https://etd.iisc.ac.in/handle/2005/23 Fri, 17 Apr 2026 19:51:25 GMT 2026-04-17T19:51:25Z https://etd.iisc.ac.in/handle/2005/6723 4D Printing of Polymer Composites to Engineer Resorbable and Deployable Implants Choudhury, Saswat Medical implants include products that are used to replace or restore the function of any damaged organ or tissue inside the body. The current generation of implants are mostly made from non-degradable materials and are implanted via open surgeries. The patients often need to undergo multiple surgical interventions in case of implant failure or secondary complications. This inevitably leads to increased pain, hospitalization times, and higher costs. Resorbable medical implants offer potential advantages, as they completely degrade inside the body into non-toxic byproducts in a timely fashion, thereby avoiding multiple revision procedures. A few examples exist of resorbable implants used in clinics, such as polymeric bone fixation devices. On the other hand, deployable implants provide the feature of implantation via minimally invasive procedures. Typical examples of such implants include Nitinol-based stents, which are non-degradable and require surgical procedures for initial implantation. However, combining both features, including absorbability and deployability, in a single implant is scarce. A typical way of achieving this is to use an absorbable smart material that can be triggered using benign stimulation methods to deploy at the site minimally invasively. The thesis encompasses engineering such absorbable and stimuli-responsive polymer composites fabricated into customized designs of potential implants using design- aided additive manufacturing. The first part of the thesis aims at design optimization, using an absorbable shape memory polymer (SMP) that can exhibit shape recovery at physiological temperatures. Using anisotropic design principles, the SMP was programmed to generate out- of-plane shape deformations in as-printed planar structures, such as hollow tubes with cells in the lumen. The later parts of the thesis deal with engineering the shape memory polymer with functional nanoparticles that are responsive to non-contact stimuli, such as alternating magnetic field, or near-infrared (NIR) for remotely deployable medical implants. Lastly, as a proof-of- concept, a biliary stent is fabricated using absorbable polymer and later endowed with NIR- responsiveness and imaging potential for potential image-guided deployment. Chapter 1 presents a comprehensive literature survey on resorbable and deployable medical implants, focusing on the materials and manufacturing employed. The need for resorbable polymers, additive manufacturing (3D printing and 4D printing) as potential manufacturing techniques, the role of design and smart materials on shape change, and different stimulation methods to trigger shape change are outlined. A brief overview of the potential biomedical applications is also presented, emphasizing biliary stents and deployable bone tissue scaffolds prepared by such materials. In Chapter 2, details of experimental methods and characterization techniques employed to carry out the work in this thesis are mentioned. Chapter 3 presents a dual shape-morphing strategy comprising design-aided additive manufacturing and shape memory properties of polymers to fabricate complex shapes, such as cellularized hollow tubes. FEA simulations are used to predict the different types of shape deformations, such as out-of-plane bending and twisting in the as-printed structures by varying infill angles during printing. Hollow tubes of varying lengths and diameters can be obtained by quantitative predictions from the simulations. The obtained tubes can then be cellularized by utilizing the shape memory property of the polymer, resulting in cellularized vascular grafts for improved patency. Chapter 4 utilizes an alternating magnetic field as a stimulation for fabricating deployable tissue scaffolds. The shape memory polymer was reinforced with magnetic nanoparticles to realize remote heating under an alternating magnetic field and at physiological temperatures. The as-printed magnetic scaffolds could be deployed minimally invasively following shape recovery from deformed shapes into original shapes under magnetic heating. Furthermore, the composites exhibited in vitro osteogenesis, cytocompatibility, and in vivo compatibility. Thus, the 4D printed shape memory magnetic nanocomposite presented here could be an excellent candidate biomaterial for engineering deployable scaffolds and medical implants, among other implantable applications. In Chapter 5, near-infrared (NIR) light was used as a potential stimulation to realize