Degradable and Removable Tough Adhesive Hydrogels.

The development of tough adhesive hydrogels has enabled unprecedented adhesion to wet and moving tissue surfaces throughout the body, but they are typically composed of nondegradable components. Here, a family of degradable tough adhesive hydrogels containing ≈90% water by incorporating covalently networked degradable crosslinkers and hydrolyzable ionically crosslinked main-chain polymers is developed. Mechanical toughness, adhesion, and degradation of these new formulations are tested in both accelerated in vitro conditions and up to 16 weeks in vivo. These degradable tough adhesives are engineered with equivalent mechanical and adhesive properties to nondegradable tough adhesives, capable of achieving stretches >20 times their initial length, fracture energies >6 kJ m-2 , and adhesion energies >1000 J m-2 . All degradable systems show complete degradation within 2 weeks under accelerated aging conditions in vitro and weeks to months in vivo depending on the degradable crosslinker selected. Excellent biocompatibility is observed for all groups after 1, 2, 4, 8, and 16 weeks of implantation, with minimal fibrous encapsulation and no signs of organ toxicity. On-demand removal of the adhesive is achieved with treatment of chemical agents which do not cause damage to underlying skin tissue in mice. The broad versatility of this family of adhesives provides the foundation for numerous in vivo indications.

Replenishable drug depot to combat post-resection cancer recurrence.

Local drug presentation made possible by drug-eluting depots has demonstrated benefits in a vast array of diseases, including in cancer, microbial infection and in wound healing. However, locally-eluting depots are single-use systems that cannot be refilled or reused after implantation at inaccessible sites, limiting their clinical utility. New strategies to noninvasively refill drug-eluting depots could dramatically enhance their clinical use. In this report we present a refillable hydrogel depot system based on bioorthogonal click chemistry. The click-modified hydrogel depots capture prodrug refills from the blood and subsequently release active drugs locally in a sustained manner. Capture of the systemically-administered refills serves as an efficient and non-toxic method to repeatedly refill depots. Refillable depots in combination with prodrug refills achieve sustained release at precancerous tumor sites to improve cancer therapy while eliminating systemic side effects. The ability to target tissues without enhanced permeability could allow the use of refillable depots in cancer and many other medical applications.

Ultrasound-sensitive nanoparticle aggregates for targeted drug delivery.

Here we describe injectable, ultrasound (US)-responsive, nanoparticle aggregates (NPAs) that disintegrate into slow-release, nanoscale, drug delivery systems, which can be targeted to selective sites by applying low-energy US locally. We show that, unlike microbubble based drug carriers which may suffer from stability problems, the properties of mechanical activated NPAs, composed of polymer nanoparticles, can be tuned by properly adjusting the polymer molecular weight, the size of the nanoparticle precursors as well as the percentage of excipient utilized to hold the NPA together. We then apply this concept to practice by fabricating NPAs composed of nanoparticles loaded with Doxorubicin (Dox) and tested their ability to treat tumors via ultrasound activation. Mouse studies demonstrated significantly increased efficiency of tumor targeting of the US-activated NPAs compared to PLGA nanoparticle controls (with or without US applied) or intact NPAs. Importantly, when the Dox-loaded NPAs were injected and exposed to US energy locally, this increased ability to concentrate nanoparticles at the tumor site resulted in a significantly greater reduction in tumor volume compared to tumors treated with a 20-fold higher dose of the free drug.

Deterministic encapsulation of single cells in thin tunable microgels for niche modelling and therapeutic delivery.

Existing techniques to encapsulate cells into microscale hydrogels generally yield high polymer-to-cell ratios and lack control over the hydrogel's mechanical properties. Here, we report a microfluidic-based method for encapsulating single cells in an approximately six-micrometre layer of alginate that increases the proportion of cell-containing microgels by a factor of ten, with encapsulation efficiencies over 90%. We show that in vitro cell viability was maintained over a three-day period, that the microgels are mechanically tractable, and that, for microscale cell assemblages of encapsulated marrow stromal cells cultured in microwells, osteogenic differentiation of encapsulated cells depends on gel stiffness and cell density. We also show that intravenous injection of singly encapsulated marrow stromal cells into mice delays clearance kinetics and sustains donor-derived soluble factors in vivo. The encapsulation of single cells in tunable hydrogels should find use in a variety of tissue engineering and regenerative medicine applications.

Shear-Activated Nanoparticle Aggregates Combined With Temporary Endovascular Bypass to Treat Large Vessel Occlusion.

