Polymer microarrays for cell based applications

Abstract

The development and identification of new biomaterials that can replace specific tissues and organs is desirable. In the presented PhD thesis polymer microarrays were applied for the screening of polyacrylates and polyurethanes and evaluation for material discovery for applications in the life sciences.

In the first part of the thesis, the largest polymer microarray ever made with more than 7000 features was fabricated and subsequently used for the screening of polyacrylates that can control the fate of human embryonic stem cells. As stem cells have unique properties that offer the potential of replacing damaged or diseased tissue in future, the identification of cultivation substrates that can replace current biological and animal derived products was desirable. The water contact angle, roughness and cell doubling time of the cells on the identified polymers was determined and the stem cells characterised after 5 passages and compared to the currently most widely used animal derived substrate MatrigelTM.

In the second part of the thesis, the development of a new polymer gradient microarray is presented. Initial studies involved the optimisation of printing parameters for the generation of linear polymer gradient lines and confirmed by XPS analysis. Cellular binding studies with the suspension cell line K562 and the adherent cell line HeLa were carried out and compared to previous binding studies to confirm the success of the concept. In further studies, the polymer gradients were functionalised with small molecules and proteins, allowing the generation of a protein gradient microarray with Semaphorin 3F. In binding studies with neuron cells it could be shown that the binding of the cells was concentration-dependent.

The identification of polyacrylates for the effective and rapid activation and aggregation of platelets is described in the third part of the presented thesis. Here, polymer microarrays were applied for the binding of platelets in human blood samples. The amount of bound platelets as well as their activation state was compared to the natural agonist collagen by employing fluorescence intensity studies and scanning electron microscopy. In shear studies, the activation of the platelets by the polymers was evaluated under physiological conditions. The mechanism by which the polymer triggered the activation was further explored by protein binding studies. It was shown that the initial adsorption of fibrinogen and von Willebrand factor on the polymers lead to the adherence and aggregation of platelets.

In the final part of the presented thesis, polymer microarrays were used to identify polymers that can sort and collect the precursor cells of platelets (megakaryocytes).

For this purpose, the cell lines K562 and MEG-01 were used as cellular models. The identified polymers and the effect on the immobilised cells was further investigated by scanning electron microscopy, flow cytometry and miRNA studies. The adsorbed proteins on the different polymers were found to influence the cellular morphology on the different substrates.