Giulia Morgese

Next-Generation Polymer Shells for Inorganic Nanoparticles are Highly Compact, Ultra-Dense, and Long-Lasting Cyclic Brushes

Cyclic poly-2-ethyl-2-oxazoline (PEOXA) ligands for superparamagnetic Fe3 O4 nanoparticles (NPs) generate ultra-dense and highly compact shells, providing enhanced colloidal stability and bio-inertness in physiological media. When linear brush shells fail in providing colloidal stabilization to NPs, the cyclic ones assure long lasting dispersions. While the thermally induced dehydration of linear PEOXA shells cause irreversible aggregation of the NPs, the collapse and subsequent rehydration of similarly grafted cyclic brushes allow the full recovery of individually dispersed NPs. Although linear ligands are densely grafted onto Fe3 O4 cores, a small plasma protein such as bovine serum albumin (BSA) still physisorbs within their shells. In contrast, the impenetrable entropic shield provided by cyclic brushes efficiently prevents nonspecific interaction with proteins.

Nanoassemblies of Tissue-Reactive, Polyoxazoline Graft-Copolymers Restore the Lubrication Properties of Degraded Cartilage

Osteoarthritis leads to an alteration in the composition of the synovial fluid, which is associated with an increase in friction and the progressive and irreversible destruction of the articular cartilage. In order to tackle this degenerative disease, there has been a growing interest in the medical field to establish effective, long-term treatments to restore cartilage lubrication after damage. Here we develop a series of graft-copolymers capable of assembling selectively on the degraded cartilage, resurfacing it, and restoring the lubricating properties of the native tissue. These comprise a polyglutamic acid backbone (PGA) coupled to brush-forming, poly-2-methyl-2-oxazoline (PMOXA) side chains, which provide biopassivity and lubricity to the surface, and to aldehyde-bearing tissue-reactive groups, for the anchoring on the degenerated cartilage via Schiff bases. Optimization of the graft-copolymer architecture (i.e., density and length of side chains and amount of tissue-reactive functions) allowed a uniform passivation of the degraded cartilage surface. Graft-copolymer-treated cartilage showed very low coefficients of friction within synovial fluid, reestablishing and in some cases improving the lubricating properties of the natural cartilage. Due to these distinctive properties and their high biocompatibility and stability under physiological conditions, cartilage-reactive graft-copolymers emerge as promising injectable formulations to slow down the progression of cartilage degradation, which characterizes the early stages of osteoarthritis.

Cyclic Polymer Grafts That Lubricate and Protect Damaged Cartilage

Tissue-reactive graft copolymers were designed to protect the cartilage against enzymatic degradation and restore its lubrication properties during the early stages of osteoarthritis (OA). The copolymers feature a poly(glutamic acid) (PGA) backbone bearing hydroxybenzaldehyde (HBA) functions and cyclic poly(2-methyl-2-oxazoline) (PMOXA) side chains. PGA-PMOXA-HBA species chemisorb on the degraded tissue via Schiff bases and expose the biopassive and lubricious PMOXA cyclic grafts at the interface. The smaller hydrodynamic radius by cyclic PMOXA side chains coupled to the intrinsic absence of chain ends generate denser and more lubricious films on cartilage when compared to those produced by copolymers bearing linear PMOXA. Topology effects demonstrate how the introduction of cyclic polymers within tissue-reactive copolymers substantially improve their tribological and biopassive properties, suggesting a plethora of possible applications for cyclic macromolecules in biomaterials formulations.

