Direct Synthesis of Peptide-Containing Silicones: A New Way to Bioactive Materials.

A simple and efficient way to synthesize peptide-containing silicone materials is described. Silicone oils containing a chosen ratio of bioactive peptide sequences were prepared by acid-catalyzed copolymerization of dichlorodimethylsilane, hybrid dichloromethyl peptidosilane, and Si(vinyl)- or SiH-functionalized monomers. Functionalized silicone oils were first obtained and then, after hydrosilylation cross-linking, bioactive polydimethylsiloxane (PDMS)-based materials were straightforwardly obtained. The introduction of an antibacterial peptide yielded PDMS materials showing activity against Staphylococcus aureus. PDMS containing RGD ligands showed improved cell-adhesion properties. This generic method was fully compatible with the stability of peptides and thus opened the way to the synthesis of a wide range of biologically active silicones.

Double-Hydrophilic Block Copolymers Based on Functional Poly(ε-caprolactone)s for pH-Dependent Controlled Drug Delivery.

The use of double-hydrophilic block copolymers (DHBCs) in biomedical applications is limited by their lack of degradability. This additional functionality has been obtained in the past through multistep chemical strategies associated with low yields. In this work, a series of DHBCs composed of a bioeliminable poly(ethylene glycol) (PEG) block and hydrolyzable functional poly(ε-caprolactone) (PCL) blocks bearing carboxylic (PEG-b-PCL(COOH)), amino (PEG-b-PCL(NH2)), or hydroxyl side groups (PEG-b-PCL(OH)) is synthesized in only three steps. DHBCs with 50% substitution degree with respect to the CL units are obtained for all functional groups. The pH-dependent self-assembly behavior of the DHBCs is studied showing critical micelle concentration (CMC) variations by a factor of 2 upon pH changes and micellar mean diameter variations of 20-30%. The potential of these partly degradable DHBCs as drug-loaded polyion complex micelles is further exemplified with the PEG-b-PCL(COOH) series that is associated with the positively charged anticancer drug doxorubicin (DOX). Encapsulation efficiencies, drug loadings, pH-controlled release, and cytotoxicity of the DOX-loaded micelles toward cancer cells are demonstrated. This set of data confirms the interest of the proposed straightforward chemical strategy to generate fully bioeliminable and partly degradable DHBCs with potential as pH-responsive drug-delivery systems.

Dual-Crosslinked Degradable Elastomeric Networks With Self-Healing Properties: Bringing Multi(catechol) Star-Block Copolymers into Play.

In the biomedical field, degradable chemically crosslinked elastomers are interesting materials for tissue engineering applications, since they present rubber-like mechanical properties matching those of soft tissues and are able to preserve their three-dimensional (3D) structure over degradation. Their use in biomedical applications requires surgical handling and implantation that can be a source of accidental damages responsible for the loss of properties. Therefore, their inability to be healed after damage or breaking can be a major drawback. In this work, biodegradable dual-crosslinked networks that exhibit fast and efficient self-healing properties at 37 °C are designed. Self-healable dual-crosslinked (chemically and physically) elastomeric networks are prepared by two methods. The first approach is based on the mix of hydrophobic poly(ethylene glycol)-poly(lactic acid) (PEG-PLA) star-shaped copolymers functionalized with either catechol or methacrylate moieties. In the second approach, hydrophobic bifunctional PEG-PLA star-shaped copolymers with both catechol and methacrylate on their structure are used. In the two systems, the supramolecular network is responsible for the self-healing properties, thanks to the dynamic dissociation/reassociation of the numerous hydrogen bonds between the catechol groups, whereas the covalent network ensures mechanical properties similar to pure methacrylate networks. The self-healable materials display mechanical properties that are compatible with soft tissues and exhibit linear degradation because of the chemical cross-links. The performances of networks from mixed copolymers versus bifunctional copolymers are compared and demonstrate the superiority of the latter. The biocompatibility of the materials is also demonstrated, confirming the potential of these degradable and self-healable elastomeric networks to be used for the design of temporary medical devices.

Degradable double hydrophilic block copolymers and tripartite polyionic complex micelles thereof for small interfering ribonucleic acids (siRNA) delivery.

Polymer vectors for gene therapy have been largely investigated as an alternative to viral vectors. In particular, double hydrophilic block copolymers (DHBCs) have shown potential in this domain, but to date studies mainly focus on non-degradable copolymers, which may be a restriction for further development. To overcome this limitation, we synthesized a DHBC (PEG43-b-PCL12(COOH)6.5) composed of a poly(ethylene glycol) (PEG) non-ionic and bioeliminable block and a degradable carboxylic acid-functionalized poly(ε-caprolactone) (PCL) block. The potential of this DHBC as an original vector for small interfering ribonucleic acids (siRNA) to formulate tripartite polyionic complex (PIC) micelles with poly(lysine) (PLL) was evaluated. We first studied the impact of the charge ratio (R) on the size and the zeta potential of the resulting micelles. With a charge ratio R = 1, one formulation with optimized physico-chemical properties showed the ability to complex 75% of siRNA. We showed a stability of the micelles at pH 7.4 and a disruption at pH 5, which allowed a pH-triggered siRNA release and proved the pH-stimuli responsive character of the tripartite micelles. In addition, the tripartite PIC micelles were shown to be non-cytotoxic below 40 µg/mL. The potential of these siRNA vectors was further evaluated in vitro: it was found that the tripartite PIC micelles allowed siRNA internalization to be 3 times higher than PLL polyplexes in murine mesenchymal stem cells, and were able to transfect human breast cancer cells. Overall, this set of data pre-validates the use of degradable DHBC as non-viral vectors for the encapsulation and the controlled release of siRNA, which may therefore constitute a sound alternative to non-degradable and/or cytotoxic polycationic vectors.

