Luke A. Connal

A Microreactor with Thousands of Subcompartments: Enzyme‐Loaded Liposomes within Polymer Capsules

Fully loaded: Noncovalent anchoring of liposomes into polymer multilayered films with cholesterol-modified polymers allows the preparation of capsosomes-liposome-compartmentalized polymer capsules (see picture). A quantitative enzymatic reaction confirmed the presence of active cargo within the capsosomes and was used to determine the number of subcompartments within this novel biomedical carrier system.

Antibiofouling polymer interfaces: poly(ethylene glycol) and other promising candidates

Nonspecific protein adsorption and/or microbial adsorption on biomedical materials adversely affects the efficacy of a range of biomedical systems, from implants and biosensors to nanoparticles. To address this problem, antibiofouling polymers can be coated on biomedical devices or built into nanoparticles to confer protein and/or microbial repellent properties. The current review provides an overview of the range of synthetic polymers currently used to this end and explores their biomedical potential. The most widely-used antifouling polymer, poly(ethylene glycol) (PEG) is reviewed alongside several promising alternatives, including zwitterionic polymers, poly(hydroxyfunctional acrylates), poly(2-oxazoline)s, poly(vinylpyrrolidone), poly(glycerol), peptides and peptoids. For each material, notable applications for both nanomedicine and macroscopic surface coatings are highlighted.

Reactive, Multifunctional Polymer Films through Thermal Cross-linking of Orthogonal Click Groups

The ability to produce robust and functional cross-linked materials from soluble and processable organic polymers is dependent upon facile chemistries for both reinforcing the structure through cross-linking and for subsequent decoration with active functional groups. Generally, covalent cross-linking of polymeric assemblies is brought about by the application of heat or light to generate highly reactive groups from stable precursors placed along the chains that undergo coupling or grafting reactions. Typically, these strategies suffer from a general lack of control of the cross-linking chemistry as well as the fleeting nature of the reactive species that precludes secondary chemistry. We have addressed both of these issues using orthogonal chemistries to effect both cross-linking and subsequent functionalization of polymer films by mild heating, which results in exacting control of the cross-link density as well as the density of the residual stable functional groups available for subsequent, stepwise functionalization. This methodology is exploited to develop a strategy for the independent and orthogonal triple-functionalization of cross-linked polymer thin-films through microcontact printing.

From well defined star-microgels to highly ordered honeycomb films

Star-microgels were prepared in a two-step process known as the arm first approach by Atom Transfer Radical Polymerization (ATRP). Living linear poly(methyl methacrylate) (PMMA), with molecular weight (Mn) of 10000 and 20000, was reacted with ethylene glycol dimethacrylate (EGDMA) as crosslinker and varying amounts of methyl methacrylate (MMA) as spacer, under ATRP conditions, to produce star-microgels with Mn ranging from 0.3 × 106 to 1.0 × 106 and number of arms, n(arms) from 11 to 74. As Mn of the arm was increased, a decrease in molecular weight and in the number of arms in the microgel was observed. Star-microgels, with MMA spacer incorporated in the core, were found to have lower molecular weight and lower arm number. The microgels were used as precursors to form honeycomb films. The films were cast under conditions of high humidity which produces condensed water droplets which act as the template for a precipitating polymer. This is the first report of the use of well defined star-microgels to cast highly ordered porous films. It is shown that the pore diameters decrease with increasing number of PMMA arms and with increasing molecular weight of the star-microgel.

Cholesterol-mediated anchoring of enzyme-loaded liposomes within disulfide-stabilized polymer carrier capsules

Polymer capsules containing multiple liposomes, termed capsosomes, are a promising new concept toward the design of artificial cells. Herein, we report on the fundamental aspects underpinning the assembly of capsosomes. A stable and high loading of intact liposomal cargo into a polymer film was achieved by non-covalently sandwiching the liposomes between a tailor-made cholesterol-modified poly(L-lysine) (PLL(c)) precursor layer and a poly(methacrylic acid)-co-(cholesteryl methacrylate) (PMA(c)) capping layer. The film assembly, optimized on planar surfaces, was successfully transferred onto colloidal substrates, and a polymer membrane was subsequently assembled by the alternating adsorption of poly(N-vinyl pyrrolidone) (PVP) and thiol-modified poly(methacrylic acid) (PMA(SH)) onto the pre-adsorbed layer of liposomes. Upon removal of the silica template, stable capsosomes encapsulating the enzyme luciferase or beta-lactamase within their liposomal sub-compartments were obtained at both assembly (pH 4) and physiological conditions (pH 7.4). Excellent retention of the liposomes and the enzymatic cargo within the polymer carrier capsules was observed for up to 14 days. These engineered capsosomes are particularly attractive as autonomous microreactors, which can be utilized to repetitively add smaller reactants to cause successive distinct reactions within the capsosomes and simultaneously release the products to the surrounding environment, bringing these systems one step closer toward constructing artificial cells.

