Femtosecond Laser Ablation of Electrospun Poly(L-lactide)
Nanofibrous Scaffolds Improves Cell Infiltration
Benjamin Li-Ping Lee*†, Zhiqiang Yang†, Hojeong Jeon§, C. Grigoropoulus§, S. Li*†
*
Graduate Program in Bioengineering, University of California at Berkeley and University of California at San Francisco, USA
†
Department of Bioengineering, University of California at Berkeley, Berkeley, CA 94720
§
Department of Mechanical Engineering, University of California at Berkeley, Berkeley, CA 94720
Tel: 510-666-2799 E-mail: song_li@berkeley.edu
Summary: A technique of utilizing femtosecond (FS) laser ablation to create microscale features
on electrospun poly(L-lactide) (PLLA) nanofibrous scaffolds is designed. Microscale holes of
varying sizes are created on PLLA scaffolds to improve porosity and enhance cell infiltration.
Preliminary studies to qualitatively assess the extent of cell infiltration are presented.
The technology of femtosecond (FS) laser promises to improve the engineering of artificial organs in that
applications, such as tissue-engineered vascular grafts, require host cells to infiltrate and participate in matrix
deposition as well as tissue remodeling and regeneration. Previous study has shown that FS laser ablation can
facilitate the spatial control of cells on 3D tissue-engineered scaffolds without any adverse effects on cell viability
[1]. For tissue-engineered scaffolds, much progress has been made to address the issue of porosity and its limitations
on cell infiltration. In fact, small pore sizes interfere with cell infiltration in scaffolds, which is critical for cell
ingrowth as well as tissue remodeling and morphogenesis. We previously showed that aligned PLLA nanofibers can
enhance cell infiltration in vitro and in vivo and heparin modification of nanofibers promotes cell infiltration into 3D
scaffolds in vivo [2]. In this study, we employed a different strategy to enhance cell infiltration by using FS laser to
ablate and create micro-holes in PLLA scaffolds as a means to increase overall scaffold porosity.
a)
b)
Fig. 1. a) SEM image of PLLA nanofibrous scaffolds with 100μm-diameter holes made by FS laser ablation. b) DAPI staining of cells in PLLA
scaffold (delineated by dashed lines) with 100μm-diameter holes (indicated by arrows) after 1-week in vivo. Scale bars: 100μm (a); 200μm (b).
We fabricated the nanofibrous scaffold via electrospinning. Using FS laser, we were able to control and create an
array of small-sized (100μm-diameter) holes and large-sized (500μm-length) squares with 500μm spacing. We
characterized the scaffolds by examining them with field emission scanning electron microscope. In addition, we
first investigated the effects of these modifications on cell infiltration in vitro by seeding and culturing BAECs for 5
days, and then in vivo by implanting the scaffolds subcutaneously into Sprague-Dawley rats and explanting after 1
week. For both studies, the extent of cell penetration was assessed by nuclear staining with DAPI.
Our findings indicate that the FS laser-ablated PLLA scaffolds do indeed exhibit excellent cell infiltration. As
shown in scanning electron microscopy image (Fig. 1a), the network of nanofibers is not compromised as a result of
the ablation and overall structural integrity is maintained. Furthermore, cell infiltration after one-week in vivo (Fig.
1b) reveals that cells are able to penetrate into and distribute throughout the scaffold. In fact, we believe that cell
ingrowth is facilitated as cells first migrate into the holes and then infiltrate the scaffold. Most importantly, FS laser
ablation is a promising method that can reduce the adverse effects of insufficient porosity of electrospun nanofibrous
scaffolds and improve their biological performance for artificial organ and other tissue engineering applications.
[1] Lim, YC, Johnson, J, Fei, Z, Wu, Y, Farson, DF, Lannutti, JJ, Choi, HW, Lee, LJ. “Micropatterning and Characterization of Electrospun
Poly(ε-Caprolactone)/Gelatin Nanofiber Tissue Scaffolds by Femtosecond Laser Ablation for Tissue Engineering Applications”, Biotechnology
and Bioengineering. 2011 Jan; 108(1):116-26.
[2] Kurpinski, K, Stephenson, JT, Janairo, RRR, Lee, H, Li, S. “The effect of fiber alignment and heparin coating on cell infiltration into
nanofibrous PLLA scaffolds”, Biomaterials 2010; 31:3536-42.
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