Femtosecond laser nanofabrication of hydrogel biomaterial
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Introduction Hydrogels are biomaterials consisting of hydrophilic polymer networks that have been widely researched in various fields of biomedicine, including tissue engineering scaffolds, controlled release drug delivery systems, and biosensors. The reason hydrogels have such wide applications resides in its tissue-like properties of high water content and superb flexibility.1–3 Predominantly, both natural and synthetic hydrogels have been investigated for producing tissue engineering scaffolds, which provide a natural mimicking environment to promote cell growth and tissue regeneration. Natural hydrogels such as hyaluronic acid (HA), collagen, gelatin, fibrin, and agarose have largely been used to fabricate scaffolds because of their innate biomimetic chemical, biological, and mechanical properties.4–7 However, since natural hydrogels are not as conducive to fabrication processes as synthetic hydrogels, more research interest has been focused on synthetic hydrogels, such as poly(ethylene glycol) (PEG), poly(vinyl alcohol) (PVA), poly(acrylic acid) (PAA), poly(lactic-co-glycolic acid) (PLGA), and poly(L-lactic acid) (PLLA).8–11 Synthetic hydrogels have two advantages compared to natural hydrogels: First, the mechanical and chemical properties of synthetic hydrogels are more controllable. By
adjusting the molecular weight and cross-linking density of a polymer, synthetic hydrogels of various stiffness and water content can be designed and produced for scaffolds in a variety of applications, such as bone, cartilage, and muscle. The surface chemical properties of synthetic hydrogels can also be modified by attaching growth factors or peptides on the surface. Second, the properties of synthetic hydrogels are more reproducible. A specific synthetic hydrogel can be accurately reproduced by employing the same molecular weight monomer and crosslinking time in a consistent manufacturing environment. PEG, one of the most extensively used synthetic hydrogel biomaterials, was chosen for this work. Three properties of PEG have made it an attractive material for tissue engineering scaffolds. First, PEG is biocompatible but does not interact with proteins or cells since it is inert to most biological molecules. This neutrality makes it an ideal base material upon which the desired bio-properties can be built. Additionally, researchers have shown that by grafting different peptides on the backbone of PEG, the hydrogel can be modified to be both bioactive and biodegradable.12,13 Second, various PEG derivatives possess properties that allow fabrication via photopolymerization. The most widely used PEG derivative in tissue engineering
Wande Zhang, University of California, San Diego; [email protected] Shaochen Chen, University of California, San Diego; [email protected] DOI: 10.1557/mrs.2011.275
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MRS BULLETIN • VOLUME 36 • DECEMBER 2011 • www.mrs.org/bulletin
© 2011 Materials Research Society
FEMTOSECOND LASER NANOFABRICATION OF HYDROGEL BIOMATERIAL
is diacrylated PEG (PEGDA). Upon enough light irradiation, the acrylate groups i
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