Favoring osseointegration and avoiding bacterial contamination are the key challenges in the design of implantable devices for orthopedic applications. To meet these goals, a promising route is to tune the biointerface of the devices, that can regulate interactions with the host cells and bacteria, by using nanostructured antibacterial and bioactive coatings. Indeed, the selection of adequate metal-based coatings permits to discourage infection while avoiding the development of bacterial resistance and nanostructuring permits to tune the release of the antimicrobial compounds, allowing high efficacy and decreasing possible cytotoxic effects. In addition, metal-doped calcium phosphates-based nanostructured coatings permit to tune both composition and morphology of the biointerfaces, allowing to regulate host cells and bacteria response. To tune the biointerfaces of implantable devices, nanostructured coatings can be used, but their use is challenging when the substrate is heat-sensitive and/or porous.

Here, we propose the use of Ionized Jet Deposition (IJD) to deposit metallic and ion-doped calcium phosphates materials onto different polymeric substrates, without heating and damaging the substrate morphology. 3D printed scaffolds in polylactic acid (PLA) and polyurethane (PU), and electrospun matrices in polycaprolactone (PCL) and PLA were used as substrates. Biogenic apatite (HA), ion doped (zinc, copper and iron) tricalcium phosphate (TCP) and silver (Ag) coatings were obtained on porous and custom-made polymeric substrates.

Chemical analyses confirmed that coatings composition matches that of the target materials, both in terms of main phase (HA or TCP) and ion doping (presence of Cu, Zn or Fe ion). Deposition parameters, and especially its duration time, influence the coating features (morphology and thickness) and substrate damage. Indeed, SEM/EDS observations show the presence of nanostructured agglomerates on substrates surface. The dimensions of the aggregates and the thickness of the coating films increase increasing the deposition time, without affecting the substrate morphology (no porosity alteration or fibers damaging). The possible substrate damage is influenced by target and substrate material, but it can be avoided modulating deposition time.

Once the parameters are optimized, the models show suitable in vitro biological efficacy for applications in bone models, regenerative medicine and infection. Indeed, HA-based coatings favor cells adhesion on printed and electrospun fibers. For antibacterial applications, the ion doped TCP coatings can reduce the bacterial growth and adhesion (E.coli and S.aureus) on electrospun matrices.

To conclude, it is possible achieve different properties applying nanostructured coatings with IJD technique on polymeric substrates, modulating deposition conditions to avoid substrate damage.

Tendon regeneration is complex since the scaffold has to bear high loads and stress concentrations, while providing suitable deformability. Previous studies demonstrated a physiological orientation of the fibers and good cell adhesion on electrospun polymeric scaffolds [1]. The aims of this work were to: (i) prepare and characterize electrospun resorbable scaffolds with different compositions and (ii) develop a process to produce a multiscale bundle assembly to mimic the hierarchical structure and biomechanical properties of a real tendon.

We produced fibrous scaffolds made of blends of poly-L-lactic acid (PLLA) and collagen (Coll):

Pure PLLA;

In order to prepare 3D bundles made of aligned fibres, we used a high-speed rotating collector. The electrospun nanofibers were deposited tangentially onto the drum, the electrospun layer was manually rolled transversely along the drum and then removed. The bundles were approximately 150 mm long and 300–450 mm in diameter. Five specimens were prepared and tested for each blend.

To evaluate the mechanical properties of the bundles a tension test was applied with capstan grips on a testing machine with a 100N load cell, under the following conditions:

Gauge length: 20 mm.

For all the bundles, the stress-strain curve showed an initial non-linear part (toe region), similar to the laxity of the tendon at rest. The mechanical analysis confirmed the outstanding ductility and toughness of pure PLLA. Increasing the percentage of collagen resulted in a reduction of ductility. The PLLA/Coll 50/50 had a rather brittle behaviour.

The values of mechanical properties found for the different compositions were slightly lower but of the same order of magnitude as tendon fibers (Failure stress: 33.7±19.2 MPa; Failure strain: 21.0±9.1 %; Young Modulus: 257±101 MPa [2]). The bundles made of pure PLLA had a failure stress of 13.2±0.8 MPa; failure strain of 84.7±9.4%; Young Modulus of 78.6±7.5 MPa. The bundles made of PLLA/Coll 50/50 had: failure stress of 10.5±1.5 MPa; failure strain of 21.4±2.7%, Young Modulus of 65.7±9.8 MPa. The most promising composition was the PLLA/Coll 75/25, with a failure stress of 14.0±0.7 MPa; failure strain of 40.3±2.2 %, Young Modulus of 98.6±12 MPa.

We also tested bundles mechanical properties after aging samples in phosphate buffer at 37 °C for 48 hours, 7 and 14 days. After ageing, stress and strain values were progressively lower, while the toughness increased, compared to the dry samples.

The promising results found in this work for the electrospun PLLA-collagen blends confirm their potential use for tendon tissue regeneration. This is a starting point for developing multiscale scaffolds mimicking the structure of tendon tissue, which can potentially be used in human regenerative medicine both as bioresorbable prosthesis, or inserted in a bioreactor for in vitro production of tendon tissue.