1,721,172 research outputs found
Transition metal boride based multilayer solar selective coatings for concentrated solar power application
No full textRenewable power technologies with zero CO2 emissions are the key to regulate the current global warming scenario. Solar energy is the most affordable and sustainable green energy source. One hour of solar radiation has energy equivalent to the world’s annual energy consumption. But due to its low energy density, it requires efficient technology like concentrated solar power (CSP) to harvest and convert to useful energy. Coated with spectrally selective absorber materials, the receiver tubes of the CSP plant play the most pivotal role by converting the incident solar energy to thermal energy. The cost of heat/power generation can be reduced by increasing the photo-thermal conversion efficiency of the CSP plant. This objective can be accomplished by increasing the solar selectivity of the absorbers or increasing the operating temperature of the plant. Therefore, in recent years, significant research is being carried out to develop absorbers that can operate at high temperatures for a longer duration without undergoing degradation. Solar selective absorbers based on carbides, nitrides, borides, and oxides of transition metals, known as ultra-high temperature ceramics, have gained more attention in recent years due to their high thermal and chemical stability, good thermal conductivity, and mechanical properties.
This work demonstrates our efforts to develop transition metal boride-based spectrally selective absorber coatings for CSP application. The first part of the work deals with enhancing the solar selectivity and thermal stability of TiB2-based multilayer absorber coating by employing double-layer anti-reflection coating. In the second part of the work, I will present the results obtained with a new NbB2-based multilayer absorber coating. The processing challenges in our attempt to fabricate TiB2 and NbB2-based multilayer absorber coatings with high absorptance in solar irradiation range and low emissivity in the infrared region will be discussed. The developed coatings exhibit good thermal stability at 500°C for 250 hrs in vacuum. Extensive experiments have been carried out to investigate the microstructure and optical properties of the optimised coatings. Based on the obtained results, we have attempted to understand the governing physical phenomena to explain the origin of spectral selectivity and the thermal stability of the developed ceramic coatings
Understanding the influence of electric field and dual doping on cytocompatibility of calcium phosphate bioceramics: Experimental and computational study
No full textAlthough doped bioceramics have been widely investigated for biomedical applications, the co-doped bioceramics remain mostly unexplored for bone regeneration and dental applications. Given this background, we have successfully developed Fe/Sr co-doped biphasic calcium phosphate (BCP) with varying dopant content and assessed its cytocompatibility with respect to different cell lines together with functional characterization. The Co-doped BCPs were found to be dielectric in nature and an increase in conductivity with dopant amount was recorded. The changes in lattice parameters were also probed using XRD based Rietveld refinement technique. An important observation is that, while the singular dopant of Sr/Fe at 20 mol% or higher amount reduces cell viability significantly, osteoblast viability is not compromised to any significant extent on Sr/Fe co-doped BCP, compared to undoped BCP. Our results indicate that one can tailor osteoblast functionality by controlling the co-dopant content.
From the clinical perspective of a dental implant, we have examined the cytocompatibility of the dual doped BCPs with epithelial cells. The cellular study showed a significant increase in both cellular viability and functionality with an increase in conductivity. Besides this, PCR study confirmed an absence of tumorigenic potential. Taken together, our study establishes unique advantage of Sr/Fe co-doping approach towards realizing their hard tissue replacement application.
Another fundamental goal of biomaterials science is to develop an understanding of the interaction between a living organism and inorganic material surface at the molecular level. Given these facts, we examined the influence of external electric field stimulation (up to 1.00 V/nm) on fibronectin adsorption on hydroxyapatite (HA) (001) surface at 300K using all-atom classical MD simulation method. The molecular level interaction was found to be regulated by the attractive electrostatic interaction, which changed with the external field strength. Non-monotonous changes in the structural integrity of fibronectin were recorded with the change in field strength /direction due to the spatial rearrangement of local charges and global structural changes of the protein. The dipole moment vectors of fibronectin, water and HA quantitatively exhibited a similar pattern of orienting themselves parallel to the field direction. One of the striking observations in the context of the cell-material interaction is that the RGD sequence of FN was exposed to solvent side, when the field was applied along +z-direction.
