In this study we describe novel polyionic dendrimer – PEG hydrogels for drug delivery. Hydrogels have a crosslinked insoluble network of polymer chains, which have found many applications including drug delivery and tissue regeneration. Dendrimers provide an ideal platform for drug delivery as they possess a well-defined highly branched nanoscale architecture with many reactive surface groups. Their highly clustered surface groups allow for targeted drug delivery and high drug payload to enhance therapeutic effectiveness. This study presented a new type of polyionic hydrogels based on dendrimers with potential applications in drug delivery and tissue engineering. Polyethylene glycol (PEG) with various chain lengths [1500, 6000 , 12000 Da] was first conjugated to the Starburst™ G3.0 PAMAM dendrimer to form stealth dendrimers through one ending site of PEG using p-nitro phenyl chloroformate and Triethylamine. The free hydroxyl group of PEG was further converted to an acrylate group using acrolyl chloride and Triethylamine. The conjugation was characterized with 1H-NMR. The Ninhydrin assay was used to estimate the loading degree of PEG on the dendrimer surface. The molecular weight and loading degree of PEG was varied. Hydrogel formation was realized by subjecting dendrimer-PEG acrylate to UV exposure for a brief period of time at the presence of Eosin Y, Triethanolamine [TEOA] and 1 vinyl 2 Pyrrolidinone [NVP] photo initiator system. Viscosity increase was observed after hydrogel formation. PEGylated G3.0 PAMAM dendrimer served as cross-linking agent to form hydrogels because of its multiple functionalities. PEGylated half generation dendrimer G3.5 was subjected to hydrogel formation and its swelling behavior was studied. Better hydrogel formation was observed with increased PEG arm length. The surface charges conferred by terminal groups on the dendrimer surface made the hydrogel polyionic with controllable charge density. This new type of hydrogel has many favorable biological properties such as non toxicity and non immunogenecity and multifunctional ties for a variety of in vivo applications. Current studies have demonstrated feasibility of chemistry and hydrogel formation. The swelling studies demonstrated pH sensitive behavior. Degradation of hydrogel was observed, for low PEGylated dendrimer degradation also demonstrated pH sensitivity. Controlled drug delivery and release were also investigated. Hydrophobic drug Cyclosprine A was used, we envision that hydrophobic dendrimer core will used for drug encapsulation and delivery, and later release in controlled fashion. The polymer and hydrogels were evaluated for in vitro cytotoxicity and cell internalization.

Individuals with sensory and multiple physical impairments, which may include the loss of the ability to speak, have very specialized communication needs. Based on the belief that the current technology does not fully meet these needs, a prototype communication aid was developed for an individual who is cortically blind, dysphonic, and motor impaired. Furthermore, the communication device has broader applications beyond the present individual. The prototype system has a direct selection of "Yes" and "No" responses, scanning access to daily phrases, rate enhancement of all scans, prompted encoding for selection of letters, two letter codes for complete sentences, access to a 500 word dynamic dictionary after two letters have been typed, and editing capabilities. Furthermore, the research includes suggestions on how letter prediction based on the dynamic dictionary might be utilized.

The clinical demand for neural stem cells drives the need for a reproducible method used to generate a large quantity of well-characterized cells to support regenerative therapies. Microcarriers are currently being used as a scaffold for stem cell culture to aid in this expansion process because they provide a larger surface area while also requiring fewer cell passages compared to monolayer culture. The main objective of this project was to investigate how human neural stem cell attachment, proliferation, and multipotency would respond to three-dimensional (3D) culture using peptide-coated microcarriers of varying diameters. In this study, multi-sized polystyrene microcarriers were fabricated using a vibration generator and solvent evaporation techniques in order to optimize the size distribution and homogeneity of the scaffold. Overall, the results indicated that when supplemented with a beneficial surface coating, the constructed microcarriers were successful at promoting stem cell attachment, growth, and viability without interference from surface curvature. This research will provide insight for further studies involving the feasibility of 3D culture on neuronal differentiation, the scale-up advantage of microcarriers, and clinical therapies.

There has been much work into getting clear and precise images of bone growing within different osteoconductive and osteoinductive scaffolds for the aim of investigating and quantifying the effect the different grafts have on the bone that forms within the graft. Before the bone structure and volume can be quantified, the images produced need to segmented into their different regions. Using images produced from x-ray computed tomography, the samples can be segmented based on their densities. As the voxels have distinct size, if just the density is used to segment out the regions, there will be some miss-identification at the edges of the regions (ghosting). To overcome this problem of misidentification, automated segmentation methods were developed which take not only the intensity of the voxels in the images (which are related to the density) into account for the segmentation but also the local properties. With correct segmentation the volume and surface area are better represented and methods for structure measurement can and were developed. These methods allow for not only the structure of the bone and implants to be quantified, but for the change in structures between the different implants to be compared. This allows for the different structures caused by the different graft materials to be seen and compared. This comparison when used on its own or with other methods such as histology not only allows for the different structures to be identified but all the change in structures due to factors such as remodelling to be identified.

