Biomaterials Science Blog

Most of us are accustomed to thinking of medicinal drugs as something we ingest or inject into our bodies.  However, if the drug can be introduced at the particular part of the body where it is needed the most, it will be more effective. Further, if we can slow down the release of the drug, we may be able to use less drugs for the same purpose.  With these long-term goals in mind, Brigitte Städler’s group has recently published a paper where they investigate the release of drugs from a biological coating.  This work can one day be used to modify the surface of implants in our body (commonly used examples include bone implants or pacemakers).  Modifying the surface of these implants would allow us to use them as drug depots in our body.  These implants can then release drugs more slowly into the bloodstream as opposed to all at once, thus making the drugs more effective.

The researchers used a structure known as a liposome – particles made out of fat that can potentially trap a drug in their centers – and surrounded them with a material that can be used to coat implant surfaces. They found that muscle cells could grow on these surfaces without dying, thus proving that the surfaces are not toxic. The liposomes were made out of a fat that fluoresces (emits light under certain conditions).  The muscle cells could absorb these fluorescent fats, which made the cells themselves fluorescent and allowed the cells to be tracked. Next, the researchers trapped a toxic drug in the liposomes, and found that the presence of the drug meant that they could control whether the cells survived or died.  While any kind of drug could in theory be trapped in the coating, a toxic drug could specifically be useful if the coating was near harmful or cancerous cells.

This work shows a great deal of promise in improving the way we deliver drugs to patients.

Cargo delivery to adhering myoblast cells from liposome-containing poly(dopamine) composite coatings
Martin E. Lynge, Boon M. Teo, Marie Baekgaard Laursen, Yan Zhang and Brigitte Städler 
Biomater. Sci., 2013, Advance Article DOI: 10.1039/C3BM60107B

Debanti Sengupta recently completed her PhD in Chemistry from Stanford University.  She is currently a Siebel postdoctoral scholar at the University of California, Berkeley.  

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The advent of regenerative medicine has begun to expand the treatment options available to patients who require tissue reconstruction due to birth defects or injuries.  However, it still offers limited solutions for those patients whose wounds span multiple layers and types of tissues.  This is in part due to the shortcomings of the barrier membranes that are typically implanted in order to maintain tissue layer separation.  In this article, researchers from the University of Sheffield propose novel biodegradable bilayer and trilayer fibrous scaffolds that can effectively segregate tissue layers and maintain proper tissue structure during healing.

Electrospinning was used to create monolayers of microfibrous polylactic acid (PLA), microfibrous poly ε-caprolactone (PCL), and nanofibrous polyhydroxy-butyrate-co-hydroxyvalerate (PHBV).  Initially, fluorescently labeled fibroblasts and mesenchymal progenitor cells (hESMP) were co-cultured on separate sides of each of the monolayer scaffolds.  After seven days, cell mixing was observed on both the PLA and PCL scaffolds.  However, cell segregation was still clearly evident on the PHBV scaffold, indicating that its nanofibrous structure was acting as a barrier to cell penetration. 

The researchers then created bilayer membranes of PHBV-PLA and PHBV-PCL that exhibited similar barrier properties and maintained high levels of cell viability.   These bilayer scaffolds were designed such that the different degradation rates of the composite polymers were comparable to the different growth rates of hard and soft tissue, thus making them better candidates for the treatment of conditions, such as cleft palate, which require bone and soft tissue segregation.  Finally, a PLA-PHBV-PLA trilayer membrane was designed with the goal of supporting two different types of soft tissue growth.  Subsequent results confirmed that the nanofibrous PHBV layer effectively separated the fibroblasts and keratinocytes that were cultured in the two PLA layers.

Ultimately the researchers were able to demonstrate that nanofibrous scaffolds are capable of promoting cell viability while maintaining separation between different cell types.  The methodology used is simple and reproducible and the resulting scaffold is biocompatible and biodegradable.

Development of bilayer and trilayer nanofibrous/microfibrous scaffolds for regenerative medicine
Frazer J. Bye, Julio Bissoli, Leanne Black, Anthony J. Bullock, Sasima Puwanun, Keyvan Moharamzadeh, Gwendolen C. Reilly, Anthony J. Ryan and Sheila MacNeil 
Biomater. Sci., 2013, 1, 942-951 DOI: 10.1039/C3BM60074B

Ellen Tworkoski is a guest web-writer for Biomaterials Science.  She is currently a second year Ph.D. student in the biomedical engineering department at Northwestern University (Evanston, IL, USA).

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