The encapsulation of gold nanoparticles using RAFT, ATRP and miniemulsion polymerisation techniques

The investigation into the encapsulation of gold nanoparticles (AuNPs) by poly(methyl methacrylate) (PMMA) was undertaken. This was performed by three polymerisation techniques including: grafting PMMA synthesised by reversible addition-fragmentation chain transfer (RAFT) polymerisation to AuNPs, grafting PMMA synthesised by atom transfer radical polymerisation (ATRP) from the surface of functionalised AuNPs and by encapsulation of AuNPs within PMMA latexes produced through photo-initiated oil-in-water (o/w) miniemulsion polymerisation. The grafting of RAFT PMMA to AuNPs was performed by the addition of the RAFT functionalised PMMA to citrate stabilised AuNPs. This was conducted with a range of PMMA of varying molecular weight distribution (MWD) as either the dithioester or thiol end-group functionalities. The RAFT PMMA polymers were characterised by gel permeation chromatography (GPC), ultraviolet-visible (UV-vis), Fourier transform infrared-attenuated total reflectance (FTIR-ATR), Fourier transform Raman (FT-Raman) and proton nuclear magnetic resonance (1H NMR) spectroscopies. The attachment of PMMA to AuNPs showed a tendency for AuNPs to associate with the PMMA structures formed, though significant aggregation occurred. Interestingly, thiol functionalised end-group PMMA showed very little aggregation of AuNPs. The spherical polymer-AuNP structures did not vary in size with variations in PMMA MWD. The PMMA-AuNP structures were characterised using scanning electron microscopy (SEM), transition electron microscopy (TEM), energy dispersive X-ray analysis (EDAX) and UV-vis spectroscopy. The surface confined ATRP grafting of PMMA from initiator functionalised AuNPs was polymerised in both homogeneous and heterogeneous media. 11,11’- dithiobis[1-(2-bromo-2-methylpropionyloxy)undecane] (DSBr) was used as the surface-confined initiator and was synthesised in a three step procedure from mercaptoundecanol (MUD). All compounds were characterised by 1H NMR, FTIR-ATR and Raman spectroscopies. The grafting in homogeneous media resulted in amorphous PMMA with significant AuNP aggregation. Individually grafted AuNPs were difficult to separate and characterise, though SEM, TEM, EDAX and UV-vis spectroscopy was used. The heterogeneous polymerisation did not produce grafted AuNPs as characterised by SEM and EDAX. The encapsulation of AuNPs within PMMA latexes through the process of photoinitiated miniemulsion polymerisation was successfully achieved. Initially, photoinitiated miniemulsion polymerisation was conducted as a viable low temperature method of miniemulsion initiation. This proved successful producing a stable PMMA with good conversion efficiency and narrow particle size distribution (PSD). This is the first report of such a system. The photo-initiated technique was further optimised and AuNPs were included into the miniemulsion. AuNP encapsulation was very effective, producing reproducible AuNP encapsulated PMMA latexes. Again, this is the first reported case of this. The latexes were characterised by TEM, SEM, GPC, gravimetric analysis and dynamic light scattering (DLS).

Solid freeform fabrication of hydrogel structures and cell encapsulation

We aim to fabricate computer-controlled hydrogel structures containing viable encapsulated cells to overcome the low seeding densities which are inherent to most pre-fabricated scaffold systems.

Encapsulation of transition metal species into zeolites and molecular sieves as redox catalysts: Part I-preparation and characterisation of nanosized TiO2, CdO and ZnO semiconductor particles anchored in NaY zeolite

In this paper, we report the preparation and characterisation of nanometer-sized TiO2, CdO, and ZnO semiconductor particles trapped in zeolite NaY. Preparation of these particles was carried out via the traditional ion exchange method and subsequent calcination procedure. It was found that the smaller cations, i.e., Cd2+ and Zn2+ could be readily introduced into the SI′ and SII′ sites located in the sodalite cages, through ion exchange; while this is not the case for the larger Ti species, i.e., Ti monomer [TiO]2+ or dimer [Ti2O3]2+ which were predominantly dispersed on the external surface of zeolite NaY. The subsequent calcination procedure promoted these Ti species to migrate into the internal surface of the supercages. These semiconductor particles confined in NaY zeolite host exhibited a significant blue shift in the UV-VIS absorption spectra, in contrast to the respective bulk semiconductor materials, due to the quantum size effect (QSE). The particle sizes calculated from the UV-VIS optical absorption spectra using the effective mass approximation model are in good agreement with the atomic absorption data.