Summarizing, this dissertation reports the development of dual doped biphasic calcium phosphates and demonstrated their cytocompatibility. On fundamental aspects, this thesis also provided quantitative insights into the influence of electric field stimulation on molecular interactions involved in fibronectin adsorption on hydroxyapatite surface
Directing cellular differentiation using biophysical cues on multifunctional biomaterial platforms for neural and osteochondral applications
No full textWorld health organization (WHO) has recognized multiple degenerative diseases as the leading causes of mortality, globally. The drugs-based clinical treatment of chronic degenerative diseases such as multiple sclerosis, Parkinson’s disease, osteoarthritis, muscular dystrophy, etc., has been accomplished with limited success. In this perspective, “stem cell-based regenerative engineering” provides a new treatment option to repair and regenerate the damaged tissue or organ. Stem cells have the unique capability to replicate themselves (self-renewal) unless they are provided with specific external factors (i.e., biochemical, and biophysical). Among various biophysical signals, the efficacy of electrical stimulation, substrate stiffness, and conductivity have been demonstrated to direct stem cell differentiation. In the present thesis, cellular differentiation has been regulated using biophysical signals on multifunctional biomaterials. The multifunctional biomaterials provide a ‘smart’ platform to deliver biophysical cues to direct stem cell differentiation. The electrical stimulation on conducting polymer (polyvinylidene difluoride, PVDF reinforced with multiwall carbon nanotubes) guided the stem cells towards neuron-like and glial-like cells. The strategy to differentiate stem cells towards functional neurons has future implications in stem cell therapy to treat neurodegenerative diseases. Also, the conducting polymeric biomaterials, developed in the present dissertation, can be further developed into an artificial nerve conduit and nerve patch to repair the damaged nerve tissues. To address the osteoarthritis-related clinical challenges, bone and cartilage mimicking polymer composites have been developed in this thesis. The electrical stimulation on a bone-mimicking polymeric platform (PVDF reinforced with Barium Titanate) induced the differentiation of stem cells towards bone-like cells. The continuous electrical signal generated higher stresses in stem cells, while the non-continuous alternative electrical signal exhibited differentiation without causing cellular stress. The bone-mimicking PVDF composite has the potential to be used as an acetabular liner in total-hip-joint replacement. The electrical stimulation technology can be translated to induce a faster bone healing with an upregulated ability of osseointegration of synthetic polymer implant. Furthermore, a novel hybrid bilayer composite with elastically stiff and compliant (soft) polymeric matrices has been fabricated to mimic the osteochondral tissue (interfacial tissue of bone and cartilage). The upregulated activity of bone cells on the elastically stiff layer and maturation of cartilage cells on the elastically compliant layer demonstrates the efficacy of the bilayer construct to repair the osteochondral defect. The modulated osteochondral functionalities on the elastically stiff and compliant substrate also revealed the role of substrate stiffness to direct cellular differentiation. Taken together, the present thesis conclusively establishes the efficacy of external biophysical signals to direct cellular differentiation using multifunctional biomaterial platforms for neural and osteochondral regeneration
Development of Polyethylene Grafted Graphene Oxide Reinforced High Density Polyethylene Bionanocomposites
Full text linkThe uniform dispersion of the nano fillers without agglomeration in a polymeric matrix is widely adapted for the purpose of mechanical properties enhancement. In the context to biomedical applications, the type and amount of nanoparticles can potentially influence the biocompatibility. In order to address these issues, High Density Polyethylene (HDPE) based composites reinforced with graphene oxide (GO) were prepared by melt mixing followed by compression moulding. In an attempt to tailor the dispersion and to improve the interfacial adhesion, polyethylene (PE) was immobilized onto GO sheets by nucleophilic addition-elimination reaction. A good combination of yield strength (ca. 20 MPa), elastic modulus (ca. 600 MPa) and an outstanding elongation at failure (ca. 70 %) were recorded with 3 wt % polyethylene grafted graphene oxide (PE-g-GO) reinforced HDPE composites. Considering the relevance of protein adsorption as a biophysical precursor to cell adhesion, the protein adsorption isotherms of bovine serum albumin (BSA) were determined to realize three times higher equilibrium constant (Keq) for PE-g-GO reinforced HDPE composites as compared to GO reinforced composites. In order to assess the cytocompatibility, osteoblast cells (MC3T3) were grown on HDPE/GO and HDPE/PE-g-GO composites, in vitro. The statistically significant increase in metabolically active cell was observed, irrespective of the substrate composition. Such observation indicated that HDPE with GO or PE-g-GO addition (upto 3 wt %) can be used as cell growth substrate. The extensive proliferation of cells with oriented growth pattern also supported the fact that tailored GO addition can support cellular functionality, in vitro. Taken together, the experimental results suggest that the PE-g-GO in HDPE can effectively be utilized to enhance both mechanical and cytocompatibility properties and can further be explored for potential biomedical applications
