Chemical and Biological Engineering PhD Thesis Defense by Tuğba Bal








Title: Design of Biomimetic Extracellular Matrix to Improve Pancreatic Islet Engraftment


Speaker: Tuğba BAL


Time: September 6, 2017, 14:00


Place: ENG208

Koc University

Rumeli Feneri Yolu

Sariyer, Istanbul

Thesis Committee Members:

Assoc. Prof. Seda Kızılel (Advisor, Koc University)

Prof. Burak Erman (Koc University)

Prof. Hakan Sedat Orer (Koc University)

Assoc. Prof. Ayşe Karakeçili (Ankara University)

Asst. Prof. Duygu Ekinci (Turkish-German University)



Pancreatic islet transplantation has emerged as a promising treatment for type 1 diabetes and engraftment of beta cells after transplantation determines the success of clinical setting. However, clinical application of islet transplantation is still limited by life-long use of immunosuppressive drugs and insufficient number of islets to achieve normoglycemia.

In this study, we tailored biochemical and biophysical properties of hydrogels to promote insulin secretion function and immunoregulatory potential through incorporation of mesenchymal stem cells (MSCs) and natural extracellular matrix mimetic peptides such as RGDS, IKVAV and insulinotropic peptide (GLP-1). We achieved higher insulin secretion function with GLP-1 and RGDS-IKVAV incorporation, while apoptotic activities were significantly reduced. Co-encapsulation of insulin secreting islets with MSCs contributed to 2-fold increases in insulin secretion compared to control islets and further increases were observed with peptide incorporation. We observed that protection against pro-inflammatory can be achieved in free and PEG hydrogel encapsulated MIN6-MSC heterospheroids.  Although deleterious effects of cytokines were not completely inhibited, MSCs laden with MIN6 beta cells in PEG hydrogels demonstrated significant differences compared to MIN6 pseudoislets. Further, improvement in stimulation of beta cells was evident in GLP-1 functionalized hydrogels, as 62% increase was accomplished in heterospheroid laden hydrogels.

To tailor biophysical properties of islet microenvironment, we developed unique type of nano-thin coating for insulin secreting beta cell aggregates. The coating is based on hydrophobic and covalent interactions of natural acrylate modified cholesterol bearing pullulan nanogels (CHPOA) on MIN6 beta cell aggregates. We demonstrated conformal bilayer coating of nanogels over beta cell aggregate surfaces, cell viability and functionality for at least 72 hours in vitro. Beta cell aggregates, derived from mice, were prepared as spheroids through hanging drop method, which was optimized with respect to hanging drop volume and initial number of beta cells. These aggregates, defined as pseudoislets, were coated with sequential layers of nanogels and were determined as viable and functional for insulin secretion. We carried out coating experiments using physiologically compatible medium, where pseudoislets were not brought in contact with toxic prepolymer solutions which is used in existing approaches. We also confirmed in vivo biocompatibility of CHPOA nanogels through subcutaneous transplantation into CD1 mouse.

This study is promising and offers new opportunities through coating of insulin secreting islets with advanced functional materials under completely physiological conditions and will contribute to longer functional islets for clinical translation of cell transplantation technology and particularly for the treatment of type 1 diabetes.