Nano-engineered adhesive biomaterials for biomedical applications

This thesis is focused on the development of adhesive systems for biomedical applications and has been carried out in the framework of the European Project “AnastomoSEAL” (EU-FP7). Within this project, a bioactive membrane based on polysaccharides was developed for the prevention of anastomotic leakage (AL) after colo-rectal cancer (CRC) resection. The membrane was designed to be wrapped around the intestinal tissue in order to stimulate the healing of the surgical wound, thus accelerating its closure. The main components of the system were the two polysaccharides alginate and hyaluronan (HA), the former representing the physical matrix, the latter exerting a bioactive function in the terms of stimulating the healing of wounds. The main goals of this thesis were to manufacture and characterize the membranes and to design tissue-adhesives that could be implemented in the medical device. In the first part of the work, the procedure for the membrane preparation was set up, followed by the characterization of the product as to its mechanical, chemical and biological properties. The membranes were prepared by freeze-drying alginate-HA hydrogels crosslinked by calcium ions (Ca2+). Several formulations of the membrane were screened to tailor its performance in the terms of mechanical resistance, stiffness and deformation. In vitro biological test pointed out the the non-cytotoxicity of the membranes, as well as the ability of the released HA to stimulate the healing of fibroblasts. Degradation tests and release studies were performed to predict the in vivo behavior of the membrane, pointing out that, in simulated physiological conditions, the release of HA occurs during the first hours, whereas a complete degradation of the membrane is achieved in 21 days. Sterilized membranes were also characterized to investigate the effect of terminal sterilization on the membrane properties; in particular, the effect of supercritical carbon dioxide (scCO2) supplemented with H2O2 was studied. In parallel, adhesive strategies were designed and tailored to the peculiar features of both membrane and intestinal tissue. The adhesive strategies developed in this thesis were based either on the use of exogenous compounds (i.e. H2O2), or on the use of molecules displaying bioadhesive properties. In the first case, adhesion studies proved the enhancement of the adhesion strength between membrane and tissue after the treatment with H2O2, and pointed out the ability of this compound to induce the formation of an adhesive interface made of gelatin, which was integrated in the structure of the tissue. In the latter case, bio-inspired adhesive strategies were designed considering the adhesion mechanism employed by natural organisms (i.e. mussels). The key adhesive molecules of mussel’s adhesive (i.e. catechol-based compounds) were implemented into the structure of the membrane by chemical modifications. In vitro adhesion tests showed an improved adhesion of the modified-membrane in simulated physiological conditions, which was confirmed in vivo by preliminary adhesion studies. A second mussel-inspired adhesive strategy was based on the development of nanoparticles displaying a catecholic core, named melanin-like nanoparticles (MNPs). MNPs were characterized from a biological point of view and used to prepared adhesive coatings for the AnastomoSEAL membrane, whose adhesive properties were evaluated by in vitro adhesion tests. In conclusion, the tests performed allowed the development of a medical device endowed with adhesive components that enabled an efficient adhesion in a physiological environment.