0
Research Papers

Effect of Laser-Induced Crystallinity Modification on Biodegradation Profile of Poly(L-Lactic Acid)

[+] Author and Article Information
Y. Lawrence Yao

Department of Mechanical Engineering,
Columbia University,
New York, NY 10027

Manuscript received September 3, 2012; final manuscript received July 2, 2013; published online November 5, 2013. Assoc. Editor: Yong Huang.

J. Manuf. Sci. Eng 136(1), 011005 (Nov 05, 2013) (9 pages) Paper No: MANU-12-1262; doi: 10.1115/1.4025394 History: Received September 03, 2012; Revised July 02, 2013

Poly(L-lactic acid) (PLLA) is of interest in drug delivery applications for its biodegradable and biocompatible properties. Polymer-controlled drug delivery relies on the release of embedded drug molecules from the polymer matrix during its degradation. PLLA degradation exhibits an induction period, during which an insignificant amount of degraded products and embedded drug can be released. Due to this induction period, drug release is initially nonlinear, a complication in drug delivery applications. PLLA degradation is a function of crystallinity, such that control over its crystallinity tailors drug release over time. In this study, the effect of laser-induced PLLA crystallinity reduction on degradation is investigated. Samples having lower surface crystallinity are shown to have higher rates of molecular weight reduction and earlier mass loss than nonlaser-treated samples, as observed from gel permeation chromatography and mass change. Wide-angle X-ray diffraction measurements show that crystallinity increases with degradation. A numerical model is implemented from hydrolysis and diffusion mechanisms to investigate the effect of laser irradiation on biodegradation. Controlled laser treatment of PLLA offers a method for constant drug release through the reduction of surface crystallinity.

FIGURES IN THIS ARTICLE
<>
Copyright © 2014 by ASME
Your Session has timed out. Please sign back in to continue.

