Microgel-Based Engineered Nanostructures and Their Applicability with Template-Directed Layer-by-Layer Polyelectrolyte Assembly in Protein Encapsulation

Hollow silver alginate microspheres for drug delivery and surface enhanced Raman scattering detection

Multifunctional silver alginate hydrogel microspheres are assembled via a template assisted approach using calcium carbonate cores.

Emerging trend in nano-engineered polyelectrolyte-based surrogate carriers for delivery of bioactives

IMPORTANCE OF THE FIELD

In recent decades a new colloidal drug delivery system based on layer-by-layer (LbL) technology has emerged, which offers promising means of delivering bioactive agents, specifically biological macromolecules including peptides and DNA. Nano-engineered capsules specifically fabricated from biocompatible and biodegradable polyelectrolytes (PEs) can provide a better option for encapsulation of cells thereby protecting cells from immunological molecules in the body, and their selective permeability can ensure the survival of encapsulated cells.

AREAS COVERED IN THIS REVIEW

This review encompasses a strategic approach to fabricate nano-engineered microcapsules through meticulous selection of polyelectrolytes and core materials based on LbL technology. The content of the article provides evidence for its wide array of applications in medical therapeutics, as indicated by the quantity of research and patents in this area. Recent developments and approaches for tuning drug release, biocompatibility and cellular interaction are discussed thoroughly.

WHAT THE READER WILL GAIN

This review aims to provide an overview on the development of LbL capsules with specific orientation towards drug and macromolecular delivery and its integration with other drug delivery systems, such as liposomes.

TAKE HOME MESSAGE

Selection of PEs for the fabrication of LbL microcapsules has a profound effect on stability, drug release, biocompatibility and encapsulation efficacy. The release can be easily modulated by varying different physicochemical as well as physiological conditions. Scale-up approaches for the fabrication of LbL microcapsules by means of automation must be considered to improve the possibility of application of LbL microcapsules on a large scale.

Mechanism of protein release from polyelectrolyte multilayer microcapsules

The development of polyelectrolyte multilayer microcapsules as a delivery system containing bioactive compounds strongly depends on understanding of the major factors that influence capsules' loading and release of incorporated substances. Mechanism of protein release from biocompatible polyelectrolyte multilayer microcapsules has been examined using two different approaches of protein encapsulation: (i) "preloading" via coprecipitation of tetramethylrhodamine isothiocyanate (TRITC)-labeled bovine serum albumin (BSA) (TRITC-BSA) into CaCO(3) particles followed by multilayer assembly and (ii) "postloading" of TRITC-BSA in preformed empty capsules templated on pure CaCO(3) particles taken in the same amount as in "preloading" approach. Polysaccharides (alginate (Alg) or dextran sulfate (Dex)) and polyarginine (PAr) were used as layer constituents. On the basis of the effects of capsule shell composition and thickness, method of protein encapsulation, volume of the surrounding medium, and frequency of medium refreshment on protein release profile, we reveal a mechanism of protein release. The key phenomenon determining the protein release is the property of multilayer polyelectrolyte shells relating to the entrapping and accumulation of protein molecules. The results obtained together with the suggested mechanism of capsule loading and protein release allow us to propose the use of polyelectrolyte microcapsules as a depot system to supply and maintain a defined level of macromolecular drug concentration in surrounding medium.

Uptake of biodegradable gel-assisted LBL nanomatrix by Leishmania donovani-infected macrophages

The aim of this study was to develop novel gel-assisted layer-by-layer (LBL) nanomatrix with high payload of doxorubicin (DOX) and to assess its efficacy against Leishmania donovani. The biodegradable LBL nanomatrix was fabricated using LBL technique using polyions (protamine and sodium alginate) on decomposable core. The developed system was characterized in vitro in terms of layer-by-layer growth and payload efficiency. The efficacy of optimized formulations was evaluated against L. donovani strain in terms of inhibitory concentration (IC50). Uptake studies by infected macrophages were investigated both qualitatively and quantitatively using fluorescence microscopy and flow cytometry. The autogelling property subsequent to core removal inside the nanomatrix resulted in high payload efficiency of DOX (i.e., >70%). The reversal in charge followed the same trend with additional layers, and the magnitude of the charge remained constant up to five complete bilayers of polyions. The DOX can be effectively encapsulated, delivered, and subsequently taken up by L. donovani-infected macrophage cells. The matrix is completely internalized into macrophages showing improved efficacy (IC50 of formulation is almost <or=1.9-fold as compared to plain drug, P<0.05) against intracellular amastigotes. Having ample of opportunity to manipulate surface architecture, this system demonstrates unique platform as a low cost ideal substitute for visceral leishmaniasis to expensive lipid-based formulations.

Encapsulation of synthetically valuable biocatalysts into polyelectrolyte multilayer systems

Layer-by-Layer (LbL) technology recently turned out to be a versatile tool for the encapsulation of bioactive entities. In this study, the factual potential of this technology to encapsulate synthetically valuable biocatalysts, that is enzymes and whole cells expressing a specific catalytic activity, was investigated. The biocatalysts were embedded into a polyelectrolyte multilayer system involving poly(allylamine) hydrochloride (PAH) and poly(styrene sulfonate) sodium salt (PSS). The enzymes were adsorbed to CaCO3 or DEAE-cellulose previous to encapsulation. A slight increase (32%) of the catalytic performance was observed for lipase B from Candida antarctica when four layers of polyelectrolytes were applied. On the whole, however, the residual activity of the investigated enzymes after encapsulation was rather low. Similar results were obtained with whole-cell biocatalysts. It was found that the activity decrease can be attributed to mass transfer restrictions as well as direct interactions between polyelectrolytes and catalytically active molecules. Both effects need to be understood in more detail before LbL technology can be advanced to technically efficient biocatalysis.

Assembly of multilayer microcapsules on CacO3 particles from biocompatible polysaccharides

Multilayer microcapsules were fabricated by layer-by-layer (LbL) assembly of natural polysaccharides onto CaCO3 particles, following with core removal. The micron-sized CaCO3 particles were synthesized by reaction between Ca(NO3)2 and Na2CO3 solutions in the existence of carboxylmethyl cellulose (CMC). The incorporated amount of CMC in the CaCO3 particles was found to be 5.3 wt% by thermogravimetric analysis. Two biocompatible polysaccharides, chitosan and sodium alginate were alternately deposited onto the CaCO3(CMC) templates to obtain hollow microcapsules. Regular oscillation of surface charge as detected by zeta potential demonstrated that the assembly proceeded surely in a LbL manner. The stability of the microcapsules was effectively improved by cross-linking of chitosan with glutaraldehyde. The chemical reaction was verified by infrared spectroscopy. The microcapsules thus fabricated could be spontaneously filled with positively charged low molecular weight substances such as rhodamine 6G and showed good biocompatibility, as detected by in vitro cell culture.