Layer-by-layer assembly of poly-l-lysine/hyaluronic acid protein reservoirs on poly(glycerol sebacate) surfaces

The modification of biomaterial surfaces has become increasingly relevant in the context of ongoing advancements in tissue engineering applications and the development of tissue-mimicking polymer materials. In this study, we investigated the layer-by-layer (LbL) deposition of polyelectrolyte multilayer protein reservoirs consisting of poly-l-lysine (PLL) and hyaluronic acid (HA) on the hydrophobic surface of poly(glycerol sebacate) (PGS) elastomer. Using the methods of isothermal titration calorimetry and surface plasmon resonance, we systematically investigated the interactions between the polyelectrolytes and evaluated the deposition process in real time, providing insight into the phenomena associated with film assembly. PLL/HA LbL films deposited on PGS showed an exceptional ability to incorporate bone morphogenetic protein-2 (BMP-2) compared to other growth factors tested, thus highlighting the potential of PLL/HA LbL films for osteoregenerative applications. The concentration of HA solution used for film assembly did not affect the thickness and topography of the (PLL/HA)10 films, but had a notable impact on the hydrophilicity of the PGS surface and the BMP-2 release kinetics. The release kinetics were successfully described using the Weibull model and hyperbolic tangent function, underscoring the potential of these less frequently used models to compare the protein release from LbL protein reservoirs.

Biomimetic polyelectrolyte coating of stem cells suppresses thrombotic activation and enhances its survival and function

Mesenchymal stem cells (MSCs) therapy is a promising approach for treating inflammatory diseases due to their immunosuppressive and tissue repair characteristics. However, allogenic transplantation of MSCs induces thrombotic complications in some patients which limits its potential for clinical translation. To address this challenge, we have exploited the bioactivity of heparin, a well-known anticoagulant and immunosuppressive polysaccharide that is widely used in clinics. We have developed a smart layer-by-layer (LbL) coating strategy using gelatin and heparin polymers exploiting their overall positive and negative charges that enabled efficient complexation with the MSCs' glycocalyx. The stable coating of MSCs suppressed complement attack and mitigated thrombotic activation as demonstrated in human whole blood. Gratifyingly, the MSC coating retained its immunosuppressive properties and differentiation potential when exposed to inflammatory conditions and differentiation factors. We believe the simple coating procedure of MSCs will increase allogenic tolerance and circumvent the major challenge of MSCs transplantation.

Preparation, characterization, and evaluation of flaxseed oil liposomes coated with chitosan and pea protein isolate hydrolysates

The effect of layer-by-layer coating of liposomes with chitosan and pea protein isolate hydrolysates (PPIH) was evaluated. Traditional flaxseed oil liposomes (FL Lipo) were used as a model for comparison to liposomes coated with chitosan and PPIH (FL LipoCP). The potential of PPIH as a coating material was evaluated. Additionally, the influence of chitosan and PPIH on vesicle size and zeta potential of liposomes was investigated. The chitosan layer of liposomes exhibited a loose structure. After the second layer of coating with PPIH, chitosan molecules were rearranged on the liposome surface, leading to a more compact and dense shell structure of liposomes. Electrostatic interactions, hydrogen bonds, and hydrophobic interactions favored the stability of FL LipoCP. Compared to FL Lipo, FL LipoCP displayed higher oxidation stability during storage and a slower release of flaxseed oil during in vitro digestion.

Nanoarchitectonics of Layer-by-Layer (LbL) coated nanostructured lipid carriers (NLCs) for Enzyme-Triggered charge reversal

HYPOTHESIS

Combined usage of Layer-by-Layer (LbL) coating and alkaline phosphatase (ALP) - responsive charge reversal strategies can improve the cellular internalisation of the colloidal drug delivery systems by also decreasing their cytotoxic effects.

EXPERIMENTS

Anionic core NLCs were formed by combining the melt emulsification method and ultrasonication. The resulting core NLCs were coated sequentially first with protamine (Prot NLCs) and then with sodium tripolyphosphate (TPP) or sodium polyphosphate (Graham's salt, PP) generating TPP or PP NLCs, respectively. The developed NLCs were characterised regarding their size and zeta potential. Enzyme-induced charge reversal of the TPP and PP NLCs was evaluated by zeta potential measurements upon their incubation with alkaline phosphatase (ALP). In parallel, time-dependent phosphate release was monitored in the presence of isolated as well as cell-associated ALP. Morphological evaluations were performed by scanning electron microscopy (SEM) studies. Moreover, cell viability and cellular uptake studies were carried out in vitro on Caco-2 cells.