C1q-Mediated Complement Activation and C3 Opsonization Trigger Recognition of Stealth Poly(2-methyl-2-oxazoline)-Coated Silica Nanoparticles by Human Phagocytes

Poly(2-methyl-2-oxazoline) (PMOXA) is an alternative promising polymer to poly(ethylene glycol) (PEG) for design and engineering of macrophage-evading nanoparticles (NPs). Although PMOXA-engineered NPs have shown comparable pharmacokinetics and in vivo performance to PEGylated stealth NPs in the murine model, its interaction with elements of the human innate immune system has not been studied. From a translational angle, we studied the interaction of fully characterized PMOXA-coated vinyltriethoxysilane-derived organically modified silica NPs (PMOXA-coated NPs) of approximately 100 nm in diameter with human complement system, blood leukocytes, and macrophages and compared their performance with PEGylated and uncoated NP counterparts. Through detailed immunological and proteomic profiling, we show that PMOXA-coated NPs extensively trigger complement activation in human sera exclusively through the classical pathway. Complement activation is initiated by the sensing molecule C1q, where C1q binds with high affinity ( Kd = 11 ± 1 nM) to NP surfaces independent of immunoglobulin binding. C1q-mediated complement activation accelerates PMOXA opsonization with the third complement protein (C3) through the amplification loop of the alternative pathway. This promoted NP recognition by human blood leukocytes and monocyte-derived macrophages. The macrophage capture of PMOXA-coated NPs correlates with sera donor variability in complement activation and opsonization but not with other major corona proteins, including clusterin and a wide range of apolipoproteins. In contrast to these observations, PMOXA-coated NPs poorly activated the murine complement system and were marginally recognized by mouse macrophages. These studies provide important insights into compatibility of engineered NPs with elements of the human innate immune system for translational steps.

Easy to Apply Polyoxazoline-Based Coating for Precise and Long-Term Control of Neural Patterns

Arranging cultured cells in patterns via surface modification is a tool used by biologists to answer questions in a specific and controlled manner. In the past decade, bottom-up neuroscience emerged as a new application, which aims to get a better understanding of the brain via reverse engineering and analyzing elementary circuitry in vitro. Building well-defined neural networks is the ultimate goal. Antifouling coatings are often used to control neurite outgrowth. Because erroneous connectivity alters the entire topology and functionality of minicircuits, the requirements are demanding. Current state-of-the-art coating solutions such as widely used poly(l-lysine)-g-poly(ethylene glycol) (PLL-g-PEG) fail to prevent primary neurons from making undesired connections in long-term cultures. In this study, a new copolymer with greatly enhanced antifouling properties is developed, characterized, and evaluated for its reliability, stability, and versatility. To this end, the following components are grafted to a poly(acrylamide) (PAcrAm) backbone: hexaneamine, to support spontaneous electrostatic adsorption in buffered aqueous solutions, and propyldimethylethoxysilane, to increase the durability via covalent bonding to hydroxylated culture surfaces and antifouling polymer poly(2-methyl-2-oxazoline) (PMOXA). In an assay for neural connectivity control, the new copolymers ability to effectively prevent unwanted neurite outgrowth is compared to the gold standard, PLL-g-PEG. Additionally, its versatility is evaluated on polystyrene, glass, and poly(dimethylsiloxane) using primary hippocampal and cortical rat neurons as well as C2C12 myoblasts, and human fibroblasts. PAcrAm-g-(PMOXA, NH2, Si) consistently outperforms PLL-g-PEG with all tested culture surfaces and cell types, and it is the first surface coating which reliably prevents arranged nodes of primary neurons from forming undesired connections over the long term. Whereas the presented work focuses on the proof of concept for the new antifouling coating to successfully and sustainably prevent unwanted connectivity, it is an important milestone for in vitro neuroscience, enabling follow-up studies to engineer neurologically relevant networks. Furthermore, because PAcrAm-g-(PMOXA, NH2, Si) can be quickly applied and used with various surfaces and cell types, it is an attractive extension to the toolbox for in vitro biology and biomedical engineering.

