Fabricating Tubular Devices from Polymers of Lactic and Glycolic Acid for Tissue Engineering

Abstract

Polymers of lactic and glycolic acid are attractive candidates to fabricate devides to transplant cells and engineer new tissues. These polymers are biocompatible, and exhibit a wide range of erosion times and mechanical properties. This manuscript describes the fabrication and characterization, in vitro and in vivo, of hollow, tubular devices from porous films of various polymers of this family. Porous films of these polymers were formed using a particulate leaching technique, and sealed around Teflon cylinders to form hollow tubular devices. The erosion rate of devices was controlled by the specific polymer utilized for fabrication, and ranged from months to years. Devices fabricated from a 50/50 copolymer of D,L-lactic acid and glycolic acid were completely eroded by 2 months, while devices fabricated from a homopolymer of L-lactic acid showed little mass loss after 1 year. Erosion times for devices fabricated from the other polymers [poly-(D,L-lactic acid) and a 85/15 copolymer] were between these two extremes. Devices were capable of resisting significant compressional forces (150 raN) in vitro, and the compression resistance was controlled by the polymer utilized to fabricate the devices. The ability of the devices to maintain their structure after implantation into the mesentery or omentum of laboratory rats was also dependent of the specific polymer utilized to fabricate the device. These results indicate that it is possible to fabricate tubular devices for tissue engineering applications that exhibit a wide range of erosion rates and mechanical properties.

Bioactive and bioresorbable cellular cubic-composite scaffolds for use in bone reconstruction

“…We predict that these materials might be replaced with natural bone within approximately 1.5 years under in vivo loading conditions, although this will vary depending upon the size and initial Mv value of each device. Interestingly, a P(D/L)LA sample with an initial Mv of 15 kDa was previously reported to achieve complete mass loss in vitro after 1 year (Mooney et al 1995). In the current study, a P(D/L)LA sample with an initial Mv of 77 kDa decreased to an equivalent value after approximately six months, and thereafter took approximately 1 year to reach a minimum Mv of approximately 5 kDa.…”

“…Fourth, amorphous P(D/L)LA and PGA/(D/L)LA polymers can be rapidly resorbed (after 1 and 0.5 years, respectively; Mooney et al 1995); the replacement of these porous composites with natural hard tissues is achieved significantly faster than that of semi-crystalline PLLA.…”

Design concepts and strategies for tissue engineering scaffolds

“…Crystallinity has a significant effect on the degradation rate of aliphatic polyesters because it determines how easily water molecules can swell the copolymer and access the ester linkages to cause chain cleavage [117]. Different degradation times may be required of devices being used to engineer different types of tissues such as the walls of blood vessels versus intestines [120]. This can be incorporated into the design with appropriate copolymerization chemistry and polymer and fiber processing to ensure the desired level of crystallinity.…”

“…However, at the other end of the spectrum, the half-life rises again when the copolymer contains mostly PGA and the polymer becomes more crystalline [25]. Mooney et al [120] compared the erosion time of 50/50 PLGA, 85/15 PLGA, and 100% PLLA tubular porous scaffolds in a buffered saline solution. Structures fabricated from 50/50 PLGA began to show significant weight loss after only 7 weeks and were completely eroded at 10 weeks, whereas the 85/15 PLGA took 35 weeks to completely erode, and the PLLA had no weight loss even after 40 weeks.…”

“…They include phase separation [89], gas foaming, freeze-drying, solvent casting, particulate leaching [84], [120], thermal processing [62], and molding, as well as combinations of these techniques. Solvent casting and particulate leaching with salt and sugar are representative methods of using porogens to achieve porous sponge-like structures [15].…”