in situ deployable tissue scaffolds. The shape memory polymer was nanoengineered with photothermal nanofillers to fabricate composites by 3D printing. The composites demonstrated significantly higher osteogenic potential in vitro, as revealed by the significantly enhanced alkaline phosphatase (ALP) secretion and mineral deposition compared to the neat polymer. Intraoperative deployability and in vivo bone regeneration ability of the composites were demonstrated using self-fitting scaffolds in critical-sized cranial bone defects in rabbits. The composite scaffolds fabricated here offer an innovative strategy for minimally invasive deployment to fit irregular and complex tissue defects for bone tissue regeneration. In Chapter 6, bioresorbable biliary stents were fabricated as a different class of implants using 3D printing and elcectrospinning to obtain covered stents of custom lattice designs. The stents were tested for in vitro mechanical properties and degradation properties and their deployment was assessed in pre-clinical porcine model using the Seldinger technique. In Chapter 7, NIR-responsive composites were prepared using photothermal nanoparticles with imaging potential using fluorescent imaging and photoacoustic imaging techniques. In Chapter 8, the overall findings of the work are summarized, and a brief perspective on the scope of future work based on the findings of this thesis is also presented. Taken together, this thesis presents a combination of engineering materials, design optimization, smart use stimulation strategies, for the rationale development of bioresorbable and deployable implants. https://etd.iisc.ac.in/handle/2005/6723 https://etd.iisc.ac.in/handle/2005/5891 Analysis of vocal sounds in asthmatic patients Yadav, Shivani Around 334 million people have asthma worldwide. Asthma is an inflammatory disease of the airways which causes cough, breathlessness, chest tightness, and other peculiar sounds during breathing. The golden standard test spirometry is used to diagnose and monitor asthma. Spirometry is a lung function test that measures the time and volume of air a person can exhale after a deep inhalation. In general, patients repeat the test multiple times to get accurate readings, making it very time-consuming, and strenuous, especially for children and older people. A spirometer is also an expensive and bulky device that is not suitable for a home monitoring setup. Hence, a need for an easy and fast method exists. Sound-based analysis can be one such method. The motivation behind using sounds for monitoring and diagnosis of asthma originates from the sound production mechanism. In literature, non-speech sounds, namely, cough and breath recorded at the chest, have been explored. However, the analysis of speech and non-speech sounds recorded at the mouth is least investigated. Therefore, the work done in this thesis addresses this problem. For the analysis, we started with two tasks, namely classification and spirometry prediction for each sound category. Therefore, the thesis is divided into two parts.\\ Analysis of speech sounds For speech sound analysis, classification between the asthmatic and healthy subjects and spirometry prediction tasks have been performed. Results of the classification and spirometry prediction task show that \textipa{/oU/} (as in 'Home') is the best for the classification task, whereas \textipa{/i:/} (as in 'Meet') is best for the spirometry prediction. Results of the classification task suggest that Mel-frequency cepstral coefficients (MFCC) statistics carry maximum information for the discrimination in the case of all speech sounds considered in this work. Spirometry variables prediction task results show that the low frequency carries more information in best-performing sound \textipa{/i:/}.\\ Analysis of non-speech sounds Classification performed with non-speech sounds, cough, and breath, indicates that MFCC's are best, but interestingly, static MFCC coefficients are more informative than the velocity and acceleration coefficients. Breath performs the best for the classification task in the non-speech sound group. Further analysis of breath signal shows that discriminative information for classification is not uniform in the entire breath signal. Interestingly, the middle 50\% of the breath signal carries maximum information for the classification. To extract the middle 50\% of a breath, prior knowledge of breath boundaries is required. Therefore, we developed an unsupervised breath segmentation algorithm using dynamic programming. Classification results using predicted boundaries are found to be on par with the ground truth boundaries. Comparison of speech sounds and breath for the