Plaintext awareness in identity-based key encapsulation

The notion of plaintext awareness ( PA ) has many applications in public key cryptography: it offers unique, stand-alone security guarantees for public key encryption schemes, has been used as a sufficient condition for proving indistinguishability against adaptive chosen-ciphertext attacks ( IND-CCA ), and can be used to construct privacy-preserving protocols such as deniable authentication. Unlike many other security notions, plaintext awareness is very fragile when it comes to differences between the random oracle and standard models; for example, many implications involving PA in the random oracle model are not valid in the standard model and vice versa. Similarly, strategies for proving PA of schemes in one model cannot be adapted to the other model. Existing research addresses PA in detail only in the public key setting. This paper gives the first formal exploration of plaintext awareness in the identity-based setting and, as initial work, proceeds in the random oracle model. The focus is laid mainly on identity-based key encapsulation mechanisms (IB-KEMs), for which the paper presents the first definitions of plaintext awareness, highlights the role of PA in proof strategies of IND-CCA security, and explores relationships between PA and other security properties. On the practical side, our work offers the first, highly efficient, general approach for building IB-KEMs that are simultaneously plaintext-aware and IND-CCA -secure. Our construction is inspired by the Fujisaki-Okamoto (FO) transform, but demands weaker and more natural properties of its building blocks. This result comes from a new look at the notion of γ -uniformity that was inherent in the original FO transform. We show that for IB-KEMs (and PK-KEMs), this assumption can be replaced with a weaker computational notion, which is in fact implied by one-wayness. Finally, we give the first concrete IB-KEM scheme that is PA and IND-CCA -secure by applying our construction to a popular IB-KEM and optimizing it for better performance.

Encapsulation of nanoparticles into single-crystal ZnO nanorods and microrods

One-dimensional single crystal incorporating functional nanoparticles of other materials could be an interesting platform for various applications. We studied the encapsulation of nanoparticles into single-crystal ZnO nanorods by exploiting the crystal growth of ZnO in aqueous solution. Two types of nanodiamonds with mean diameters of 10 nm and 40 nm, respectively, and polymer nanobeads with size of 200 nm have been used to study the encapsulation process. It was found that by regrowing these ZnO nanorods with nanoparticles attached to their surfaces, a full encapsulation of nanoparticles into nanorods can be achieved. We demonstrate that our low-temperature aqueous solution growth of ZnO nanorods do not affect or cause degradation of the nanoparticles of either inorganic or organic materials. This new growth method opens the way to a plethora of applications combining the properties of single crystal host and encapsulated nanoparticles. We perform micro-photoluminescence measurement on a single ZnO nanorod containing luminescent nanodiamonds and the spectrum has a different shape from that of naked nanodiamonds, revealing the cavity effect of ZnO nanorod.

Encapsulation of Hydrocortisone and Mesalazine in Zein Microparticles

Zein was investigated for use as an oral-drug delivery system by loading prednisolone into zein microparticles using coacervation. To investigate the adaptability of this method to other drugs, zein microparticles were loaded with hydrocortisone, which is structurally related to prednisolone; or mesalazine, which is structurally different having a smaller LogP and ionizable functional groups. Investigations into the in vitro digestibility, and the electrophoretic profile of zein, and zein microparticles were conducted to shed further insight on using this protein as a drug delivery system. Hydrocortisone loading into zein microparticles was comparable with that reported for prednisolone, but mesalazine loading was highly variable. Depending on the starting quantities of hydrocortisone and zein, the average amount of microparticles equivalent to 4 mg hydrocortisone, (a clinically used dose), ranged from 60-115 mg, which is realistic and practical for oral dosing. Comparatively, an average of 2.5 g of microparticles was required to deliver 250 mg of mesalazine (a clinically used dose), so alternate encapsulation methods that can produce higher and more precise mesalazine loading are required. In vitro protein digestibility revealed that zein microparticles were more resistant to digestion compared to the zein raw material, and that individual zein peptides are not preferentially coacervated into the microparticles. In combination, these results suggest that there is potential to formulate a delivery system based on zein microparticles made using specific subunits of zein that is more resistant to digestion as starting material, to deliver drugs to the lower gastrointestinal tract.