FINDINGS

The core NLCs were obtained with a mean size of 272.27 ± 5.23 nm and a zeta potential of -25.70 ± 0.26 mV. Upon coating with protamine, the zeta potential raised to positive values with a total change up to Δ29.3 mV also displaying an increase in particle size. The second layer coating with TPP and PP provided a negative surface charge. Subsequent to ALP treatment, the zeta potential of the TPP and PP NLCs reversed from negative to positive values with total changes of Δ8.56 and Δ7.47 mV, respectively. Conformably, significant amounts of phosphate were released from both formulations. Compared with core NLCs, improved cellular viability as well as increased cellular uptake were observed in case of Prot, TPP and PP NLCs.

Development and characterization of layer-by-layer coated liposomes with poly(L-lysine) and poly(L-glutamic acid) to increase their resistance in biological media

Multilayered coated liposomes were prepared using the layer-by-layer (LbL) technique in an effort to improve their stability in biological media. The formulation strategy was based on the alternate deposition of two biocompatible and biodegradable polyelectrolytes - poly(L-lysine) (PLL) and poly(L-glutamic acid) (PGA) - on negatively charged small unilamellar vesicles (SUVs). Some parameters of the formulation process were optimized such as the polyelectrolyte concentration and the purification procedure. This optimized procedure has allowed the development of very homogeneous formulations of liposomes coated with up to 6 layers of polymers (so-called layersomes). The coating was characterized by dynamic light scattering (DLS), zeta potential measurements and Förster resonance energy transfer (FRET) between two fluorescently labeled polyelectrolytes. Studies on the stability of the formulations at 4 °C in a buffered solution have shown that most structures are stable over 1 month without impacting their encapsulation capacity. In addition, fluorophore release experiments have demonstrated a better resistance of the layersomes in the presence of a non-ionic detergent (Triton™ X-100) as well as in the presence of phospholipase A₂ and human plasma. In conclusion, new multilayered liposomes have been developed to increase the stability of conventional liposomes in biological environments.

Multicellular spheroid based on a triple co-culture: A novel 3D model to mimic pancreatic tumor complexity

The preclinical drug screening of pancreatic cancer treatments suffers from the absence of appropriate models capable to reproduce in vitro the heterogeneous tumor microenvironment and its stiff desmoplasia. Driven by this pressing need, we describe in this paper the conception and the characterization of a novel 3D tumor model consisting of a triple co-culture of pancreatic cancer cells (PANC-1), fibroblasts (MRC-5) and endothelial cells (HUVEC), which assembled to form a hetero-type multicellular tumor spheroid (MCTS). By histological analyses and Selective Plain Illumination Microscopy (SPIM) we have monitored the spatial distribution of each cell type and the evolution of the spheroid composition. Results revealed the presence of a core rich in fibroblasts and fibronectin in which endothelial cells were homogeneously distributed. The integration of the three cell types enabled to reproduce in vitro with fidelity the influence of the surrounding environment on the sensitivity of cancer cells to chemotherapy. To our knowledge, this is the first time that a scaffold-free pancreatic cancer spheroid model combining both tumor and multiple stromal components has been designed. It holds the possibility to become an advantageous tool for a pertinent assessment of the efficacy of various therapeutic strategies.

STATEMENT OF SIGNIFICANCE

Pancreatic tumor microenvironment is characterized by abundant fibrosis and aberrant vasculature. Aiming to reproduce in vitro these features, cancer cells have been already co-cultured with fibroblasts or endothelial cells separately but the integration of both these essential components of the pancreatic tumor microenvironment in a unique system, although urgently needed, was still missing. In this study, we successfully integrated cellular and acellular microenvironment components (i.e., fibroblasts, endothelial cells, fibronectin) in a hetero-type scaffold-free multicellular tumor spheroid. This new 3D triple co-culture model closely mimicked the resistance to treatments observed in vivo, resulting in a reduction of cancer cell sensitivity to the anticancer treatment.

Colon-targeted dexamethasone microcrystals with pH-sensitive chitosan/alginate/Eudragit S multilayers for the treatment of inflammatory bowel disease

Oral colon-targeted drug delivery has gained popularity as an effective strategy for treatment of inflammatory bowel disease (IBD). In this study, we prepared colon-targeted dexamethasone microcrystals (DXMCs) coated with multilayers of chitosan oligosaccharide (CH), alginate (AG), and finally Eudragit S 100 (ES) (ES₁AG₄CH₅-DXMCs) using a layer-by-layer (LBL) coating technique. Particle size, surface charge, in vitro drug release, and in vivo anti-inflammatory activity of ES₁AG₄CH₅-DXMCs were evaluated. ES₁AG₄CH₅-DXMCs had an average particle size of 2.34 ± 0.19 μm and a negative surface charge of - 48 ± 9 mV. ES₁AG₄CH₅-DXMCs demonstrated pH-dependent dexamethasone release, avoiding initial burst drug release in acidic pH conditions of the stomach and small intestine, and providing subsequent sustained drug release in the colonic pH. Importantly, ES₁AG₄CH₅-DXMCs exhibited a significant therapeutic activity in a mouse model of colitis compared to other DXMCs. Overall, the LBL-coated DXMCs presented here could be a promising colon-targeted therapy for IBD.