classification tasks shows that breath sound outperformed speech sounds. Experiments conducting for spirometry prediction tasks using non-speech sound indicate that breath performance is better than cough. In the spirometry prediction task, speech sounds outperformed the non-speech sounds. As asthma is not curable, patients needs to be on continuous medication known as bronchodilaotrs to reduce inflammation in the airways. But what kind of changes introduced due to airway change is not known. A linear discriminant-based analysis has been carried out to determine what kind of spectral changes occur in an asthmatic patient's sound before and after taking a bronchodilator. For this task, breath sounds have been chosen. It has been observed that frequency bands 400Hz-500Hz and 1480Hz -1900Hz are more sensitive to obstruction change in breath sound. https://etd.iisc.ac.in/handle/2005/5891 https://etd.iisc.ac.in/handle/2005/6456 Bacterial cellular heterogeneity in inducible gene expression and drug susceptibility Ratnasri, K Biological processes are inherently noisy, and such stochasticity can result in significant cell to cell variability in isogenic bacterial populations. Functionally, cellular heterogeneity can have significant impact on the survival of the bacterial population in nature, as well as in our ability to understand, predict and control them. Since most of our knowledge in biology comes from ensemble experiments which measure average behaviour, there is a need to design studies that can identify and characterize variability present in the population. In this thesis, cellular heterogeneity and its consequences in bacterial inducible gene expression systems and in bacterial response to antimicrobial treatment was studied, using a combination of complementary bulk and single cell assays. In the first part of the thesis, antimicrobial action on bacterial populations was examined. Bacterial resistance to antibiotics is a major threat to public health today. Significant efforts in research and health policy have been directed towards understanding and combatting this issue. While genetic mechanisms of resistance development are well understood, there are several phenotypic responses such as persistence, tolerance and heteroresistance resulting due to transient variations within sub populations of cells that allow them to survive an antimicrobial stress. Clinically, these phenomena have been linked to recurrence of various infections such as tuberculosis, cystic fibrosis and urinary tract infections. To overcome these issues, several alternatives to antibiotics are being tested, including antimicrobial peptides (AMPs). These molecules are part of the innate immune system, known for their broad-spectrum activity and immunomodulatory effects. While they have shown promising results in combatting resistant bacteria, the efficacy of these peptides on persistent and heteroresistant cells haven’t been thoroughly investigated. With this background, the action of antibiotics and AMPs on bacterial populations was investigated for their ability to kill such phenotypically different cells. Significant difference was observed in the efficacy of these antimicrobials, when tested on actively growing and growth arrested E. coli. While, both are equally efficient on exponentially growing cells, diverse responses were observed with stationary phase cells. Variability existed even amongst the peptides. Particularly, colistin was found to induce heteroresistant behaviour. This observation was further studied and found to have link with hypermutations in the bacterial genome. In addition, cross resistance to other antimicrobials was also observed. Finally, single cell imaging of this heteroresistant population confirmed the variability in response of individual cells to colistin treatment. Overall, deeper understanding of the interaction between bacterial cells and these antimicrobials was obtained, which can form a basis for designing efficient treatment strategies in the future. In the second part of the thesis, heterogeneity of gene expression from the inducible arabinose operon in E. coli was studied. The arabinose operon is known for its graded response to arabinose concentrations at the population level. At the individual cell level, however, it exhibits an all-or-none response due to stochasticity in the numbers of the arabinose import proteins, AraE and AraFGH. By using different mutant strains of E. coli with varying levels of these transporters, the gene expression response from this operon was characterized for its uniformity, tunability and sensitivity to a range of arabinose concentrations. Varying the levels of each transporter was found to influence