Biofunctional Polyelectrolyte Multilayers and Microcapsules: Control of Non‐Specific and Bio‐Specific Protein Adsorption

Layers of the polyelectrolytes poly(allylamine hydrochloride) (PAH, polycationic) and poly(styrene sulfonate) (PSS, polyanionic) are consecutively adsorbed on flat silicon oxide surfaces, forming stable, ultrathin multilayer films. Subsequently, a final monolayer of the polycationic copolymer poly(L ‐lysine)‐graft‐poly(ethylene glycol) (PLL‐g‐PEG) is adsorbed onto the PSS‐terminated multilayer in order to impart protein resistance to the surface. The growth of each of the polyelectrolyte layers and the protein resistance of the resulting [PAH/PPS]_n(PLL‐g‐PEG) multilayer (n = 1–4) are followed quantitatively ex situ using X‐ray photoelectron spectroscopy and in situ using real‐time optical‐waveguide lightmode spectroscopy. In a second approach, the same type of [PAH/PSS]_n(PLL‐g‐PEG) multilayer coatings are successfully formed on the surface of colloidal particles in order to produce surface‐functionalized, hollow microcapsules after dissolution of the core materials (melamine formaldehyde (MF) and poly(lactic acid) (PLA; colloid diameters: 1.2–20 μm). Microelectrophoresis and confocal laser scanning microscopy are used to study multilayer formation on the colloids and protein resistance of the final capsule. The quality of the PLL‐g‐PEG layer on the microcapsules depends on both the type of core material and the dissolution protocols used. The greatest protein resistance is achieved using PLA cores and coating the polyelectrolyte microcapsules with PLL‐g‐PEG after dissolution of the cores. Protein adsorption from full serum on [PAH/PPS]_n(PLL‐g‐PEG) multilayers (on both flat substrates and microcapsules) decreases by three orders of magnitude in comparison to the standard [PAH/PPS]_n layer. Finally, biofunctional capsules of the type [PAH/PPS]_n(PLL‐g‐PEG/PEG‐biotin) (top copolymer layer with a fraction of the PEG chains end‐functionalized with biotin) are produced which allow for specific recognition and immobilization of controlled amounts of streptavidin at the surface of the capsules. Biofunctional multilayer films and capsules are believed to have a potential for future applications as novel platforms for biotechnological applications such as biosensors and carriers for targeted drug delivery.     

Construction and Evaluation of Hemoglobin‐Based Capsules as Blood Substitutes

Hemoglobin‐based capsules for use as blood substitutes are successfully fabricated by covalent layer‐by‐layer assembly. Dialdehyde heparin (DHP) is used both as one of the wall components and a cross‐linker without employing other extraneous or toxic crosslinking agents. The biocompatibility of (Hb/DHP)₆ microcapsules is evaluated through the 3‐(4,5‐dimethylthiazol‐2‐yl)‐2,5‐diphenyltetrazolium bromide) (MTT) assay and cell experiments. The hemocompatibility of (Hb/DHP)₆ microcapsules is characterized in terms of prothrombin time, thrombin time, activated partial thromboplastin time, and hemolysis rate. The oxygen‐carrying capacity of the microcapsules is demonstrated by converting the deoxy‐Hb state of the microcapsules into the oxy‐Hb state. All these results demonstrate that the hemoglobin‐based microcapsules exhibit oxygen‐carrying capacity as well as biocompatibility and hemocompatility, indicating that the as‐prepared capsules have great potential to function as blood substitutes.     

Surfactant‐Free One‐Step Synthesis of Dual‐Functional Polyurea Microcapsules: Contact Infection Control and Drug Delivery

Surface functionalized polyurea microcapsules (MCQ) are synthesized in one step. Dimethyl‐dodecyl‐(5‐hydroxy‐pentyl)‐ammonium bromide (DAB), a hydroxyl‐end‐capped quaternary ammonium salt, is synthesized and adopted as a new surfmer for the synthesis of MCQ. It is confirmed by fluorescein adsorption that DAB is covalently bonded to MCQ. The so‐formed MCQ possess dual‐functionality: contact infection control and sustained drug delivery. Agar diffusion antimicrobial tests confirm successful inhibition of multi‐drug‐resistant E. coli by MCQ alone instead of by leaching of free quaternary ammonium salts. Furthermore, few E. coli colonies survive on an agar plate coated with 3–4 layers of MCQ. Dissolution tests show a typical first‐order release profile of courmarin‐1, a model dye, from MCQ.     

