Mesoporous silicon/biopolymer composites for orthopedic tissue engineering and drug delivery applications

There are a number of useful properties that make mesoporous silicon (PSi) an interesting candidate as an active biomaterial: resorption in vitro/in vivo with a negligible inflammatory response; a porous morphology, thereby permitting drug release; and an ability to stimulate calcification. Recent work from our lab has focused on nanostructured composite materials composed of PSi and common biopolymers such as poly (epsilon-caprolactone) (PCL). When fabricated in microfibrous form, such composites can stimulate the deposition of calcium phosphate (the inorganic component of bone) not only in simulated body fluid (SBF), but also on the surface of cell layers adhering to the scaffolds during proliferation. Human mesenchymal stem cells and mouse stromal cells were used for cell proliferation and differentiation assays, along with scaffold attachment experiments. The results of alkaline phosphatase expression as a specific biomarker for mensenchymal to bone cell differentiation show that the scaffolds have the ability to mediate such processes. Cell ultra-structural studies using transmission electron microscopy (TEM) also reveal that PSi plays a role in accelerating the calcification process.;Drug loaded PSi/PCL composites also have the potential to be used as target drug delivery vehicles. In one study, PSi was loaded with Cis -- (2, 2'-bipyridine) dichloro ruthenium (II) (CBDR) and Tris-- (2, 2'-bipyridine) ruthenium chloride (TBRC) as model hydrophobic and hydrophilic drugs, respectively. In order to study how the spatial location of the loaded PSi affects the drug release behaviors, two types of composites were prepared: one is where drug loaded PSi was fully encapsulated into PCL fibers; the other involved drug loaded PSi surface embedded onto PCL fibers. Both of the release profiles show the same trend in that the initial release of CBDR or TBRC from fully encapsulated PSi in PCL is much slower than that released from surface embedded PSi. The controlled-release of CBDR and TBRC both depend on both the amount of drug loading and their spatial distribution in the PCL fibrous scaffolds.;Overall, the results show that electrospun PSi composites can be considered as biocompatible scaffolds with the potential as drug delivery materials for orthopedic tissue engineering applications.