Polymer encapsulation of magnesium to control biodegradability and biocompatibility

Clinical utility of biodegradable magnesium implants is undermined by the untimely degradation of these materials in vivo. Their high corrosion rate leads to loss of mechanical integrity, peri–implant alkalization and localised accumulation of hydrogen gas. Biodegradable coatings were produced on pure magnesium using RF plasma polymerisation. A monoterpene alcohol with known anti-inflammatory and antibacterial properties was used as a polymer precursor. The addition of the polymeric layer was found to reduce the degradation rate of magnesium in simulated body fluid. The in vitro studies indicated good cytocompatibility of non-adherent THP–1 cells and mouse macrophage cells with the polymer, and the polymer coated sample. The viability of THP–1 cells was significantly improved when in contact with polymer encapsulated magnesium compared to unmodified samples. Collectively, these results suggest plasma enhanced polymer encapsulation of magnesium as a suitable method to control degradation kinetics of this biomaterial.

Materials and methods for encapsulation of OPV: A review

Amongst alternative energy sources, photovoltaics hold a considerable promise for it is a plentiful, easily accessible and renewable source of power. Yet, the overall cost of generating electricity using the most advanced silicon based solar cells remains high compared to both traditional and other renewable power generation approaches. Organic thin film photovoltaics are an emerging economically competitive photovoltaic technology that combines manufacturing adaptability, low-cost processing and a lightweight, flexible device end-product. At present, however, commercial use of organic photovoltaics is hindered by low conversion efficiency and poor overall stability of the devices. Encapsulation with high barrier performance materials and structures is one of the key ways to address these issues and improve device lifetime. This paper will briefly outline the current understanding of the major degradation mechanisms, their interrelation and the internal and external factors that initiate these processes. Then, the paper will provide an overview of currently available encapsulant materials, their utility in limiting chemical (water vapor and oxygen penetration) and mechanical degradation within individual layers and device as a whole, and potential drawbacks to their application in organic photovoltaic devices.

Alginate encapsulation of shoot tips and nodal segments for short-term storage and distribution of the eucalypt Corymbia torelliana × C. citriodora

A protocol was developed for short-term preservation and distribution of the plantation eucalypt, Corymbia torelliana × C. citriodora, using alginate-encapsulated shoot tips and nodes as synthetic seeds. Effects of sowing medium, auxin concentration, storage temperature and planting substrate on shoot regrowth or conversion into plantlets were assessed for four different clones. High frequencies of shoot regrowth (76–100%) from encapsulated explants were consistently obtained in hormone-free half- and full-strength Murashige and Skoog (MS) sowing media. Conversion into plantlets from synthetic seeds was achieved on half-strength MS medium by treating shoot tips or nodes with 4.9–78.4 μM IBA prior to encapsulation. Pre-treatment with 19.6 μM IBA provided 62–100% conversion, and 95–100% of plantlets survived after acclimatisation under nursery conditions. Synthetic seeds containing explants pre-treated with IBA were stored for 8 weeks much more effectively at 25°C than at 4°C, with regrowth frequencies of 50–84% at 25°C compared with 0–4% at 4°C. To eliminate the in vitro culture step after encapsulation, synthetic seeds were allowed to pre-convert before sowing directly onto a range of ex vitro non-sterile planting substrates. Highest frequencies (46–90%) of plantlet formation from pre-converted synthetic seeds were obtained by transferring shoot tip-derived synthetic seeds onto an organic compost substrate. These plantlets exhibited almost 100% survival in the nursery without mist irrigation. Pre-conversion of non-embryonic synthetic seeds is a novel technique that provides a convenient alternative to somatic embryo-derived artificial seeds.

