| 1. |
- Hulsart Billström, Gry, 1982-
(författare)
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Bone Regeneration with Cell-free Injectable Scaffolds
- 2017
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Bone is a remarkable multifunctional tissue with the ability to regenerate and remodel without generating any scar tissue. However, bone loss due to injury or diseases can be a great challenge and affect the patient significantly. Autologous bone grafting is commonly used throughout the world. Autograft both fills the void and is bone inductive, housing the particular cells that are needed for bone regeneration. However, a regenerative complement to autograft is of great interest as the use of biomaterials loaded with bioactive molecules can avoid donor site morbidity and the problem of a limited volume of material. Two such regenerative products that utilise bone morphogenetic protein (BMP)-7 and -2 have been used for more than a decade clinically. Unfortunately, several side effects have been reported, such as severe swelling due to inflammation and ectopic bone formation. Additionally, the products require open surgery and use of supra physiological doses of the BMPs due to poor localisation and retention of the growth factor. The purpose of this thesis was to harness the strong inductive capacity of the BMP-2 by optimising the carrier of this bioactive protein, thereby minimising the side effects that are associated with the clinical products and facilitating safe and localised bone regeneration. We focused on an injectable hyaluronan-based carrier developed through polymer chemistry at the University of Uppsala. The strategy was to use the body’s own regenerative pathway to stimulate and enhance bone healing in a manner similar to the natural bone-healing process. The hyaluronan-based carrier has a similar composition to the natural extracellular matrix and is degraded by resident enzymes. Earlier studies have shown improved properties when adding hydroxyapatite, a calcium phosphate that constitutes the inorganic part of the bone matrix. In Paper I, the aim was to improve the carrier by adding other forms of calcium phosphate. The results indicated that bone formation was enhanced when using nano-sized hydroxyapatite. In Paper II, we discovered the importance of crushing the material, thus enhancing permeability and enlarging the surface area. We wished to further develop the carrier system, but were lacking an animal model with relatively high throughput, facilitated access, paired data, and we were also committed to the 3Rs of refinement, reduction, and replacement. To meet these challenges, we developed and refined an animal model, and this is described in Paper III. In Paper IV, we sought to further optimise the biomaterial properties of the hydrogel through covalent bonding of bisphosphonates to the hyaluronan hydrogel. This resulted in exceptional retention of the growth factor BMP-2. In Paper V, SPECT/PET/µCT was combined as a tri-modal imaging method to allow visualisation of the biomaterial’s in situ action, in terms of drug retention, osteoblast activity and mineralisation. Finally, in Paper VI the correlation between existing in vitro results with in vivo outcomes was observed for an array of biomaterials. The study identified a surprisingly poor correlation between in vitro and in vivo assessment of biomaterials for osteogenesis.
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| 2. |
- Edin, Elle, 1986-
(författare)
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Composite Regenerative Scaffolds
- 2018
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Regenerative medicine and tissue engineering solutions of heavily innervated tissues are at this point lacklustre. This thesis expands our knowledge of appropriate acellular scaffolds for tissue repair in general and nerve regeneration in particular. The optimal surgical procedure for the implantation of artificial extracellular matrix (ECM) was evaluated for recombinant human collagen (RHCIII) implants. Suturing techniques, as well as the usage of human amniotic membrane “bandages” were evaluated. While complete regeneration of corneal tissues occurred, only slight differences in effects of surgical technique could be found.The safety and efficacy of clinical trials using mesenchymal stromal cells (MSCs) was evaluated by conducting a systematic review and meta-analysis. MSC therapy was shown to be safe, with no increases mortality, rehospitalization or adverse events. There was also an indication of efficacy, as the overall mortality in the studies included was significantly smaller in the MSC treated group.Multicomponent hydrogel capsules encapsulating single cells were developed. Capsules manufactured from gelatin, agarose and fibrinogen were compared to pure gelatin capsules. The composite capsules successfully delayed cell release and prolonged cell survival.Surface patterning of collagen based biomimetic corneas was performed by microcontact printing. The ability of different sizes of fibronectin stripes to stimulate cell adhesion and proliferation was compared. The patterned surfaces improved cell adhesion, as well as proliferation markers.Conductive polymer composites were manufactured for use as nerve guides. The guides were created from electrospun polycaprolactone fibers coated with a series of different poly(3,4-ethylenedioxythiophene) films. A comparison of nerve progenitor growth and differentiation on the composite fibers was performed. Both the effects of fiber composition and MSC co-culture was investigated, with or without electrostimulation. MSC treatments and polymer coating was both important for nerve cell differentiation and growth.
