Soong Ho Um

Therapeutic cell engineering with surface-conjugated synthetic nanoparticles

A major limitation of cell therapies is the rapid decline in viability and function of the transplanted cells. Here we describe a strategy to enhance cell therapy via the conjugation of adjuvant drug–loaded nanoparticles to the surfaces of therapeutic cells. With this method of providing sustained pseudoautocrine stimulation to donor cells, we elicited marked enhancements in tumor elimination in a model of adoptive T cell therapy for cancer. We also increased the in vivo repopulation rate of hematopoietic stem cell grafts with very low doses of adjuvant drugs that were ineffective when given systemically. This approach is a simple and generalizable strategy to augment cytoreagents while minimizing the systemic side effects of adjuvant drugs. In addition, these results suggest therapeutic cells are promising vectors for actively targeted drug delivery.

Polydopamine-mediated surface modification of scaffold materials for human neural stem cell engineering

Surface modification of tissue engineering scaffolds and substrates is required for improving the efficacy of stem cell therapy by generating physicochemical stimulation promoting proliferation and differentiation of stem cells. However, typical surface modification methods including chemical conjugation or physical absorption have several limitations such as multistep, complicated procedures, surface denaturation, batch-to-batch inconsistencies, and low surface conjugation efficiency. In this study, we report a mussel-inspired, biomimetic approach to surface modification for efficient and reliable manipulation of human neural stem cell (NSC) differentiation and proliferation. Our study demonstrates that polydopamine coating facilitates highly efficient, simple immobilization of neurotrophic growth factors and adhesion peptides onto polymer substrates. The growth factor or peptide-immobilized substrates greatly enhance differentiation and proliferation of human NSCs (human fetal brain-derived NSCs and human induced pluripotent stem cell-derived NSCs) at a level comparable or greater than currently available animal-derived coating materials (Matrigel) with safety issues. Therefore, polydopamine-mediated surface modification can provide a versatile platform technology for developing chemically defined, safe, functional substrates and scaffolds for therapeutic applications of human NSCs.

Surface functionalization of living cells with multilayer patches.

We demonstrate that functional polyelectrolyte multilayer (PEM) patches can be attached to a fraction of the surface area of living, individual lymphocytes. Surface-modified cells remain viable at least 48 h following attachment of the functional patch, and patches carrying magnetic nanoparticles allow the cells to be spatially manipulated using a magnetic field. The patch does not completely occlude the cellular surface from the surrounding environment; this approach allows a functional payload to be attached to a cell that is still free to perform its native functions, as suggested by preliminary studies on patch-modified T-cell migration. This approach has potential for broad applications in bioimaging, cellular functionalization, immune system and tissue engineering, and cell-based therapeutics where cell-environment interactions are critical.

Multifunctional nanoarchitectures from DNA-based ABC monomers

The ability to attach different functional moieties to a molecular building block1,2 could lead to applications in nanoelectronics3, nanophotonics4, intelligent sensing5 and drug delivery6,7. The building unit needs to be both multivalent and anisotropic, and although many anisotropic building blocks have been created1,8,9,10,11,12, these have not been universally applicable. Recently, DNA has been used to generate various nanostructures13,14,15,16,17 or hybrid systems18,19,20,21,22,23,24,25, and as a generic building block for various applications26,27,28,29,30. Here, we report the creation of anisotropic, branched and crosslinkable building blocks (ABC monomers) from which multifunctional nanoarchitectures have been assembled. In particular, we demonstrate a target-driven polymerization process in which polymers are generated only in the presence of a specific DNA molecule, leading to highly sensitive pathogen detection. Using this monomer system, we have also designed a biocompatible nanovector that delivers both drugs and tracers simultaneously. Our approach provides a general yet versatile route towards the creation of a range of multifunctional nanoarchitectures. Supplementary information The online version of this article (doi:10.1038/nnano.2009.93) contains supplementary material, which is available to authorized users.

Bioinspired, Calcium-Free Alginate Hydrogels with Tunable Physical and Mechanical Properties and Improved Biocompatibility

Alginate hydrogels are for various biomedical applications including tissue engineering, cell therapy, and drug delivery. However, it is not easy to control swelling or viscoelastic and biophysical properties of alginate hydrogels prepared by conventional cross-linking methods (ionic interaction using divalent cations). In this study, we describe a bioinspired approach for preparing divalent ion-free alginate hydrogels that exhibit tunable physical and mechanical properties and improved biocompatibility due to the absence of cations in the gel matrices. We conjugated dopamine, a minimalized adhesive motif found in the holdfast pads of mussels, to alginate backbones (alginate-catechol) and the tethered catechols underwent oxidative cross-linking. This resulted in divalent cation-free alginate hydrogels. The swelling ratios and moduli of the alginate-catechol hydrogels are readily tunable, which is difficult to achieve in ionic bond-based alginate hydrogels. Furthermore, alginate-catechol hydrogels enhanced the survival of various human primary cells including stem cells in the three-dimensional gel matrix, indicating that intrinsic cytotoxicity caused by divalent cations becomes negligible when employing catechol oxidation for alginate cross-linking. The inflammatory response in vivo was also significantly attenuated compared to conventional alginate hydrogels with calcium cross-linking. This biomimetic approach for the preparation of alginate hydrogels may provide a novel platform technology to develop tunable, functional, biocompatible, three-dimensional scaffolds for tissue engineering and cell therapy.

BMP-2 peptide-functionalized nanopatterned substrates for enhanced osteogenic differentiation of human mesenchymal stem cells.

