Refine
Document Type
Language
- English (19)
Has Fulltext
- yes (19)
Keywords
- PSA (1)
- adhesives (1)
- biomaterials (1)
- cellular microenvironments (1)
- hydrogels (1)
- ionic crosslinking (1)
- photoremovable groups (1)
- physical crosslinking (1)
- polyampholytes (1)
- polymer entanglement (1)
Scientific Unit
The role of growth factors is important to stimulate regenerative cellular changes to rejuvenate damaged cells, tissues, and organs. Growth factor engineering and delivery systems are developed quite a lot for example, emergence of small protein like chains (peptidomimetics) and matrices for controlled release of growth factors. Despite these advancements, the use of growth factors in regenerative medicine is limited because of their low stability. In this thesis, angiogenesis inducing Engineered Living Materials (ELMs) are used as the strategy to overcome the limitations associated with traditional GF delivery methods. These ELMs contain living bacteria programmed to synthesize angiogenic protein in response to light. This thesis describes challenges and successes in developing light regulated Engineered Living Material that releases angiogenic protein. The bacteria were ontogenetically engineered to synthesize and secrete a Vascular Endothelial Growth Factor (VEGF) mimetic peptide (QK) attached to a Collagen Binding Domain (CBD). To create an ELM, the engineered bacteria were safely encapsulated in a bilayer hydrogel designed to help aid survival and to prevent bacterial escape from the material. It is proven that in-situ control over production of pro-angiogenic protein can be attained with light. Secreted protein can bind to collagen and promote endothelial cell network formation which is a hallmark of angiogenesis. These results highlight the potential of this light inducible ELM to support vascularization in endothelial cells.
Polymer networks with dynamic covalent bonds show properties and functions not achievable with covalently crosslinked systems. Among of the different polymers connected by dynamic covalent bonds, this Thesis is based on polydimethylsiloxane (PDMS) elastomers prepared via acid-catalyzed ring-opening polymerization of cyclic monomer and cross-link. This reaction presents different dynamic equilibrium reactions, such as polymer-oligomer equilibrium and bond exchange reaction. In this Thesis, I have developed three different functional materials based on acid-catalyzed PDMS. In Chapter 1, the basic concepts of dynamic bond chemistry and the state-of-the-art of dynamic covalent polymer networks are described. In Chapter 2, a new PDMS-based elastomer that can self-grow and self-degrow is presented. Chapter 3 describes how the acid-catalyzed PDMS was used to fabricate a strain sensor that could flexibly post-tailor the sensor properties. In the last part (Chapter 4), a gas-flow enhanced relaxation behavior observed in CB/dPDMS composite is described.
Two-photon (2P) activable photocleavable protecting groups (PPGs) can be introduced in polymer networks as photodegradation sites or as blocking groups for active sites, which enable the alternation of mechanical properties and biochemical signals and allow to study consequent cell response in a spatiotemporal controlled manner. So far, the design of high efficient 2P activable hydrogels is challenging. This Thesis presents novel designs of photodegradable hydrogels that contain the 4’-methoxy-4-nitrobiphenyl-3-yleth-2-yl)methyl (PMNB) PPG. PMNB-gels formed under physiological conditions and showed tuneable hydrolytic stability and adequate rate for cell encapsulation. Moreover, PMNB-gels can be photodegraded efficiently upon 2P excitation (λ = 740 nm). Preliminary experiments of PMNB-gels as 4D matrices for the investigation of cell response are presented. In a second part, a 2P-activatable PPGs endowed with an extended π conjugation was demonstrated and introduced to yield the RGD cell adhesive peptide. The targeted peptide is obtained but only in low yield due to its low stability. The results of this Thesis provide new tools for instructing cells in 3D cultures using 2P-activated processes and demonstrate the potential of photochemistry for the realization of 4D biomaterials.