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| 3. |
- Spyrou, Argyris
(författare)
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Heparan Sulfate Proteoglycans in Brain Tumor Development
- 2018
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Malignant brain tumors are aggressive neoplasms that remain challenging to treat in spite of their detailed molecular characterization. Both adults and children may suffer from brain tumors, which, if not lethal, can cause severe long-term and devastating side effects. The exceptionally invasive behavior of tumor cells, causing infiltrative disease, is among the reasons why these brain tumors often remain fatal. This thesis focuses on a group of molecules of the brain tumor microenvironment, heparan sulfate proteoglycans (HSPGs), and their roles in development of malignant brain tumors. The extracellular matrix in the brain has a unique composition with abundant HSPGs, and the hypothesis was, therefore, that heparan sulfate (HS)-degrading and HS-biosynthetic enzymes may have an important role in glioma and pediatric brain tumors.In our first study, we describe the role of the HS degrading enzyme, heparanase (HPSE), in glioblastoma (GBM) development, as well as its clinical relevance. A series of mechanistic studies revealed the effect of HPSE on signaling pathway activation and its protumorigenic activity in vitro and in vivo.Next, we expanded our work to encompass HPSE in pediatric brain tumors by presenting evidence of high HPSE expression in human tumors, and in cells derived from patients. We showed that tumor cell growth and invasion were increased by HPSE, an effect that could be inhibited by pharmacological treatment against the enzyme, suggesting that HPSE could be a targetable molecule in these tumors.We further explored the molecular mechanisms underlying the pro-tumorigenic properties of HPSE and in study III we describe a novel HPSE-CD24-L1CAM axis which was found to influence glioma tumorigenesis. Clinical data revealed a significantly shorter patient survival in HPSE-high/CD24-high tumors compared to CD24-low tumors, and experiments in mice showed that anti-CD24 and anti-L1CAM treatment inhibited tumor growth.In the fourth study, we investigated the dysregulation of the HS biosynthetic machinery and focused on N-deacetylase/N-sulfotransferase 1 (NDST1) in GBM development. We show overall low NDST1 expression levels across GBM patient samples, and patient-derived cell lines, and that low NDST1 levels correlate to poorer patient survival. Furthermore, altering the NDST1 expression had profound effects on GBM cell invasion, migration and stemness.
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| 4. |
- Asem, Heba, 1987-
(författare)
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Synthesis of Polymeric Nanocomposites for Drug Delivery and Bioimaging
- 2016
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Nanomaterials have gained great attention for biomedical applications due to their extraordinary physico-chemical and biological properties. The current dissertation presents the design and development of multifunctional nanoparticles for molecular imaging and controlled drug delivery applications which include biodegradable polymeric nanoparticles, superparamagnetic iron oxide nanoparticles (SPION)/polymeric nanocomposite for magnetic resonance imaging (MRI) and drug delivery, manganese-doped zinc sulfide (Mn:ZnS) quantum dots (QDs)/ SPION/ polymeric nanocomposites for fluorescence imaging, MRI and drug delivery.Bioimaging is an important function of multifunctional nanoparticles in this thesis. Imaging probes were made of SPION and Mn:ZnS QDs for in vitro and in vivo imaging. The SPION have been prepared through a high temperature decomposition method to be used as MRI contrast agent. SPION and Mn:ZnS were encapsulated into poly (lactic-co-glycolic) acid (PLGA) nanoparticles during the particles formation. The hydrophobic model drug, busulphan, was loaded in the PLGA vesicles in the composite particles. T2*-weighted MRI of SPION-Mn:ZnS-PLGA phantoms exhibited enhanced negative contrast with r2* relaxivity of 523 mM-1 s-1. SPION-Mn:ZnS-PLGA-NPs have been successfully applied to enhance the contrast of liver in rat model.The biodegradable and biocompatible poly (ethylene glycol)-co-poly (caprolactone) (PEG-PCL) was used as matrix materials for polymeric nanoparticles -based drug delivery system. The PEG-PCL nanoparticles have been constructed to encapsulate SPION and therapeutic agent. The encapsulation efficiency of busulphan was found to be ~ 83 %. PEG-PCL nanoparticles showed a sustained release of the loaded busulphan over a period of 10 h. The SPION-PEG-PCL phantoms showed contrast enhancement in T2*-weighted MRI. Fluorescein-labeled PEG-PCL nanoparticles have been observed in the cytoplasm of the murine macrophage cells (J774A) by fluorescence microscopy. Around 100 % cell viability were noticed for PEG-PCL nanoparticles when incubated with HL60 cell line. The in vivo biodistribution of fluorescent tagged PEG-PCL nanoparticles demonstrated accumulation of PEG-PCL nanoparticles in different tissues including lungs, spleen, liver and kidneys after intravenous administration.
