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- Wickham, Abeni
(författare)
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Multifunctional Biomimetic Scaffolds Tailored for Cardiac Regeneration
- 2015
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Nature has had millions of years to perfect the structural components of the human body, but has also produced the dysfunctions that result in the cancers and diseases, which ruin that perfection. Congenital heart defects, and myocardial infarction lead to scarring that remodels heart muscle, decreasing the contractility of the heart, with profound consequences for the host. Regenerative medicine is the study of strategies to return diseased body parts to their evolutionarily optimum structure.Nature has had millions of years to perfect the structural components of the human body, but has also produced the dysfunctions that result in the cancers and diseases, which ruin that perfection. Congenital heart defects, and myocardial infarction lead to scarring that remodels heart muscle, decreasing the contractility of the heart, with profound consequences for the host. Regenerative medicine is the study of strategies to return diseased body parts to their evolutionarily optimum structure. Cells alone cannot develop into functional tissue, as they require mechanical support and chemical signals from the extracellular matrix in order to play the correct role in the body. In order to imitate the process of tissue formation optimized by nature, scaffolds are developed as the architectural support for tissue regeneration. To mimic the elasticity and strength seen in the heart muscle is one of the major scientific conundrums of our time. The development of new multifunctional materials for scaffolds is an accepted solution for repairing failing heart muscle. In this thesis I accept the notion that endogenous cardiac cells can play a major role in addressing this problem, if we can attract them to the site of defect or injury and make them proliferate. I then proceed to show how improving on a commonly used synthetic polymer was used to develop two new biomaterials.Polycaprolactone (PCL) fibers and sheets were studied for their ability to adsorb proteins based on their surface energies. We found that although the wettability of the PCL might be similar to positive controls for cell attachment, the large differences in surface energies may account for the increased serum protein adsorption and limit cell adhesion. The effect of fiber morphology was then investigated with respect to proliferation of mesenchymal stem cells and cardiac progenitor cells. PCL was also mechanically enhanced with thiophene conjugated single walled carbon nanotubes (T-CNT); where small concentrations of the T-CNT allowed for a 2.5 fold increase in the percentage of elongation, while retaining the proliferation profile of the cardiac progenitor cells. Although PCL is a well-known implant material, the ability to attract and adhere cardiac cells was limited. Therefore we sought to develop new biomaterials with fiber morphologies similar to the muscle fiber of the heart, but with surface energies similar to positive controls for cell attachment. Poly[2,3-bis-(3-octyloxyphenyl)quinoxaline-5,8-diyl-alt-thiophene-2,5-diyl] (TQ1) was then explored as a ribbon fiber and compared to collagen with embryonic cardiac cells, in vitro, and then implanted into rats for in vivo long term evaluations. The cardiac cells had a preferential adhesion to the TQ1 fibers, and in vivo, the fibers attracted more blood vessels and regrew functional tissue compared to the collagen controls. TQ1 fibers had the added ability to emit light in the near infrared region, which would allow for consistent tracking of the material. Although this material offered the morphological preference for the cardiac cells, it does not degrade and nor did it offer electrical conductivity. The heart muscle is an electrically active muscle. The dead tissue that is formed in the ischemic area loses its ability to transfer the electrical signals. Hence, I have then developed collagen fibrous materials with silver nanowires to help store and inject charges that would be generated during the contraction of the heart muscle. The silver nanowires served to help carry charges whilst providing resistance to bacterial growth on the material. The collagen/silver nanowires composites were mechanically apt for the culture of embryonic cardiac cells.
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| 2. |
- Skyttner, Camilla, 1985-
(författare)
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Peptide-Liposome Model Systems for Triggered Release
- 2018
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Liposomes are widely used in drug delivery to improve drug efficacy and to reduce side effects. For liposome-encapsulated drugs to become bioavailable and provide a therapeutic effect they must be released, which typically is a slow process that primarily relies on passive diffusion, liposome rupture or endocytotic uptake. Achieving drug concentrations within the therapeutic window can thus be challenging, resulting in poor efficacy and higher risks drug resistance. Finding means to modulate lipid membrane integrity and to trigger rapid and efficient release of liposomal cargo is thus critical to improve current and future liposomal drug delivery systems. The possibilities to tailor lipid composition and surface functionalization is vital for drug delivery applications but also make liposomes attractive model systems for studies of membrane active biomolecules.The overall aim of this thesis work has been to develop new strategies for triggering and controlling changes in lipid membrane integrity and to study the interactions of membrane active peptides with model lipid membranes using both de novo designed and biologically derived synthetic amphipathic cationic peptides. Two different sets of designed peptides have been explored that can fold and heterodimerize into a coiled coil and helix-loop-helix fourhelix bundle, respectively. Conjugation of the cationic lysine rich peptides to liposomes triggered a rapid and concentration dependent release. The additions of their corresponding glutamic acid-rich complementary peptides inhibited the release of liposomal cargo. Possibilities to reduce the inhibitory effect by both proteolytic digestion of the inhibitory peptide and by means of heterodimer exchange have been investigated. Moreover, the effects of peptide size and composition and ability to fold have been studied in order to elucidate the factors that influence the membrane permeabilizing effects of the peptides.In addition, the membrane activity of a the two-peptide bacteriocin PLNC8α and PLNC8β has been explored using liposomes as a model system. PLNC8αβ are expressed by Lactobacillus plantarum and were shown to display pronounced membrane-partition folding coupling, leading to rapid release of liposome encapsulated carboxyfluorescein. PLNC8αβ also kill and suppressed growth of the gram-negative bacteria Porphyromonas gingivalis by efficiently damaging the bacterial membrane.Although membrane active peptides are highly efficient in perturbing lipid membrane integrity, possibilities to trigger release using external stimuli are also of large interest for therapeutic applications. Light-induced heating of liposome encapsulated gold nanoparticles (AuNPs) has been shown by others as a potential strategy to trigger drug release. To facilitate fabrication of thermoplasmonic liposome systems we developed a simple method for synthesis of small AuNPs inside liposomes, using the liposomes as nanoscale reaction vessels.The work presented in this thesis provides new knowledge and techniques for future development of liposome-based drug delivery systems, peptide-based therapeutics and increase our understanding of peptide-lipid interactions.
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