Chiara Gualandi

Electrospun gelatin nanofibers: Optimization of genipin cross-linking to preserve fiber morphology after exposure to water

The development of suitable biomimetic three-dimensional scaffolds is a fundamental requirement of tissue engineering. This paper presents the first successful attempt to obtain electrospun gelatin nanofibers cross-linked with a low toxicity agent, genipin, and able to retain the original nanofiber morphology after water exposure. The optimized procedure involves an electrospinning solution containing 30 wt.% gelatin in 60/40 acetic acid/water (v/v) and a small amount of genipin, followed by further cross-linking of the as-electrospun mats in 5% genipin solution for 7 days, rinsing in phosphate-buffered saline and then air drying at 37°C. The results of scanning electron microscopy investigations indicated that the cross-linked nanofibers were defect free and very regular and they also maintained the original morphology after exposure to water. Genipin addition to the electrospinning solution dramatically reduced the extensibility of the as-electrospun mats, which displayed further remarkable improvements in elastic modulus and stress at break after successive cross-linking up to values of about 990 and 21 MPa, respectively. The results of the preliminary in vitro tests carried out using vascular wall mesenchymal stem cells indicated good cell viability and adhesion to the gelatin scaffolds.

Effect of Electrospun Fiber Diameter and Alignment on Macrophage Activation and Secretion of Proinflammatory Cytokines and Chemokines

Macrophage activation can be modulated by biomaterial topography according to the biological scale (micrometric and nanometric range). In this study, we investigated the effect of fiber diameter and fiber alignment of electrospun poly(L-lactic) (PLLA) scaffolds on macrophage RAW 264.7 activation and secretion of proinflammatory cytokines and chemokines at 24 h and 7 days. Macrophages were cultured on four different types of fibrous PLLA scaffold (aligned microfibers, aligned nanofibers, random microfibers, and random nanofibers) and on PLLA film (used as a reference). Substrate topography was found to influence the immune response activated by macrophages, especially in the early inflammation stage. Secretion of proinflammatory molecules by macrophage cells was chiefly dependent on fiber diameter. In particular, nanofibrous PLLA scaffolds minimized the inflammatory response when compared with films and microfibrous scaffolds. The histological evaluation demonstrated a higher number of foreign body giant cells on the PLLA film than on the micro- and nanofibrous scaffolds. In summary, our results indicate that the diameter of electrospun PLLA fibers, rather than fiber alignment, plays a relevant role in influencing in vitro macrophage activation and secretion of proinflammatory molecules.

Scaffold for tissue engineering fabricated by non-isothermal supercritical carbon dioxide foaming of a highly crystalline polyester

Porous scaffolds of a random co-polymer of omega-pentadecalactone (PDL) and epsilon-caprolactone (CL) (poly(PDL-CL)), synthesized by biocatalysis, were fabricated by supercritical carbon dioxide (scCO(2)) foaming. The co-polymer, containing 31 mol.% CL units, is highly crystalline (T(m) = 82 degrees C, DeltaH(m) = 105 J g(-1)) thanks to the ability of the two monomer units to co-crystallize. The co-polymer can be successfully foamed upon homogeneous absorption of scCO(2) at T > T(m). The effect of soaking time, depressurization rate and cooling rate on scaffold porosity, pore size distribution and pore interconnectivity was investigated by micro X-ray computed tomography. Scaffolds with a porosity in the range 42-76% and an average pore size of 100-375 microm were successfully obtained by adjusting the main foaming parameters. Process conditions in the range investigated did not affect the degree of crystallinity of poly(PDL-CL) scaffolds. A preliminary study of the mechanical properties of the scaffolds revealed that poly(PDL-CL) foams may find application in the regeneration of cartilage tissue.

Co-electrospun gelatin-poly(L-lactic acid) scaffolds: modulation of mechanical properties and chondrocyte response as a function of composition.

Bio-synthetic scaffolds of interspersed poly(l-lactic acid) (PLLA) and gelatin (GEL) fibers are fabricated by co-electrospinning. Tailored PLLA/GEL compositions are obtained and GEL crosslinking with genipin provides for the maintenance of good fiber morphology. Scaffold tensile mechanical properties are intermediate between those of pure PLLA and GEL and vary as a function of PLLA content. Primary human chondrocytes grown on the scaffolds exhibit good proliferation and increased values of the differentiation parameters, especially for intermediate PLLA/GEL compositions. Mineralization tests enable the deposition of a uniform layer of poorly crystalline apatite onto the scaffolds, suggesting potential applications involving cartilage as well as cartilage-bone interface tissue engineering.

Poly(butylene/diethylene glycol succinate) multiblock copolyester as a candidate biomaterial for soft tissue engineering: Solid-state properties, degradability, and biocompatibility

A multiblock bioresorbable copolyester, poly(butylene/diethylene glycol succinate), was synthesized by reactive blending, and it was used, together with the corresponding poly(butylene succinate) homopolymer, to form films and to fabricate biomimetic electrospun scaffolds. The poly(butylene/diethylene glycol succinate) scaffold had a more pronounced elastomeric behavior than poly(butylene succinate). It also underwent hydrolytic degradation faster than poly(butylene succinate) since the incorporated diethylene glycol succinate units rendered the copolymer more hydrophilic than poly(butylene succinate). The films degraded faster than electrospun samples due to the autocatalytic effect of carboxylic end-groups. The biodegradable poly(butylene/diethylene glycol succinate) scaffold supported the growth and preserved the cardiac phenotype markers of H9c2 cells, demonstrating its potential utility in soft tissue engineering applications.

