Since stem cells emerged as a new generation of medicine, there are increasing efforts to deliver the stem cells to a target tissue via intravascular injection. However, the therapeutic stem cells lack a capacity to detect and adhere to the target tissue. Therefore, this study presents synthesis of a bioactive hyper-branched polyglycerol (HPG) which can non-invasively 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.

Nano-sized polymersomes functionalized with peptides or proteins are being increasingly studied for targeted delivery of diagnostic and therapeutic molecules. Earlier computational studies have suggested that ellipsoidal nanoparticles, compared to spherical ones, display enhanced binding efficiency with target cells, but this has not yet been experimentally validated. We hypothesize that hydrophilic polymer chains coupled to vesicle-forming polymers would result in ellipsoidal polymersomes. In addition, ellipsoidal polymersomes modified with cell adhesion peptides bind with target cells more actively than spherical ones. We examine this hypothesis by substituting polyaspartamide with octadecyl chains and varying numbers of poly(ethylene glycol) (PEG) chains. Increasing the degree of substitution of PEG from 0.5 to 1.0 mol% drives the polymer to self-assemble into an ellipsoidal polymersome with an aspect ratio of 2.1. Further modification of these ellipsoidal polymersomes with peptides containing an Arg-Gly-Asp sequence (RGD peptides) lead to a significant increase in the rate of association and decrease in the rate of dissociation with a substrate coated with αvβ3 integrins. In addition, in a circulation-mimicking flow, the ellipsoidal polymersomes linked with RGD peptides adhere to target tissues more favorably than their spherical equivalents do. Overall, the results of this study will greatly serve to improve the efficiency of targeted delivery of a wide array of polymersomes loaded with various biomedical modalities.

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.

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-linker's 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.

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 approximately 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.