Mei Hsiu Lai

Leukocyte-mimicking stem cell delivery via in situ coating of cells with a bioactive hyperbranched polyglycerol.

Since stem cells emerged as a new generation of medicine, there are increasing efforts to deliver stem cells to a target tissue via intravascular injection. However, the therapeutic stem cells lack the capacity to detect and adhere to the target tissue. Therefore, this study presents synthesis of a bioactive hyperbranched polyglycerol (HPG) that can noninvasively associate with stem cells and further guide them to target sites, such as inflamed endothelium. The overall process is analogous to the way in which leukocytes are mobilized to the injured endothelium.

Tailoring polymersome bilayer permeability improves enhanced permeability and retention effect for bioimaging.

Self-assembled nanoparticles conjugated with various imaging contrast agents have been used for the detection and imaging of pathologic tissues. Inadvertently, these nanoparticles undergo fast, dilution-induced disintegration in circulation and quickly lose their capability to associate with and image the site of interest. To resolve this challenge, we hypothesize that decreasing the bilayer permeability of polymersomes can stabilize their structure, extend their lifetime in circulation, and hence improve the quality of bioimaging when the polymersome is coupled with an imaging probe. This hypothesis is examined by using poly(2-hydroxyethyl-co-octadecyl aspartamide), sequentially modified with methacrylate groups, to build model polymersomes. The bilayer permeability of the polymersome is decreased by increasing the packing density of the bilayer with methacrylate groups and is further decreased by inducing chemical cross-linking reactions between the methacrylate groups. The polymersome with decreased bilayer permeability demonstrates greater particle stability in physiological media and ultimately can better highlight tumors in mice over 2 days compared to those with higher bilayer permeability after labeling with a near-infrared (NIR) fluorescent probe. We envisage that the resulting nanoparticles will not only improve diagnosis but also further image-guided therapies.

The spatiotemporal control of erosion and molecular release from micropatterned poly(ethylene glycol)-based hydrogel

Hydrogels have been extensively studied as a carrier of various hydrophilic molecular compounds and cells for local delivery and subsequent controlled release. One of key design parameters in the hydrogel assembly is an ability to control spatiotemporal gel degradation, in order to tailor release rates of multiple drugs and also regulate phenotypic activities of co-cultured cells. To achieve this goal, this study presents a simple but innovative implantable, microfabricated hydrogel patch that undergoes micropatterned surface erosion at controlled rates and subsequently discharges two molecular compounds of interests at desired rates. This device was prepared by first fabricating a non-degradable poly(ethylene glycol) dimethacrylate (PEGDMA) hydrogel patch containing micro-pockets of controlled spacing and subsequently filling micro-pockets with a hydrogel of poly(ethylene imine) (PEI) and PEG diacrylate (PEGDA) that was tailored to degrade at controlled rates. Separate incorporation of vascular endothelial growth factor (VEGF)121 and VEGF165, known to orchestrate vascular development, into the PEI-PEGDA gel and PEGDMA hydrogel resulted in enhanced neovascularization at the implantation sites due to bimodal, sequential release of two VEGF isoforms. We believe that the hydrogel patch fabricated in this study will be highly useful to better understand a broad array of complex biological processes and also improve the efficacy of molecular cargos in varied applications.

Tailoring the dependency between rigidity and water uptake of a microfabricated hydrogel with the conformational rigidity of a polymer cross-linker