Electric Stimuli as Instructive Cues to Guide Cellular Differentiation on Electrically Conductive Biomaterial Substrates in vitro
Full text linkDirecting differential cellular response by manipulating the physical characteristics of the material is regarded as a key challenge in biomaterial implant design and tissue engineering. In developing various biomaterials, the influence of substrate properties, like surface topography, stiffness and wettability on the cell functionality has been investigated widely. However, such study to probe into the influence of substrate conductivity on cell fate processes is rather limited. The need for such an understanding is based on the fact that specific tissues in the body are electrically active in nature, such as in brain, heart and skeletal muscle. These tissues make use of electrical conductivity as an effective cue for tissue homeostasis, development, regeneration and so on. Moreover, understanding the importance of underlying conductivity in basic biological processes is essential in developing electrically conductive biomaterials with the ability to simulate normal electrophysiology of the body by interfacing with bioelectric fields in cells and tissues. Electrical stimulation and charge conduction can regulate numerous intracellular signalling pathways, can interact with cytoskeleton proteins to modulate the morphology, increase protein synthesis and on the more can favor the ECM protein conformational changes. On these grounds, the present dissertation illustrates that persistent electrical activation influences the multipotency of hMSCs and acts like a promoter towards selective differentiation of hMSCs into neural/cardiomyogenic or osteogenic lineage. Besides, continual exposure to electric field stimulated conducting culture environments lead to growth arrest while enhancing differentiation. In total, this dissertation suggests the dominant role of conductivity in inducing my oblast differentiation and hMSc lineage commitment that involves EF stimulated in vitro culture conditions. Also, a knowledge base with qualitative and quantitative understanding of stem cells and their response to substrate physical properties and external field effect was developed through this comprehensive study. Such an improved understanding of the ability of hMSCs in sensing electrical conductivity may lead to the development of culture additives/conditions that better induce directed stem cell differentiation
Development of novel bionanocomposites for musculoskeletal reconstruction applications
No full textWith an increase in the aging population worldwide, a surge in demand for joint replacement has been observed. It has been anticipated that by 2030, the demand for primary total hip joint replacement (THR) will increase by 171% for patients less than 65 years of age. Although THR is considered to be the most efficacious surgical intervention in load-bearing orthopedic applications, its overall success is constrained by unavoidable clinical issues such as osteolysis and aseptic loosening resulting in implant failure.
In this context, Ultra-high molecular weight polyethylene (UHMWPE) has been playing a significant role as an acetabular liner over the last six decades due to its attractive mechano-chemical, tribological, and biocompatibility properties. Yet, the challenges posed by UHMWPE, particularly those associated with its in vivo wear and oxidation, need to be addressed. A substantial part of this dissertation will explore the science behind the processibility, physicomechanical properties, and biocompatibility of the new generation modified graphene oxide reinforced HDPE/UHMWPE (HUmGO) nanocomposite for acetabular liner applications. Overall, the HUmGO proved to be a promising biomaterial when benchmarked against commercially available medical-grade UHMWPE and XL-UHMWPE and also with Trident®X3® (Stryker, orthopedics) implant in terms of the manufacturing, following dimensions, and properties.
On the other hand, another aspect to be considered for THR success is the physical interlocking between the reamed acetabulum and the metal-backed (especially Ti-6Al-4V) acetabular assembly. The bioinertness of the Ti-6Al-4V-backed acetabular shell interferes with implant-bone bonding; hence, a bioactive material-coated acetabular shell is used. Even though hydroxyapatite (HA)-coated Ti-6Al-4V shells are used in clinical settings, due to cell-mediated resorption and lack of suitable properties, there is a constant need to introduce stable and adherent new generation coating material for bioinert Ti-6Al-4V acetabular shell. This dissertation will also discuss the deposition of an adherent pDOPA co-doped Barium Titanium reinforced (BT) functionalized PVDF nanocomposite coating on Ti-6Al-4V with desired physicochemical and cytocompatibility properties for acetabular shell applications concerning better osseointegration. Herein, the fundamental aspects of cell-material interactions have been correlated with the substrate functionalities. Taken together, our observations indicate that osteoblast functionality can be tailored by providing a cell-instructive surface modification to the acetabular components.