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| 5. |
- Bergman, Kristoffer, 1975-
(författare)
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Hyaluronan Derivatives and Injectable Gels for Tissue Engineering
- 2008
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The present work describes the preparation of hyaluronan derivatives and hydrogels with potential use in tissue engineering applications. A potentially injectable hydrogel consisting of hyaluronan and collagen was successfully used to grow neurons in vitro by encapsulation of neural stem and progenitor cells. Attempts were further made to establish a suitable modification strategy which could be used for the preparation of in vivo cross-linkable hyaluronan derivatives. The synthesis of a model substance consisting of a D-glucuronate derivative which could simplify the development of such a modification technique is described, although a new method to prepare hyaluronan derivatives was found without its use. The modification strategy involves the use of a triazine-reagent which enables the covalent attachment of hydrophilic and hydrophobic amines to hyaluronan carboxyl groups in a controlled fashion under mild conditions. Using triazine-activated amidation we synthesized an aldehyde-derivative of hyaluronan which was used to prepare gels by cross-linking with hydrazide-modified polyvinyl-alcohol. Gels were formed in less than 1 minute by mixing equal volumes of the polymer derivatives and they were subsequently used as a carrier for bone morphogenetic protein-2. An in vitro release study showed that approximately 88% of the growth factor is retained in the gel over a 4 week period. The ability to form new bone in vivo was further evaluated in an ectopic rat model by the injection of gels containing 30 µg BMP-2. Radiographic and histological examination 4 and 10 weeks after injection showed the formation of new bone without any signs of inflammation or foreign body response. Hydroxyapatite particles were further added to improve the mechanical properties of the gel, and a comparative study was conducted. This time the induced tissue consisted not only of bone, but also of interconnected cartilage and tendon, as confirmed by histology and immunohistochemistry.
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| 6. |
- Bermejo-Velasco, Daniel, 1985-
(författare)
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Insights into Covalent Chemistry for the Development of Biomaterials
- 2019
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Covalent cross-linking chemistry is currently exploited in the preparation of biomaterial for biomedical applications. Choice of these chemistries for the preparation of biomaterials and bioconjugates strongly influences the biological output of these materials. Therefore, this thesis aims to develop novel bioconjugation strategies understanding their advantages and drawbacks. Our results provide new insight to adapt these chemical transformations for a specific application.The first part of this thesis points out the relevance of tuning different properties of biomaterials with specific emphasis on the development of hyaluronic acid (HA) hydrogels. The second part of the thesis describes how different chemical transformations including hydrazone formation (Paper I), thiazolidine formation (Paper II), cross-aldol addition reaction (Paper III) and disulfide formation (Paper IV) dictate material properties.This thesis explores both basic organic reaction mechanism and application of these reactions to influence material characteristics. The detailed study of the reaction conditions, kinetics, and stability of the products will help to understand the mechanical properties, hydrolytic stability, and degradability of the materials described here.Additionally, we performed degradation studies of gadolinium labeled HA hydrogels using magnetic resonance imaging. Furthermore, we also explored post-synthetic modification of hydrogels to link model fluorescent moieties as well as explored the tissue adhesive properties using Schiff-base formation.In summary, this thesis presents a selection of different covalent chemistries for the design of advanced biomaterials. The advantages and disadvantages of these chemistries are rigorously investigated. We believe, such an investigation provides a better understanding of the bioconjugation strategies for the preparation of biomaterials with potential clinical translation.
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| 7. |
- Kootala, Sujit, 1981-
(författare)
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Evaluation of Functionalized Biopolymers as a Step Toward Targeted Therapy of Osteoporosis
- 2015
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The work presented in this thesis focuses on the development of strategies and smart bioactive materials for the treatment of osteoporosis. High and low molecular weight soluble hyaluronic acid-bisphosphonate (HA-BP) derivatives were investigated for their ability to inhibit osteoclasts. Low molecular weight HA-BP (L-HA-BP) was most effective in inhibiting active resorption of both murine and human osteoclasts (without affecting osteoblasts) compared to free bisphosphonate (BP). Precursor monocytes were unaffected, suggesting the specificity of HA-BP towards osteoclasts. This new class of functionalized hyaluronic acid could lead to rapid development of tailor-made pro-drugs for targeted treatment of osteoporosis.Polyphosphoesters (PEP) have been widely studied for their pro-osteoblast effects, primarily due to their involvement in cellular energy production pathway leading to the formation of inorganic phosphates that contribute to mineralized bone. Given that the effect of PEP on human osteoclasts is little studied, this work on poly(ethylene sodium phosphate) (PEP.Na) explores the potential to use PEP.Na as an inhibitor of osteoclast activity for the first time. PEP.Na exposure led to a dose-dependent toxicity of osteoclasts with reduction in their capacity to form resorption pits over 24h.Currently, there is a dearth of in vitro cell-culture systems that can study osteoclast-related resorption and osteoblast-related mineralization in a single co-culture system, and to simultaneously quantify the effects of soluble factors on these processes. Described here, is the development of a novel and simple two-sided co-culture system that can overcome these limitations with reliable and quantifiable readouts. In comparison with traditional one-sided co-culture systems, the two-sided co-culture was able to generate similar readouts for alkaline phosphatase (ALP) and tartrate-resistant acid phosphatase (TRAP) markers. There is also the advantage of distinctly separate and quantifiable readouts for mineralization and resorption, which has been demonstrated using Pamidronate.Finally, HA-BP was synthesized with pre-determined amounts of BP groups. The BP groups attached to HA allowed the tunable incorporation of BMP-2 in hydrogels. The charge-based affinity of BMP-2 and BP allowed stable incorporation of specific amounts of BMP-2, which could be tuned by the ratio of BP groups. 125I-labelled BMP-2 was loaded into hydrogels and their release was studied. Radioactive measurements revealed the tunable sequestration and controlled release of protein over time. This result was corroborated by ALP measurements of cells exposed to released BMP-2. ALP production was found to be almost 5-fold higher in HA-BP hydrogels loaded with BMP-2 which suggested that the sequestered BMP-2 is not only available to cells but also remains highly potent, even in entrapped form, The release of BMP-2 is dependent upon the rate of diffusion, swelling in hydrogels and degradation pattern of the gels and may assist in the long-term and rapid regeneration of osteoblasts in vitro.