BACKGROUND AND PURPOSE: The goal of this study is to combine temporary endovascular bypass (TEB) with a novel shear-activated nanotherapeutic (SA-NT) that releases recombinant tissue-type plasminogen activator (r-tPA) when exposed to high levels of hemodynamic stress and to determine if this approach can be used to concentrate r-tPA at occlusion sites based on high shear stresses created by stent placement. METHODS: A rabbit model of carotid vessel occlusion was used to test the hypothesis that SA-NT treatment coupled with TEB provides high recanalization rates while reducing vascular injury. We evaluated angiographic recanalization with TEB alone, intra-arterial delivery of soluble r-tPA alone, or TEB combined with 2 doses of intra-arterial infusion of either the SA-NT or soluble r-tPA. Vascular injury was compared against stent-retriever thrombectomy. RESULTS: Shear-targeted delivery of r-tPA using the SA-NT resulted in the highest rate of complete recanalization when compared with controls (P=0.0011). SA-NT (20 mg) had a higher likelihood of obtaining complete recanalization as compared with TEB alone (odds ratio 65.019, 95% confidence interval 1.77, >1000; P=0.0231), intra-arterial r-tPA alone (odds ratio 65.019, 95% confidence interval 1.77, >1000; P=0.0231), or TEB with soluble r-tPA (2 mg; odds ratio 18.78, 95% confidence interval 1.28, 275.05; P=0.0322). Histological analysis showed circumferential loss of endothelium restricted to the area where the TEB was deployed; however, there was significantly less vascular injury using a TEB as compared with stent-retriever procedure (odds ratio 12.97, 95% confidence interval 8.01, 21.02; P<0.0001). CONCLUSIONS: A novel intra-arterial, nanoparticle-based thrombolytic therapy combined with TEB achieves high rates of complete recanalization. Moreover, this approach reduces vascular trauma as compared with stent-retriever thrombectomy.

Molecular recognition induced self-assembly of diblock copolymers: microspheres to vesicles.

Random diblock copolymer scaffolds grafted with diamidopyridine (DAP) hydrogen bonding recognition units self-assembled to furnish microspheres when mixed with monoblock copolymers decorated with complementary recognition elements. Through choice of block length, microspheres of various sizes could be produced. The relative length of the two blocks plays a crucial role in determining the formation of aggregates. PEG-b-P(S-co-S(DAP)) diblock copolymer was used to fabricate recognition induced pegylated microspheres, by non-covalent crosslinking with monoblock copolymer functionalized with complementary thymine (Thy) units. These self-assembled microspheres can be efficiently crosslinked via photochemical [2pi(s) + 2pi(s)] cycloaddition with the resultant morphology change into vesicular structures.

Compartmentalization of Gold Nanocrystals in Polymer Microparticles using Electrohydrodynamic Co-Jetting.

Polymer particles with micro- and nanoscale anisotropy have received increasing interest for their ability to simultaneously present different physical- and chemical properties. In this communication, we demonstrate that gold nanocrystals (NCs) can be selectively incorporated into one compartment of anisotropic polymer particles. Stable bicompartmental particles were prepared via electrohydrodynamic co-jetting of aqueous nanoparticle suspensions followed by thermal cross-linking. Bicompartmental particle populations with different NC densities were obtained by varying the NC concentration in the jetting suspension. While NC-loaded polymer particles showed different optical properties depending on the NC density, they still maintained discrete interfaces between two compartments. Moreover, the fraction of the bicompartmental particles was higher than 98% based on flow cytometry. This study delineates a new approach for preparation of inorganic/organic composite particles with precisely engineered, anisotropic nanoparticle distributions and may contribute to further developments in emerging scientific areas, such as smart materials or particle-based diagnostics.

Surface-structure-regulated cell-membrane penetration by monolayer-protected nanoparticles.

Nanoscale objects are typically internalized by cells into membrane-bounded endosomes and fail to access the cytosolic cell machinery. Whereas some biomacromolecules may penetrate or fuse with cell membranes without overt membrane disruption, no synthetic material of comparable size has shown this property yet. Cationic nano-objects pass through cell membranes by generating transient holes, a process associated with cytotoxicity. Studies aimed at generating cell-penetrating nanomaterials have focused on the effect of size, shape and composition. Here, we compare membrane penetration by two nanoparticle 'isomers' with similar composition (same hydrophobic content), one coated with subnanometre striations of alternating anionic and hydrophobic groups, and the other coated with the same moieties but in a random distribution. We show that the former particles penetrate the plasma membrane without bilayer disruption, whereas the latter are mostly trapped in endosomes. Our results offer a paradigm for analysing the fundamental problem of cell-membrane-penetrating bio- and macro-molecules.

Water-soluble amphiphilic gold nanoparticles with structured ligand shells.

Highly water-soluble mixed monolayer protected "rippled" gold nanoparticles were synthesized through a one step reaction with sodium 11-mercaptoundecanesulfonate and octanethiol ligands at various ratios.

Divalent metal nanoparticles.

Nanoparticles can be used as the building blocks for materials such as supracrystals or ionic liquids. However, they lack the ability to bond along specific directions as atoms and molecules do. We report a simple method to place target molecules specifically at two diametrically opposed positions in the molecular coating of metal nanoparticles. The approach is based on the functionalization of the polar singularities that must form when a curved surface is coated with ordered monolayers, such as a phase-separated mixture of ligands. The molecules placed at these polar defects have been used as chemical handles to form nanoparticle chains that in turn can generate self-standing films.

