Influence of charge on encapsulation and release behavior of small molecules in self-assembled layer-by-layer microcapsules

Exploiting the layer-by-layer nanoarchitectonics for the fabrication of polymer capsules: A toolbox to provide multifunctional properties to target complex pathologies

Polymer capsules fabricated via the layer-by-layer (LbL) approach have attracted a great deal of attention for biomedical applications thanks to their tunable architecture. Compared to alternative methods, in which the precise control over the final properties of the systems is usually limited, the intrinsic versatility of the LbL approach allows the functionalization of all the constituents of the polymeric capsules following relatively simple protocols. In fact, the final properties of the capsules can be adjusted from the inner cavity to the outer layer through the polymeric shell, resulting in therapeutic, diagnostic, or theranostic (i.e., combination of therapeutic and diagnostic) agents that can be adapted to the particular characteristics of the patient and face the challenges encountered in complex pathologies. The biomedical industry demands novel biomaterials capable of targeting several mechanisms and/or cellular pathways simultaneously while being tracked by minimally invasive techniques, thus highlighting the need to shift from monofunctional to multifunctional polymer capsules. In the present review, those strategies that permit the advanced functionalization of polymer capsules are accordingly introduced. Each of the constituents of the capsule (i.e., cavity, multilayer membrane and outer layer) is thoroughly analyzed and a final overview of the combination of all the strategies toward the fabrication of multifunctional capsules is presented. Special emphasis is given to the potential biomedical applications of these multifunctional capsules, including particular examples of the performed in vitro and in vivo validation studies. Finally, the challenges in the fabrication process and the future perspective for their safe translation into the clinic are summarized.

Functionalized layer-by-layer assembled film with directional 5-fluorouracil release to target colon cancer

The objective of this work was to prepare and characterize pH-sensitive capsule containing functionalized layer-by-layer (LbL) assembled polymeric film with directional drug release and evaluate its effectiveness against colon cancer. 5-Fluorouracil (5FU) loaded LbL film was prepared by sequential adsorption of chitosan and alginate polyelectrolytes. This LbL film was coated with polycaprolactone (PCL, 95% w/w) as a backing layer to restrict 5FU release on one-side. The other side constituted the folic acid conjugated chitosan layer for cancer targeting. This film was encapsulated into a gelatin capsule coated with pH-sensitive Eudragit S100. 5FU loaded LbL film was characterized for physical and mechanical properties. Mucoadhesion studies performed using excised rabbit colon showed that chitosan-side of LbL film adhered with significantly (p < 0.05) greater strength compared with PCL-side. Non-everted rat colon-sac model and open colon membrane model studies showed greater permeation of 5FU across the colon wall when adhered to chitosan-side of LbL film compared with PCL-side of the film. Cell monolayer and 3D-spheroid model studies using Caco-2 and COLO 320DM colorectal cancer cells showed significant (p < 0.05) growth inhibition by 5FU loaded LbL film compared with free 5FU solution. In conclusion, pH-sensitive capsule containing 5FU loaded LbL film can be developed to target colorectal cancer for regional drug delivery.

Smart Microcapsules with Molecular Polarity- and Temperature-Dependent Permeability

Microcapsules with molecule-selective permeation are appealing as microreactors, capsule-type sensors, drug and cell carriers, and artificial cells. To accomplish molecular size- and charge-selective permeation, regular size of pores and surface charges have been formed in the membranes. However, it remains an important challenge to provide advanced regulation of transmembrane transport. Here, smart microcapsules are designed that provide molecular polarity- and temperature-dependent permeability. With capillary microfluidic devices, water-in-oil-in-water (W/O/W) double-emulsion drops are prepared, which serve as templates to produce microcapsules. The oil shell is composed of two monomers and dodecanol, which turns to a polymeric framework whose continuous voids are filled with dodecanol upon photopolymerization. One of the monomers provides mechanical stability of the framework, whereas the other serves as a compatibilizer between growing polymer and dodecanol, preventing macrophase separation. Above melting point of dodecanol, molecules that are soluble in the molten dodecanol are selectively allowed to diffuse across the shell, where the rate of transmembrane transport is strongly influenced by partition coefficient. The rate is drastically lowered for temperatures below the melting point. This molecular polarity- and temperature-dependent permeability renders the microcapsules potentially useful as drug carriers for triggered release and contamination-free microreactors and microsensors.