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| 8. |
- Lin, Jinjian, 1995-
(författare)
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Synthesis and characterization of “Clickable” triazine-trione based thermosets and composites via Thiol-Ene and Thiol-Yne Photochemistry
- 2024
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Triazine trione (TATO)-based thiol-ene and thiol-yne (TEC and TYC) thermosets and hydroxyapatite (HA) composites have proven their potential as bone fracture fixation implants for use in open reduction internal fixation (ORIF), a field which is currently dominated by metal implants which usually require a second operation for removal. These composites demonstrate high flexural modulus and strength as well as excellent biocompatibility. As injectable implants they are well-aligned with the surgeons needs for more patient-customized solutions to treat bone fractures. While promising, the non-degradable properties of current systems hinder their full potential to fully resorbable implants after complete bone healing. Hence, the foundation of this thesis was to expand the family of TATO thermosets and composites targeting key requirements on future biomaterials suited for bone tissue regeneration. Two different approaches were adopted in this thesis, namely the formulation of composites based on newly synthesized TATO-based monomers, and infusing polyester dendrimers into the existing TATO-HA formulation. The rationale behind both approaches was that the introduction of hydrolysable groups, from either the new TATO monomers or the dendrimers, would increase degradation but also impact the mechanical properties of the composite. The potential clinical applications of these new formulations were investigated through the evaluation of their mechanical, processability, biocompatibility and degradation properties.In the first approach, TATO-based alkene and alkyne monomers, containing either ester or amide linkages, were synthesized via fluoride promoted esterification (FPE) chemistry. Thermosets and composites were formulated with the resulting triester TATO monomers (TESTATO), commercially available triester TATO thiol (TEMPIC) and biocompatible hydroxyapatite (HA) filler. These formulations generated photo-initiated TEC and TYC crosslinked composites containing hydrolysable ester groups. These ester-rich materials displayed soft and flexible properties, differing from the previouspreviously formulated rigid and strong TATO-based composites. Cytotoxicity testing showed the new composites did not negatively affect cell viability. The high customizability of the TESTATO based composites was demonstrated through the drop-casting of objects such as rings, rods, tubes, and thin films (Paper I). These soft and flexibility composites were not suitable for bone fixation; however, they were investigated for their applications as tissue engineering (TE) scaffolds (Paper III) and anti-soft tissue adhesion coatings on metal implants (Paper IV). In the work of Paper III, numerous characterizations were applied to study the potential of the TESTATO based thermosets as tissue-engineering scaffolds, including mechanical testing, surface analysis, enzymatic degradation testing, and biocompatibility with bone marrow mesenchymal stromal cells (BMSCs). Collected results suggested that these ester-rich TEC and TYC thermoset materials showcased competitive properties to medical grade PCL, especially in the sense of biocompatibility and flexibility. Meanwhile, their convenient viscosity and ability to be cured on demand with light-initiated TEC and TYC chemistry allowed them to be fabricated into TE devices using different methodologies including drop-casting, salting leaching, thin filming and 3D printing. Moreover, the merits of flexibility and high processability of TESTATO based HA composites were applied to create flexible anti-soft tissue adhesion coatings on metal implants (Paper IV). Initial studies demonstrated that these soft TATO-HA composite coated metal plates were hydrophilic and able to withstand flexural displacement of 2 mm, under both dry and wet conditions, which is advantageous for potential future in vivo studies.In the second approach, polyester dendrimers with 1 and 3 generations were successfully integrated into the previously established rigid and strong TATO-HA composites in small weight percentages via HEV light-initiated TEC reactions. The addition of the dendrimers did not negatively affect the composites’ flexural modulus and strength under both dry and wet conditions. Moreover, the addition of these dendrimers was found to impact the viscosity of the resins of all formulations and reduce the size distribution of trapped bubbles in the composite cross sections.Both approaches aimed at introducing hydrolysable linkages into the TATO based systems. The inclusion of the G1 dendrimer significantly improved degradation while the TESTATO-alkene based composite showed the best hydrolytic degradation. However, the improvements to the degradation kinetics were more modest than expected, demonstrating that additional work, such using fillers that are more degradable than HA, will be required in the future.