Reverse poly(ε-caprolactone)-g-dextran graft copolymers. Nano-carriers for intracellular uptake of anticancer drugs.

A new fully biodegradable "reverse" oligosaccharide-based amphiphilic graft copolymer structure with a hydrophobic backbone and hydrophilic side chains, poly(ε-caprolactone)-g-dextran (PCL-g-Dex) was synthetized. For this purpose, "clickable" propargylated PCL (PCL-yne) and azido-dextran (Dex-N3) were prepared to further synthesize PCL-g-Dex copolymer by a Huisgen's cycloaddition. This "reverse" copolymer architecture self-assembled in biodegradable nano-carriers, in the shape of dynamic polymeric micelles, and were loaded with doxorubicin (Dox) anti-cancer drug. Dox-loaded micelles showed different drug releases depending on the pH. Cytotoxicity tests showed that Dox-loaded micelles can selectively kill colon cancer cells (HCT-116) while they have no cytotoxic effect towards healthy cells (CCD-45SK). Fluorescent micelles based on FITC-labelled PCL-g-Dex copolymer were used for fluorescence imaging and flow cytometry assays. These experiments proved the effective and specific internalization of micelles by cancer cells, whereas healthy cells showed a very poor uptake. These results show that PCL-g-Dex micelles may be a promising Dox nano-carrier in cancer chemotherapy.

Ultrafast in situ forming poly(ethylene glycol)-poly(amido amine) hydrogels with tunable drug release properties via controllable degradation rates.

Fast in situ forming, chemically crosslinked hydrogels were prepared by the amidation reaction between N-succinimidyl ester end groups of multi-armed poly(ethylene glycol) (PEG) and amino surface groups of poly(amido amine) (PAMAM) dendrimer generation 2.0. To control the properties of the PEG/PAMAM hydrogels, PEGs were used with different arm numbers (4 or 8) as well as different linkers (amide or ester) between the PEG arms and their terminal N-succinimidyl ester groups. Oscillatory rheology measurements showed that the hydrogels form within seconds after mixing the PEG and PAMAM precursor solutions. The storage moduli increased with crosslink density and reached values up to 2.3 kPa for hydrogels based on 4-armed PEG. Gravimetrical degradation experiments demonstrated that hydrogels with ester linkages between PEG and PAMAM degrade within 2 days, whereas amide-linked hydrogels were stable for several months. The release of two different model drugs (fluorescein isothiocyanate-dextran with molecular weights of 4·103 and 2·106 g/mol, FITC-DEX4K and FITC-DEX2000K, respectively) from amide-linked hydrogels was characterized by an initial burst followed by diffusion-controlled release, of which the rate depended on the size of the drug. In contrast, the release of FITC-DEX2000K from ester-containing hydrogels was governed mainly by degradation of the hydrogels and could be modulated via the ratio between ester and amide linkages. In vitro cytotoxicity experiments indicated that the PEG/PAMAM hydrogels are non-toxic to mouse fibroblasts. These in situ forming PEG/PAMAM hydrogels can be tuned with a broad range of mechanical, degradation and release properties and therefore hold promise as a platform for the delivery of therapeutic agents.

In vivo evaluation of hybrid patches composed of PLA based copolymers and collagen/chondroitin sulfate for ligament tissue regeneration.

Biomaterials for soft tissues regeneration should exhibit sufficient mechanical strength, demonstrating a mechanical behavior similar to natural tissues and should also promote tissues ingrowth. This study was aimed at developing new hybrid patches for ligament tissue regeneration by synergistic incorporation of a knitted structure of degradable polymer fibers to provide mechanical strength and of a biomimetic matrix to help injured tissues regeneration. PLA- Pluronic® (PLA-P) and PLA-Tetronic® (PLA-T) new copolymers were shaped as knitted patches and were associated with collagen I (Coll) and collagen I/chondroitine-sulfate (Coll CS) 3-dimensional matrices. In vitro study using ligamentocytes showed the beneficial effects of CS on ligamentocytes proliferation. Hybrid patches were then subcutaneously implanted in rats for 4 and 12 weeks. Despite degradation, patches retained strength to answer the mechanical physiological needs. Tissue integration capacity was assessed with histological studies. We showed that copolymers, associated with collagen and chondroitin sulfate sponge, exhibited very good tissue integration and allowed neotissue synthesis after 12 weeks in vivo. To conclude, PLA-P/CollCS and PLA-T/CollCS hybrid patches in terms of structure and composition give good hopes for tendon and ligament regeneration. © 2016 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 105B: 1778-1788, 2017.