Layer-by-layer Polyelectrolytes Coating of Alginate Microgels for Sustained Release of Sodium Benzoate and Zosteric Acid

The potential of sustaining release of very small (Mw < 250 g/mol) hydrophilic drugs up to several days from layer-by-layer (LbL) polyelectrolyte coated alginate microgels (Alg-Ms) was investigated. One purpose is to minimize post-surgical adhesions, which develop in 12 h to 3 days after surgery. The LbL polyelectrolyte layer would serve as a diffusion barrier for their release. The LbL polyelectrolyte bilayers were prepared using poly(allylamine) (PAH) and poly(styrene sulfonate) (PSS). Sodium benzoate (NaB, Mw = 144 g/mol) and zosteric acid (ZA, Mw = 244 g/mol), two anti-inflammatory and anti-microbial compounds, were used as model drugs. A higher number of PAH/PSS bilayer lead to a greater sustained release of both drugs, and with 4 bilayers, the release of NaB and ZA was prolonged from 24 h to 72 h and 120 h, respectively. Fitting the data to the Ritger-Peppas' equation showed that as the bilayer number increased, the release constant and/or exponent decreased, indicating the LbL PAH/PSS bilayer effectively reduced the permeability of these two very small hydrophilic drugs. The ability to prolong the release of such small hydrophilic molecules, which has rarely been investigated previously, would find broad applications in fields such as anti-adhesion treatment and antifouling coatings.

Graphene Oxide-Assisted Accumulation and Layer-by-Layer Assembly of Antibacterial Peptide for Sustained Release Applications

Fabrication of antibacterial materials with sustained release of active components is of great importance for long-term antibacterial applications. Graphene oxide (GO) has been found to be an excellent carrier for accumulating the antibacterial peptide of G(IIKK)₄I-NH₂ and mediating its loading into the layer-by-layer (LBL) films for sustained release applications. G(IIKK)₄I-NH₂ takes random coiled conformation in monomeric state below 0.17 mM but self-assembles into supramolecular aggregates with α-helical secondary structure at higher concentrations. It can bind onto GO surface in both monomeric and aggregate states to form stable GO@G(IIKK)₄I-NH₂ composites. Upon binding, the local amphiphilic environment of GO surface induces a conformational transition of G(IIKK)₄I-NH₂ monomers from random coils to α-helix. The aggregate binding enhances the loading amount greatly. GO (1 mg) can load as high as 1.7 mg of peptide at saturation. This enables the GO@G(IIKK)₄I-NH₂ composites to serve as reservoirs for sustained release of active G(IIKK)₄I-NH₂ monomers. Moreover, G(IIKK)₄I-NH₂ itself shows low efficiency in LBL assembly, whereas the GO@G(IIKK)₄I-NH₂ composites are ideal LBL assembling units with highly enhanced loading efficiency of G(IIKK)₄I-NH₂. The LBL films involving degradable poly(β-amino esters) can realize sustained release of G(IIKK)₄I-NH₂ for bacteria killing in a well-controlled manner. This study demonstrates an efficient strategy for fabrication of long-durable antibacterial materials and surface coatings by using GO as the carrier for drug accumulation and loading.

Effective melanoma cancer suppression by iontophoretic co-delivery of STAT3 siRNA and imatinib using gold nanoparticles

Co-delivery of chemotherapeutic agents improve anti-tumor efficacy and reduce cancer resistance. Here, we report development of layer-by-layer assembled gold nanoparticles (LbL-AuNP) containing anti-STAT3 siRNA and imatinib mesylate (IM) to treat melanoma. The combination treatment with STAT3 siRNA and IM in B16F10 melanoma cells showed greater suppression of STAT3 protein, decreased cell viability and increased apoptotic events compared with LbL-AuNP containing either STAT3 siRNA or IM. In vivo efficacy studies in melanoma tumor bearing mice showed that non-invasive topical iontophoretic administration (0.5mA/cm²) of LbL-AuNP was comparable with intratumoral administration. Co-delivery of STAT3 siRNA and IM using LbL-AuNP showed significant (p<0.05) reduction in percentage tumor volume, tumor weight and suppressed STAT3 protein expression compared with either STAT3 siRNA or IM loaded LbL-AuNP. Taken together, LbL-AuNP can be developed as nanocarrier system for co-delivery of siRNA and small molecule drugs for topical iontophoretic delivery.