Intracoronary injection is a frequently used clinical protocol for stem/progenitor cell therapy to the heart. Initial donor cell retention in the heart is the key to the success of this approach; however, this process has been poorly investigated. I established an original model to quantitatively assess initial donor cell retention after intracoronary cell injection in rats using an ex-vivo heart perfusion system and investigated factors that could affect retention. The initial retention efficiency of bone marrow mononuclear cells (BMMNC) was 20% after injection into normal hearts. The majority (>90%) of BMMNC loss into the coronary effluent occurred within the first minute of injection. Increased BMMNC dose increased absolute retention with a linear dose-effect relationship, while retention efficiency was unaltered. Retention efficiency increased to 30% in hearts with ischaemia-reperfusion, while flow cytometric studies showed that surface marker expression was unchanged between the pre-injection donor cell population and the population in the coronary effluent in both normal and ischemia-reperfused hearts. This suggests that active interactions between donor cells and coronary endothelium were not critical for donor cell retention using these experimental conditions. Instead, cell size assessment revealed that larger subpopulations of BMMNC were preferentially retained compared to smaller BMMNC in both normal and ischemia-reperfused hearts. Furthermore, a larger cell type, bone-marrow derived mesenchymal stem cells (MSC; median cell size=10.1 μm), had a markedly increased retention efficiency (80%) compared to BMMNC (median cell size=7.0 μm). A greater proportion of MSC with a larger diameter were retained compared to smaller diameter MSC; this enhanced retention plateaued with MSC ≥ 9 μm. Immunohistochemical analysis using fluorescently labeled donor cells demonstrated that all BMMNC retained in normal and ischaemia-reperfusion hearts were located within the coronary vasculature, without extravasation, up to 60 minutes after injection. Heart perfusion parameters and histological features exhibited evidence of coronary embolism after intracoronary injection of MSC, but not BMMNC (up to 40x106). These data collectively suggest that passive mechanical entrapment, and not active endothelial cell-donor cell interactions, is responsible for initial donor cell retention after intracoronary injection. This has important implications for future clinical protocols of intracoronary injection of stem / progenitor cells to the heart.

<p> Bacterial sensing systems have evolved to detect complex biomolecules, operating near fundamental physical limits for biosensing. No modern engineered biosensor has managed to match the efficiency of bacterial systems, which optimize for each sensing application under constraints on response time and sensitivity. An emerging approach to address this shortfall is to build biosensors that electronically couple microbes and devices to combine the sensing capabilities of bacteria with the communication and data processing capabilities of electronics. This dissertation presents three techniques that advance engineering at the interface between bacteria and electronics, all working towards the integration of living material into hybrid biosensing platforms. In the first technique, we embed current-producing <i>Shewanella oneidensis</i> inside a conductive PEDOT:PSS matrix to electronically interface and structure the bacteria into 3D conductive biocomposite films to our specifications. In the second technique, we observe large numbers of chemotactic bacterial flagellar motor (BFM) behavior to infer environmental conditions, using machine learning to co-opt <i>Escherichia coli'</i>s motor response for the front end of a biosensor. In the final technique, we demonstrate progress towards a method to electronically monitor BFM rotation over time for electrochemical biosensing. Together, this body of work contributes to more functional interfaces between silicon- and carbon-based materials for advanced biosensing applications including persistent in situ environmental sensing and microbiorobotics.</p><p>

Thesis (Ph. D.)--Massachusetts Institute of Technology, Division of Bioengineering and Environmental Health, 1999. / Includes bibliographical references (leaves 186-205). / by Xiaocheng Li-Suckoleiki. / Ph.D.

Thesis (S.M.)--Massachusetts Institute of Technology, Division of Bioengineering and Environmental Health, 1999. / Includes bibliographical references (leaves 63-69). / by Curtis Lee X. Glover. / S.M.

No description available.

Fluorescence lifetime imaging microscopy (FLIM) which is capable of visualizing local molecular and physiological parameters in living cells, plays a significant role in biological sciences, chemistry, and medical research. In order to unveil dynamic cellular processes, it is necessary to develop high-speed FLIM technology. Thanks to the development of highly parallel time-to-digital convertor (TDC) arrays, especially when integrated with single-photon avalanche diodes (SPADs), the acquisition rate of high-resolution fluorescence lifetime imaging has been dramatically improved. On the other hand, these technological advances and advanced data acquisition systems have generated massive data, which significantly increases the difficulty of FLIM analysis. Traditional FLIM systems rely on time-consuming iterative algorithms to retrieve the FLIM parameters. Therefore, lifetime analysis has become a bottleneck for high-speed FLIM applications, let alone real-time or video-rate FLIM systems. Although some simple algorithms have been proposed, most of them are only able to resolve a simple FLIM decay model. On the other hand, existing FLIM systems based on CPU processing do not make use of available parallel acceleration. In order to tackle the existing problems, my study focused on introducing the state-of-art general purpose graphics processing units (GPUs) to the FLIM analysis, and building a data processing system based on both CPU and GPUs. With a large amount of parallel cores, the GPUs are able to significantly speed up lifetime analysis compared to CPU-only processing. In addition to transform the existing algorithms into GPU computing, I have developed a new high-speed and GPU friendly algorithm based on an artificial neural network (ANN). The proposed GPU-ANN-FLIM method has dramatically improved the efficiency of FLIM analysis, which is at least 1000-folder faster than some traditional algorithms, meaning that it has great potential to fuel current revolutions in high-speed high-resolution FLIM applications.