Aims: A mounting research effort has recently been devoted to design a biocompatible, sterile and safe material as nucleus polposus substitute.

Several chemical modifications of Hyaluronic acid (HA), a biodegradable linear polysaccharide, have been devised to provide mechanically and chemically robust materials in medical applications.

This study was specially designed to assess whether such a kind of materials are capable to substitute natural NP by suitable viscoelastic properties.

Methods: The NPs were obtained from pigs (L4-L5, L6-L7). Bromide of 2-Hydroxy-4-hydroxyethoxy-2-methyl-propriophenone ester of HA (50% of degree of esterification, cross-linked gel) (HYAFF120p50A8) and dodecylic amide of Hyaluronic acid (11% of carboxyl group substitution of 200 kDa HA) (HYADD3A8) solutions, supplied by FAB, were studied at different ionic strength (0 and 0.15M).

Small amplitude oscillatory shear tests were performed to study linear viscoelastic properties by using a strain controlled rheometer (Bohlin VOR). In particular, the elastic modulus (G’) and the viscous modulus G’’ were evaluated.

Results: Porcine NP showed a rheological behaviour typical of “weak gel”. Indeed, G’ values were always higher than G” ones all over the frequency range and both moduli were almost frequency independent. In particular, at 1 Hz G’ and G” values were respectively 310 and 81 Pa.

The same rheological behaviour was observed for all HA derivatives. In particular, G’ and G’’ were respectively equal to 400 and 91Pa for HYADD3A8 solutions at 1Hz and at 20mg/ml (0,15M), and 210 and 51Pa for HYAFF120p50A8 at 50 mg/ml(0M).

Conclusions: HYADD3A8 and HYAFF120p50A8 solutions seem promising candidates as NP substitute from a viscoelastic point of view. In particular, HYADD3A8 (20mg/ml,0.15M solution) properly matched the rheological behaviour of porcine NPs.

Tissue engineering regards the generation, regeneration, augmentation or limitation of the structure and function of living tissues by the application of scientific and engineering principles. Skeletal defects resulting from tumor resection, congenital abnormalities or trauma often require surgical intervention to restore the function. Current option for bone replacement include autografts,allografts,metals,ceramic and polymers.However, all these materials have drawbacks, and their selection usually require some compromises.

Skeletal tissues are under extensive investigation in tissue engineering research and beside the biological issues, the scaffolds design plays an important role. A number of biodegradable and bioabsorbable materials as well as scaffold designs, have been experimentally and, in some cases clinically studied. An appropriate scaffold should posses highly porous with interconnected pore network for cell growth and flow transport of nutrient and metabolic waste; biocompatible and bioresorbable with a controlled degradation and resorption rate to match cell/ tissue growth, suitable surface chemistry for cell attachment, proliferation and differentiation, and mechanical properties to match those of the implanted tissue. Synthetic biodegradable polymers and inorganic materials are promising as extracellular matrix analogue to facilitated tissue development and growth; these include: polyglycolic acid, poly-l-lactic acid, copolymers, poly-caprolactones, hydroxyapatite, tricalcium phosphates. All these scaffolds are well performing from biological and chemical-physical but they have some limitations from mechanical point of view. To overcome this problem a composite structure made by Polycaprolactone and Hydroxyapatite is studied by mechanical and biological analysis. To obtain a porous structure, the casting and salt leaching technique is implemented. The composite shows mechanical properties in the range of the spongy bone and interesting biological properties with regards to osteoblasts.

Injectable gels made of collagen are analysed to carry cells, a preliminary results of collagen gel loaded with MSC cells have been performed and rheological and proliferation study are showing the feasibility to obtain a bioactive materials/cells to be inject in the defined body site defects avoiding massive surgery.