A Universal and Ultrastable Mineralization Coating Bioinspired from Biofilms

A simple and universal method for manufacturing a mineralization coating on various surfaces is developed using a biofilm‐based material obtained from engineered curli nanofibers. The amyloid protein (CsgA) is the main proteinaceous component in the Escherichia coli (E. coli) biofilm, which can withstand detergents in the harsh environment. The peptide sequence DDDEEK is bioinspired from salivary acquired pellicles in the dental plaque biofilm, having a strong ability to absorb mineral ions and induce the formation of biominerals. The bioinspired coating is successfully secreted by the engineered E. coli, which is transformed with a recombinant plasmid for expression with T7 promoter (PET), namely PET‐22b‐CsgA‐DDDEEK plasmid. The uniform coating can bear shear force and stay on virtually any type of material surface for at least one month. Moreover, the coated slices had a good mineralization performance and better stability than hydroxyapatite (HA)‐spray slices. Furthermore, MG63 cells on the bioactive HA layer induced by the coating possess a better growth capacity than those on the commercial product Matrigel. The animal experiment results suggest that the coated Ti₆Al₄V screws with induced HA present better osteogenicity and osseointegration than HA‐sprayed screws after 12 weeks, as well as no extra immunogenicity. Thus, the coating is highly promising for biomedical applications.     

Modulation of Dendritic Cells by Lipid Grafted Polyelectrolyte Microcapsules

Polyelectrolyte microcapsules are fabricated by layer‐by‐layer deposition of dextran sulfate and poly‐L ‐arginine layers at the surface of calcium carbonate template microparticles followed by core removal to produce hollow microcapsules. In the context of vaccination, these biodegradable LbL capsules emerge as promising antigen carriers and are believed to have potential for the co‐delivery of antigens and immunomodulators associated within the same particle to enhance and steer the type of immune response. To this end, it is shown that LbL microcapsules can be functionalized at their surface with lipid layers containing immunopotentiators of lipid nature. The potency of the different lipid modified microcapsules to activate dendritic cells (DCs) is demonstrated by increased expression levels of the migration marker CCR7 and the maturation markers CD40 and CD86. Additionally, the DCs cytokine secretion profile is evaluated. The findings reveal that the lipid grafted microcapsules are superior to non‐modified microcapsules in DC activation and suggest their potential as immune modulating antigen delivery systems.     

Perfluorooctyl Bromide Polymeric Capsules as Dual Contrast Agents for Ultrasonography and Magnetic Resonance Imaging

Polymeric capsules with a thick shell made of biodegradable and biocompatible polymer and a liquid core of perfluorooctyl bromide (PFOB) were evaluated for stability as well as for ultrasound and magnetic resonance imaging (MRI) contrast enhancement. The method of preparation allows the mean capsule diameter to be regulated between 70 nm and 25 µm and the capsule thickness‐to‐radius ratio from 0.25 to 0.54. Capsule diameter remains stable at 37 °C in phosphate buffer for at least 4 and 6 h for nanocapsules and microcapsules, respectively. The in vitro ultrasound signal‐to‐noise ratio (SNR) was measured from 40 to 60 MHz for 6 µm and 150 nm capsules: the SNR increases with capsule concentration up to 20–25 mg mL⁻¹, and then reaches a plateau that depends on capsule diameter (13.5 ± 1.5 dB for 6 µm and 6 ± 2 dB for the 150 nm capsules). The ultrasound SNR is stable for up to 20 min for microcapsules and for several hours for nanocapsules. For nanocapsules, the thinner the shell, the larger the SNR and the more compressible the capsules. Nanocapsule suspensions imaged in vitro with a commercial ultrasound imaging system (normal and tissue harmonic imaging modes, 7–14 MHz probe) were detected down to concentrations of 12.5 mg mL⁻¹. Injections of nanocapsules (200 µg ml⁻¹) in mice in vivo reveal that the initial bolus passage presents significant ultrasound enhancement of the blood pool during hepatic imaging (7–14 MHz probe, tissue harmonic imaging mode). ¹⁹F‐MRI images were obtained in vitro at 9.4T using spin‐echo and gradient echo sequences and allow detecting nanocapsules in suspension (50 mg mL⁻¹). In conclusion, these results show initial feasibility for development of these capsules toward a dual‐modality contrast agent.     