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| 9. |
- Piskounova, Sonya
(författare)
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Biomaterials for Promoting Self-Healing of Bone Tissue
- 2011
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The present work addresses poor bone/implant integration and severe bone defects. In both conditions external stimuli is required for new bone to form. A multilayered functional implant coating, comprised of an inner layer of crystalline titanium dioxide (TiO2) and an outer layer of hydroxyapatite (HAP), loaded with bone morphogenetic protein-2 (BMP-2), was proposed as a tool for providing both improved initial bone formation and long-term osseointegration. The in vitro characterization of the implant coatings showed that TiO2 and HAP were more favorable for cell viability, cell morphology and initial cell differentiation, compared to native titanium oxide. Furthermore, significantly higher cell differentiation was observed on surfaces with BMP-2, indicating that a simple soaking process can be used for incorporating bioactive molecules. Moreover, the results suggest that there could be a direct interaction between BMP-2 and HAP, which prolongs the retention of the growth factor, improving its therapeutic effect. For treating severe bone defects a strategy involving BMP-2 delivery from hyaluronan hydrogels was explored. The hydrogels were prepared from two reactive polymers – an aldehyde-modified hyaluronan and a hydrazide-modified poly(vinyl alcohol). Upon mixing, the two components formed a chemically crosslinked hydrogel. In this work the mixing of the hydrogel components was optimized by rheological measurements. Furthermore, an appropriate buffer was selected for in vitro experiments by studying the swelling of hydrogels in PBS and in cell culture medium. A detection method, based on radioactive labeling of BMP-2 with 125I was used to monitor growth factor release both in vitro and in vivo. The results showed a biphasic release profile of BMP-2, where approximately 16 % and 3 % of the growth factor remained inside the hydrogel after 4 weeks in vitro and in vivo, respectively. The initial fast release phase corresponded to the early ectopic bone formation observed 8 d after injection of the hydrogel formulation in the thigh muscle of rats. The hydrogel formulation could be improved by incorporation of HAP powder into the hydrogel formulation. Furthermore, bone formation could be increased by pre-incubation of the premixed hydrogel components inside the syringe prior to injection. Crushed hydrogels were also observed to induce more bone formation compared to solid hydrogels, when implanted subcutaneously in rats. This was thought to be due to increased surface area of the hydrogel, which allowed for improved cell infiltration.
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| 10. |
- Shi, Liyang, 1991-
(författare)
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Injectable Composite Hydrogels Based on Metal-Ligand Assembly for Biomedical Applications
- 2018
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This thesis presents new strategies to construct injectable hydrogels and their various biomedical applications, such as 3D printing, regenerative medicine and drug delivery. These hydrogels cross-linked by dynamic metal-ligand coordination bonds exhibit shear-thinning and self-healing properties, resulting in the unlimited time window for injection. Compared with non-dynamic networks based on chemically reactive liquid polymer precursors that forms covalent bond during and/or post-injection, our injectable hydrogels with dynamic cross-linkages can be injected from an already cross-linked hydrogel state. Hyaluronic acid (HA) has been selected as the polymer due to its high biocompatibility and biodegradability. HA has been modified by attaching the bisphosphonates (BP) functionality as ligands for chelation of the metal ions or metal salts to form coordination cross-linkages. In the first part of this thesis, I presented the different chemical approaches to synthesize BP-modified HA (HA-BP) derivatives as well as HA derivatives dually modified with BP and acrylamide (Am) groups (Am-HA-BP). The structures of HA-BP derivatives were confirmed by NMR characterizations, e.g. by the peak at 2.18 ppm for methylene protons adjacent to the bridging carbon of BP in 1H-NMR spectrum and phosphorus peak at 18.27 ppm in 31P-NMR spectrum, respectively. In the next part, the hydrogels were constructed by simple mixing of HA-BP or Am-HA-BP solution with Ca2+ ions (Paper I), Ag+ ions (Paper II), calcium phosphonate coated silk microfibers (CaP@mSF) (Paper III), and magnesium silicate (MgSiO3) nanoparticles (Paper IV). The presented hydrogels exhibited dynamic features determined by reversible nature of coordination networks formed between of BP moieties of HA-BP or Am-HA-BP and metal ions or metal salts on the surface of the inorganic particles. Dynamic properties were characterized by rheological strain sweep experiments and strain-alternating time sweep experiments. Additionally, reversible coordination hydrogels were demonstrated to be further covalently cross-linked by UV light to form a secondary cross-linkage, allowing an increase of the strength and modulus of the hydrogels. In the last part of this thesis, biomedical applications of these hydrogels were presented. Am-HA-BP•Ca2+ hydrogel was extruded, using home-made 3D printer, then fixed by UV irradiation to fabricate multi-layered 3D tube-like construct (Paper I). In full-thickness skin defects of rat model, HA-BP•Ag+ hydrogel accelerated the wound healing process and increased thickness of newly-regenerated epidermal layer (Paper II). In the rat cranial critical defect model, double cross-linked Am-HA-BP•CaP@mSF hydrogel induced new bone formation without addition of biological factors and cells (Paper III). The anti-cancer drug loaded hydrogel was also prepared by mixing of the drug loaded MgSiO3 nanoparticles with HA-BP solution. The released particles from the hydrogel were shown to be taken up by cancer cells to induce a toxic response (Paper IV).In summary, this thesis presents metal-ligand coordination chemical strategies to build injectable hydrogels with dynamic cross-linking resulting in time-independent injection behavior. These hydrogels open new possibilities for use in biomedical areas.
