Effect of Film Formation Method and Annealing on Crystallinity of Poly(L-Lactic Acid) Films

Abstract

Poly(L-lactic acid) (PLLA) has been shown to have potential medical usage such as in drug delivery because it can degrade into bioabsorbable products in physiological environments, and its degradation is affected by crystallinity. In this paper, the effect of film formation method and annealing on the crystallinity of PLLA are investigated. The films are made through solvent casting and spin coating methods, and subsequent annealing is conducted. The resulting crystalline morphology, structure, conformation, and intermolecular interaction are examined using optical microscopy, X-ray diffraction, and Fourier transform infrared spectroscopy. It is observed that solvent casting produces category 1 spherulites while annealed spin coated films leads to spherulites of category 2. Distinct lamellar structures and intermolecular interactions in the two kinds of films have been shown. The results enable better understanding of the crystallinity in PLLA, which is essential for its drug delivery application. INTRODUCTIONThere is a significant interest in use of biodegradable polymers due to their biocompatibility and biodegradability. Poly lactic acid (PLA) is a biodegradable polymer and can be obtained from renewable sources such as corn starch. It has a wide range of applications, such as in food packaging and tissue engineering. PLA is also of interest in drug delivery application because it can degrade into bioabsorbable products in physiological environments. Its degradation mainly comes from the cleavage of its ester groups, and is sensitive to chemical hydrolysis. In polymeric drug delivery system, drugs are encapsulated in polymer. As the polymer degrades, the drugs are released, and the release rate is determined by the polymer degradation rate. Crystallinity of polymer is a factor affecting the degradation rate. A good review on the effect of crystallinity on degradation and drug release can be found in [1]. In general, less crystallinity accelerates degradation and drug release rate. To create polymeric drug delivery system, drug molecules are dispersed or dissolved in the polymeric solution, formed through melting the polymer or dissolving it in a solvent. During the process the polymer may crystallize. The crystal structure also influences the degradation rate. Tsuji and Ikada [2] studied the hydrolysis of PLA films and proposed that it begins in the amorphous region between the crystalline lamellae, followed by the disorientation of the lamellae and disappearance of the spherulitic structure.

Functionalization Strategies and Fabrication of Solvent-Cast PLLA for Bioresorbable Stents

“…The SC films presented a percentage of crystallinity four times lower than the PL65 pellet employed for its synthesis. This decrease of crystallinity due to the solvent casting process has already been reported [49] and is mainly associated with the fast chloroform evaporation not allowing polymer macromolecules to diffuse to the crystal growth front and overcome the energy barrier of deposition [50]. As expected, the thermal treatment helped increase crystallinity, which doubled in TT due to the chain reorganization [45,51].…”

Effect of excimer laser irradiation of biodegradable polymer on its chemical bonding

“…Higher fluence irradiation generates appreciable bubbles since laser energy penetrates into the bulk with low absorption coefficients. This phenomenon has also been reported in poly(methyl methacrylate) (PMMA) under excimer laser irradiation [30,31]. Its absorption coefficient is on the same order as PLLA (10 3 cm -1 ), and the fluences of several J/cm 2 generate bubbles in both materials.…”

“…The inherent viscosity of PLLA in chloroform at 25°C is 1.6 dl/g, and the molecular weight is 56,274 g/mol [30]. Films were prepared by solvent casting method described in [31]. The film thickness is 20-25 μm.…”

Tyrosol Derived Poly(ester-arylate)s for Sustained Drug Delivery from Microparticles

“…The crystalline nature of the polymer decreased slightly when the polymer was formulated into particles. This can be attributed to the disruption of a primary nucleus formation during the fast removal of the solvent combined with the bumping of particles caused by the mechanical stirring during the solvent evaporation step . Upon the introduction of the drug into the formulations, the drug crystals reduced the degree of order in the polymer crystals as indicated by the broadening of the polymer crystalline peak.…”