Local anesthetic lidocaine delivery system: chitosan and hyaluronic acid-modified layer-by-layer lipid nanoparticles

CONTEXT

Transdermal local anesthesia is one of the most applied strategies to avoid systemic adverse effects; there is an appealing need for a prolonged local anesthetic that would provide better bioavailability and longer pain relief with a single administration.

OBJECTIVE

Layer-by-layer (LBL) technique was used in this study to explore a nanosized drug delivery system for local anesthetic therapy.

MATERIALS AND METHODS

LBL-coated lidocaine-loaded nanostructured lipid nanoparticles (LBL-LA/NLCs) were prepared and characterized in terms of particle size (PS), zeta potential, drug encapsulation efficiency (EE), in vitro skin permeation and in vivo local anesthetic studies.

RESULTS

Evaluation of the in vitro skin permeation and in vivo anesthesia effect illustrated that LBL-LA/NLCs can enhance and prolong the anesthetic effect of LA.

DISCUSSION AND CONCLUSION

LBL-LA/NLCs could function as a promising drug delivery strategy for overcoming the barrier function of the skin and could deliver anesthetic through the skin with sustained release behavior for local anesthetic therapy.

Combined chemo- and photo-thermal therapy delivered by multifunctional theranostic gold nanorod-loaded microcapsules

A polyelectrolyte microcapsule-based, cancer-targeting, and controlled drug delivery system has been developed as a multifunctional theranostic agent for synergistic cancer treatment. This new system, called FA-MC@GNR, is composed of folic acid (FA)-modified, multi-layered, hollow microcapsules loaded with gold nanorods (GNRs), and undergoes thermal degradation under near infrared (NIR) light. Either an NIR dye (MPA) or anti-cancer drug (doxorubicin, DOX) was loaded into the microcapsules via physical adsorption, yielding FA-MC@GNRs/MPA or FA-MC@GNRs/DOX, both of which exhibit no obvious toxicity, high stability, and remarkably improved tumor-targeting capabilities in vivo. Utilizing the strong NIR absorption of FA-MC@GNRs/DOX, we demonstrate the system's ability to simultaneously elicit photothermal therapy and controlled chemotherapy, achieving synergistic cancer treatment both in vitro cellular and in vivo animal experiments. Our study presents a new type of multifunctional micro-carrier for the delivery of chemotherapeutic drugs and photothermal agents, which has been shown to be an effective therapeutic approach for combined cancer treatment.

Encapsulation of albumin in self-assembled layer-by-layer microcapsules: comparison of co-precipitation and adsorption techniques

OBJECTIVE

The objective of this study is to prepare and characterize polymeric self-assembled layer-by-layer microcapsules (LbL-MC) to deliver a model protein, bovine serum albumin (BSA). The aim is to compare the BSA encapsulation in LbL-MC using co-precipitation and adsorption methods.

MATERIALS AND METHODS

In co-precipitation method, BSA was co-precipitated with growing calcium carbonate particles to form a core template. Later, poly(styrene sulfonate) and poly(allylamine hydrochloride) were sequentially adsorbed onto the CaCO3 templates. In adsorption method, preformed LbL-MC were incubated with BSA and encapsulation efficiency is optimized for pH and salt concentration. Free and BSA-encapsulated LbL-MC were characterized using Zetasizer, scanning electron microscopy (SEM), Fourier transform infrared spectroscopy and differential scanning calorimeter. Later, in vitro release studies were performed using dialysis membrane method at pH 4, 7.4 and 9.

RESULTS AND DISCUSSION

Results from Zetasizer and SEM showed free LbL-MC with an average size and zeta-potential of 2.0 ± 0.6 μm and 8.1 ± 1.9 mV, respectively. Zeta-potential of BSA-loaded LbL-MC was (-)7.4 ± 0.7 mV and (-)5.7 ± 1.0 mV for co-precipitation and adsorption methods, respectively. In adsorption method, BSA encapsulation in LbL-MC was found to be greater at pH 6.0 and 0.2 M NaCl. Co-precipitation method provided four-fold greater encapsulation efficiency (%) of BSA in LbL-MC compared with adsorption method. At pH 4, the BSA release from LbL-MC was extended up to 120 h. Polyacrylamide gel electrophoresis showed that BSA encapsulated in LBL-MC through co-precipitation is stable toward trypsin treatment.

CONCLUSION

In conclusion, co-precipitation method provided greater encapsulation of BSA in LbL-MC. Furthermore, LbL-MC can be developed as carriers for pH-controlled protein delivery.