A variety of biophysical and biochemical factors control stem cell differentiation. In this study, we developed a nanopatterned substrate platform to surface immobilize osteoinductive bone morphogenetic protein-2 (BMP-2) peptides. Specifically, polyurethane acrylate (PUA) substrates with nanometer-scale groove- and dot-shaped topography were fabricated. The nanopatterned PUA surface was uniformly coated with poly(glycidyl methacrylate) (pGMA) by initiated chemical vapor deposition (iCVD) followed by covalent immobilization of BMP-2 peptides. This approach resulted in much more efficient BMP-2 peptide immobilization than physical adsorption. The combined effects of biochemical signals from BMP-2 peptides and nanotopographical stimulation on osteogenic differentiation of hMSCs were examined in culture with and without soluble osteogenic factors. Results of Alizarin Red S staining, immunostaining, and quantitative real-time polymerase chain reaction revealed that hMSCs cultured on nanopatterned surfaces with immobilized BMP-2 peptides exhibited greater potential for osteogenic differentiation than hMSCs on a flat surface. Furthermore, the nanopatterned substrates with BMP-2 peptides directed osteogenic differentiation of hMSCs even without osteogenesis soluble inducing factors. Substrates with nanotopography and bioactive signals that induce differentiation of stem cells towards specific lineages could be used to develop functional stem cell culture substrates and tissue engineered scaffolds for therapeutic applications.

Dendrimer-like DNA-based fluorescence nanobarcodes.

A major challenge in clinical diagnostics and environmental analysis is the difficulty in rapid and sensitive detection of multiple target molecules simultaneously (i.e., multiplexed detections). Our group has designed and synthesized a dendrimer-like DNA (DL-DNA) that is multivalent and anisotropic; using this unique DNA structure, we have developed a fluorescence-tagged nanobarcode system for multiplex detection. This nanobarcode system allows the rapid and sensitive detection of multiple pathogens simultaneously using the ratios of two different fluorescent dyes, green and red, with which different DL-DNAs are labeled. The key step of our nanobarcode model lies in the monodisperse preparation of DL-DNA. Two methods, solution phase and solid phase, are presented here. With slight modifications, this platform technology can also be extended to the multiplexed detection of RNA and proteins. This protocol can be completed in 2–5 d.

DNAsomes: Multifunctional DNA-Based Nanocarriers

Nonviral drug delivery systems, [ 1 ] traditionally based on synthetic carriers such as polymeric materials and liposomes offer valuable possibilities for disease prevention and treatment. [ 2 ] Such systems are now being extended to achieve the co-delivery of multiple drugs and/or nucleic acid drugs, which can lead to synergistic effects. [ 3 ] However, due to the fact that most building blocks of polymeric materials and liposomes are isotropic and polydisperse, it remains challenging to rationally engineer building blocks with multiple functionalities within a single molecule for tailored multidrug delivery. The powerful molecular recognition capabilities of DNA [ 4 ] has enabled the controlled assembly of anisotropic building blocks, leading to multifunctional DNA nanostructures. [ 5 ] Recently, we have developed DNA-based anisotropic, branched, crosslinkable (ABC) monomers that can carry multiple moieties on a single molecule with precise control. [ 6 ]

Role of Physicochemical Properties in Nanoparticle Toxicity

With the recent rapid growth of technological comprehension in nanoscience, researchers have aimed to adapt this knowledge to various research fields within engineering and applied science. Dramatic advances in nanomaterials marked a new epoch in biomedical engineering with the expectation that they would have huge contributions to healthcare. However, several questions regarding their safety and toxicity have arisen due to numerous novel properties. Here, recent studies of nanomaterial toxicology will be reviewed from several physiochemical perspectives. A variety of physiochemical properties such as size distribution, electrostatics, surface area, general morphology and aggregation may significantly affect physiological interactions between nanomaterials and target biological areas. Accordingly, it is very important to finely tune these properties in order to safely fulfill a bio-user’s purpose.

Sonic hedgehog intradermal gene therapy using a biodegradable poly(β-amino esters) nanoparticle to enhance wound healing.

Biodegradable cationic poly(β-amino esters) (PBAE) nanoparticles are promising tools for delivering genes into various types of cells and tissues. Specific end-modification of the PBAE terminal parts significantly improves the efficiency of gene delivery in vitro and in vivo, and reduces cytotoxicity. Here, we demonstrated that amine end-modified PBAE nanoparticles can be used for intradermal delivery of therapeutic genes for wound healing in an animal skin wound model. Sonic hedgehog (SHH), a prototypical morphogen with angiogenic potential, was applied as a therapeutic gene to regenerate skin tissue. Amine end-modified PBAEs showed higher gene transfection efficiency in vitro than the commercial reagent, Lipofectamine 2000. Intradermal delivery of the SHH gene using amine end-modified PBAEs was tested in a readout mouse model of SHH signaling. We evaluated its therapeutic efficacy in mice with full-thickness skin wounds. SHH gene therapy significantly increased the expression of the angiogenic growth factor, vascular endothelial growth factor, and the stromal cell-derived factor-1α chemokine within the wounded regions early after injection. Ultimately, wound closure was accelerated in mice receiving the PBAE/SHH gene therapy compared to mice receiving intradermal delivery of a control gene (β-galactosidase plasmid) by PBAE nanoparticles. Quantitative real-time polymerase chain reaction and histological analysis revealed that there were significant improvements in epidermis regeneration and blood vessel formation in the mice treated with PBAE/SHH nanoparticles. In conclusion, SHH intradermal gene therapy using biodegradable PBAE nanoparticles is a potential treatment to promote wound healing.