Anti‐liquid‐Interfering and Bacterially Antiadhesive Strategy for Highly Stretchable and Ultrasensitive Strain Sensors Based on Cassie‐Baxter Wetting State

As a large number of strain sensors are put into practical use, their stability should be considered, especially in harsh environments containing water or microorganisms, which could affect strain sensing. Herein, a novel strategy to overcome liquid interference is proposed. The strain sensor is constructed with a sandwich architecture through layer‐by‐layer (LBL) spray‐coating of a 3‐(aminopropyl)triethoxysilane (APTES) bonding layer and multi‐walled carbon nanotubes/graphene (MWCNT/G) conductive layers on an elastomeric polydimethysiloxane (PDMS) substrate, and is further decorated with silver (Ag) nanoparticles and the (heptadecafluoro‐1,1,2,2‐tetradecyl) trimethoxysilane (FAS, F in short) to obtain a F/Ag/MWCNG/G‐PDMS (FAMG) strain sensor. The superhydrophobicity and underwater oleophobicity of the outer cover layer causes this FAMG strain sensor surface to exhibit stable strain sensing resistant to liquid interference upon stretching in the Cassie?Baxter wetting state, and resistance to bacterial adhesion (Staphylococcus aureus (S. aureus) and Escherichia coli (E. coli)). The sensor attains ultrasensitivity (with a maximum gauge factor of 1989 in the condition of liquid interference), broad strain range (0.1–170%), fast response time (150 ms), and stable response after 1000 stretching–releasing cycles. The ultrasensitivity is provided by propagation of cracks in MWCNT/G conductive layers and terminal fracture of the intermediate separating layers (APTES/MWCNT/G). The microbridge effect of MWCNTs and slippage of APTES/MWCNT/G provide a large strain range. The FAMG strain sensor is successfully used to monitor a series of human activities and an electronic bird under artificial rain and bacterial droplets, indicating the potential use of this sensor in complex environments.     

Self‐Healing Properties of Protein Resin with Soy Protein Isolate‐Loaded Poly(d,l‐lactide‐co‐glycolide) Microcapsules

Self‐healing soy protein isolate (SPI)‐based “green” thermoset resin is developed using poly(d,l ‐lactide‐co‐glycolide)(PLGA) microcapsules containing SPI, as crack healant. The SPI–PLGA microcapsules with an average diameter of 778 nm that contain sub‐capsules are prepared using a water‐in‐oil‐in‐water double‐emulsion solvent evaporation technique. The encapsulation efficiency is found to be high, up to 89%. Thermoset green SPI resin containing the SPI–PLGA microcapsules successfully arrests and retards the microcracks. The healing efficiency is investigated using mode I fracture toughness test for resins containing different concentrations of microcapsules from 5 to 20 wt% and glutaraldehyde as a crosslinker at 9 or 12 wt%. The SPI resin containing 12 wt% glutaraldehyde and 15 wt% microcapsules shows self‐healing efficiency of up to 48%. It is observed that the SPI released from SPI–PLGA microcapsules can react with the excess glutaraldehyde present in the resin when the two come in contact within the microcracks and bridge the two fracture surfaces. The results of this study show for the first time that SPI–PLGA microcapsules can self‐heal protein‐based green resins. The same method can be extended to self‐heal other proteins as well as protein‐based green composites resulting in higher fracture toughness and longer useful life.     

