Polylactic Acid PLA

Presented by:

• K. Sugiura and T. Hayami, chief researchers
• S. Ogawa, Y. Tsumura and M. Kurahashi, researchers
• Y. Kitao, head of the research section
• S. Inoue, division head, the Dyeing Division

INTRODUCTION

Synthetic fibers, by the fact that they are often endowed with special qualities not found in natural fibers (tensile strength, dyeability, durability, chemical resistance etc.) and through innovations and modifications achieved in line with the progress of technology in fiber synthesis and processing, are broadly exploited in various industries other than apparel. Although they hold an important position as a material indispensable in the medical field, their being non-bioabsorbable leaves the possibility of wearing out in long-term use and the constant fear of inflammatory reaction, though not strong, in contact with the body.

In recent years, attention has been drawn to naturally-derived, bio-degradable polymer materials, not only because they can be effective measures for the waste disposal or environmental issues, but also for their use in the medical field due to the biocompatibility of some among them. This is owing to the fact that, in addition to their compliance with the obvious requirement of medical materials for biosafety and biocompatibility regarding the inevitable direct contact with the body, it may concern, with them also being biodegradable and bioabsorbable, exploitation as a material or in technologies for the alleviation of a patient's physical burden, or as a structural material in the Drug Delivery System (DDS), designed to optimize drug delivery.

Some medical materials made from biodegradable polymers, including suture threads, have already been practically used, however, exploitation remains in their primary attributes such as biodegradability and thermal plasticity, and the development of medical materials with a higher functionality is being anticipated.

This research has been conducted, with a view to utilization as a fiber material with the DDS functions, to examine the possibilities of drug delivery in a biodegradable fiber material, employing the dry processing method and supercritical CO2 as a medium, as well as its performance as a medical material through determination of the post-process drug sorption and observation of its characteristics from the dynamics point of view and how the drug is released. 

TESTING

Fiber and chemical specimens

Employed were the Lacty #5000 pellets (Shimadzu Corporation), made of poly L-lactic acid (PLLA), melt-spun into fiber, tranilast (Kissei Pharmaceutical), N-(3, 4 dimethoxycinnamoyl) anthranilic acid, used as provided. For supercritical CO2 treatment, carbon dioxide of 99.999% purity (Iwatani Industrial Gases) was used. The top-quality ethanol reagent as a co-solvent, dimethylformamide (DMF) as an extractant, and the liquid chromatograph solvent (Wako Pure Chemical Industries) was used for the quantity determination through high performance chromatograph and tandem mass spectrometry. For adjusting the solvent of phosphate-buffered saline (PBS), PBS agent (Sigma) was used. 

Preparation of PLLA fiber

PLLA fibers at various draw ratios were produced by melt spinning the PLLA pellets at 200°C using a single screw extruder. 

Supercritical CO2 treatment

LLA fiber, wrapped around a holder, and tranilast were placed in the environment of supercritical CO2, and treated under various temperatures and pressures for a given period of time. The pressure valves were then opened, and after confirming the shift of the in-device environment to the atmospheric pressure, PLLA fiber was taken out and the following evaluation was carried out. 

Evaluation of physical characteristics of the fiber

The mechanical characteristics of supercritically-treated PLLA fiber were examined, using the AG-I Series Autograph (Shimadzu Corporation), through tensile tests carried out at 100mm/min. with grip-to-grip distance at 100mm. The thermal characteristics of PLLA fiber were examined with the use of the differential scanning calorimeter DSC8230 (Rigaku Corporation) in a nitrogen atmosphere with temperature rising 10°C/min. For observing the side and section of PLLA fiber, it was treated with gold deposition and a scanning electron microscope (Hitachi) was used. 

Determination of tranilast sorption

Tranilast sorption in the supercritically-treated PLLA fiber was determined by soaking the fiber in DMF at 40°C for two hours, with the use of the high performance chromatograph L-7000 (Hitachi). The measuring conditions were: 0.1% solution of acetic acid/acetonitrile (2/3) used as eluent, the 34.6 x 150mm Inertsil ODS (GL Sciences) as column, the flow speed set at 0.6ml/min., column temperature at 50°C and wave length at 340nm. 

Determination of tranilast release

Tranilast release from the treated PLLA fiber was measured with 1ml samples taken from PBS solution (pH=7.4) in which the fiber was soaked with temperature retained at 37°C for a given period of time, with the same amount of fresh PBS solution added. From the sampled PBS solution, released amount of tranilast was determined under the same conditions as for its sorption. 

Determination of tranilast release and evaluation of safety on laboratory rats

A specimen (the treated PLLA fiber) was implanted in an 8-week-old female laboratory rat, anaesthetized with the injection of nembutal (sodium pentobarbital) in the abdominal cavity, with fur removed and skin cut open in the back region, then the cut was sewn up and treated with iodine-based disinfectant. The conditions and weight of the rat were observed for safety evaluation of the specimen, taken out and re-imbedded periodically, 1, 3, 5, 7 14, 30, 45, 60 day(s) after the initial implantation. Tranilast release in the rat was measured by comparing the amounts of tranilast contained in the specimen before and after the implant.

For determining the amount of tranilast remaining in the specimen, the specimen was precisely weighed, diffused in 1ml of chloroform with methanol added to make precisely 20ml. This 400μ l solution was centrifugally filtered (12000rpm, 15min.) using the ultrafiltration device YM-30 (Millipore), and 10μl from the filtered liquid was poured into the mass spectrometer system API3000 (LC/MS/MS, SCIEX - Shimadzu Corporation) for measurement. As measuring conditions, 10mmol/l gradient of ammonium acetate solution/methanol was used as eluent, Inertsil C8, 1.5 x 150mm as column, flow speed set at 0.15ml/min., column temperature at 40°C, and detection was carried out by MS/MS.