A Facile Synthesis of Dynamic, Shape‐Changing Polymer Particles

We herein report a new facile strategy to ellipsoidal block copolymer nanoparticles that exhibit a pH-triggered anistropic swelling profile. In a first step, elongated particles with an axially stacked lamellae structure are selectively prepared by utilizing functional surfactants to control the phase separation of symmetric polystyrene-b-poly(2-vinylpyridine) (PS-b-P2VP) in dispersed droplets. In a second step, the dynamic shape change is realized by cross-linking the P2VP domains, thereby connecting glassy PS discs with pH-sensitive hydrogel actuators.

Precise Synthesis of Molecularly Defined Oligomers and Polymers by Orthogonal Iterative Divergent/Convergent Approaches

The synthesis of perfectly defined (macro)molecules has been a constant challenge for polymer and organic chemists. This paper highlights the main applications of the iterative divergent/convergent approach for the synthesis of discrete mass oligomers and polymers. We will discuss the orthogonal deprotection and coupling strategies involved in this powerful strategy where chain length doubles at each iteration and which has been applied to the synthesis of conjugated rigid rods as well as amorphous and crystalline oligomers and polymers. The synthesis of perfectly defined oligomers in respect to emerging highly efficient and orthogonal chemistries will also be highlighted.

ATRP-mediated continuous assembly of polymers for the preparation of nanoscale films

The continuous assembly of polymers (CAP) via atom transfer radical polymerisation (ATRP) is reported as an efficient approach for the preparation of dense, cross-linked, nanoscale engineered films as surface coatings, hollow capsules and replica particles. These films can be reinitiated to allow the preparation of thicker films without loss of film growth efficiency while maintaining similar film density.

Photochromic, Metal-Absorbing Honeycomb Structures

We demonstrate the synthesis and use of a spiropyran functional polymer to form highly ordered honeycomb materials by the breath figure technique, which is based on the self-assembly of water droplets. These materials undergo rapid and intense color changes both in solution and as porous films by irradiation with light (UV or visible). We also demonstrate the metal binding ability of these polymers ultimately to create hybrid organic-inorganic porous structures. Furthermore, by reduction of the metal and calcination of the organic materials, unique palladium microrings can be prepared. The methods described are general techniques that may be applied to a range of heavy metals.

Nanoparticle PET/CT Imaging of Natriuretic Peptide Clearance Receptor in Prostate Cancer

Atrial natriuretic peptide has been recently discovered to have anticancer effects via interaction with cell surface natriuretic peptide receptor A (NPRA) and natriuretic peptide clearance receptor (NPRC). In a preclinical model, NPRA expression has been identified during tumor angiogenesis and may serve as a potential prognostic marker and target for prostate cancer (PCa) therapy. However, the presence of NPRC receptor in the PCa model has not yet been assessed. Furthermore, there is still no report using nanoparticle for PCa positron emission tomography (PET) imaging. Herein, an amphiphilic comb-like nanoparticle was synthesized with controlled properties through modular construction containing C-atrial natriuretic factor (CANF) for NPRC receptor targeting and 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid (DOTA) chelator for high specific activity Cu-64 radiolabeling. The pharmacokinetics of (64)Cu-CANF-Comb exhibited tuned biodistribution and optimized in vivo profile in contrast to the nontargeted (64)Cu-Comb nanoparticle. PET imaging with (64)Cu-CANF-Comb in CWR22 PCa tumor model showed high blood pool retention, low renal clearance, enhanced tumor uptake, and decreased hepatic burden relative to the nontargeted (64)Cu-Comb. Immunohistochemistry staining confirmed the presence of NPRC receptor in tumor tissue. Competitive PET receptor blocking study demonstrated the targeting specificity of (64)Cu-CANF-Comb to NPRC receptor in vivo. These results establish a new nanoagent for prostate cancer PET imaging.