Biomaterials Science Blog

When I was in elementary school, I remember having lots of fun making papier-mâché piñatas.  To form a spherical, hollow structure, I would inflate a balloon and layer papier-mâché on top. Once the papier-mâché dried, I popped the balloon with great satisfaction to leave behind a hollow sphere, which I then painted and filled with candy to complete my piñata. The best part of the whole process was enjoying the candy.

The Anseth Lab at the University of Colorado in Boulder has developed a clever biomaterials technique that reminds me of my favorite arts & crafts activity. In their Biomaterials Science paper Katherine Lewis et al. describe how they used photodegradable PEG microspheres (analogous to balloons) coated with lung epithelial cells (analogous to papier-mâché) to generate cyst structures that mimic lung alveoli in vitro. In alveoli, lung epithelial cells form tight junctions to create a barrier between the airway and blood vessels. To appropriately model this barrier in vitro, the photodegradable microspheres were functionalized with the adhesive peptide CRGDS to allow epithelial cell attachment to the surface of the microsphere. Subsequently, cell-coated microspheres were encapsulated in a PEG hydrogel with stiffness similar to lung tissue, which was functionalized with CRGDS and enzymatically-cleavable peptide cross-linkers. Finally, the photodegradable microspheres were degraded away with cell-compatible light to form cysts, similar to popping the balloon when making a piñata. The cells forming the spherical cysts retained their tight junctions because they also adhered to the surrounding encapsulating hydrogel. The morphology and cell–cell junctions of the cysts were elegantly characterized with confocal microscopy and immuno-staining to demonstrate barrier formation. These 3D models of alveolar cysts demonstrate yet another unique application of photodegradable PEG hydrogels. These cysts may be used to develop models of diseases including pulmonary fibrosis for in vitro screening of potential therapeutics. Discovering treatments to lung-associated diseases using this technology in the future would certainly be a sweeter success than enjoying candy from a piñata.

Check out the June cover article here: In vitro model alveoli from photodegradable microsphere templates by Katherine J.R. Lewis, Mark W. Tibbitt, Yi Zhao, Kelsey Branchfield, Xin Sun, Vivek Balasubramaniam, and Kristi S. Anseth

Dr. Brian Aguado (@BrianAguado) completed his Ph.D. in Biomedical Engineering from Northwestern University as an NSF fellow in 2015. He holds a B.S. degree in Biomechanical Engineering from Stanford University and a M.S. degree in Biomedical Engineering from Northwestern University. Read more about Brian’s research publications here.

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The development of antibacterial materials that can guard against microbial infections during medical procedures has been a topic of increasing interest. In this paper, a team of researchers from Beijing University of Chemical Technology and the University of Bremen describe a facile synthesis method for a hybrid nanomaterial that has previously demonstrated excellent antibacterial activity: reduced graphene oxide films decorated with silver nanoparticles. The efficient, dimensionally scalable, and environmentally friendly nature of this method make it a potentially valuable tool for other groups interested in fabricating these hybrid films for applications ranging from medical biomaterials, to cell culture scaffolds, to drug delivery platforms, to environmental remediation.

Zhang et al. created these hybrid films by using sodium citrate to simultaneously reduce aqueous graphene oxide (GO) and aqueous silver nitrate to reduced graphene oxide (RGO) and silver nanoparticles (AgNPs), respectively. This was followed by a prolonged incubation at 80°C to induce thermal evaporation-driven self-assembly of the hybrid RGO/AgNP films. The mass ratio of silver nitrate to GO in the initial solution could be adjusted to produce films with varying densities of AgNPs. In addition, this mass ratio as well the thermal evaporation duration provided some control over the thickness of the resulting hybrid film. The film’s size could be readily changed via adjustments to the dimensions of the reaction container and the film could be later transferred to other substrates without any additional post processing steps.

Subsequent characterisation of the film confirmed the successful reduction of GO as well as the formation of primarily spherical AgNPs between 12 and 30 nm in size on the surface of the film. The resulting material was found to be very hydrophilic and supported the adhesion and proliferation of mouse osteoblasts. An antibacterial assay measuring E. coli adhesion on the surface of silicon wafers coated with these RGO/AgNP films found that the few bacteria that did manage to adhere to the film’s surface exhibited damaged cell walls. A subsequent E. coli colony viability assay proved that no living bacterial colonies were present on the surface of the hybrid film, a result that could not be obtained when using either an uncoated silicon wafer or a pure RGO film.

The biocompatibility, hydrophilicity, durability, and antibacterial activity of these RGO/AgNP hybrid films make them intriguing candidates for a number of medical and environmental applications. The simple, dimension-scalable, and environmental friendly synthesis method presented by Zhang et al. in this paper opens up new avenues for the creation and widespread use of these versatile hybrid films.

Check out the full article:
Graphene film doped with silver nanoparticles: self-assembly formation, structural characterizations, antibacterial ability, and biocompatibility by Panpan Zhang, Haixia Wang, Xiaoyuan Zhang, Wei Xu, Yang Li, Qing Li, Gang Wei, and Zhiqiang Su

Ellen Tworkoski is a Web Writer for Biomaterials Science and is currently a graduate student in the biomedical engineering department at Northwestern University (Evanston, IL, US).

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