Polymer‐Based Porous Microcapsules as Bacterial Traps

Exposure to live bacteria and accumulation of dead bacteria during bactericidal processes can cause bacterial infectious diseases, implant failure, and antibacterial surface deterioration. Microcapsules with asymmetrically distributed, funnel‐shaped pores, which are capable of capturing, retaining, and killing bacteria are developed, offering a solution to bacterial contamination in liquids. It is found that bacterial isolation inside microcapsules is mainly driven by the bacteria's own motility and the microcapsules' geometry. After entry into the microcapsule cavity, the bacteria are stably retained inside. The microcapsules shield surrounding cells from exposure to bacterial toxins, as demonstrated by the coculture of rat embryonic fibroblast cells with microcapsules loaded with live Escherichia coli. The microcapsules can be enhanced with a bactericidal coating covering only the interior cavity. This confines the bacteria‐killing process, thereby further increasing biocompatibility. The microcapsules may offer a viable bacteria combatant approach as a potentially advantageous method to eradicate bacterial contamination.     

An Engineered Mannoside Presenting Platform: Escherichia coli Adhesion under Static and Dynamic Conditions

The study of the adhesion mechanisms of pathogens to host tissues has gained increased interest as bacterial adhesion is involved in the early stages of surface colonization and infection. Here we describe a platform to study the specific binding of the bacterium Escherichia coli (E. coli) K‐12 strain to molecularly well‐defined surfaces mimicking cellular interfaces. This approach uses a poly(ethylene glycol) brush interface, which displays synthetic determinants of the high mannose N‐linked glycans in a range of densities (3.8 × 10⁴–1.6 × 10⁵ mannosides µm^?2) for the investigation of multivalent interactions with bacteria. The bacterial attachment is mediated by specific interactions between the adhesive protein FimH located on the tip of the bacterial type 1 pili and the mannosylated surfaces. With synthetically engineered mannoses, it is found that the number of strongly adhering bacteria is co‐regulated by many structural physical parameters. Beyond the dependency on carbohydrate density, higher numbers of E. coli attach to the branched trimannose Man(α1–3)(Man(α1–6))Man compared to the monomannose, while larger oligomannoses exposing Man(α1–2) Man at their non reducing end show low binding capacity. The linker used between the mannose moiety and PEG is also affecting the binding efficacy of E. coli. The (hydrophobic) propyl linker results in higher bacteria numbers in comparison to the (hydrophilic) tri(EG), likely a consequence of additional stabilization of the binding complex by hydrophobic interactions. Furthermore, differences are observed in bacteria attachment between stagnant and flow conditions that depend on the type of mannose ligand. Finally, a photolithographic resist lift‐off combined with site‐selective assembly of the glycopolymers is used to produce micropatterns with bacteria colonies confined to defined areas and at controlled colony numbers.     

Bacteria‐Assisted Selective Photothermal Therapy for Precise Tumor Inhibition

Photothermal therapy (PTT) has drawn extensive research attention as a promising approach for tumor treatment. In this study, a bacteria‐assisted strategy relying on the selective reduction of perylene diimide derivative based supramolecular complex (CPPDI) to radical anions (RAs) by Escherichia coli in hypoxic tumors is developed to realize highly precise PTT of tumors. Noninvasive E. coli are first injected intravenously for selectively accumulating and replicating in the tumor due to the hypoxia tropism. Then, CPPDI is loaded in a peptide‐hybrid matrix metalloproteinase‐2 (MMP‐2) responsive liposome (MRL) and injected intravenously. After accumulated and released from MRL in the tumor where MMP‐2 is overexpressed, CPPDI is reduced by E. coli in the hypoxic tumor environment to produce CPPDI RAs (CRAs), which serve as effective photothermal agents for tumor cells thermal ablation under near‐infrared light irradiation. Since E. coli accumulate and grow in tumor sites selectively, this strategy accurately limits the production of CRAs in tumors for highly selective PTT, which will find great potential for precise tumor inhibition.     

