Biomaterials Tailoring at the Nanoscale for Tissue Engineeringand Advanced Therapies

The definition of the term “biomaterial” dates back to 1991, during the 2nd Consensus Conference on the Definitions in Biomaterials organized by the European Society of Biomaterials in Chester (UK) [...

Use of Polyesters in Fused Deposition Modeling for Biomedical Applications

In recent years, 3D printing techniques experience a growing interest in several sectors, including the biomedical one. Their main advantage resides in the possibility to obtain complex and personalized structures in a cost-effective way impossible to achieve with traditional production methods. This is especially true for fused deposition modeling (FDM), one of the most diffused 3D printing methods. The easy customization of the final products' geometry, composition, and physicochemical properties is particularly interesting for the increasingly personalized approach adopted in modern medicine. Thermoplastic polymers are the preferred choice for FDM applications, and a wide selection of biocompatible and biodegradable materials is available to this aim. Moreover, these polymers can also be easily modified before and after printing to better suit the body environment and the mechanical properties of biological tissues. This review focuses on the use of thermoplastic aliphatic polyesters for FDM applications in the biomedical field. In detail, the use of poly(epsilon-caprolactone), poly(lactic acid), poly(lactic-co-glycolic acid), poly(hydroxyalkanoate)s, thermoplastic poly(ester urethane)s, and their blends is thoroughly surveyed, with particular attention to their main features, applicability, and workability. The state-of-the-art is presented and current challenges in integrating the additive manufacturing technology in the medical practice are discussed

Designing multifunctional devices for regenerative pharmacology based on 3D scaffolds, drug-loaded nanoparticles, and thermosensitive hydrogels: a proof-of-concept study

Regenerative pharmacology combines tissue engineering/regenerative medicine (TERM) with drug delivery with the aim to improve the outcomes of traditional TERM approaches. In this work, we aimed to design a multicomponent TERM platform comprising a three-dimensional scaffold, a thermosensitive hydrogel, and drug-loaded nanoparticles. We used a thermally induced phase separation method to obtain scaffolds with anisotropic mechanical properties, suitable for soft tissue engineering. A thermosensitive hydrogel was developed using a Poloxamer® 407-based poly(urethane) to embed curcumin-loaded nanoparticles, obtained by the single emulsion nanoprecipitation method. We found that encapsulated curcumin could retain its antioxidant activity and that embedding nanoparticles within the hydrogel did not affect the hydrogel gelation kinetics nor the possibility to progressively release the drug. The porous scaffold was easily loaded with the hydrogel, resulting in significantly enhanced (4-fold higher) absorption of a model molecule of nutrients (fluorescein isothiocyanate dextran 4kDa) from the surrounding environment compared to pristine scaffold. The developed platform could thus represent a valuable alternative in the treatment of many pathologies affecting soft tissues, by concurrently exploiting the therapeutic effects of drugs, with the 3D framework acting as a physical support for tissue regeneration and the cell-friendly environment represented by the hydrogel

Thermosensitive bioartificial hydrogels as smart injectable and biocompatible systems allowing post-injection chemical crosslinking

