Graphene and its Derivatives for Bone Tissue Engineering: In Vitro and In Vivo Evaluation of Graphene-Based Scaffolds, Membranes and Coatings

We measured the elastic properties and intrinsic breaking strength of free-standing monolayer graphene membranes by nanoindentation in an atomic force microscope. The force-displacement behavior is interpreted within a framework of nonlinear elastic stress-strain response, and yields second- and third-order elastic stiffnesses of 340 newtons per meter (N m(-1)) and -690 Nm(-1), respectively. The breaking strength is 42 N m(-1) and represents the intrinsic strength of a defect-free sheet. These quantities correspond to a Young's modulus of E = 1.0 terapascals, third-order elastic stiffness of D = -2.0 terapascals, and intrinsic strength of sigma(int) = 130 gigapascals for bulk graphite. These experiments establish graphene as the strongest material ever measured, and show that atomically perfect nanoscale materials can be mechanically tested to deformations well beyond the linear regime.

Despite its long history and some preliminary work in tissue engineering nearly 30 years ago, electrospinning has not gained widespread interest as a potential polymer processing technique for applications in tissue engineering and drug delivery until the last 5-10 years. This renewed interest can be attributed to electrospinning's relative ease of use, adaptability, and the ability to fabricate fibers with diameters on the nanometer size scale. Furthermore, the electrospinning process affords the opportunity to engineer scaffolds with micro to nanoscale topography and high porosity similar to the natural extracellular matrix (ECM). The inherently high surface to volume ratio of electrospun scaffolds can enhance cell attachment, drug loading, and mass transfer properties. Various materials can be electrospun including: biodegradable, non-degradable, and natural materials. Electrospun fibers can be oriented or arranged randomly, giving control over both the bulk mechanical properties and the biological response to the scaffold. Drugs ranging from antibiotics and anticancer agents to proteins, DNA, and RNA can be incorporated into electrospun scaffolds. Suspensions containing living cells have even been electrospun successfully. The applications of electrospinning in tissue engineering and drug delivery are nearly limitless. This review summarizes the most recent and state of the art work in electrospinning and its uses in tissue engineering and drug delivery.

Detailed descriptions of the structural features of bone abound in the literature; however, the mechanical properties of bone, in particular those at the micro- and nano-structural level, remain poorly understood. This paper surveys the mechanical data that are available, with an emphasis on the relationship between the complex hierarchical structure of bone and its mechanical properties. Attempts to predict the mechanical properties of bone by applying composite rule of mixtures formulae have been only moderately successful, making it clear that an accurate model should include the molecular interactions or physical mechanisms involved in transfer of load across the bone material subunits. Models of this sort cannot be constructed before more information is available about the interactions between the various organic and inorganic components. Therefore, further investigations of mechanical properties at the 'materials level', in addition to the studies at the 'structural level' are needed to fill the gap in our present knowledge and to achieve a complete understanding of the mechanical properties of bone.