Advantages of Surface-Initiated ATRP (SI-ATRP) for the Functionalization of Electrospun Materials

Surface-initiated atom transfer radical polymerization (SI-ATRP) is successfully applied to electrospun constructs of poly(L-lactide). ATRP macroinitiators are adsorbed through polyelectrolyte complexation following the introduction of negative charges on the polyester surface through its blending with a six-armed carboxy-terminated oligolactide. SI-ATRP of glycerol monomethacrylate (GMMA) or 2-(N,N-diethylamino)ethyl methacrylate (DEAEMA) allows then to grow surface films with controllable thickness, and in this way also to control the wetting and interactions of the construct.

Easily synthesized novel biodegradable copolyesters with adjustable properties for biomedical applications

Current compositions of biodegradable aliphatic polyesters experience a number of limitations associated with the difficulty of customizing mechanical, physicochemical, and biological properties for different biomedical applications. In this study, we propose a new class of multiblock copolyesters made using butylene succinate (BS) and triethylene succinate (TES). In particular, four copolyesters with the same chemical composition but different block lengths – P(BS18TES18), P(BS9TES9), P(BS4TES4), and P(BS2TES2) – were synthesized by reactive blending. Physicochemical characterization (DSC, WAXS, tensile tests, WCA, hydrolysis experiments) demonstrated that, by simply varying block length, it is possible to control polymer crystallinity, thermal and mechanical properties, wettability, and degradation rate. Copolymers displayed different stiffness, depending on the crystallinity degree, a tunable range of degradation rates, and different surface hydrophilicity. In vitro drug release and cell culture experiments were performed to evaluate the potential of these new copolyesters in the biomedical field. In particular, fluorescein isothiocyanate (FITC) was used as a model molecule to study the release profile of small molecules, and polymer cytocompatibility and fibronectin absorption capability were assessed. Depending on comonomer distribution, the polyesters are capable of releasing FITC in a tailorable manner. Moreover, the newly developed biomaterials are not cytotoxic and they are able to absorb proteins and, consequently, to tailor cell adhesion according to their surface hydrophilicity.

Nanovascularization of polymer matrix: generation of nanochannels and nanotubes by sacrificial electrospun fibers.

Several methods for creating vascular structures, made of either discrete or interconnected channels have been developed. The currently employed methods enable the formation of channels with diameters in the millimetric and micrometric scale. However, the formation of an interconnected three-dimensional (3D) vasculature by using a rapid and scalable process is a challenge and largely limits the fields of applicability of these innovative materials. Here, we propose the use of electrospun nonwoven mats as sacrificial fibers to easily generate 3D macroscale vascularized composites containing interconnected networks with channels and tubes having submicrometric and nanometric diameters. The novel approach has the potentialities to give rise to a novel generation of composites potentially displaying new and enhanced functionalities thanks to the nanoscale features of the cavities.

Tailoring chemical and physical properties of fibrous scaffolds from block copolyesters containing ether and thio-ether linkages for skeletal differentiation of human mesenchymal stromal cells

Bioactive scaffolds for tissue engineering call for demands on new materials which can enhance traditional biocompatibility requirements previously considered for clinical implantation. The current commercially available thermoplastic materials, such as poly(lactic acid) (PLA), poly(glycolic acid) (PGA), poly(ε-caprolactone) (PCL) and their copolymers, have been used to fabricate scaffolds for regenerative medicine. However, these polymers have limitations including lacking of broadly tuning mechanical and degradable properties, and activation of specific cell-scaffold interactions, which limit their further application in tissue engineering. In the present study, electrospun scaffolds were successfully fabricated from a new class of block poly(butylene succinate)-based (PBS-based) copolyesters containing either butylene thiodiglycolate (BTDG) or butylene diglycolate (BDG) sequences. The polyesters displayed tunable mechanical properties and hydrolysis rate depending on the molecular architecture and on the kind of heteroatom introduced along the polymer backbone. To investigate their potential for skeletal regeneration, human mesenchymal stromal cells (hMSCs) were cultured on the scaffolds in basic, osteogenic and chondrogenic media. Our results demonstrated that PBS-based copolyesters containing thio-ether linkages (i.e. BTDG segments) were more favorable for chondrogenesis of hMSCs than those containing ether linkages (i.e. BDG sequences). In contrast, PBS-based copolyesters containing ether linkages showed enhanced mineralization. Therefore, these new functional scaffolds might hold potential for osteochondral tissue engineering applications.

Effect of oxide nanoparticles on thermal and mechanical properties of electrospun separators for lithium-ion batteries

This study reports the fabrication and characterization of poly(ethylene oxide) (PEO) and poly(vinylidenefluoride-cochlorotrifluoroethylene) (PVDF-CTFE) nanofibrous separators for lithium-ion batteries loaded with different amounts of fumedsilica and tin oxide nanoparticles. Membrane morphological characterization (SEM, TEM) showed the presence of good-quality nanofibres containing nanoparticles. Thermal degradation and membrane mechanical properties were also investigated, and a remarkable effect of nanoparticle addition on membrane mechanical properties was found. In particular, PEO membranes were strengthened by the addition of metal oxide, whereas PVDF-CTFE membranes acquired ductility.