Solid Free‐Form Fabrication of Tissue‐Engineering Scaffolds with a Poly(lactic‐co‐glycolic acid) Grafted Hyaluronic Acid Conjugate Encapsulating an Intact Bone Morphogenetic Protein–2/Poly(ethylene glycol) Complex

Despite wide applications of bone morphogenetic protein–2 (BMP‐2), there are few methods to incorporate BPM‐2 within polymeric scaffolds while maintaining biological activity. Solid free‐form fabrication (SFF) of tissue‐engineering scaffold is successfully carried out with poly(lactic‐co‐glycolic acid) grafted hyaluronic acid (HA‐PLGA) encapsulating intact BMP‐2/poly(ethylene glycol) (PEG) complex. HA‐PLGA conjugate is synthesized in dimethyl sulfoxide (DMSO) by the conjugation reaction of adipic acid dihydrazide modified HA (HA‐ADH) and PLGA activated with N,N′‐dicyclohexylcarbodiimide (DCC) and N‐hydroxysuccinimide (NHS). BMP‐2 is complexed with PEG, which is encapsulated within the PLGA domain of the HA‐PLGA conjugate by SFF to prepare tissue‐engineering scaffolds. In vitro release tests confirm the sustained release of intact BMP‐2 from the scaffolds for up to a month. After confirmation of the enhanced osteoblast cell growth, and high gene‐expression levels of alkaline phosphatase (ALP), osteocalcin (OC), and osterix (OSX) in the cells, the HA‐PLGA/PEG/BMP‐2 scaffolds are implanted into calvarial bone defects of Sprague Dawley (SD) rats. Microcomputed tomography (μCT) and histological analyses with Masson's trichrome, and hematoxylin and eosin (H&E) staining reveal effective bone regeneration on the scaffolds of HA‐PLGA/PEG/BMP‐2 blends.     

Pyridylamino‐β‐cyclodextrin as a Molecular Chaperone for Lipopolysaccharide Embedded in a Multilayered Polyelectrolyte Architecture

Layer‐by‐layer self‐assembled polyelectrolyte films containing a charged cyclodextrin and lipopolysaccharide (LPS) are developed for the first time as a potential model for local endotoxin antagonist delivery. We have examined the biological activity of a lipopolysaccharide from E. coli incorporated into multilayered architectures made of poly‐(L ‐lysine) and poly‐(L ‐glutamic acid). Used in such build‐ups, a polycationic cyclodextrin, heptakis(6‐deoxy‐6‐pyridylamino)‐β‐cyclodextrin showed molecular chaperone properties by enabling restoration of the LPS biological activity whenever lost upon interaction with poly‐(L ‐lysine).     

Quaternized Silicon Nanoparticles with Polarity‐Sensitive Fluorescence for Selectively Imaging and Killing Gram‐Positive Bacteria

With the emergence of antibiotic resistance, developing new antibiotics and therapies for combating bacterial infections is urgently needed. Herein, a series of quaternized fluorescent silicon nanoparticles (SiNPs) are facilely prepared by the covalent reaction between amine‐functionalized SiNPs and carboxyl‐containing N‐alkyl betaines. It is found that the bactericidal efficacy of these quaternized SiNPs increases with the length of the N‐alkyl chain, and SiNPs conjugated with N,N‐dimethyl‐N‐octadecylbetaine (BS‐18), abbreviated as SiNPs‐C₁₈, show the best antibacterial effect, whose minimum inhibitory concentrations for Gram‐positive bacteria are 1–2 μg mL^?1. In vivo tests further confirm that SiNPs‐C₁₈ have excellent antibacterial efficacy and greatly reduce bacterial load in the infectious sites. The SiNPs‐C₁₈ exhibit low cytotoxicity toward mammalian cells (including normal liver and lung cells, red blood cells, and macrophages), enabling them to be useful for clinical applications. Besides, the quaternized SiNPs exhibit polarity‐dependent fluorescence emission property and can selectively image Gram‐positive bacteria, thereby providing a simple method to successfully differentiate Gram‐positive and Gram‐negative bacteria. The present work represents the first example that successfully turns fluorescent SiNPs into metal‐free NP‐based antibiotics with simultaneous bacterial imaging and killing capability, which broadens the applications of fluorescent SiNPs and advances the development of novel antibacterial agents.     

