Effects of surface functionalization and physical constraints of poly (dimethylsiloxane) on cellular behaviors

Mammalian cell behaviors are highly regulated by the complex cell microenvironments. In vitro models with precise manipulation of cell-substrate interactions can provide realistic insights into the chemical and topographical signals which critically affect cell functions. Poly(dimethylsiloxane) (PDMS) based systems are increasingly used in in vitro cell studies due to several advantages such as low cost, mechanical viability and convenience of rapid prototyping of cellular/subcellular environments. However, the high surface hydrophobicity and low surface reactivity of PDMS surfaces impose serious practical limitations in long-term studies of complex yet therapeutically significant behaviors such as the mesenchymal stem cell (hMSCs) and neuronal cell systems. To address these critical problems, a silanization based chemical modification of PDMS surfaces was employed against the traditional approaches, for covalent immobilization of extracellular matrix (ECM) proteins. The resulting modification promoted stable adhesion, highly spread morphology and viability of hMSCs with stronger cell sheet formation which positively affected cell differentiation. The strategy could be successfully applied to facilitate long-term culture and osteogenic differentiation within PDMS micro-chip. Moreover, the inclusion of hybrid physical micro-features further enhanced hMSC adhesion and differentiation. Eventually, the ECM proteins relevant in nascent neuron development were immobilized by silanization route, which resulted in a healthy neurite density and morphology. Additionally, diverse physical signals in neuronal cell vicinity was studied on micro-fabricated geometrical arrays of varying angularity/curvature which critically affected neurite growth, branching and directional commitment. Taken together, a tunable model was developed to study the independent and synergistic influences of both chemical and physical cues on both cell types. The simple, reproducible and adaptable system devised in this work, could be readily employed in strategic design of cell instructive bio-materials and interfaces to promote tissue regeneration as well as to understand the intricacies and abnormalities associated with cell development.Doctor of Philosophy (MAE

Laser irradiation of WE54 surface through simulated body fluid layer

© 2017 SPIE. Introduction: Magnesium and its alloys are promising biomaterials for temporary implant application because of their degradability and biocompatibility [1,2]. The surface morphology, micro-structure, and chemical composition of material are vital for cell adhesion. In this study, laser treatment of WE54 in simulated body fluid (SBF) has been carried out to explore the technique to produce bio-structures through various ion deposition such as Ca/P on WE54 surface so as to improve its surface bio-functionality. Methods: WE54 was immersed in SBF in a beaker. The immersed height of SBF solution above WE54 sample surface was 2 mm. A 500 watt pulsed Nd: YAG laser, having a wavelength of 1064 nm, frequency of 7000 Hz and pulse duration of 38 ns was used to irradiate WE54 surfaces through SBF. Cell viability test was performed after 3h and 8h of stem cell culture. SEM microscopy was performed to observe WE54 surface. Results: Water molecules were evaporated by laser-induced high energy of plasma in SBF during laser irradiation [3,4]. Remaining supersaturated ions (Ca, P) in SBF are deposited on the WE54 surface. Conclusion: Laser treatment through SBF layer has successfully produced the layered surface morphology and active Ca/P ions layer on the WE54 surface. The presence of supersaturated Ca/P ion has led to significant improvement on the cell viability.status: publishe

Laser irradiation of WE54 surface through simulated body fluid layer

Magnesium and its alloys are promising biomaterials for temporary implant application because of their degradability and biocompatibility [1,2]. The surface morphology, micro-structure, and chemical composition of material are vital for cell adhesion. In this study, laser treatment of WE54 in simulated body fluid (SBF) has been carried out to explore the technique to produce bio-structures through various ion deposition such as Ca/P on WE54 surface so as to improve its surface bio-functionality.Published versio

Fast dynamic MPI cytometry

We developed in vivo fast dynamic MPI “cytometry” to quantify and localize the accumulation of SPIO-labeled stem cells in different organs after intra-arterial injection on a time scale of minutes. Bone marrow-derived mesenchymal stem cells (MSCs) and superoxide dismutase 1 gene-corrected neural precursor cells (NPCs) were labeled with Resovist and injected into Rag2 mice using four separate injections. Whole body standard 2D/3D MPI scans were obtained, quantified and co-registered with CT. Using cell calibration fiducials, cells could be clearly visualized and quantified by MPI in vivo in the brain, liver, and lung. The cytometric ratio of the number of cells in the liver/lung vs. the brain was 1.5 for MSCs and 15.6 for NPCs, respectively, at 24 min post-injection. Fast dynamic MPI cytometry may find applications for optimizing the dose, volume, speed and route of administration when performing interventional cell therapy procedures in real-time

Versatile superparamagnetic radiopaque nanocomplex for in vivo MPI, MRI, and CT stem cell tracking

There are currently over 800 registered clinical trials that use mesenchymal stem cells (MSCs) for tissue repair and immunomodulation. However, the fate of MSCs in vivo including their overall biodistribution and local tissue quantities is not fully known, especially how these parameters change over time. Multi-modal imaging techniques that can track cell therapeutics may allow facilitation and optimization of clinical translation therapeutic outcome. We developed a novel superparamagnetic radiopaque nanocomplex, Albumin-Bi2S3-SPIO (ABS), for labeling of MSCs. ABS exhibited excellent in MPI, MRI, and CT imaging properties, allowing tri-modal imaging use a single nanoplatform

Enhanced <i>In Vitro</i> Biocompatibility of Chemically Modified Poly(dimethylsiloxane) Surfaces for Stable Adhesion and Long-term Investigation of Brain Cerebral Cortex Cells

Studies on the mammalian brain cerebral cortex have gained increasing importance due to the relevance of the region in controlling critical higher brain functions. Interactions between the cortical cells and surface extracellular matrix (ECM) proteins play a pivotal role in promoting stable cell adhesion, growth, and function. Poly­(dimethylsiloxane) (PDMS) based platforms have been increasingly used for on-chip <i>in vitro</i> cellular system analysis. However, the inherent hydrophobicity of the PDMS surface has been unfavorable for any long-term cell system investigations due to transitory physical adsorption of ECM proteins on PDMS surfaces followed by eventual cell dislodgement due to poor anchorage and viability. To address this critical issue, we employed the (3-aminopropyl)­triethoxysilane (APTES) based cross-linking strategy to stabilize ECM protein immobilization on PDMS. The efficiency of surface modification in supporting adhesion and long-term viability of neuronal and glial cells was analyzed. The chemically modified surfaces showed a relatively higher cell survival with an increased neurite length and neurite branching. These changes were understood in terms of an increase in surface hydrophilicity, protein stability, and cell–ECM protein interactions. The modification strategy could be successfully applied for stable cortical cell culture on the PDMS microchip for up to 3 weeks <i>in vitro</i>

Cellular Stiffness Measurement for 3D Biological Printing

During 3D biological printing, cells can sense their environment and change their own properties accordingly. In order to understand how cells modulate their stiffness with resp ect to their environmental stiffness, micropipette aspiration method was used to measure the aspiration lengths of porcine mesenchymal stem cells (pMSCs), which were cultured on polydimethylsiloxane (PDMS) substrates with different stiffness for different time periods, under certain pressure. After the measurem ents, both elastic and viscoelastic models were used to analyze the elasticity of the cell. Clear relationship between PDMS stiffness and cell stiffness could not be obtained with elastic model. However, from viscoelastic model, it gives that cells cultured on softest PDMS had the largest elastic modulus while on stiffest PDMS had lowest elastic modulus.Published versio