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| 11. |
- Yang, Ting, 1983-
(författare)
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Mechanical and swelling properties of hydrogels
- 2012
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Hydrogels have been used as one of the novel soft materials in many biomedical applications such as drug delivery and tissue engineering for recent decades.In the main part of this work, bi-functional poly(ethylene glycol) (PEG) precursors with either thiols (PEG-SH) or allyls (PEG-Al) , covering molecular weights from 3 kDa to 8 kDa were synthesized and thoroughly characterized by 1H NMR, 13C NMR, FT-Raman and MALDI-TOF techniques. By combining PEG precursors with complementary trifunctional crosslinkers, a library of well-defined single-network hydrogels was efficiently constructed via the robust UV-initiated thiol-ene coupling (TEC) chemistry. Novel sequential interpenetrating network (seqIPN) hydrogels based on PEG were fabricated by diffusing and afterwards crosslinking secondary-network precursors within dense (2 kDa) to loose (8 kDa) primary networks. The impacts of polymer chain length and diffusion time on the swelling and mechanical properties were assessed for the seqIPN hydrogels. Additionally, disperse red 13 decorated PEG 2 kDa and 8 kDa were synthesized and used as probes to monitor the secondary-network precursor diffusion rate by UV/Vis spectroscopy. FT-Raman and leaching tests were conducted to evaluate the efficiency of the TEC reaction for the development of PEG networks and their gel fractions. All gels were fully crosslinked within 5 minutes and with the gel fraction above 84%. The chain length of PEG, location of functional groups of PEGs, solvents, solid content were found to have directly influence on the mechanical and swelling properties of PEG single-network hydrogels. The utilization of the diffusion time dependent seqIPN strategy enabled further freedom to control the swelling and mechanical properties of PEG hydrogels, with the degree of water swelling ranged from 280 – 870% and the tensile modulus ranging from 1135 kPa to 175 kPa.Furthermore, the seqIPN strategy was utilized for fiber reinforced free radical polymerized hydrogels. N, N-dimethylacrylamide (DMA) with crosslinker poly(ethylene glycol) diacrylate were diffused in bacterial cellulose (BC) aerogel thereafter UV crosslinked to form BC-DMA hydrogels. FT-Raman and leaching tests were conducted to evaluate the efficiency of the free radical polymerization and the BC-DMA gel fractions. After UV cure for 10 minutes, robust DMA networks were formed within BC aerogels with over 94% gel fraction. The high porosity and robust interpenetrating DMA network within BC fibers were further analysed with FE-SEM. Compression tests showed that fiber reinforced DMA hydrogels have higher compression modulus than DMA hydrogels, ranging from 4.4 to 8.3 MPa with water content from 78 to 70%.
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| 12. |
- Asplund, Basse, 1974-
(författare)
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Biodegradable Thermoplastic Elastomers
- 2007
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- A novel strategy for synthesising segmented poly(urethane urea) (PUU) without using a chain extender but nevertheless with the opportunity to vary the hard segment content has been developed. The strategy is based on amine formation from isocyanate upon reaction with water. By adding a dissolved soft segment to an excess of diisocyanate followed by the addition of water in the gas phase, amines are formed in situ. Urea linkages are then formed when these amines react with the excess of isocyanate groups. The gas phase addition facilitates addition in a slow and continuous manner. The hard segment content can easily altered by varying the diisocyanate/soft segment ratio. Even though the strategy is shown to be applicable to different diisocyanates, the focus has been on the potentially biodegradable methyl-2,6-diisocyanatehexanoate (LDI) and 1.4-butanediisocyanate (BDI) and various well known biodegradable polyesters and polycarbonates. All the synthesised materials exhibited pronounced phase separation and hydrogen bonding within the hard domains. However, a major increase in hydrogen bonding strength was seen when a symmetric diisocyanate was used instead of an asymmetric. Based on FTIR measurements, PUUs with BDI and a polydisperse hard segment can exhibit the same degree of phase separation and hydrogen bonding as the monodisperse product.The elastic properties of this new group of PUUs were exceptional with an elongation at break from 1600% to almost 5000% and the elastic modulus could be varied from a few MPa up to a couple of hundreds. Hydrolytic degradation was greater in the polyester-based than in the polycarbonate-based PUUs due to the more reactive ester bonds. Low mass loss but a considerable loss in molecular weight was seen in the polyester PUUs. The tensile strength decreased dramatically due to the loss of strain hardening.An MTT seeding assay using human fibroblasts and an in vivo biocompatibility study were performed and no signs of cytotoxicity were seen and the inflammatory response was comparable to other inert polymers.A biodegradable PUU with properties that can be tailored through an easy synthesis is here presented.
