Liposomes as drug deposits in multilayered polymer films

The ex vivo growth of implantable hepatic or cardiac tissue remains a challenge and novel approaches are highly sought after. We report an approach to use liposomes embedded within multilayered films as drug deposits to deliver active cargo to adherent cells. We verify and characterize the assembly of poly(l-lysine) (PLL)/alginate, PLL/poly(l-glutamic acid), PLL/poly(methacrylic acid) (PMA), and PLL/cholesterol-modified PMA (PMAc) films, and assess the myoblast and hepatocyte adhesion to these coatings using different numbers of polyelectrolyte layers. The assembly of liposome-containing multilayered coatings is monitored by QCM-D, and the films are visualized using microscopy. The myoblast and hepatocyte adhesion to these films using PLL/PMAc or poly(styrenesulfonate) (PSS)/poly(allyl amine hydrochloride) (PAH) as capping layers is evaluated. Finally, the uptake of fluorescent lipids from the surface by these cells is demonstrated and compared. The activity of this liposome-containing coating is confirmed for both cell lines by trapping the small cytotoxic compound thiocoraline within the liposomes. It is shown that the biological response depends on the number of capping layers, and is different for the two cell lines when the compound is delivered from the surface, while it is similar when administered from solution. Taken together, we demonstrate the potential of liposomes as drug deposits in multilayered films for surface-mediated drug delivery.

A naonoporous cell-therapy device with controllable biodegradation for long-term drug release

Herein we describe the development and implementation of a nanoporous cell-therapy device with controllable biodegradation. Dopamine-secreting PC12 cells were housed within newly formulated alginate-glutamine degradable polylysine (A-GD-PLL) microcapsules. The A-GD-PLL microcapsules provided a 3-D microenvironment for good spatial cell growth, viability and proliferation. The microcapsules were subsequently placed within a poly(ethylene glycol) (PEG)-coated poly(ε-caprolactone) (PCL) chamber covered with a PEG-grafted PCL nanoporous membrane formed by phase inversion. To enhance PC12 cell growth and to assist in controlled degradation of both the PC12 cells and the device construct, small PCL capsules containing neural growth factor (PCL-NGF) and a poly(lactic-co-glycolic acid) pellet containing glutamine (PLGA-GLN) were also placed within the PCL chamber. Release of NGF from the PCL-NGF capsules facilitated cell proliferation and viability, while the controlled release of GLN from the PLGA-GLN pellet resulted in A-GD-PLL microcapsule degradation and eventual PC12 cell death following a pre-specified period of time (4 weeks in this study). In vivo, our device was found to be well tolerated and we successfully demonstrated the controlled release of dopamine over a period of four weeks. This integrated biodegradable device holds great promise for the future treatment of a variety of diseases.

Roles of hydrophobicity and charge density on the dynamics of polyelectrolyte complex formation and stability under modeled physicochemical blood conditions

To improve the understanding of the physicochemical behavior of polyplexes (DNA-polycation complexes) and to avoid the complexity of blood, the formation and stability of polyelectrolyte complexes of degradable polycations and polyanions, we previously studied under pH, temperature, and ionic strength typical of human blood. In this study, the investigation is extended to polycationic macromolecules added into mixtures of polyanions selected to mimic polyanionic species present in blood. The poly(l-lysine) polycation was added to binary mixtures of degradable polyanions with different charge densities and hydrophobicity. The polyanions were poly(l-lysine citramide imide), poly(l-lysine citramide), and poly(l-lysine citramide) partially esterified with heptyl groups. We found selectivity and fractionation in the molar mass, which depended on the structural characteristics of the polyanions. The affinity of polycationic poly(l-lysine) macromolecules to polyanions increased in the following order: poly(l-lysine citramide imide) < poly(l-lysine citramide) < hydrophobized poly(l-lysine citramide). These data complements the previous information with respect to the possibility of polyplex destabilization and/or the interactions of polycationic macromolecules in excess with the polyanionic species present in blood, depending on the physicochemical characteristics of the polyplex, the excess polycation, and blood elements.

Dynamics of polyelectrolyte complex formation and stability as a polyanion is progressively added to a polycation under modeled physicochemical blood conditions

To understand the fate of anionic macromolecular species when injected into blood, poly(acrylic acid) and poly(L-lysine citramide) polyanions, with better charge densities, and the poly(L-lysine) polycation were used as models of negatively charged polymer—drug conjugates and positively charged blood proteins, respectively. To mimic an intravenous injection, the polyanion was added to the poly(L-lysine) stepwise at room temperature. The polyelectrolyte complexes formed as precipitates and the molar mass fractionation was observed from one fraction to the other, especially in the case of largely polydispersed poly(L-lysine). The salt concentration necessary to return each fraction of complexed polyelectrolyte back to solution varied linearly with the logarithm of the molar mass of the polycation component. The physicochemical characteristics data of the polyelectrolytes and the media are compared to previously reported reverse mixing mode when the polycation is introduced into a solution of polyanions.

Dynamics of polyelectrolyte complex formation and stability when a polycation is progressively added to a polyanion under physico-chemical conditions modeling blood

The formation of polyelectrolyte complexes is known to depend on many factors, especially pH, temperature, and ionic strength, as well as acid—base properties and mixing conditions. In an approach aimed at by-passing the complexity of blood, the formation and the stability of complexes between oppositely charged polymers were studied in salted media (0.15N NaCl and 0.13 M, pH 7.4 PBS) at room temperature. Different molar masses of poly(L-lysine) were reacted with polyanions with different chemical structures and charge densities, namely: poly(acrylic acid), poly(L-lysine citramide), poly(L-lysine citramide imide), and poly(malic acid). A stepwise protocol was used to investigate the fractionation phenomena reported previously. After each addition, the precipitate was separated and analyzed. The polyanion macromolecules were fractionated according to their structure; no significant fractionation was observed for the polycation. The NaCl concentration, required to destabilize the complexes in the isolated fractions, was found to depend on the polycation molar mass and to vary linearly with log(polyanion Mw). Based on these data, the possible fate of polycationic species, and of polycation-based polyelectrolytic complex, when injected into blood, are addressed.

Tunable film degradation and sustained release of plasmid DNA from cleavable polycation/plasmid DNA multilayers under reductive conditions

The controllable and sustained release of DNA from the surfaces of biomaterials or biomedical devices represents a new method for localized gene delivery. We report the synthesis of a novel polycation containing disulfide bonds in its backbone and the fabrication of polycation/plasmid DNA multilayered thin films by layer-by-layer assembly. The films are very stable during preparation and in storage, however, they gradually degrade and release the incorporated DNA when incubated in PBS buffer containing dithiothreitol (DTT), which results from the degradation of a disulfide-contained polymer under reductive conditions. The film degradation rate and DNA release rate can be tuned by the concentration of reducing agent. This approach will be useful in gene therapy and tissue engineering by controlled administration of therapeutic DNA deposited on the surface of implantable biomedical devices or tissue engineering scaffolds.