Encapsulation and release of rifampicin using poly(vinyl pyrrolidone)-poly (methacrylic acid) polyelectrolyte capsules

Poly(vinyl pyrrolidone) and poly(methacrylic acid) multilayer capsules based on hydrogen bonding have been prepared by the layer-by-layer approach and used to encapsulate and release rifampicin, an antituberculosis drug. Removal of silica core using a buffer of ammonium fluoride and hydrofluoric acid at about pH 3 was found to produce better capsules than hydrofluoric acid alone. An eight-layered capsule had a wall thickness of 20 rim. Maximum encapsulation was found to be about 86 mu g at 40 degrees C with 1 +/- 0.2 x 10(6) capsules. Release studies showed a burst kind of release and maximum release was obtained above pH 7 where the capsules disintegrate rapidly thereby releasing the drug in a short period. Interactions studies with Mycobacterium smegmatis showed that the capsules were cytocompatible and the released drug functioned with the same efficacy as the free drug.

Dendritic encapsulation of amino acid-metal complexes. Synthesis and studies of dendron-functionalized L-tyrosine-metal (Zn-II, Co-II) complexes

This paper describes the synthesis, characterization and studies of dendrimers possessing an amino acid-metal complex as the core. Using Frechet-type polyaryl ether dendrons, L-tyrosine-metal (Zn-II and Co-II) complex cored dendrimers of 0-4 generations were synthesized. The metal complexation of the tyrosine unit at the focal point of these dendrons took place smoothly, in excellent yields, even though the sizes of the dendrons increase as the generations advance. Spectrophotometric titrations with CoII metal ion confirmed the formation of a 2 : 1 dendritic ligand to metal complex and the existence of a pseudotetrahedral geometry at the metal centre is also inferred. Cyclic voltammetric studies of dendrimer-Co-II complexes showed that while the electron transfer of Co-II to Co-I was facile for generations 0-2, such a process was difficult with generations 3 and 4, indicating a rigid encapsulation of the metal ion centre by proximal dendron groups. Further reduction of Co-I to Co-0 and the corresponding oxidation processes appear to be limited by adsorption at the surfaces of the electrodes.

Encapsulation of cobalt phthalocyanine in zeolite-Y: Evidence for nonplanar geometry

Cobalt (11) phthalocyanine (CoPc) molecules have been encapsulated within the supercage of zeolite-Y. The square-planar complex, being larger than the almost spherical cage, is forced to adopt a distorted geometry on encapsulation. A comparative spectroscopic and magnetic investigation of CoPc encapsulated in zeolite-Y and in the unencapsulated state is reported. These results supported by molecular modeling have been used to understand the nature and extent of the loss of planarity of CoPc on encapsulation. The encapsulated molecule is shown to be the trans-diprotonated species in which the center of inversion is lost due to distortions required to accommodate the square complex within the zeolite. Encapsulation also leads to an enhancement of the magnetic moment of the CoPc. This is shown to be a consequence of the nonplanar geometry of the encapsulated molecule resulting in an excited high-spin state being thermally accessible.

Enhanced Survival of Probiotic Lactobacillus acidophilus by Encapsulation with Nanostructured Polyelectrolyte Layers through Layer-by-Layer Approach

The encapsulation of probiotic Lactobacillus acidophilus through layer-by-layer self-assembly of polyelectrolytes (PE) chitosan (CHI) and carboxymethyl cellulose (CMC) has been investigated,to enhance its survival m adverse conditions encountered in the GI tract The survival of encapsulated cells in simulated gastric (SGF) and intestinal fluids (SIF) is significant when compared to nonencapsulated cells On sequential exposure to SGF and SIF fox 120 nun, almost complete death of free cells is observed However, for cells coated with three nanolayers of PEs (CHI/CMC/CHI) about 33 log % of the cells (6 log cfu/500 mg) survived under the same conditions The enhanced survival rate of encapsulated L acidophilus can be attributed to the impermeability of polyelectrolyte nanolayers to large enzyme molecules like pepsin, and pancreatin that cause proteolysis and to the stability of the polyelectrolyte nanolayers in gastric and intestinal pH The PE coating also serves to reduce viability losses during freezing and freeze- drying About 73 and 92 log % of uncoated and coated cells survived after freeze:drying, and the losses occurring between freezing and freeze-drying were found to be lower for coated cells