Ultrasound micromolding technique and real-time x-ray diffraction using synchrotron radiation. Applications to porous scaffolds for biomedical devices and study of thermal-induced transitions
- Autores: Cristian Olmo Osuna
- Directores de la Tesis: Jordi Puiggalí Bellalta (dir. tes.), María Lourdes Franco García (codir. tes.)
- Lectura: En la Universitat Politècnica de Catalunya (UPC) ( España ) en 2021
- Idioma: español
- Materias:
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- Resumen
Current market trend is moving to miniaturized specimens, especially in the biomedical field seeking high effective and less invasive treatrnent. Ultrasound (US) micromolding is a new technique developed to the aim of producing microsized pieces based on the use of ultrasound waves as a heating source. This heating method is highly precise and can lead to produce microsized pieces with high energy and material efficiencies by using short cycling times compared to other conventional techniques.
This PhD work explores further possibilities of ultrasound micromolding to the production of polymers with added value. The work is divided in two main blocks: the production of micropieces based on biodegradable polymers focused on biomedical applications and the application of this technique as a new method to obtain nanocomposites with a homogenous dispersion ofthe reinforcing material.
Polylactide (PLA) was selected as polymer matrix in the first block to produce drug loaded pieces and scaffolds with antibacterial activity or increased osteoconductivity by the incorporation of hydroxyapatite (HAp). Chlorhexidine (CHX) and triclosan (TCS), selected as representative bactericide agents, were successfully loaded with a homogenous distribution into the polymer matrix Drugs were slowly released from micropieces and presented clear bactericide and bacteriostatic effect against both Gram-positive and Gram-negative bacteria. Microporous scaffolds have been produced from the subsequent leaching of incorporated salts. By using NaCI cavitation problems could be avoided but pores interconnections were insufficient anda small amount of water soluble polymer (i.e. polyethylene glycol) was required in order to improve the leaching process. Final scaffolds showed enhanced cell proliferation compared to non-porous PLA PLNHAp scaffolds with a porosity degree close to 35% could be achieved with relatively good mechanical properties. lncorporation of HAp increased the thermal stability, hydrophilicity and cell proliferation with respect to neat PLA specimens.
Ultrasound waves are usuallycombined with the conventional method to produce nanocomposite (i.e. solution intercalation and melt mixing) to avoid nanoparticles aggregation and improve their distribution within the polymer matrix Hence the second block ofthis PhD work studies the use of ultrasound micromolding technology in nanocomposites production. To this end, Polycaprolactone and polyamide 12 were selected as polymer matrices whereas multi-walled carbon nanotubes (MWCNT) and Nanofil 757 (a non-organo modified clay) were chosen as reinforcing agent. Both neat polymers and their nanocom posites were successfully micromolded with minimal polymer degradation under optimal molding condition (amplitude, force and time). US micromolding technique was revealed to be efficient in getting fully exfoliated nanocomposites even when Nanofil 757 was selected. Moreover, the influence of both, MWCNTand Nanofil 757, on crystallization behaviorand morphology were systematically studied by time resolved synchrotron experiments. Crystalline polymorphic transitions of nylon 12 were also evaluated through analyses of real time synchrotron.
A final chapter of this thesis is devoted to the study of structural transitions of nylons 12 9, 8 9, 4 9, 4 5 and copolymers derived from 1,4-diam inobutane and different ratios of glutaric and azelaic acids (nylon 4, 5+9) in order to achieve deeper knowledge on the series of even-odd polyam ides. These polyamides show different crystalline structure and structural transitions compared to the conventional polyamides, which root cause is still unclear.
