Biological hydrogels such as collagen and gelatin are highly attractive materials for tissue engineering and biomedicine. Due to their excellent biocompatibility and biodegradability, they represent promising candidates in regenerative medicine, cell culture, tissue replacement and wound dressing applications. Thereby, precisely tuned material properties are indispensable for customization. High-energy electron-treatment is a highly favourable crosslinking technique to tailor the material properties. In five sub-projects, this thesis investigates the potential of high-energy electron-treatment to precisely modify collagen hydrogels, to develop thermo- as well as hydration-sensitive systems and functional surfaces from gelatin for biomedical applications. The first sub-project focusses on the modification of collagen hydrogels by electron-induced crosslinking with potential application as biomimetic extracellular matrix material. Thereby, it is shown that the material properties can be precisely tailored by adapting electron-induced crosslinking while high cytocompatibility is maintained. Within the second sub-project, an electron-crosslinking-induced shape-memory effect in gelatin is described in order to develop a thermo-responsive system. The effect is described experimentally as well as theoretically to demonstrate the fundamental physical processes. The third sub-project develops an electroncrosslinked hydration-sensitive gelatin system. The work discusses how swelling of electroncrosslinked gelatin is influenced by the pH-value and salt concentration of the swelling liquid. Thereby, response of the hydration-sensitive gelatin system can be further modified towards biological actuatoric systems. The fourth sub-project develops a two-step process to mechanically pattern gelatin surfaces. Within the first step, thin gelatin surfaces are mechanically patterned by a highly focussed electron beam. In a second step, they are stabilized by homogeneous electron-crosslinking for applications at physiological conditions. Another method to develop functional gelatin surfaces is described in the last sub-project. Here, gelatin is topographically patterned via a moulding technique. The resulting micro-structures are then stabilized via electron-crosslinking. In addition, the presented work investigates pattern transfer, long time stability at physiological conditions as well as cytocompatibility.:1 Introduction and Objective 1.1 Biomimetic ECM Models 1.2 Stimuli-Responsive Hydrogels 1.3 Functional Hydrogel Surfaces 2 General Background 2.1 Hydrogels 2.1.1 Collagen 2.1.2 Gelatin 2.2 Polymer Crosslinking 2.2.1 High-Energy Electron-Treatment of Polymers 2.2.2 Electron-Irradiation-Induced Crosslinking of Gelatin 2.3 High-Energy Electron Accelerator 3 Cumulative Part 3.1 High-Energy Electron-Induced Modification of Collagen 3.2 Thermo-Responsive Gelatin System 3.3 Hydration-Responsive Gelatin System 3.4 Mechanically Patterned Gelatin Surfaces 3.5 Topographically Patterned Gelatin Surfaces 4 Summary and Conclusion 5 Outlook Bibliography Author Contributions List of Abbreviations List of Figures Acknowledgements Scientific Curriculum Vitae Publication List Selbstständigkeitserklärung / Biologische Hydrogele wie Kollagen und Gelatine sind wichtige Materialien vor allem in biomedizinischen Anwendungsbereichen. Durch deren exzellente Biokompatibilität und biologische Abbaubarkeit werden sie vor allem bei der Züchtung von biomimetischem Gewebe, in der Zellkultur, als Gewebeersatz in der regenerativen Medizin oder auch als Wundverband eingesetzt. In der Verwendung solcher Materialien besteht eine wesentliche Herausforderung darin, deren Eigenschaften so präzise wie möglich einzustellen, um speziell angepasste Substrate und Gewebe entwickeln zu können. Eine äußerst vorteilhafte Methode zu Adaptierung der Materialeigenschaften ist die elektronenstrahlbasierte Vernetzung, die auf die Verwendung zusätzlicher chemischer Vernetzer verzichtet. Die vorgelegte Arbeit untersucht in fünf Teilprojekten das Potential von Elektronenstrahlvernetzung zur Modifizierung von Kollagen- sowie Gelatinehydrogelen für biomedizinische Anwendungen. Das erste Teilprojekt fokussiert sich