The biomimetic scaffolds play a key role in the approaches of Tissue Engineering as it may affect the adhesion, proliferation and cellular differentiation (Owen et al. JBMRA 2010). The use of scaffolds characterized by chemical- physical signals and a structure that mimics the extracellular matrix (ECM) allows to control and influence of specific cellular response. Is therefore essential to replicate the scaffold the macro-and nano-structure of the ECM (Agarwal et al., Polymer 2008). In addition, functionalizing the scaffolds with suitable chemical-physical stimuli is possible to realize an environment engineered able to influence the cellular response (Ren et al., Biomaterials 2009).
A) Scaffolds obtained with electrospinning
The electrospinning is an effective technology for producing nonwoven tissues consisting of continuous fibers of sub- micrometric well-defined size, with controlled morphological characteristics, shape, thickness and surface properties. able to mimic the morphology of the fibrous component of the extracellular matrix protein .
The high porosity of the resulting structures determines a good permeability, which is an important parameter in controlling the spread of substances and cells in the scaffold and at the implant site. So, the electrospun es-PLLA scaffold represents a versatile tool with potential applications in many types of nerve injury. Moreover, the good mechanical properties and high flexibility of electrospun scaffolds allow for great versatility in terms of tissue engineering applications, by filling cavities, winding of nerves, to cover breaches lesional.
However, the microenvironment created by electrospun nanofibers may not be sufficient by itself to induce differentiation of cells. In this case, the functionalization chemical and physical of the elctrospun scaffold (to increase the functional chemical groups, for conjugated matrix proteins, to incorporate drugs) could ampiare enormously application sectors and the versatibilità of the device, also for the purposes of the control of the inflammatory reaction of the tissue as a result of injury. Many polymeric materials, both synthetic and natural, can be electrospun. Trai synthetic polymers, polylactic acid PLLA) is a resorbable and biocompatible material with which it is possible to fabricate scaffolds electrospun (eg-PLLA) that represent a versatile tool with potential applications in many types of nerve injury.
B) Thermosensitive gel
The thermosensitive gels are advantageous because they become gels as a result of variations in temperature and the temperature of gelation can be controlled by varying the ratio between hydrophobic and hydrophilic units in the polymer chain (Tang et al., Singh J. Int J Pharm 2009.).
The thermosensitive gel have been widely used for the realization of matrices incorporating cells and drugs: the cells and bioactive molecules are added to aqueous solutions of the polymer at room temperature; the system gels after its administration in vivo, by encapsulating the cells and the drug . However, the thermosensitive polymers commercially available (Pluronic, PNIPAAM) are not degradable.
Examples of commercially available and degradable temperature sensitive gel and instead include block copolymers (bi-, tri-, multi-block) consisting of hydrophobic blocks A and hydrophilic blocks B, where A is the polyethyleneglycol (PEG) and B is one of the three biodegradable polymers: poly (lactide-co-glycolide) (PLGA), polylactic acid (PLA) or polycaprolactone (PCL) (Fedorovich et al., Tissue Eng 2007). However, they do not possess functional groups biomimetic, generally have poor mechanical properties and are not biodegradable (ie not degrade by enzymatic action in a biological environment). Such copolymers are also degradable by hydrolysis, with the formation of degradation products from acids, which may, however, degrade the drug embedded in the material where they are particularly sensitive to an acidic pH.
The segmented polyurethanes (PU) are biomaterials with modular mechanical characteristics, good processability and biocompatibility (Rechichi et al., J. Biomed. Mater. Res A 2007) and can be rendered biodegradable with introduction of appropriate chain segments sensitive to the action of enzymes (Scott. et al., Tissue Eng B 2008). Recently, were synthesized thermosensitive gels based on hydrophobic blocks of poly (hexamethylene urethane serinol) and hydrophilic blocks of PEG, containing an amino group for repeating unit, thus making possible the biofunzionalizzazione with peptides (Park et al., Biomaterials 2010). The thermosensitive gel PU are very versatile, because it can be prepared by various combinations of diols, diisocyanates and chain extenders, so as to control the biodegradability, mechanical properties and the biofunzionalizzazione through reactive side groups.