Self‐Defensive Biomaterial Coating Against Bacteria and Yeasts: Polysaccharide Multilayer Film with Embedded Antimicrobial Peptide

Prevention of pathogen colonization of medical implants is a major medical and financial issue since infection by microorganisms constitutes one of the most serious complications after surgery or critical care. Immobilization of antimicrobial molecules on biomaterials surfaces is an efficient approach to prevent biofilm formation. Herein, the first self‐defensive coating against both bacteria and yeasts is reported, where the release of the antimicrobial peptide is triggered by enzymatic degradation of the film due to the pathogens themselves. Biocompatible and biodegradable polysaccharide multilayer films based on functionalized hyaluronic acid by cateslytin (CTL), an endogenous host‐defensive antimicrobial peptide, and chitosan (HA‐CTL‐C/CHI) are deposited on a planar surface with the aim of designing both antibacterial and antifungal coating. After 24 h of incubation, HA‐CTL‐C/CHI films fully inhibit the development of Gram‐positive Staphylococcus aureus bacteria and Candida albicans yeasts, which are common and virulent pathogens agents encountered in care‐associated diseases. Hyaluronidase, secreted by the pathogens, leads to the film degradation and the antimicrobial action of the peptide. Furthermore, the limited fibroblasts adhesion, without cytotoxicity, on HA‐CTL‐C/CHI films highlights a medically relevant application to prevent infections on catheters or tracheal tubes where fibrous tissue encapsulation is undesirable.     

Core–Shell Colloids and Hollow Polyelectrolyte Capsules Based on Diazoresins

Hollow polyelectrolyte microcapsules containing diazoresins (DZR) were fabricated by the layer‐by‐layer self‐assembly of a polycation, DZR, in alternation with poly(styrenesulfonate) (PSS) onto polystyrene (PS) particles, followed by dissolution of the PS core by tetrahydrofuran (THF). The multilayer film buildup on the colloids was observed by UV‐visible spectroscopy, single particle light scattering (SPLS), and transmission electron microscopy (TEM). The data confirmed regular and stepwise layer formation of DZR and PSS on the colloid particles, with a thickness of about 10 nm for each DZR/PSS bilayer when exposed to aqueous solution, and approximately 5 nm in the “dry state”. The photosensitive nature of the DZR layers was exploited to construct highly stable, covalently attached (polymerized) films by exposure of the ionic self‐assembled DZR/PSS multilayer films to UV‐irradiation. TEM and atomic force microscopy (AFM) confirmed the formation of hollow DZR/PSS multilayer capsules. Osmotic pressure experiments followed by confocal laser scanning microscopy revealed a high mechanical stability of the hollow DZR/PSS capsules. The mechanically robust polymerized multilayer films on the colloids and as free‐standing three‐dimensional hollow capsules are more stable in various chemical environments (i.e., resistant to etching by solvents) than their ionically linked counterparts.     

Spider Silk Capsules as Protective Reaction Containers for Enzymes

Spider silk fibres are well known for their high tensile strength in combination with high elasticity. Based on the possibility of recombinant production of spider silk proteins, technical applications of spider silk materials are nowadays feasible. The engineered recombinant spider silk protein eADF4(C16) is based on the sequence of ADF4 (Araneus diadematus fibroin), one out of at least three proteins of the dragline silk of the European garden spider A. diadematus. The protein eADF4(C16) can be processed into different morphologies. Here, capsules of eADF4(C16) are assembled at an oil/water interface. These microcapsules are mechanically stable and can be used as a transport system for higher molecular weight compounds such as enzymes or chemical catalysts. Further, they can be regarded as a small enclosed reaction chamber with a semi‐permeable membrane. Reactions can be initiated by diffusion of the reactants through the silk membrane. The eADF4(C16) capsules protect the enzyme β‐galactosidase, used as model, against proteolysis. Functional α‐complementation of β‐galactosidase visualizes the controllable activation of an enzyme within such spider silk capsule, highlighting the broad applicability thereof as reaction containers, e.g., for enzymes.     