References

Amass, W., Amass, A., and Tighe, B., 2008, “A Review of Biodegradable Polymers: Uses, Current Developments in the Synthesis and Characterization of Biodegradable Polyesters, Blends of Biodegradable Polymers and Recent Advances in Biodegradation Studies.” Polym. Int., 47, pp. 89–144. [CrossRef]
Lao, L. L., Venkatraman, S. S., and Peppas, N. A., 2009, “A Novel Model and Experimental Analysis of Hydrophilic and Hydrophobic Agent Release From Biodegradable Polymers,” J. Biomed. Mater. Res. A, 90, 1054–1065. [CrossRef] [PubMed]
Chu, C. C., 1981, “Hydrolytic Degradation of Polyglycolic Acid: Tensile Strength and Crystallinity Study,” J. Appl. Polym. Sci., 26, pp. 1727–1734. [CrossRef]
Tsuji, H., and Ikada, Y., 1998, “Properties and Morphology of Poly(L-Lactide). II. Hydrolysis in Alkaline Solution,” J. Polym. Sci. A: Polym. Chem., 36, pp. 59–66. [CrossRef]
Siparsky, G. L., Voorhees, K. J., and Miao, F., 1998, “Hydrolysis of Polylactic Acid (PLA) and Polycaprolactone (PCL) in Aqueous Acetonitrile Solutions: Autocatalysis,” J. Environ. Polym. Degrad., 6, pp. 31–41. [CrossRef]
Zong, X. H., Wang, Z. G., Hsiao, B. S., Chu, B., Zhou, J. J., and Jamiolkowski, D. D., 1999, “Structure and Morphology Changes in Absorbable Poly(Glycolide) and Poly(Glycolide-co-Lactide) During in Vitro Degradation,” Macromolecules, 32, pp. 8107–8114. [CrossRef]
Renouf-Glausera, A. C., Roseb, J., Farrarb, D. F., and Cameron, R. E., 2005, “The Effect of Crystallinity on the Deformation Mechanism and Bulk Mechanical Properties of PLLA,” Biomaterials, 26, pp. 5771–5782. [CrossRef] [PubMed]
Bhatla, A., and Yao, Y. L., 2009, “Effect of Laser Surface Modification on the Crystallinity of Poly(L-Lactic Acid),” ASME J. Manuf. Sci. Eng., 131, 051004. [CrossRef]
Dunn, D. S., and Ouderkirk, A. J., 1990, “Chemical and Physical Properties of Laser-Modified Polymers,” Macromolecules, 23, pp. 770–774. [CrossRef]
Hsu, S.-T., Tan, H., and Yao, Y. L., 2012, “Effect of Excimer Laser Irradiation on Crystallinity and Chemical Bonding of Biodegradable Polymer,” Polym. Degrad. Stab., 97, pp. 88–97. [CrossRef]
Weir, N. A., Buchanan, F. J., Orr, J. F., Farrar, D. F., and Dickson, G. R., 2004, “Degradation of Poly-L-Lactide. Part 2: Increased Temperature Accelerated Degradation,” Proc. Inst. Mech. Eng., Part. H: J. Eng. Med., 218, pp. 321–330. [CrossRef]
Yamamoto, T., 2010, “Molecular Dynamics of Reversible and Irreversible Melting in Chain-Folded Crystals of Short Polyethylene-Like Polymer,” Macromolecules, 43, pp. 9384–9393. [CrossRef]
Pitt, C. G., and Gu, Z., 1987, “Modification of the Rates of Chain Cleavage of Poly(ε-Caprolactone) and Related Polyesters in the Solid State,” J. Controlled Release, 4, pp. 283–292. [CrossRef]
Li, S. M., Garreau, H., and Vert, M., 1990, “Structure-Property Relationships in the Case of the Degradation of Massive Poly(α-Hydroxy Acids) in Aqueous Media: Part 2 Degradation of Lactide-Glycolide Copolymers: PLA37.5GA25 and PLA75GA25,” J. Mater. Sci.: Mater. Med., 1, pp. 131–139. [CrossRef]
Lyu, S., Schley, J., Loy, B., Lind, D., Hobot, C., Sparer, R., and Untereker, D., 2007, “Kinetics and Time-Temperature Equivalence of Polymer Degradation,” Biomacromolecules, 8, pp. 2301–2310. [CrossRef] [PubMed]
Wang, Y., Pan, J., Han, X., Sinka, C., and Ding, L., 2008, “A Phenomenological Model for the Degradation of Biodegradable Polymers,” Biomaterials, 29, pp. 3393–3401. [CrossRef] [PubMed]
Stephens, C. H., Whitmore, P. M., Morris, H. R., and Bier, M. E., 2008, “Hydrolysis of the Amorphous Cellulose in Cotton-Based Paper,” Biomacromolecules, 9, pp. 1093–1099. [CrossRef] [PubMed]
Tsuji, H., and Tsuruno, T., 2010, “Accelerated Hydrolytic Degradation of Poly(L-Lactide)/Poly(D-Lactide) Stereocomplex up to Late Stage,” Polym. Degrad. Stab., 95, pp. 477–484. [CrossRef]
Tsuji, H., and Ikarashi, K., 2004, “In Vitro Hydrolysis of Poly(L-Lactide) Crystalline Residues as Extended-Chain Crystallites: II. Effects of Hydrolysis Temperature,” Biomacromolecules, 5, pp. 1021–1028. [CrossRef] [PubMed]
Fischer, E. W., Sterzel, H. J., and Wegner, G., 1973, “Investigation of the Structure of Solution Grown Crystals of Lactide Copolymers by Means of Chemical Reactions,” Kolloid Z. Z. Polym., 251, pp. 980–990. [CrossRef]
Toda, A., Tomita, C., Hikosaka, M., and Saruyama, Y., 1998, “Melting of Polymer Crystals Observed by Temperature Modulated D.S.C. and Its Kinetic Modeling,” Polymer, 39, pp. 5093–5104. [CrossRef]
Li, S., and McCarthy, S., 1999, “Influence of Crystallinity and Stereochemistry on the Enzymatic Degradation of Poly(lactide)s,” Macromolecules, 32, pp. 4454–4456. [CrossRef]
Avrami, M., 1941, “Granulation, Phase Change, and Microstructure: Kinetics of Phase Change. III,” J. Chem. Phys., 9, pp. 177–184. [CrossRef]
Alexander, L. E., 1969, X-Ray Diffraction Methods in Polymer Science, Wiley, New York, Chap. 1.
Avrami, M., 1939, “Kinetics of Phase Change. I: General Theory,” J. Chem. Phys., 7, pp. 1103–1112. [CrossRef]
Menczel, J., and Wunderlich, B., 1981, “Heat Capacity Hysteresis of Semicrystalline Macromolecular Glasses,” J. Polym. Sci.: Polym. Lett. Ed., 19, pp. 261–264. [CrossRef]
Belyayev, O. F., 1988, “Mechanism of Melting of Oriented Polymers,” Polym. Sci. U.S.S.R., 30, pp. 2545–2552. [CrossRef]
Lam, C. X. F., Savalani, M. M., Teoh, S. H., and Hutmacher, D. W., 2008, “Dynamics of in Vitro Polymer Degradation of Polycaprolactone-Based Scaffolds: Accelerated Versus Simulated Physiological Conditions,” Biomed. Mater., 3, 034108. [CrossRef] [PubMed]
Breitenbach, J., and Lewis, J., 2003, Modified-Release Drug Delivery Technology, M. J.Rathbone, J.Hadgraft, and M. S.Roberts, eds., Marcel Dekker, New York, Chap. 11.