Immobilization of Colloidal Monolayers at Fluid–Fluid Interfaces

Monolayers of colloidal particles trapped at an interface between two immiscible fluids play a pivotal role in many applications and act as essential models in fundamental studies. One of the main advantages of these systems is that non-close packed monolayers with tunable inter-particle spacing can be formed, as required, for instance, in surface patterning and sensing applications. At the same time, the immobilization of particles locked into desired structures to be transferred to solid substrates remains challenging. Here, we describe three different strategies to immobilize monolayers of polystyrene microparticles at water–decane interfaces. The first route is based on the leaking of polystyrene oligomers from the particles themselves, which leads to the formation of a rigid interfacial film. The other two rely on in situ interfacial polymerization routes that embed the particles into a polymer membrane. By tracking the motion of the colloids at the interface, we can follow in real-time the formation of the polymer membranes and we interestingly find that the onset of the polymerization reaction is accompanied by an increase in particle mobility determined by Marangoni flows at the interface. These results pave the way for future developments in the realization of thin tailored composite polymer-particle membranes.

Design and characterization of ultrastable, biopassive and lubricious cyclic poly(2-alkyl-2-oxazoline) brushes

Bilayer polymer brushes presenting surface-bound poly(glycidyl methacrylate) (PGMA) films and interfacial cyclic poly(2-alkyl-2-oxazoline) (PAOXA) brushes show excellent biopassivity and lubrication, while displaying long-term stability in chemically harsh aqueous environments. Due to their lower radii of gyration (Rg), cyclic poly(2-methyl-2-oxazoline)s (PMOXAs) and poly(2-ethyl-2-oxazoline)s (PEOXAs) react at high temperatures with PGMA grafts producing ∼50% denser brushes compared to linear analogues featuring comparable molar masses. This generates significantly more hydrated brush interfaces, which quantitatively prevent unspecific surface contamination by biomolecules after several hours of exposure. In addition, the more compact and denser character of cyclic brushes imparts excellent lubricating properties to the bilayered coatings, with the more hydrophilic cyclic PMOXA interfaces reaching a coefficient of friction (μ) of 0.05 against a silica AFM probe in aqueous medium. In addition to their unique physicochemical properties, cyclic PMOXA and PEOXA brushes grafted on PGMA layers demonstrate extremely robust films, which could withstand one month incubation in phosphate buffered saline (PBS) solution, tap water or water from Lake Zurich.

Robust and Biocompatible Functionalization of ZnS Nanoparticles by Catechol-Bearing Poly(2-Methyl-2-Oxazoline)s

Zinc sulfide (ZnS) nanoparticles (NPs) are particularly interesting materials for their electronic and luminescent properties. Unfortunately, their robust and stable functionalization and stabilization, especially in aqueous media, has represented a challenging and not yet completely accomplished task. In this work, we report the synthesis of colloidally stable, photoluminescent and biocompatible core-polymer shell ZnS and ZnS:Tb NPs by employing a water-in-oil miniemulsion (ME) process combined with surface functionalization via catechol-bearing poly-2-methyl-2-oxazoline (PMOXA) of various molar masses. The strong binding of catechol anchors to the metal cations of the ZnS surface, coupled with the high stability of PMOXA against chemical degradation, enable the formation of suspensions presenting excellent colloidal stability. This feature, combined with the assessed photoluminescence and biocompatibility, make these hybrid NPs suitable for optical bioimaging.

Molecularly Engineered Biolubricants for Articular Cartilage

Lubrication within articular joints plays a crucial role in daily life, providing an extremely low coefficient of friction and preventing wear at the surface of the articular cartilage. Natural biomacromolecules responsible for lubrication are part of the synovial fluid and their degradation is associated with the onset of degenerative diseases, such as osteoarthritis (OA). The current absence of effective treatments for OA has captured the attention of chemists and material scientists over the last two decades, triggering the development of partially or fully synthetic biolubricants aimed to reduce friction within the joints and restore cartilage functions. Although there is still a long way to go before synthetic replacements of natural biolubricants can be applied clinically, this review highlights those formulations that meet the fundamental requirements for being efficient lubricants for articular cartilage.