Summarizing, this dissertation will broadly revolve around the development of novel for the acetabular components with the view to eliminate long-standing clinical issues of osteolysis and aseptic loosening, resulting in a shorter implant lifespan. On fundamental aspects, this dissertation will also provide qualitative and quantitative insights into the process-structure-properties of these new generation bionanocomposites.Department of Biotechnology-Centre of Excellence through ‘Programme support on translational research on biomaterials for orthopedic and dental applications’ (No. BT/PR13466/COE/34/26/2015), Science and Engineering Research Board (SERB)-Department of Science and Technology (DST)-IMPRINT (IMP/2018/000622), Govt. of Indi
Development of multifunctional polydimethylsiloxane-based polyurethanes as an ‘off-the-shelf’ alloplastic platform for urological reconstruction
No full textOver 400 million patients suffer from urinary bladder-associated physiological disorders
globally, which often necessitate surgical intervention for a reconstructive procedure. The
current gold standard for bladder reconstruction, an autologous graft, is proven not to be an
ideal substitute in clinics. Such unmet clinical needs drive the continuous surge for structural
and functional substitutes of urinary tissues, including ureters, bladder-wall, and urethra.
Against this backdrop, the present dissertation explores a biomaterial-based, functionalised
alloplastic platform for urological reconstruction. This strategy for an alloplastic urinary tissue
encompasses a biostable, 'off-the-shelf' available therapeutic option that simplifies and shortens
surgical treatment. Furthermore, it presents the potential to evade the challenges and
complications of autografts and scaffold-based regenerative techniques.
Considering the prerequisites of a urological alloplast, the combination of
polydimethylsiloxane and thermoplastic polyurethanes (TPU/PDMS) is deemed most
advantageous. The synergistic integration of varying contents of PDMS within the molten TPU
matrix is realised through a processing methodology of dynamic vulcanisation (DV). The
experimental outcomes are evaluated and correlated with different phenomenological models
to understand DV induced strengthening of structure. The theoretical predictions, in
conjunction with material property characterisation, allow a better understanding of the
improved interfacial behaviour and superior performance of the crosslinked polymer system.
The in situ compatibilised blends are further investigated for clinically relevant viscoelastic
properties to sustain high pressure, large distensions, and surgical handling/manipulation.
Moreover, non-exhaustive chemical strategies are harnessed to counter urinary tract infections
through the covalent incorporation of polycationic moieties. The new generation alloplasts,
endowed with contact killing surfaces, are assessed for their efficacy in pathogenically infected
artificial urine. In addition, the adhesion and proliferation of murine fibroblasts on different
polymeric compositions to establish their cytocompatibility.
Building further upon the knowledge of the antibacterial and antifouling activity of
polycationic modifications, layer-by-layer (LbL) assembled multifunctional surface grafting
are conceived to sustain long-term stability in a urinary environment, to suppress encrustation
and biofilm formation. The performance of the single-step and LbL-grafted blends is
benchmarked against the conventional urological alloplasts, using a customised lab-scale
bioreactor set-up. Post-six weeks of incubation in the dynamic assembly simulating ureasepositive microbial infection, the contact-active blends exhibited a remarkable ability to resist
calcium and magnesium encrustation, while retaining adequate grafting integrity. As high as
4-fold log reduction in the planktonic growth of bacterial strains associated with bladder stones
and renal calculi is recorded. In vitro cellular assessment is carried out with human
keratinocytes and human embryonic kidney cells to evaluate the cytocompatibility of the
surface grafted blends against the medical-grade control polymer. Finally, the optimum LbL
grafted formulations are investigated for their performance in a phase-I pre-clinical study
utilising human urine samples collected from 129 patients. The newly developed blends meet
the clinically desirable attributes and present a strong potential as a stable, contact-active, antiencrustation biomaterial platform for urinary implantation.
