make their degradation pH-responsive, resulting in pH-responsive release of Se NPs from these dressings. The dressings’ mechanical properties, degradation rates and releasing rates of Se NPs were investigated. The results showed that the addition of CaP NPs can increase both tensile strength and elongation of alginate dressings and make the degradation rate of alginate dressings faster at a relatively high pH than that at a relatively low pH. Similar to these degradation results, when Se NPs have been introduced, the release rate of Se NPs from the scaffolds at a relatively high pH also showed faster than that at a relatively low pH. In conclusion, the potential of using Se NPs as antibacterial agents has been investigated, and 3D printed alginate dressings with pH-responsive release of Se NPs have been developed.