Introduction Injectable hydrogels as carriers for drugs and/or cells have gained increasing interest in the last years due to the possibility to vehicle their payload in the desired loco through mini-invasive procedures [1, 2]. In this work, a new library of bioartificial hydrogels was designed combining the chemical versatility and reproducible physicochemical properties of a synthetic polymer with the enhanced cell adhesiveness of a natural polymer. Specifically, an amphiphilic polyurethane (PEU) bearing amino groups was first synthesised and then blended with hyaluronic acid (HA) to obtain thermosensitive bioartificial formulations. The influence of HA molecular weight on polymers miscibility was investigated as well as the thermosensitivity and the injectability of the newly designed bioartificial systems. Modification of the PEU and the HA may allow post-injection chemical crosslinking enhancing the chemical stability of the hydrogel. Experimental Methods The amphiphilic PEU was synthesised in a two step procedure under nitrogen by reacting a commercial triblock copolymer (Poloxamer 407, Poly(ethylene oxide)-Poly(propylene oxide)-Poly(ethylene oxide)) with 1,6-hexamethylene diisocyanate. Then, the prepolymer was chain extended with a diol (N-Boc diethanolamine) containing protected secondary amino groups. Infrared (IR) spectroscopy and Size Exclusion Chromatography (SEC) were then performed to assess the success of the synthesis and to evaluate PEU molecular weight, respectively. Subsequently, the synthesised PEU was subjected to an acidic treatment in chloroform/trifluoroacetic acid 90/10 V/V to remove BOC-protecting groups and the exposed secondary amino groups were quantified through a colorimetric assay (Orange Sodium salt). The synthetic component (D-DHP407) was then blended with a high (HA_400kDa) and low (HA_82kDa) molecular weight HA, reaching different weight ratios. Lastly, formulations were prepared by dissolving both polymers in physiological saline solution and then characterized in terms of thermosensitivity by means of tube investing test and gelation time test at 37 °C; injectability in the sol state through needles of different diameters (G18, G21 and G22) and cytocompatibility according to ISO10993-5. Secondary amino groups in PEU and carboxyl groups in HA may be exploited to graft functional molecules for in situ post-injection crosslinking. Results and Discussion The successful PEU synthesis was proved through IR spectroscopy by the appearance of new bands ascribed to urethane bonds, while SEC analysis gave a molecular weight in the range 30000 – 35000 Da with 1.4 polydispersity index. Secondary amino groups were quantified to be 4.5x1020 groups/g of polymer by means of Orange II Sodium Salt assay. For what concerns hydrogel preparation, D-DHP407 and HA_400kDa were mixed at 98/2, 95/5, 92/8, 88/12 and 83/17 wt. ratios. All tested formulations formed compatible blends, but, due to the high molecular weight of HA_400kDa, further increase in the natural component content highly increased system viscosity affecting injectability. Hence, D-DHP407 was blended with a low molecular weight HA (HA_82kDa) obtaining compatible and injectable blends even at 50/50 wt. ratio. Subsequently, hydrogel temperature-driven gelation was tested and all considered formulations turned out to gel within few minutes at 37 °C, thus suggesting that HA introduction did not affect PEU thermosensitivity. Regarding hydrogel injectability, all blends could not be extruded through G22 needle, while they could be injected through larger needle diameters (G21 and G18). Finally, by increasing HA content, thus decreasing the synthetic component, an increase of hydrogel biocompatibility was observed. Conclusion A new platform of thermosensitive bioartificial hydrogels was developed by blending a custom-made amphiphilic polyurethane, which ensures hydrogel thermo-responsiveness, with hyaluronic acid, responsible for an improved cytocompatibility. Furthermore, the presence of exposed secondary amino groups along PEU chains and carboxylic groups in HA chains opens the possibility to graft functional moieties to both molecules for post-injection crosslinking. Such injectable system is under development as a matrix for in situ treatment of myocardial tissue, by releasing agents promoting direct reprogramming of cardiac fibroblasts into cardiomyocytes. References [1]Zhang Z., Expert. Opin. Biol. Ther., 17:1, 49-62, 2017. [2] Boffito M. et al., J. Biomed. Mater. Res. A, 103(3):1276-90, 2015. Acknowledgement The activity has been carried within the research project BIORECAR. This project has received funding from the European Research Council (ERC) under the European Union’s Horizon 2020 research and innovation programme (grant agreement No 772168)

Supramolecular hydrogels based on custom-made poly(ether urethane)s and cyclodextrins as potential drug delivery vehicles: design and characterization

The design of supramolecular (SM) hydrogels based on host-guest complexes represents an effective strategy to develop drug delivery systems. In this work, we designed SM hydrogels based on α-cyclodextrin and high-molar mass amphiphilic poly(ether urethane)s (PEUs, ) based on Poloxamer® 407 and differing in their chain extender. The successful formation of poly(pseudo)rotaxanes and their supramolecular interactions were chemically demonstrated. Then, self-healing (80-100% mechanical recovery) supramolecular hydrogels were developed by mixing PEU and α-cyclodextrin solutions at different concentrations. Stability in physiological-like environment and mechanical properties improved with increasing α-cyclodextrin content (9-10% w/v), meanwhile gelation time decreased. A synergistic effect of poly(pseudo)rotaxanes crystals and PEU micellar structures on gel properties was observed: the first were predominant at low PEU concentrations (1-5% w/v), while the latter prevailed at high PEU concentrations (7-9% w/v). Increasing PEU concentration led to gels with increased dissolution rate, not-fully developed networks and slight cytotoxicity, meanwhile residence time in aqueous media improved (>7 d). At low PEU concentrations (1-5% w/v), cytocompatible gels (100% cell viability) were obtained, which maintained their shape in aqueous medium up to 5 d and completely dissolved within 7 d. PEU chemical composition affected PEU/α-cyclodextrin interactions, with longer gelation time and lower mechanical properties in gels based on PEU with pendant functionalities. Gels progressively released a model molecule (fluorescein isothiocyanate-dextran) within 3-4 days with no initial burst release. We thus demonstrated the suitability of custom-made PEUs as constituent of SM hydrogels with α-cyclodextrin and the high potential of the resulting systems for drug delivery applications