auf die Auswirkungen hochenergetischer Elektronen auf Kollagenhydrogele und deren Eigenschaften für potentielle Anwendungen als biomimetisches Modell der extrazellulären Matrix. Dabei wird gezeigt, dass sich die Materialeigenschaften in Abhängigkeit der Elektronenbestrahlung präzise einstellen lassen und dass diese Gele eine hohe Zellkompatibilität aufweisen. Das zweite Teilprojekt beschreibt den Effekt des thermischen Formgedächtnisses in Gelatine nach Elektronenstrahlvernetzung und dessen Potential für die Entwicklung biologischer Aktuatoren. Die Effizienz des Formgedächtniseffekts wird in diesem Teilprojekt ausführlich theoretisch beschrieben und mit experimentellen Untersuchungen an Gelatine verglichen. Im dritten Teilprojekt wird ein elektronenstrahlvernetztes, hydrations-responsives Gelatinesystem beschrieben. Zusätzlich wird der Einfluss von pH-Wert und Salzkonzentration der Quelllösung auf das Quellen von elektronenstrahlvernetzter Gelatine untersucht um das Reaktionsverhalten noch präziser einstellen zu können. Das vierte Teilprojekt beschreibt einen Zwei-Schritt-Prozess, bei dem dünne Gelatineschichten mittels hochenergetischer Elektronen mechanisch funktionalisiert werden können. Dabei wird in einem ersten Schritt die Oberfläche durch hoch fokussierte Elektronen mechanisch strukturiert, um im zweiten Schritt mittels homogener Elektronenstrahlvernetzung für die Anwendung unter physiologischen Bedingungen stabilisiert zu werden. Eine weitere Methode zur Funktionalisierung der Oberfläche von Gelatinehydrogelen wird im letzten Teilprojekt dieser Arbeit dokumentiert. Dabei werden topographische Mikrostrukturen auf Gelatineoberflächen aufgebracht und mittels Elektronenstrahlvernetzung stabilisiert. Dieses Teilprojekt untersucht zusätzlich den Strukturtransfer, die Langzeitstabilität unter physiologischen Bedingungen sowie die Zellkompatibilität.:1 Introduction and Objective 1.1 Biomimetic ECM Models 1.2 Stimuli-Responsive Hydrogels 1.3 Functional Hydrogel Surfaces 2 General Background 2.1 Hydrogels 2.1.1 Collagen 2.1.2 Gelatin 2.2 Polymer Crosslinking 2.2.1 High-Energy Electron-Treatment of Polymers 2.2.2 Electron-Irradiation-Induced Crosslinking of Gelatin 2.3 High-Energy Electron Accelerator 3 Cumulative Part 3.1 High-Energy Electron-Induced Modification of Collagen 3.2 Thermo-Responsive Gelatin System 3.3 Hydration-Responsive Gelatin System 3.4 Mechanically Patterned Gelatin Surfaces 3.5 Topographically Patterned Gelatin Surfaces 4 Summary and Conclusion 5 Outlook Bibliography Author Contributions List of Abbreviations List of Figures Acknowledgements Scientific Curriculum Vitae Publication List Selbstständigkeitserklärung

While composite structures exhibit exceptional strength and weight saving possibilities for engineering applications, sometimes their overall cost and/or material performance can limit their usage when compared to conventional structural materials. Meanwhile ‘biocomposites’, composite structures consisting of natural fibers (i.e. bamboo fibers), display higher cost efficiency and unique structural benefits such as ‘sustainability’. This analysis will determine if the integration of these two different types of composites are beneficial to the overall structure. Specifically, the structure will consist of a one internal bamboo veneer biocomposite ply; and two external carbon fiber weave composite plies surrounding the bamboo biocomposite. To acquire results of this study, the hypothesized composite structure will consist of varied trapezoidal corrugated specimens and tested in uniaxial compression loading. Thereafter, this test data will be used to ultimately design, manufacture, and test a structural biocomposite/composite box, intended to carry extremely high compressive loads; relative to its own weight. A finite element analysis of this test will be used to validate experimental data. After running the experiment, the carbon fiber with bamboo test sample results were compared to that of only carbon fiber test sample. The carbon fiber samples resulted in a maximum compressive load difference of only 23% higher loads when compared to the carbon fiber with bamboo, on average. These findings are discussed throughout.