Liquid Crystal Emulsions as the Basis of Biological Sensors for the Optical Detection of Bacteria and Viruses

A versatile sensing method based on monodisperse liquid crystal (LC) emulsion droplets detects and distinguishes between different types of bacteria (Gram +ve and ?ve) and viruses (enveloped and non‐enveloped). LCs of 4‐cyano‐4'‐pentylbiphenyl transition from a bipolar to radial configuration when in contact with Gram ?ve bacteria (E. coli) and lipid‐enveloped viruses (A/NWS/Tokyo/67). This transition is consistent with the transfer of lipid from the organisms to the interfaces of the micrometer‐sized LC droplets. In contrast, a transition to the radial configuration is not observed in the presence of Gram +ve bacteria (Bacillus subtilis and Micrococcus luteus) and non‐enveloped viruses (M13 helper phage). The LC droplets can detect small numbers of E. coli bacteria (1–5) and low concentrations (10⁴ pfu mL^?1) of A/NWS/Tokyo/67 virus. Monodisperse LC emulsions incubated with phosholipid liposomes (similar to the E. coli cell wall lipid) reveal that the orientational change is triggered at an area per lipid molecule of ～46 Ų on an LC droplet (～1.6 × 10⁸ lipid molecules per droplet). This approach represents a novel means to sense and differentiate between types of bacteria and viruses based on their cell‐wall/envelope structure, paving the way for the development of a new class of LC microdroplet‐based biological sensors.     

Preparation of Protamine–Titania Microcapsules Through Synergy Between Layer‐by‐Layer Assembly and Biomimetic Mineralization

A novel approach combining layer‐by‐layer (LbL) assembly with biomimetic mineralization is proposed to prepare protamine–titiania hybrid microcapsules. More specifically, these microcapsules are fabricated by alternative deposition of positively charged protamine layers and negatively charged titania layers on the surface of CaCO₃ microparticles, followed by dissolution of the CaCO₃ microparticles using EDTA. During the deposition process, the protamine layer induces the hydrolysis and condensation of a titania precursor, to form the titania layer. Thereafter, the negatively charged titania layer allows a new cycle of deposition step of the protamine layer, which ensures a continuous LbL process. The morphology, structure, and chemical composition of the microcapsules are characterized by scanning electron microscopy, transmission electron microscopy, Fourier transform infrared, and X‐ray photoelectron spectroscopy. Moreover, these protamine–titania hybrid microcapsules are first employed as the carrier for the immobilization of yeast alcohol dehydrogenase (YADH), and the encapsulated YADH displays enhanced recycling stability. This approach may open a facile, general, and efficient way to prepare organic–inorganic hybrid materials with different compositions and shapes.     

Harnessing Interfacial Phenomena to Program the Release Properties of Hollow Microcapsules

The generation of near‐infrared (NIR)‐sensitive microcapsules is presented and it is demonstrated that the release properties of these microcapsules can be tailored by controlling their morphology. A biocompatible polymer, poly(DL‐lactic‐co‐glycolic)acid (PLGA) is used to form hollow microcapsules from monodisperse water‐in‐oil‐in‐water (W/O/W) double emulsions. Both the composition of PLGA and the oil phase of W/O/W double emulsions significantly affect the morphology of the subsequently formed microcapsules. PLGA microcapsules with vastly different morphologies, from spherical to “snowman‐like” capsules, are obtained due to changes in the solvent quality of the oil phase during solvent removal. The adhesiveness of the PLGA‐laden interface plays a critical role in the formation of snowman‐like microcapsules. NIR‐sensitive PLGA microcapsules are designed to have responsive properties by incorporating Au nanorods into the microcapsule shell, which enables the triggered release of encapsulated materials. The effect of capsule morphology on the NIR responsiveness and release properties of PLGA microcapsules is demonstrated.