Summarising, this dissertation contemplates the new-generation, infection and encrustationresistant alloplasts. In pursuit of this vision, multifunctional polymeric biomaterials are
designed to sustain desirable performance in a urinary environment. These next-gen
biomaterials pave the way for an alloplastic platform that can integrate into clinical practice to
improve the quality of modern urological treatment
Fabrication, micro-computed tomography based quantitative 3D microstructure evaluation of 3D printed bioceramic scaffolds and FE modelling of biomedical implant prototypes
No full textIn summary, this thesis provides the following outcomes:
a) Formulation of novel powder-binder combination for 3D powder printing of
resorbable bone-tissue scaffold. b) The effect of post-processing approach on
the macro and microstructure, phase composition and mechanical properties
of a 3DPP system (POP-based). c) Extensive use of ¹CT to provide 3D qualitative
and quantitative microstructural analyses along with in situ mechanical
characterisation of failure behaviour. d) Establishment of a non-destructive
workflow on the basis of ¹CT imaging coupled with FE modelling or analysis
(FEM or FEA) for local mechanical property prediction. Taken together, this dissertation
established 3D powder printing as a viable manufacturing technique
to fabricate designed porous scaffolds and also the efficacy of ¹CT-FEA modelling
based combinatorial approach for local mechanical response in porous
scaffolds and dense biomedical device prototype
Development of Multifunctional Biomaterials and Probing the Electric Field Stimulated Cell Functionality on Conducting Substrates : Experimental and Theoretical Studies
Full text linkMaterials with appropriate combinations of multifunctional properties (strength, toughness, electrical conductivity and piezoelectricity) together with desired biocompatibility are promising candidates for biomedical applications. Apart from these material properties, recent studies have shown the efficacy of electric field in altering cell functionality in order to elicit various cell responses, like proliferation, differentiation, apoptosis (programmed cell death) on conducting substrates in vitro. In the above perspective, the current work demonstrates how CaTiO3 (CT) addition to Hydroxyapatite (HA) can be utilised to obtain an attractive combination of long crack fracture toughness (up to 1.7 MPa.m1/2 measured using single edge V-notch beam technique) and a flexural strength of 155 MPa in addition to moderate electrical conductivity. The enhancement of fracture toughness in HA-CT composites has been explained based on the extensive characterization of twinned microstructure in CT along with the use of theoretical models for predicting the enhancement of toughening through crack tip tilt and twist mechanisms. Subsequent in vitro studies on HA-CT composites with human Mesenchymal Stem cells (hMSCs) in the presence of electric field has shown enhanced differentiation towards bone like cells (osteogenic lineage) as evaluated by ALP activity, Collagen content and gene expression analyses through Polymerase Chain Reaction (PCR) at the end of two weeks. he extracellular matrix mineralization analysis at the end of 4 weeks of hMSC culture further substantiated the efficacy of electric field as a biochemical cue that can influence the stem cell fate processes on conducting substrates. The electric field stimulation strategy was also implemented in in vitro studies with C2C12 mouse myoblast (muscle) cells on elastically compliant poly(vinylidene difluoride) (PVDF)-multiwall carbon nanotube (MWNT) composite substrates. PVDF is a piezoelectric polymer and the addition of MWNTs makes the composite electrically conducting. Upon, electric field stimulation of C2C12 mouse myoblast cells on these composites, has been observed that in a narrow window of electric field parameters, the cell viability was enhanced along with excellent cell alignment and cell-cell contact indicating a potential application of PVDF-based materials in the muscle cell regeneration. In an effort to rationalise such experimental observations, a theoretical model is proposed to explain the development of bioelectric stress field induced cell shape stability and deformation. A single cell is modelled as a double layered membrane separating the culture medium and the cytoplasm with different dielectric properties. This system is linearized by invoking Debye-Huckel approximation of the Poisson-Boltzmann equation. With appropriate boundary conditions, the system is solved to obtain intracellular and extracellular Maxwell stress as a function of multiple parameters like cell size, intracellular and extracellular permittivity and electric field strength. Based on the stresses, we predict shape changes of cell membrane by approximating the deformation amplitude under the influence of electric field. Apart from this, the shear stress on the membrane has been used to determine the critical electric field required to induce membrane breakdown. The analysis is conducted for a cell in suspension/on a conducting substrate and on an insulating substrate to illustrate the effect of substrate properties on cell response under the influence of external electric field
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