Bacterial growth and metabolic activity are sensitive to the mechanical properties of their environment. Understanding how the 3D spatial confinement regulates the cell behavior is crucial not only for understanding biofilm development but also for the design and safe application of engineered materials containing living cells. This Thesis explores the use of Pluronic-based hydrogels to encapsulate genetically modified Escherichia coli bacteria. Hydrogels with different viscoelastic properties were prepared by mixing Pluronic and Pluronic diacrylate components in different ratios, giving physical hydrogels with variable degree of covalent crosslinking and different mechanical responses. Rheological properties of the hydrogels as well as the growth rate and morphology of the embedded bacterial colonies were characterized. The results provided correlations between material parameters and bacterial cell responses. Further, a bilayer thin film model was developed for long term encapsulation of the organisms, preventing leakage of cells for up to two weeks while maintaining their activity as drug/protein eluting devices or biosensing units. The bacterial bilayer thin films did not elicit significant immune responses in primary immune cells from healthy donors. The results of this Thesis demonstrate the potential of Pluronic-based biohybrid as a suitable and safe prototype for further in vitro and in vivo testing of engineered living material designs.
o-Nitrobenzyl (oNB)-based polymers have been used as photodegradable materials/surfaces, and responsive biomaterials. While previous studies have mainly focused on the photodegradation of the material by intercalating oNB derivatives in the polymer chains, this thesis pays attention to the utilization of oNB photolysis to tailor the properties of materials, including interface functions, network topology, and bulk properties. To this end, two kinds of oNB based molecules with multifunctional units were designed and synthesized: 2-bromo-N-(2-nitro-3, 4-dihydroxyphenethyl)-2-methylpropanamide (NO2-BDAM, nitrodapomine based initiator) and 2-((2-bromo-2-methylpropanoyl)oxy)ethyl 4-(4-(1-(acryloyloxy)ethyl)-2-methoxy-5-nitrophenoxy) butanoate (vinyl-oNB-Br, photolabile inimer). In part 1, NO2-BDAM, in combination with Mn2(CO)10 as a visible light-sensitive additive, was used to control the growth and detachment of polymer brushes independently. In part 2, vinyl-oNB-Br was introduced into a double network material for in situ regulating topology from connected double network (c-DN) to disconnected double network (d-DN) by light exposure. In the last part, vinyl-oNB-Br was used to graft and detach polymer brushes from a network, leading to the change of network topology and material toughness. These results contribute to the topic of functionalized oNB based polymer systems and tunable topological polymer networks, providing useful strategies both in chemistry and materials.
Engineered antigen-presenting hydrogels: model platforms for studies of T cell mechanotransduction
(2020)
T cells apply forces and eventually sense and then respond to the mechanical properties of their surroundings, including those of antigen presenting cells (APC) when they form the immunological synapse (IS). The identification of the mechanosensitive receptors and time scales at which they sense and actuate is experimentally difficult at the natural cell-cell interface. Inspired by the tools used in cell-matrix mechanobiology, this thesis presents synthetic, hydrogel-based models of APCs to study T cell mechanotransduction, focusing on the early T cell activation. Polyacrylamide (PAAm) hydrogels (1-50 kPa) were micropatterned with streptavidin and APC ligands (antibody against CD3 co-receptor (anti-CD3) and intercellular cell adhesion molecule-1 (ICAM-1)) at controlled ligand density and in geometries with defined dimensions. The anti-CD3 patterned hydrogels were used to study the interplay between hydrogel stiffness and CD3-mediated early T cell activation markers. In the last chapter, the regulatory role of ICAM-1 coupled to anti-CD3 and hydrogel stiffness in early T cell activation was studied on hydrogels with patterned anti-CD3 microdots surrounded by a background of ICAM-1. The results contribute to the understanding of the factors involved in T cell mechanotransduction, providing useful information for the future design of immunomodulatory materials.
