F Carfì Pavia

PLLA Scaffold via TIPS for Bone Tissue Engineering

Tissue engineering offers a promising new approach to repair bone fractures, fractures that do not heal, and fractures due to bone tumors. In this work, two different approaches were tested in order to obtain Poly-LLactic Acid (PLLA) porous scaffolds via Thermally Induced Phase Separation (TIPS) for bone tissue engineering application. First, the possibility to produce a composite material, by incorporating Hydroxyapatite (HA) particles in a Poly-L-lactic acid (PLLA) matrix was investigated. Two PLLA/HA weight ratios (70/30 and 50/50) were tested. The results showed that the presence of HA does not influence the phase separation process, i.e. the composite scaffolds microstructure is similar to pure PLLA scaffolds. WAXD analysis confirmed the full incorporation of HA particles into the polymer matrix. Moreover, compression tests showed a fourfold increase of Young module with respect to pure PLLA scaffold. Since the production of scaffolds for bone tissue regeneration is a challenging target, scaffolds must mimic the bone morphology, thus requiring a gradient of pore dimension and morphology along one dimension. To attain this goal, the second part of the work describes the design, set up and test of an experimental apparatus able to set different thermal histories on the two sides of a sample. Scaffolds were produced by following various thermal protocols on both sample surfaces. The results showed that through this technique it is possible to produce scaffolds with a pore size that increases along sample thickness. As a matter of fact, the obtained average pore dimension on one side of the sample was about 70 μm, whereas it was around 240 μm on the opposite surface. By moving along the sample thickness, the pore dimension increased steadily. All things considered, a reliable route for the production of composite PLLA/HA scaffolds with a controlled pore size distribution was assessed, thus offering a valid support to bone tissue engineering.

A poly-L-lactic acid/ collagen/glycosaminoglycan matrix for tissue engineering applications

Adhesion of tissue cells to biomaterials is a prerequisite of paramount importance for the effectiveness of a tissue engineering construct (cell and scaffolds). Functionalization of polymeric scaffolds with organic polymers, such as collagen or proteoglycans, is a promising approach in order to improve the cytocompatibility. As a matter of fact, organic polymers, isolated directly from the extracellular matrix, contain a multitude of surface ligand (fibronectin, laminin, vitronectin) and arginine–glycine–aspartic acid-containing peptides that promote cell adhesion. In tissue engineering, the combination of organic and synthetic polymers gives rise to scaffolds characterized simultaneously by the mechanical strength of synthetic materials and the biocompatibility of natural materials. In this work, porous poly-L-lactide acid scaffolds were functionalized with a synthetic collagen–glycosaminoglycans matrix in order to improve cell adhesion. For this purpose, a protocol for collagen–glycosaminoglycans conjugation into the pores of the scaffolds was set up. Moreover, an innovative protocol for the quantification of the conjugated glycosaminoglycans inside the scaffolds was created and adopted. The results have confirmed the effectiveness of the developed protocol: a collagen–glycosaminoglycans conjugation, with an efficiency of about 21% was obtained inside the scaffold. Moreover, SEM analysis highlighted the presence of the homogeneous synthetic matrix into the bulk of porous scaffolds. Finally, cell culture assays carried out by utilizing mouse embryonic fibroblasts showed that cell proliferation on poly-L-lactide acid-collagen–glycosaminoglycans scaffold is higher than on poly-L-lactide acid collagen scaffold (utilized as control). Therefore, it can be stated that the presence of glycosaminoglycans not only increases the mechanical strength of the matrix, thanks to their cross-linking effect, but also it seems to lead to a more significant cell growth. Overall, it is reasonable to state that the concerned protocol may be proposed as a reliable route to increase the rate of proliferation and in some cases to stimulate the cell differentiation in tissue engineering devices.

Polymeric scaffolds prepared via Thermally Induced Phase Separation (TIPS): tuning of structure and morphology

Scaffolds suitable for tissue engineering applications were prepared by Thermally Induced Phase Separation (TIPS) starting from a ternary solution PLLA/dioxane/water. The experimental protocol consisted of three consecutive steps, a first quench from the homogeneous solution to an appropriate demixing temperature (within the metastable region), a holding stage for a given residence time and a final quench from the demixing temperature to a low temperature (within the unstable region). A large variety of morphologies, in terms of average pore size and interconnection, were obtained upon modifying the demixing time and temperature, owing to the interplay of nucleation and growth processes during the residence in the metastable state. An interesting combination of micro and macro‐porosity was observed for long residence times in the metastable state (above 30 min at 35°C).