Dirk Steinhilber

A facile approach for dual-responsive prodrug nanogels based on dendritic polyglycerols with minimal leaching.

A novel pH and redox dual-responsive prodrug nanogel was prepared by an inverse nanoprecipitation method, which is mild and surfactant free, and based on a thiol-disulfide exchange reaction and thiol-Michael addition reaction. Highly biocompatible hyperbranched polyglycerol (hPG) was cross-linked with disulfide bonds, to obtain biodegradable nanogels, which could be degraded under intracellular reductive conditions. Doxorubicin (DOX) was conjugated to the biodegradable nanogel matrix via an acid-labile hydrazone linker. This is the first dual-responsive prodrug nanogel system that shows very low unspecific drug leaching, but efficient intracellular release of the payload triggered by the intracellular conditions. Two different prodrug nanogels were prepared with a size of approximately 150nm, which is big enough to take the advantage of the enhanced permeation and retention (EPR) effect in tumor tissue. Cell culture analysis by microscopy and flow cytometry revealed that the prodrug nanogels were efficiently internalized by tumor cells. Distinct release profiles of DOX were achieved by adjusting the nanogel architecture, and online detection of cytotoxicity showed that, unlike free DOX, the dual-responsive prodrug nanogels exhibited a delay in the onset of toxicity, indicating the different uptake mechanism and the need for prodrug activation to induce cell death.

Hyperbranched polyglycerols on the nanometer and micrometer scale

We report the preparation of polyglycerol particles on different length scales by extending the size of hyperbranched polyglycerols (3 nm) to nanogels (32 nm) and microgels (140 and 220 μm). We use miniemulsion templating for the preparation of nanogels and microfluidic templating for the preparation of microgels, which we obtain through a free-radical polymerization of hyperbranched polyglycerol decaacrylate and polyethylene glycol-diacrylate. The use of mild polymerization conditions allows yeast cells to be encapsulated into the resultant microgels with cell viabilities of approximately 30%.

Surfactant free preparation of biodegradable dendritic polyglycerol nanogels by inverse nanoprecipitation for encapsulation and release of pharmaceutical biomacromolecules.

In this paper we report a novel approach to generate biodegradable polyglycerol nanogels on different length scales. We developed a mild, surfactant free inverse nanoprecipitation process to template hydrophilic polyglycerol nanoparticles. In situ crosslinking of the precipitated nanoparticles by bioorthogonal copper catalyzed click chemistry allows us to obtain size defined polyglycerol nanogels (100-1000nm). Biodegradability was achieved by the introduction of benzacetal bonds into the net points of the nanogel. Interestingly, the polyglycerol nanogels quickly degraded into low molecular weight fragments at acidic pH values, which are present in inflamed and tumor tissues as well as intracellular organelles, and they remained stable at physiological pH values for a long time. This mild approach to biodegradable polyglycerol nanogels allows us to encapsulate labile biomacromolecules such as proteins, including the therapeutic relevant enzyme asparaginase, into the protein resistant polyglycerol network. Enzymes were encapsulated with an efficacy of 100% and after drug release, full enzyme activity and structural integrity were retained. This new inverse nanoprecipitation procedure allows the efficient encapsulation and release of various biomacromolecules including proteins and could find many applications in polymer therapeutics and nanomedicine.

A microgel construction kit for bioorthogonal encapsulation and pH-controlled release of living cells.

pH-Cleavable cell-laden microgels with excellent long-term viabilities were fabricated by combining bioorthogonal strain-promoted azide-alkyne cycloaddition (SPAAC) and droplet-based microfluidics. Poly(ethylene glycol)dicyclooctyne and dendritic poly(glycerol azide) served as bioinert hydrogel precursors. Azide conjugation was performed using different substituted acid-labile benzacetal linkers that allowed precise control of the microgel degradation kinetics in the interesting pH range between 4.5 and 7.4. By this means, a pH-controlled release of the encapsulated cells was achieved upon demand with no effect on cell viability and spreading. As a result, the microgel particles can be used for temporary cell encapsulation, allowing the cells to be studied and manipulated during the encapsulation and then be isolated and harvested by decomposition of the microgel scaffolds.