To implement light-based diagnosis and therapies in the clinic, implantable patient-friendly devices that can deliver light inside the body while being compatible with soft tissues are needed. This Thesis presents the development of optical waveguides for guiding light into tissue, obtained by printing technologies from three different polymer combinations. Firstly, D,L-dithiothreitol (DTT) bridged PEG diacrylate were synthesized and printed into waveguides, which exhibited tunable mechanical properties and degradability, and low optical losses (as low as 0.1 dB cm-1 in visible range). Secondly, degradable waveguides from amorphous poly(D,L-lactide) and derived copolymers were developed by printing, which showed elasticity at body temperature and could guide VIS to NIR light in tissue for tens of centimeters. At last, soft and stretchable optical waveguides consisting of polydimethylsiloxane (PDMS) core and acrylated Pluronic F127 cladding were fabricated by coaxial extrusion printing, which could be stretched to 4 times of their length and showed optical loss values in tissue as low as 0.13 -0.34 dB cm-1 in the range of 405-520 nm. For proof-of-concept, above printed optical waveguides were used to deliver light across 5-8 cm tissue to remotely activate photochemical processes in in vitro cell cultures. The presented work exemplifies how rational study of medically approved biomaterials can lead to useful and cost-effective optical components for light applications.
Living organisms share the ability to grow that allows them to absorb, transport, and integrate nutrient to continually increase in size, change in shape and modulate in strength. In contrast, synthetic polymers are constructed in fundamentally different ways and possess fixed structures after fabricated. This thesis presents various approaches to guide synthetic soft materials to grow and to mimic this fundamental growing capability: i) A photo-activation approach to probe the growth of bulky soft materials with controllable size, strength and compositions, ii) Light-induced site-specific self-growth of microstructures from the surface a dynamic soft substrate, iii) Self-growth of fully interlocked poly(disulfide)s based polycatenane elastomers with unique intermolecular interlocking topologies. These functional materials contribute to the supplement of dynamic soft substrates, providing useful information for the future both in chemistry and materials.
Tissue regeneration and remodeling after damage requires enhanced collagen deposition at the site of damage. In collagen disorders like keratoconus and brittle bone disease this ability is lost due to collagen misfolding, poor crosslinking and deposition. For this purpose, tools that allow to control and regulate collagen biosynthesis and folding are required. Ideally, such tools should be collagen-specific and allow remote control, which available strategies fail to fulfill.In this context, a collagen-specific molecular chaperone, Hsp47, was chosen as it has multiple roles in collagen biosynthesis. Recombinant Hsp47 can be delivered in the endoplasmic reticulum of mammalian cells via KDEL receptor mediated endocytosis. Exogenous delivery of Hsp47 stimulates fibrillar collagen I, III and V in cells. A photoactivatable derivative of Hsp47 (H47Y<ONBY)was developed containing an un‐natural light‐responsive tyrosine (o‐nitro benzyl tyrosine (ONBY)),which renders Hsp47 inactive toward collagen binding. On-demand, localized and in situ activation of this tool, stimulating collagen production in disease-state cells, was tested in vitro.Also, this tool can be easily delivered precisely in cells of damage corneal tissue from keratoconus patients. Site-selective exposure after H47Y<ONBY treatment,allowing localized remodeling of the extracellular collagen matrix, was demonstrated ex vivo. This tool has potential to trigger collagen deposition in collagen deficient disorders.Tissue regeneration and remodeling after damage requires enhanced collagen deposition at the site of damage. In collagen disorders like keratoconus and brittle bone disease this ability is lost due to collagen misfolding, poor crosslinking and deposition. For this purpose, tools that allow to control and regulate collagen biosynthesis and folding are required. Ideally, such tools should be collagen-specific and allow remote control, which available strategies fail to fulfill.In this context, a collagen-specific molecular chaperone, Hsp47, was chosen as it has multiple roles in collagen biosynthesis. Recombinant Hsp47 can be delivered in the endoplasmic reticulum of mammalian cells via KDEL receptor mediated endocytosis. Exogenous delivery of Hsp47 stimulates fibrillar collagen I, III and V in cells. A photoactivatable derivative of Hsp47 (H47Y<ONBY)was developed containing an un‐natural light‐responsive tyrosine (o‐nitro benzyl tyrosine (ONBY)),which renders Hsp47 inactive toward collagen binding. On-demand, localized and in situ activation of this tool, stimulating collagen production in disease-state cells, was tested in vitro.Also, this tool can be easily delivered precisely in cells of damage corneal tissue from keratoconus patients. Site-selective exposure after H47Y<ONBY treatment,allowing localized remodeling of the extracellular collagen matrix, was demonstrated ex vivo. This tool has potential to trigger collagen deposition in collagen deficient disorders.