Many diverse applications utilize hydrogels as carriers, sensors, and actuators, and these applications rely on the refined control of physical properties of the hydrogel, such as elastic modulus and degree of swelling. Often, hydrogel properties are interdependent; for example, when elastic modulus is increased, degree of swelling is decreased. Controlling these inverse dependencies remains a major barrier for broader hydrogel applications. We hypothesized that polymer cross-linkers with varied chain flexibility would allow us to tune the inverse dependency between the elastic modulus and the degree of swelling of the hydrogels. We examined this hypothesis by using alginate and poly(acrylic acid) (PAA) modified with a controlled number of methacrylic groups as model inflexible and flexible cross-linkers, respectively. Interestingly, the polyacrylamide hydrogel cross-linked by the inflexible alginate methacrylates exhibited less dependency between the degree of swelling and the elastic modulus than the hydrogel cross-linked by flexible PAA methacrylates. This critical role of the cross-linkers inflexibility was related to the difference of the degree of hydrophobic association between polymer cross-linkers, as confirmed with pyrene probes added in pregel solutions. Furthermore, hydrogels cross-linked with alginate methacrylates could tune the projection area of adhered cells by solely altering elastic moduli. In contrast, gels cross-linked with PAA methacrylates failed to modulate the cellular adhesion morphology due to a lower, and smaller, elastic modulus range to be controlled. Overall, the results of this study will significantly advance the controllability of hydrogel properties and greatly enhance the performance of hydrogels in various biological applications.

Flow-mediated stem cell labeling with superparamagnetic iron oxide nanoparticle clusters.

This study presents a strategy to enhance the uptake of superparamagnetic iron oxide nanoparticle (SPIO) clusters by manipulating the cellular mechanical environment. Specifically, stem cells exposed to an orbital flow ingested almost a 2-fold greater amount of SPIO clusters than those cultured statically. Improvements in magnetic resonance (MR) contrast were subsequently achieved for labeled cells in collagen gels and a mouse model. Overall, this strategy will serve to improve the efficiency of cell tracking and therapies.

Worm-Like Superparamagnetic Nanoparticle Clusters for Enhanced Adhesion and Magnetic Resonance Relaxivity

Nanosized bioprobes that can highlight diseased tissue can be powerful diagnostic tools. However, a major unmet need is a tool with adequate adhesive properties and contrast-to-dose ratio. To this end, this study demonstrates that targeted superparamagnetic nanoprobes engineered to present a worm-like shape and hydrophilic packaging enhance both adhesion efficiency to target substrates and magnetic resonance (MR) sensitivity. These nanoprobes were prepared by the controlled self-assembly of superparamagnetic iron oxide nanoparticles (SPIONs) into worm-like superstructures using glycogen-like amphiphilic hyperbranched polyglycerols functionalized with peptides capable of binding to defective vasculature. The resulting worm-like SPION clusters presented binding affinity to the target substrate 10-fold higher than that of spherical ones and T2 molar MR relaxivity 3.5-fold higher than that of conventional, single SPIONs. The design principles discovered for these nanoprobes should be applicable to a range of other diseases where improved diagnostics are needed.

Enzyme-Induced Matrix Softening Regulates Hepatocarcinoma Cancer Cell Phenotypes

The progression of cancer is often accompanied by changes in the mechanical properties of an extracellular matrix. However, limited efforts have been made to reproduce these biological events in vitro. To this end, this study demonstrates that matrix remodeling caused by matrix metalloproteinase (MMP)-1 regulates phenotypic activities and modulates radiosensitivity of cancer cells exclusively in a 3D matrix. In this study, hepatocarcinoma cells are cultured in a collagen-based gel tailored to present an elastic modulus of ≈4.0 kPa. The subsequent exposure of the gel to MMP-1 decreases the elastic modulus from 4.0 to 0.5 kPa. In response to MMP-1, liver cancer cells undergo active proliferation, downregulation of E-cadherin, and the loss of detoxification capacity. The resulting spheroids are more sensitive to radiation than the spheroids cultured in the stiffer gel not exposed to MMP-1. Overall, this study serves to better understand and control the effects of MMP-induced matrix remodeling.

Spatiotemporally controlled molecular release from micropatterned hydrogel

This work demonstrates the fabrication of a hydrogel-based dual drug carrier, its capability to sequential release of dual protein drugs and its impact on neovascularization at the chick chorioallantoic membrane.