Thermosensitive nanogels based on dendritic polyglycerol and N-isopropylacrylamide for biomedical applications

In this paper we describe a methodology for the synthesis of thermoresponsive polyglycerol-based nanogels through precipitation polymerization. A systematic analysis of the preparative conditions and composition regarding the nanogel size is presented. The thermoresponsive properties of the synthesized nanogels, as well as the cytotoxicity and uptake in three different cell lines were investigated. The thermoresponsive behavior, the enhanced biocompatible profile, and the cell penetrating properties of the nanogels highlight the potential of such constructs for application as smart, environmentally-responsive materials.

Functional Nanogels for Biomedical Applications

This review addresses current and future perspectives of nanogel technology for nanomedicine. The synthetic methodologies and material properties of nanogels prepared by chemical meanings are discussed in detail, and examples that illustrate the different methodologies are presented. Applications in the fields of drug and gene delivery, smart imaging modalities, responsive materials, and multivalency as a therapeutic approach highlight the enormous potential of the functional nanogels as novel polymeric platforms for biomedicine.

Fabrication of thermoresponsive nanogels by thermo-nanoprecipitation and in situ encapsulation of bioactives

A synthetic method for thermoresponsive, glycerol based nanogels has been developed. The nanogels were synthesized by nanoprecipitation of the orthogonally functionalized macromonomers and their gelation in water. The crosslinking points were generated by strain promoted azide–alkyne cycloaddition which enabled the in situ encapsulation of Doxorubicin HCl. The mild and surfactant free reaction conditions make these nanogels ideal candidates for biomedical applications.

The effect of polyglycerol sulfate branching on inflammatory processes.

In this study, the extent to which the scaffold architecture of polyglycerol sulfates affects inflammatory processes and hemocompatibility is investigated. Competitive L-selectin binding assays, cellular uptake studies, and blood compatibility readouts are done to evaluate distinct biological properties. Fully glycerol based hyperbranched polyglycerol architectures are obtained by either homopolymerization of glycidol (60% branching) or a new copolymerization strategy of glycidol with ethoxyethyl glycidyl ether. Two polyglycerols with 24 and 42% degree of branching (DB) are synthesized by using different monomer feed ratios. A perfectly branched polyglycerol dendrimer is synthesized according to an iterative two-step protocol based on allylation of the alcohol and subsequent catalytic dihydroxylation. All the polyglycerol sulfates are synthesized with a comparable molecular weight and degree of sulfation. The DB make the different polymer conjugates perform different ways. The optimal DB is 60% in all biological assays.

Hybrid Microgels with Thermo-Tunable Elasticity for Controllable Cell Confinement

Stimuli-responsive hydrogels are able to change their physical properties such as their elastic moduli in response to changes in their environment. If biocompatible polymers are used to prepare such materials and if living cells are encapsulated within these networks, their switchability allows the cell-matrix interactions to be investigated with unprecedented consistency. In this paper, thermo-responsive macro- and microscopic hydrogels are presented based on azide-functionalized copolymers of poly(N-(2-hydroxypropyl)-methacrylamide) and poly(hydroxyethyl methacrylate) grafted with poly(N-isopropylacrylamide) side chains. Crosslinking of these comb polymers is realized by bio-orthogonal strain-promoted azide-alkyne cycloaddition with cyclooctyne-functionalized poly(ethylene glycol). The resulting hybrid hydrogels exhibit thermo-tunable elasticity tailored by the polymer chain length and grafting density. This bio-orthogonal polymer crosslinking strategy is combined with droplet-based microfluidics to encapsulate living cells into stimuli-responsive microgels, proving them to be a suitable platform for future systematic stem-cell research.

Structure related transport properties and cellular uptake of hyperbranched polyglycerol sulfates with hydrophobic cores

A set of six hydrophobically derivatized polymers based on polyglycerol sulfates have been investigated to determine the influence of scaffold architecture on the encapsulation properties of hydrophobic guests. Each of three block and statistical copolymers has been synthesized with phenyl, naphthyl, and biphenyl substituents in a one-pot procedure. The copolymers have been functionalized with sulfate groups in order to introduce an electrostatically repulsive surface that can stabilize the aggregated carriers. In addition, sulfates provide a highly active targeting moiety for inflammation and cellular uptake. UV measurements show a supramolecular encapsulation of the investigated guest molecules in the low μM range. The transport studies with pyrene and an indocarbocyanine dye further indicated a core–shell-type architecture which provides a distinct amphiphilicity as required for supramolecular guest complexation. The combination of a host functionality with an active sulfate targeting moiety has been used to investigate the structure related cellular transport properties.