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| 13. |
- Atthoff, Björn, 1973-
(författare)
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Tailoring of Biomaterials using Ionic Interactions : Synthesis, Characterization and Application
- 2006
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The interactions between polymers and components of biological systems are an important area of interest within the fields of tissue engineering, polymer chemistry, medicine and biomaterials. In order to create such a biomimetic material, it must show the inherent ability to reproduce or elicit a biological function. How do we design synthetic materials in order to direct their interactions with biological systems?This thesis contributes to this research with aspects of how polymers interact with biological materials with the help of ionic interactions. Polyesters, biodegradable or not, may after a hydrolytic cleavage interact ionically with protonated amines by the liberated carboxylate functions. Amines are found in proteins and this fact will help us to anchor proteins to polyester surfaces. Another type of interaction is to culture cells in polymeric materials, i.e. scaffolds. We have been working on compliant substrates, knitted structures, to allow cell culture in three dimensions. A problem that arises here is how to get a high cell seeding efficiency? By working on the interactions between polymers, proteins and finally cells, it is possible to create a polarized protein membrane that allows for very efficient cell seeding, and subsequent three dimensional cell cultures. Finally a synthetic route to taylor interaction was developed. Here a group of polymers known as ionomers were synthesized. In our case ionic end groups have been placed onto biodegradable polycarbonates, we have created amphiphilic telechelic ionomers. Functionalization, anionic or cationic, changes the properties of the material in many ways due to aggregation and surface enrichment of ionic groups. It is possible to add functional groups for a variety of different interactions, for example introducing ionic groups that interact and bind to the complementary charge of proteins or on the other hand one can chose groups to prevent protein interactions, like the phosphorylcholine zwitterionomers. Such interactions can be utilized to modulate the release of proteins from these materials when used in protein delivery applications. The swelling properties, Tg, degradation rate and mechanical properties are among other things that will easily be altered with the choice of functional groups or backbone polymer.
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| 14. |
- Aulin, Cecilia, 1979-
(författare)
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Extracellular Matrix Based Materials for Tissue Engineering
- 2010
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The extracellular matrix is (ECM) is a network of large, structural proteins and polysaccharides, important for cellular behavior, tissue development and maintenance. Present thesis describes work exploring ECM as scaffolds for tissue engineering by manipulating cells cultured in vitro or by influencing ECM expression in vivo. By culturing cells on polymer meshes under dynamic culture conditions, deposition of a complex ECM could be achieved, but with low yields. Since the major part of synthesized ECM diffused into the medium the rate limiting step of deposition was investigated. This quantitative analysis showed that the real rate limiting factor is the low proportion of new proteins which are deposited as functional ECM. It is suggested that cells are pre-embedded in for example collagen gels to increase the steric retention and hence functional deposition. The possibility to induce endogenous ECM formation and tissue regeneration by implantation of growth factors in a carrier material was investigated. Bone morphogenetic protein-2 (BMP-2) is a growth factor known to be involved in growth and differentiation of bone and cartilage tissue. The BMP-2 processing and secretion was examined in two cell systems representing endochondral (chondrocytes) and intramembranous (mesenchymal stem cells) bone formation. It was discovered that chondrocytes are more efficient in producing BMP-2 compared to MSC. The role of the antagonist noggin was also investigated and was found to affect the stability of BMP-2 and modulate its effect. Finally, an injectable gel of the ECM component hyaluronan has been evaluated as delivery vehicle in cartilage regeneration. The hyaluronan hydrogel system showed promising results as a versatile biomaterial for cartilage regeneration, could easily be placed intraarticulary and can be used for both cell based and cell free therapies.