Figures

Grahic Jump Location
Fig. 1

Schematic representation of (a) semicrystalline structure and (b) crystalline residue of polymer after hydrolysis, which preferentially occurs in amorphous region and on crystal fold surface, leading to mass loss [19]

Grahic Jump Location
Fig. 2

Nondegraded PLLA sample (a) before and (b) after laser treatment with a fluence of 3 J/cm2. Laser-irradiated spots show less transparency due to increased surface roughness. The laser-treated sample degraded for 14 days is given in (c) and its high crystallinity reduces the transparency.

Grahic Jump Location
Fig. 3

PLLA crystallinity and the ratio of O1s to C1s as a function of laser fluence. The error bar represents the standard deviation of 3 data points.

Grahic Jump Location
Fig. 4

Surface morphology of the laser-treated sample (a) before and after degradation for (b) 3, (c) 8, and (d) 14 days under the stereomicroscope. The squares in (a) are laser spots. The edges of laser spots become less defined with degradation period, suggesting the erosion of laser melted layer. Degradation in the nonmelted bulk volume occurs in the later stage.

Grahic Jump Location
Fig. 5

Cross section of the laser-treated sample degraded for 14 days. The bulk remains solid, suggesting that autocatalysis is not dominant.

Grahic Jump Location
Fig. 6

WAXD profiles of the (a) nonlaser-treated and (b) laser-treated (F = 3 J/cm2) samples degraded for regular periods. Intensity of crystalline peaks increases with degradation period, suggesting a higher crystallinity. Profiles are shifted in y direction for viewing clarity.

Grahic Jump Location
Fig. 7

Crystallinity as a function of degradation period determined from WAXD. Crystallinity increases with degradation period. A significant increase occurs on day 0.5 for both types of samples. Crystallinity also increases on day 8 and day 5 for the nonlaser-treated and laser-treated samples, respectively. The error bar represents the standard deviation of 3 data points.

Grahic Jump Location
Fig. 10

Experimental results of sample mass with and without laser treatments. Mass decrease is observed after day 8 for nonlaser-treated sample and after day 3 for laser-treated sample. The error bar represents the standard deviation of 3 data points.

Grahic Jump Location
Fig. 8

GPC profiles of the (a) nonlaser-treated and (b) laser-treated samples after regular degradation periods. For (a), the distribution becomes wider and shifts left as the degradation period increases to day 5, representing the random chain scission in the amorphous region. After day 8, a distinct new peak is developed due to selective chain scission of the fold surface of crystals. For (b), the MW distribution extends to the left before day 3, signifying the random chain scission of the laser melt layer. At day 5, two distinct peaks are developed due to the selective chain scission of the partially melted crystal fold surfaces. Profiles are shifted in y direction for viewing clarity.

Grahic Jump Location
Fig. 9

Mw, Mn, and PDI of the (a) nonlaser-treated and (b) laser-treated samples after regular degradation periods. Mw and Mn decrease at a higher rate for the laser treated samples, as a result of fast degradation in the laser-melted layer. The nonhomogeneous degradation of the melted layer and bulk increases PDI. The error bar represents the standard deviation of 3 data points.

Grahic Jump Location
Fig. 11

Simulated spatial distribution of monomer concentration in the (a) nonlaser-treated sample and (b) laser-treated sample degraded for 0.5 days

Grahic Jump Location
Fig. 12

Simulated MW of the nonlaser-treated and laser-treated samples

Grahic Jump Location
Fig. 13

Simulated mass change of the nonlaser-treated and laser-treated samples

Grahic Jump Location
Fig. 14

Molar concentration of the simulated species as a function of degradation period

Tables

Errata

Discussions

Some tools below are only available to our subscribers or users with an online account.

Related Content

Customize your page view by dragging and repositioning the boxes below.

Related Journal Articles
Related eBook Content
Topic Collections

Sorry! You do not have access to this content. For assistance or to subscribe, please contact us:

  • TELEPHONE: 1-800-843-2763 (Toll-free in the USA)
  • EMAIL: asmedigitalcollection@asme.org
Sign In