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This work investigated the effect of poly(l -lysine) (PLL) molecular weight and concentration on chondrogenesis of cocultures of mesenchymal stem cells (MSCs) and articular chondrocytes (ACs) in PLL-loaded hydrogels. An injectable dual-network hydrogel composed of a poly(N -isopropylacrylamide)-based synthetic thermogelling macromer and a chondroitin sulfate-based biological network was leveraged as a model to deliver PLL and encapsulate the two cell populations. Incorporation of PLL into the hydrogel did not affect the hydrogel's swelling properties and degradation characteristics, nor the viability of encapsulated cells. Coculture groups demonstrated higher type II collagen expression compared to the MSC monoculture group. Expression of hypertrophic phenotype was also limited in the coculture groups. Histological analysis indicated that the ratio of MSCs to ACs was an accurate predictor of the degree of long-term chondrogenesis, while the presence of PLL was shown to have a more substantial short-term effect. Altogether, this study demonstrates that coculturing MSCs with ACs can greatly enhance the chondrogenicity of the overall cell population and offers a platform to further elucidate the short- and long-term effect of polycationic factors on the chondrogenesis of MSC and AC cocultures. Unlabelled Image • Coculturing mesenchymal stem cells (MSCs) with chondrocytes enhanced the chondrogenic differentiation of MSCs in vitro. • The presence of chondrocytes limited the expression of hypertrophic genes from MSCs. • Loaded poly(l -lysine) in the hydrogel transiently affected the gene expression profiles of the encapsulated cell populations. • The extent of cartilage-like matrix secretion depended on the coculture ratio. [ABSTRACT FROM AUTHOR]

Biodegradable and non-toxic multi-block copolymers based on poly(l-lysine) and poly(ethylene glycol) were synthesized. Synthesized copolymers showed almost negligible cytotoxicity above 95% cell viability and transfection efficiency compared to the PLL homopolymer with molecular weight of 25,700. Biodegradation under physiological conditions revealed that the molecular weight of copolymers decreased to 20% of the initial molecular weight within 72 h. Transfection efficiencies of copolymers were not affected by the presence of serum, while that of PLL homopolymer decreased to the level of naked DNA in the presence of serum. Based on the results, the new copolymers are believed to be a potentially efficient carrier for the delivery of bioactive agents. [Copyright &y& Elsevier]

Non-viral gene delivery systems utilise either amine lipids or polyamines and although non-viral gene delivery systems are said to have a superior safety profile to viruses, the polyamines such as poly(l-lysine) are toxic when used without derivatisation and usually require specific receptor mediated uptake and/or endosomolytic agents to be effective. However, the conversion of poly(l-lysine) and poly(l-ornithine) polyamino acids into amphiphilic vesicle forming polymers reduces the toxicity of the polyamino acids and enables the resulting polyamino acid vesicles to deliver genes both in vitro and in vivo in the absence of receptor specific ligands and endosomolytic agents. The incorporation of a distearoylphosphatidylethanolamine poly(ethylene glycol)–galactosamine conjugate (with the galactosamine unit at the distal end of the poly(ethylene glycol) moiety) into the polyamino acid formulations improved in vitro gene transfer in the case of the amphiphilic poly(l-ornithine) (POP) although no in vivo targeting was detected with the galactosamine formulations. We conclude that the conversion of poly(l-lysine) and poly(l-ornithine) into amphiphilic colloid forming molecules reduces their toxicity, thus allowing these systems to be used for gene transfer in vivo. It is possible that this approach may be extended to other polyamines. [Copyright &y& Elsevier]

Poly(lactic-co-glycolic acid) (PLGA)-grafted poly(l-lysine) (PLL) (PLL-g-PLGA) was synthesized to demonstrate its micelle-forming property in an aqueous solution. The micelles were used as a gene delivery carrier. The hydrodynamic diameter of PLL-g-PLGA micelles in an aqueous solution was ca. 149 nm with a narrow size distribution. Critical micelle concentration (cmc) was 9.6 mg/l. The PLL-g-PLGA micelles could be used to produce compact nanoparticulate complexes with plasmid DNA, which could efficiently protect the complexed DNA from enzymatic degradation by DNase I. The micelle/DNA complexes had highly compacted structure sized between 200–300 nm with a positive surface charge value. The PLL-g-PLGA micelles exhibited much higher transfection efficiency with lower cytotoxicity than PLL. Here, we demonstrated that biodegradable and cationic PLL-g-PLGA micelles could be used as an effective DNA condensation carrier for gene delivery system. [Copyright &y& Elsevier]