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| 15. |
- Oliveros Anerillas, Luis, 1995-
(författare)
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Development and optimization of a 3D in vitro model for osteogenic biomaterial evaluation
- 2023
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Despite the innate regenerative capabilities of bone tissue, self-repair is impaired when an injury exceeds the critical size threshold because of trauma, congenital, or pathological conditions. Autologous transplantation is the gold standard to reconstruct large bone defects. However, this method has drawbacks such as limited amount of graftable material, limited accessibility, and donor site morbidity. For these reasons, alternative regenerative medicine and tissue engineering approaches are being developed, including implantable scaffolds.The use of in vitro-made scaffolds containing biomaterials that mimic the functional characteristics and composition of extracellular bone matrix has been favored in 3D vs 2D in vitro culture systems. Adult stem cells such as mesenchymal stem cells (MSCs), that give rise to bone building cells, have been used in combination with various biomaterials. The development of an implantable scaffold with or without cells requires extensive in vitro validation and optimization prior to its testing in vivo. Thus, the primary aim of this thesis was to develop a 3D model for the optimization of MSC differentiation. Further aims were to utilize this 3D model to evaluate the MSC response to a novel osteogenic biomaterial. To achieve these objectives human bone marrow MSCs (BMSCs) were utilized in various hydrogels in combination with chemical differentiation factors or biomaterials. Moreover, the osteogenic capability of the tested biomaterials and their induced inflammatory/angiogenic responses were investigated, and the culture conditions were optimized for clinical application. In this thesis, a comparison between 2D and 3D (hydrogels) in vitro culture models was developed with the purpose of studying osteogenic differentiation in BSMCs. Testing various hydrogels revealedt he superiority of type I collagen hydrogels for the osteogenic 3D in vitro culture system. Further, cell culture conditions were improved for the expansion and differentiation of BMSCs to fulfill clinically approved standards according to Good Manufacturing Practice (GMP) conditions. Comparisons between fetal bovine serum (FBS) and human platelet lysate (PLT) showed superior cellular differentiation in FBS, while PLT enhanced cell proliferation. Based on the developed 3D model, the osteogenic properties of a novel nanoporous silica calcium phosphate (nSCP) material were investigated. The results indicated that nSCP was osteoinductive, involving different pathways compared with the traditional chemical differentiation protocols or other tested osteogenic biomaterials. Finally, the inflammatory and angiogenic responses from human BMSCs and an immortalized monocyte cell line (THP-1) exposed to nSCP in the established 3D model were assessed.The results indicated limited inflammatory effect of nSCP, while inducing the secretion of pro-angiogenic cytokines. The bioactivity of these released factors was confirmed in an assay using human endothelial cells.Taken together, this thesis presents a 3D in vitro model for studying osteogenic differentiation in MSCs, which can be utilized to evaluate, validate, and optimize biomaterial candidates for bone regeneration applications.
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| 16. |
- Paidikondala, Maruthibabu, 1985-
(författare)
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Regulating Gene Expression to Promote Osteoblastic Differentiation of Stem Cells
- 2019
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Bone is a tissue that heals by itself, unless the defect is too large (critical size). Today, novel regenerative medicine approaches have emerged as an alternative to treat such defects. This thesis explores alternative therapeutic strategies for bone tissue engineering which are biocompatible and clinically translatable. Many types of scaffolds that can act as reservoirs for growth factors such as rh-BMP-2 have been developed for bone tissue engineering in the past. However, the role of cross-linking chemistries that are employed to make hydrogels on the integrity and function of the loaded growth factors is not well understood. In this thesis, we have explored the influence of cross-linking chemistry on rh-BMP-2 integrity and bioactivity both in-vitro and in-vivo. These studies have demonstrated that thiol-Michael addition cross-linking chemistry greatly affects the integrity and bio-functionality of the loaded protein BMP-2 and leads to poor bone formation in an in-vivo rat model. On the other hand, hydrogels employing hydrazone chemistry did not significantly affect the integrity and bioactivity of BMP-2, which lead to a superior bone formation in-vivo. Since the high dose of rh-BMP-2 is known to confer many side effects, alternative ex-vivo strategies involving transient transfection of BMP-2 expressing plasmid DNA and silencing of anti-osteogenic genes using siRNA are developed. Our optimized method involves rapid transfection of hMSCs in suspension (5 minutes) with plasmid DNA followed by centrifugation and encapsulation in a hydrogel not only reduced cytotoxicity but also lead to efficient osteoblast differentiation of stem cells. Furthermore, this thesis presents the role of ECM-derived polymer HA in interacting with siRNA and trafficking across the plasma membrane, presumably through CD44 receptors and successfully silencing the target gene in-vitro. We explored the potential of such a non-cationic transfection method to deliver functional siRNA (anti-Pleckho-1 siRNA) in MSCs and compared it with commercially available cationic lipid LipofectamineTMRNAiMAX, using our optimized suspension transfection method. Our novel ex-vivo strategy employing HA hydrogels enabled efficient silencing of BMP-2 signaling pathway antagonist Pleckho-1 while avoiding the cytotoxicity issues in 3D, which further qualifies them for potential clinical application for cell-based therapies.
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