YCN representative - UK

Else Ellermann

YCN representative for the UK

University of Cambridge

ee310@cam.ac.uk

My name is Else Ellermann, and I am a fourth-year PhD student at the Cambridge Centre of Medical Materials (CCMM). I studied biomedical engineering at the University of Groningen and joined the CCMM group to undertake my master’s project where I analysed different types of collagen scaffolds for the purpose of tissue engineering. Because of my strong interest in this topic, I decided to apply for a PhD within that same group.

For my PhD, I transitioned from a polymer to a ceramic specialisation with a focus on calcium phosphates for bone tissue engineering (BTE). BTE aims to heal critical-size fractures or bone voids using a degradable construct similar in composition to the body’s own material. Synthetic hydroxyapatite (HA) closely mimics the mineral component of bone, making it an attractive material for orthopaedic surgery, but for BTE much research is still required to optimise the induced biological response. Ways by which researchers have attempted to improve the bioactivity of HA include ion substitutions, as bone is known to naturally contain various ions. Silicon substitution, in particular, has shown promising results, inducing enhanced bone mineralisation, mechanical stability and bone cell (osteoblast) attachment and proliferation. Despite this, a major challenge in tissue engineering remains the development of an interconnected blood vessel network into scaffolds, with only a few studies showing successful conduction of blood vessels on silicon-substituted HA (Si-HA) in in vitro monocultures. While monocultures can be useful for assessing the direct response of one cell type to certain surface properties, heterotypic cell-cell contact, as will occur in vivo, will ultimately alter their response, since cells are known to stimulate other cell types to proliferate, differentiate, survive, and produce certain growth factors.

My research, therefore, aims to obtain more in-depth knowledge of the simultaneous growth of endothelial cells (for blood vessel formation) and bone cells in response to Si-HA, using an in vitro co-culture. Sequential seeding of osteoblasts (OBs) and endothelial cells (ECs) at an OB to EC cell ratio of 70:30 without external stimuli, was found to induce a more complex vessel-like network on Si-HA as opposed to HA in a 2D environment. Furthermore, using this set-up, our research attempts to obtain reliable knowledge on the extent to which differences in material properties between Si-HA and HA contribute to the observed cell response through single-variable analysis, using a novel method to deconvolute between surface properties.