ETD system

Electronic theses and dissertations repository


Tesi etd-02032010-104900

Thesis type
Tesi di dottorato di ricerca
Synthesis of Nanostructured Polymeric Materials for Pharmaceutical and Biomedical Applications
Settore scientifico disciplinare
Corso di studi
tutor Prof. Chiellini, Emo
tutor Dott. Chiellini, Federica
Parole chiave
  • polymethacrylamide
  • nanoparticles
  • hydrogels
  • DEHP
  • chitosan
  • biomaterials
  • bioeliminable
  • PVC
Data inizio appello
Data di rilascio
Riassunto analitico
Biomaterials technology represents one of the most rapidly advancing areas of science in which several disciplines, such as chemistry, pharmaceutical technology, and medicine are contributing to human health care.
In the framework of a long–standing research activity ongoing at the laboratory of Polymeric Materials for Biomedical and Environmental Applications of the Department of Chemistry and Industrial Chemistry of the University of Pisa, the present PhD thesis work was focused on the following four main topics: (I) Preparation and characterization of new bioeliminable polymeric systems for drug delivery applications, (II) Combination of natural and synthetic polymeric systems for the preparation of hybrid nanoparticles for drug and bioactive agents delivery, (III) Synthesis and characterization of polymethacrylamide based scaffolds for tissue engineering applications and (IV) Investigation of PVC based medical devices degradation and leakage of DEHP in newborns service life.
The first objective was the preparation of bioeliminable nanoparticles based on copolymers of hydroxypropylmethacrylamide (HPMA) and methacryloylglycylglycine (MAGlyGly) with different molar ratio of the two components. In order to obtain bioeliminable polymeric materials with a molecular mass limited to 40 kDa or below to ensure renal excretion the radical polymerization processes was opportunely adjusted.
Human serum albumin (HSA) loaded nanoparticles based on the prepared bioeliminable copolymers were obtained by the co-precipitation technique. In order to improve nanoparticles formation and stability, modified β–cyclodextrin derivative were synthesized and added to the formulation as steric stabilizers. HSA loaded nanoparticles displayed a monomodal distribution with an average size of 120 nm. A careful in vitro cytotoxicity tests on polymeric matrices and on the resulting nanoparticles were carried out and the results showed an excellent compatibility of the analyzed materials.
Moreover, hybrid nanoparticles to be employed in drug delivery technology were prepared through in situ polymerization of MAGlyGly anionic monomer in aqueous solution containing Chitosan (CS). Careful investigation was carried out in order to establish the type of the interactions between MAGlyGly and CS. From FT-IR, it is proposed that the p(MAGlyGly) carboxylic groups interact with the CS amino groups with formation of a polyelectrolyte complex, leading to nanoparticle formations. XPS analysis confirmed the formation of crosslinked hybrid polyelectrolyte.
CS-p(MAGlyGly) nanoparticles were obtained for both samples of MAGlyGly and CS (50/50 and 75/25). No difference in morphology and size (120 nm) of nanoparticles was observed. Furthermore thermogravimetric analyses were performed to evaluate the thermal stability of the nanoparticles, in the perspective of their in vivo application. The analyses showed that nanoparticle samples are stable up to 110°C and their stability should not be compromised under physiological conditions.
Studies regarding the application of polymeric materials in Tissue Engineering (TE) were also carried out. In particular a synthetic strategy that allows for the preparation under physiological conditions of hydrogels and semi-IPNs based on polymethacrylamide was developed. HPMA and MAGlyGly based hydrogels were obtained by free radical polymerization by using ethylenglycoldimethacrylate (EGDMA) as crosslinker agent and a redox system, active at room temperature, consisting of sodium metabisulfite and ammonium persulfate as radical initiator. The prepared hydrogels presented good swelling behaviour both in water and in PBS and degradation tests performed in PBS at 37°C showed a mass loss of about 20% for both type of hydrogels after 28 days. Careful in vitro cytotoxicity tests on hydrogels were carried out and revealed that both types of hydrogels were non toxic. In addition the hydrogel of MAGlyGly alone was able to promote significant cell adhesion and proliferation. In order to increase the bioactivity in terms of cell adhesion and proliferation of p(HPMA) based hydrogels, an methacryloilated monomer of agmatine was successfully prepared and it was employed as comonomer in the preparation of HPMA hydrogels.
Moreover, a semi-IPN combining the good biocompatibility of MAGlyGly based hydrogel with the ability of CS to trigger cell adhesion and proliferation was successfully prepared by radical polymerization of MAGlyGly in aqueous CS solution. The network presented good swelling behaviour both in PBS and in water with ability to degrade after 28 days in PBS solution containing lysozyme.
Finally, the last objective was focused on a chemical-physical characterization aimed at investigating the occurrence in PVC endotracheal cathetes the leaching of the DEHP plasticizer as consequence of application in high risk newborns. The TGA analysis showed a weight loss percent of DEHP from used tubes lower than the corresponding value of virgin tubes taken as control, indicating a release of DEHP from the catheters as a consequence of their in vivo application. The analysis also displayed that the evaporation of DEHP from used tubes occurred with a different speed in comparison to that of virgin samples, indicating the occurrence of a possible material degradation due to the use. These results were also confirmed by the increase of the glass transition temperature (Tg) of tubes after their application, as monitored by DSC analysis.
Moreover, in order to compare the concentration of DEHP in virgin and used cactheters, HPLC analyses were carried out. The results obtained showed that the protocol of extraction of DEHP from PVC tubing of the International Pharmacopeia was not efficient in the case of catheters applied in vivo. A new and efficient extraction method was developed.