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Indiana University-Purdue University Indianapolis (IUPUI) / Hydrogels prepared from photopolymerization have been used for a variety of tissue engineering and controlled release applications. Polymeric biomaterials with high cytocompatibility, versatile degradation behaviors, and diverse material properties are particularly useful in studying cell fate processes. In recent years, step-growth thiol-ene photochemistry has been utilized to form cytocompatible hydrogels for tissue engineering applications. This radical-mediated gelation scheme utilizes norbornene functionalized multi-arm poly(ethylene glycol) (PEGNB) as the macromer and di-thiol containing molecules as the crosslinkers to form chemically crosslinked hydrogels. While the gelation mechanism was well-described in the literature, the network properties and degradation behaviors of these hydrogels have not been fully characterized. In addition, existing thiol-ene photopolymerizations often used type I photoinitiators in conjunction with an ultraviolet (UV) light source to initiate gelation. The use of cleavage type initiators and UV light often raises biosafety concerns. The first objective of this thesis was to understand the gelation and degradation properties of thiol-ene hydrogels. In this regard, two types of step-growth hydrogels were compared, namely thiol-ene hydrogels and Michael-type addition hydrogels. Between these two step-growth gel systems, it was found that thiol-ene click reactions formed hydrogels with higher crosslinking efficiency. However, thiol-ene hydrogels still contained significant network non-ideality, demonstrated by a high dependency of hydrogel swelling on macromer contents. In addition, the presence of ester bonds within the PEGNB macromer rendered thiol-ene hydrogels hydrolytically degradable. Through validating model predictions with experimental results, it was found that the hydrolytic degradation of thiol-ene hydrogels was not only governed by ester bond hydrolysis, but also affected by the degree of network crosslinking. In an attempt to manipulate network crosslinking and degradation rate of thiol-ene hydrogels, different macromer contents and peptide crosslinkers with different amino acid sequences were used. A chymotrypsin-sensitive peptide was also used as part of the hydrogel crosslinkers to render thiol-ene hydrogels enzymatically degradable. The second objective of this thesis was to develop a visible light-mediated thiol-ene hydrogelation scheme using a type II photoinitiator, eosin-Y, as the only photoinitiator. This approach eliminates the incorporation of potentially cytotoxic co-initiator and co-monomer that are typically used with a type II initiator. In addition to investigating the gelation kinetics and properties of thiol-ene hydrogels formed by this new gelation scheme, it was found that the visible light-mediated thiol-ene hydrogels were highly cytocompatible for human mesenchymal stem cells (hMSCs) and pancreatic MIN6 beta-cells. It was also found that eosin-Y could be repeatedly excited for preparing step-growth hydrogels with multilayer structures. This new gelation chemistry may have great utilities in controlled release of multiple sensitive growth factors and encapsulation of multiple cell types for tissue regeneration.

The American Cancer Society predicts that 1,665,540 people will be diagnosed with cancer, and 585,720 people will die from cancer in 2014. One of the most common types of cancer in the United States is skin cancer. Melanoma alone is predicted to account for 10,000 of the cancer related deaths in 2014. As a highly mobile and aggressive form of cancer, melanoma is difficult to fight once it has metastasized through the body. Early detection in such varieties of cancer is critical in improving survival rates in afflicted patients. Present methods of detection rely on visual examination of suspicious regions of tissue via various forms of biopsies. Accurate assessment of cancerous cells via this method are subjective, and often unreliable in the early stages of cancer formation when only few cancer cells are forming. With fewer cancer cells, it is less likely that a cancer cell will appear in a biopsied tissue. This leads to a lower detection rate, even when cancer is present. This lack of detection when cancer is in fact present is referred to as a false negative. False negatives can have a highly detrimental effect on treating the cancer as soon as possible. More accurate methods of detecting cancer in early stages, in a nonsubjective form would alleviate these problems. A proposed alternative to visual examination of biopsied legions is to utilize fluorescent nanocrystalline biomarker constructs to directly attach to the abnormal markers found on cancerous tissues. Quantum dots (QDs) are hydrophobic nanoscale crystals composed of semiconducting materials which fluoresce when exposed to specific wavelengths of radiation, most commonly in the form of an ultraviolet light source. The QD constructs generated were composed of cadmium-selenium (CdSe) cores encapsulated with zinc-sulfide (ZnS) shells. These QDs were then encapsulated with phospholipids in an effort to create a hydrophilic particle which could interact with polar fluids as found within the human body. The goal of this thesis is to develop a method for the solubilization, encapsulation, and initial functionalization of CdSe/ZnS QDs. The first stage of this thesis focused on the generation of CdSe/ZnS QDs and the fluorescence differences between unshelled and shelled QDs. The second stage focused on utilizing the shelled QDs to generate hydrophilic constructs by utilizing phospholipids to bind with the QDs. Analysis via spectroscopy was performed in an effort to characterize the difference in QDs both prior to and after the encapsulation process. The method generated provides insight on fluorescence trends and the encapsulation of QDs in polar substances. Future research focusing on the repeatability of the process, introducing the QD constructs to a biological material, and eventual interaction with cancer cells are the next steps in generating a new technique to target and reveal skin cancer cells in the earliest possible stages without using a biopsy.

Instrumental disparities and soil moisture are two of the key limitations in implementing spectroscopic techniques in the field. This study sought to address these challenges through two objectives. The first objective was to assess Visible-near infrared (VisNIR) and mid-infrared (MIR) spectroscopic approaches and explore the feasibility of transferring calibration models between laboratory and portable spectrometers. The second objective addressed the challenge of soil moisture and its impact on spectra. The portable spectrometers demonstrated comparable performance to their laboratory-based counterparts in both regions. Spiking with extra-weight, was the most effective calibration transfer method eliminating disparities between instruments. The samples were rewetted under nine controlled conditions for the moisture study. Results showed that spiking with extra weights significantly outperformed other techniques and model enhancement was insensitive to the moisture contents. Findings of this study will be helpful for development and deployment of in situ sensors to enable field implementation of spectroscopy.