Recognition-directed orthogonal self-assembly of polymers and nanoparticles on patterned surfaces.

We demonstrate the patterning of silica substrates with thymine (Thy-PS) and positively charged N-methylpyridinium (PVMP) polymers using photolithography and the subsequent orthogonal modification of these surfaces using diaminopyridine-functionalized polystyrene (DAP-PS) and carboxylate-derivatized CdSe/ZnS core-shell nanoparticles (COO-NP) through diamidopyridine-thymine three-point hydrogen bonding and pyridinium-carboxylate electrostatic interactions, respectively. This two-component orthogonal surface modification was accomplished in a self-sorting, single-step fashion, providing a versatile tool for the rapid and efficient creation of complex materials.

Molecular recognition in structured matrixes: control of guest localization in block copolymer films.

We demonstrate the use of molecular recognition to control the spatial distribution of guest molecules within block copolymer films. Block copolymers bearing recognition units were combined with complementary and noncomplementary molecules, and the extent of segregation of these molecules into the different domain types within microphase-separated thin films was quantitatively analyzed using dynamic secondary ion mass spectrometry (SIMS). Complementarity between the guest molecules and the polymer functionalities proved to be a key factor and an efficient tool for directing the segregation preference of the molecules to the different domain types. The effect of segregation preference on the glass transition temperature was studied using differential scanning calorimetry (DSC), and the results corroborate the SIMS findings. In a complementary study, guests with tunable sizes (via dendron substituents) were used to control block copolymer morphology. Morphological characterization using transmission electron microscopy (TEM) and X-ray diffraction reveal that selectivity differences can be directly translated into the ability to obtain different morphologies from recognition unit-functionalized block copolymer scaffolds.

Stimuli responsive surfaces through recognition-mediated polymer modification.

Specific three-point hydrogen bonding between diamidopyridine (DAP) and thymine (Thy) was employed to reversibly anchor "brush-like" Tri-DAP end-functionalized polystyrene onto Thy-modified silica surfaces.

Recognition-induced polymersomes: structure and mechanism of formation.

Random polystyrene copolymers grafted with complementary recognition elements were combined in chloroform producing vesicular aggregates, that is, recognition-induced polymersomes (RIPs). Reflection interference contrast microscopy (RICM) in solution, coupled with optical microscopy (OM) and atomic force microscopy (AFM) on solid substrates, were used to determine the wall thickness of the RIPs. Rather than a conventional mono- or bilayer structure (approximately 10 or approximately 20 nm, respectively) the RIP membrane was 43+/-7 nm thick. Structural arrangement of the polymer chains on the RIP wall were characterized by using angle-resolved X-ray photoelectron spectroscopy (AR-XPS). The interior portion of the vesicle membrane was found to be more polar, containing more recognition units, than the exterior part. This gradient suggests that a rapid self-sorting of polymers takes place during the formation of RIPs, providing the likely mechanism for vesicle self-assembly.

Duplex strand formation using alternating copolymers.

The regular arrangement of complementary diaminopyridine-thymine (DAP-THY) on alternating copolymers permits cooperative binding events and the effective formation of well-controlled micrometre-scale aggregates.

Recognition-induced transformation of microspheres into vesicles: morphology and size control.

Polystyrene functionalized with diamidopyridine (DAP) recognition units self-assembles in nonpolar media to form thermally reversible micrometer-scale spherical aggregates. The size and the thermal stability of these microspheres can be controlled by the molecular weight of the polymer. The addition of thymine-functionalized polymer to these self-assembled microspheres converted them into vesicular aggregates with a controlled size. The morphology change was reversible: the addition of DAP-functionalized polymer converted the vesicles back to microspheres.

Adsorption/desorption of mono- and diblock copolymers on surfaces using specific hydrogen bonding interactions.

Diblock copolymers containing recognition units designed to participate in specific three-point hydrogen bonding were adsorbed onto modified gold surfaces. Self-assembled monolayers (SAMs) containing complementary recognition units were used to direct the adsorption process. The polymer-modified surfaces obtained were characterized using X-ray photoelectron spectroscopy, water contact angle, and ellipsometry. The role of individual block lengths on the adsorption process was followed by observing frequency changes of thymine-SAM-modified quartz crystal microbalance chips during adsorption of diamidopyridine-functionalized polymers from a nonpolar solvent. The renewable nature of these recognition unit functionalized surfaces was demonstrated by reversible binding of polymers. Adsorption onto fresh surfaces, followed by desorption and subsequent readsorption of monoblock and diblock copolymers was also investigated.

Recognition-mediated assembly of nanoparticles into micellar structures with diblock copolymers.

Polystyrene-based diblock copolymers, featuring diaminotriazine functionality on one of the blocks were used to assemble complementary uracil-functionalized nanoparticles into micellar aggregates. The size of these self-assembled aggregates was controlled by block length, as determined in solution (using dynamic light scattering), and in thin films (using transmission electron microscopy).