the system in a different way, and maximising for one property usually led to a trade-off with another property. In addition, analysis of the temporal behaviour of the gene expression process using a fast-degrading green fluorescent protein (GFP) reporter revealed a dependency on the physiological state of the cells. Overall, information obtained from this study will aid in engineering of inducible gene expression systems for better control https://etd.iisc.ac.in/handle/2005/6456 https://etd.iisc.ac.in/handle/2005/6923 Bioengineering strategies to model and modulate immune cells Joseph, Joel P Optimal activation of immune cells is necessary to elicit a protective response against pathogens and foreign objects. In dysregulated immune systems, cells are aberrantly activated or exhausted. Understanding biochemical and mechanical aspects that modulate immune responses helps us design biomaterials-based in vitro research and drug screening models for immune pathologies. Furthermore, materials science principles can be applied to synthesize immunomodulatory biomaterials to treat immune pathologies. In this study, a 3D bioprinted platform was developed to study the influence of physical microenvironment on T cell activation, roles of calcium in T cell activation in 2D and 3D and validate the principle in vivo, and the in vitro and in vivo immunomodulatory effects of 2D antimonene nanosheets were investigated. First, we developed a 3D bioprinted platform with tuneable mechanical properties to culture and activate T cells in different stiffnesses and porosities. T cells were bioprinted in gelatin methacryloyl (GelMA) hydrogels using a digital light processing (DLP)-based 3D bioprinter. The hydrogels recapitulated physiologically and pathologically relevant stiffnesses of a lymph-node mimetic tissue construct as evidenced by hydrogel characterization. The biomechanical properties of the 3D bioprinted hydrogel influence T cell activation. Some cellular responses of the 2D and 3D cultures in a soft matrix (19.83 ± 2.36 kPa) were comparable; however, they differed in a stiff matrix (52.95 ± 1.36 kPa). Furthermore, primary mouse T cells activated with PMA and ionomycin were 1.35-fold more viable in the soft matrix than in the stiff matrix. T cells bioprinted in a soft matrix and a stiff matrix released 7.4-fold and 5.9-fold higher amounts of IL-2 than 2D cultured cells, respectively. Furthermore, Th1/Tc1 cytokines were induced upon T cell activation as a function of changes in the mechanical properties, whereas Th2 cytokine production was not induced as a function of changes in the mechanical properties of the microenvironment. Second, we studied the effects of high intracellular calcium levels during in vitro T cell activation and validated the principle in vivo in a DSS-induced colitis model in mice. We investigated the effects of high intracellular calcium amounts using in vitro T cell receptor (TCR)-independent and TCR-dependent activation models. High intracellular calcium amounts increased the production of reactive oxygen species (ROS), and thereby decreased the activation-associated proliferation of T cells. This high calcium-induced inhibition of T cell proliferation could be rescued by treatment with an antioxidant, N-acetyl cysteine (NAC). We also found that high intracellular calcium inhibited T cell activation in the 3D bioprinted T cell culture platform we developed. We also tested the universality of the principle by studying the effects of tert-Butylhydroquinone (tBHQ), a SERCA inhibitor and Nrf2 activator. While tBHQ alone did not increase intracellular calcium amounts, they did so upon a combination treatment with PMA. Also, tBHQ inhibited T cell activation-associated proliferation in a dose-dependent manner. To validate this principle in vivo, we intraperitoneally injected tBHQ in mice with DSS-induced colitis. tBHQ ameliorated DSS-induced colitis in mice as evidenced by rescue of colon length shortening and lower disease activity index. Third, we synthesized, characterized, and tested the immunomodulatory effects of a two-dimensional nanomaterial, antimonene. Antimonene nanosheets were biocompatible and inhibited nitric oxide and IL6 production in thioglycollate-elicited peritoneal exudate cells. Furthermore, antimonene ameliorated DSS-induced colitis in mice, as evidenced by rescue of colon length shortening, less tissue damage, and decreased serum pro-inflammatory cytokine levels. In summary, the studies present T cell responses in an in vitro model of melanoma tumor microenvironment and suppression of innate immune cell responses to ameliorate DSS-induced colitis using 2D antimonene nanosheets. https://etd.iisc.ac.in/handle/2005/6923