Integration of Electrospun Materials in Microelectronic and Biomedical Applications

Licentiate thesis, 2009

This thesis demonstrates the use of electrospinning and the novel properties of electrospun materials in two fields. The microelectronics industry has identified thermal interface materials as one of the major bottlenecks hindering further integration at packaging level. New concepts based on metal-polymer composite architectures are needed to fulfill current and future thermal and thermomechanical requirements on thermal interface materials at maintained cost efficiency. In this thesis, an interpenetrating phase polymer-metal composite for thermal interface material applications has been developed and characterized. Both fabrication and metrology equipment has been developed for the purpose at hand. The composite is based on a porous electrospun polymer carrier infiltrated with a high thermal conductivity metal phase. The two phases form two fully interpenetrating networks in the composite. Efficient heat transfer is achieved through the continuous metal phase, while the polymeric phase defines geometry and phase composition. The devised composite architecture is believed to be a step towards meeting current and future demands on thermal performance and thermomechanical reliability in microelectronic products. Furthermore, the thesis presents initial results of human embryonic stem cell proliferation and neural differentiation in co-culture with electrospun scaffolds, of interest in future regenerative medicine based on stem cells. Results indicate that physical cues emanating from cell-scaffold interactions affect cells towards a neuronal fate during differentiation, a phenomenon consistent with reports in literature on physical cues influencing stem cell fate. To allow for deeper analysis on cell-scaffold interactions of the type described above, a microfabricated platform was developed for the purpose. A novel method for direct photolithographic micropatterning of electrospun polyurethane fibrous films over large surfaces has been devised. The method allows for assembly of complex electrospun microstructures on single substrates via a multilayer approach involving multiple photolithographic exposures, analogous to conventional photolithography in microfabrication of solid state devices. Indeed, this technique can find application in a variety of applications where it is beneficial to integrate micropatterned electrospun structures into microfabricated devices, in particular within biomedical engineering applications.