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Diseases of the cardiovascular system are the main reasons for morbidity and mortality in all western countries. The total direct and indirect costs of cardiovascular diseases (CVD) and stroke for 2007 are estimated at $286 billion for the USA alone.1 Coronary heart disease (CHD) or ischemic heart disease (IHD) plays the most important role in the field of CVD. In the recent decades great efforts have been undertaken to develop materials for artificial vascular constructs. However, bio-inert materials like expanded polytetrafluoroethylene (ePTFE) or polyethylene terephthalate (PET) do not fulfill all requirements to be applicable as material for narrow blood vessel replacements (coronary bypasses). Therefore there is the aim to design new biocompatible and biodegradable materials to overcome this. The standard materials in this field are polyesters such as poly(lactic acid) (PLA) or poly(glycolic acid) (PGA).2 At this, the large amounts of free acids generated upon degradation are on of the main problems, since this can lead to inflammations of the adjacent tissue.
Another key factor is the mechanical properties of the final scaffold. At this, the graft should exhibit mechanical properties similar to those of the substituted tissue with a rather low Young’s modulus around 500 kPa, tensile strength around 1000 kPa, elongation at break between 100 and 150% and high suture tear resistance. Moreover, natural blood vessels exhibit a highly complex, hierarchical architecture with different layers. Hence, not only the biocompatibility and the mechanical properties of the final graft have to be taken into consideration but also the three-dimensional structure.4 For this purpose lithography-based Additive Manufacturing Technologies (AMTs) are very capable methods since they offer the possibility to create cellular structures within the grafts that might enable a uniform ingrowth of cells into the scaffold.5 In this contribution the use of photoelastomers for artificial vascular constructs is discussed since they can be readily structured by means of lithography-based AMTs such as Digital Light Processing (DLP).
Classic materials generated by this technology are rather densely crosslinked polymers based on (meth)acrylic monomers which are too stiff and too brittle for the designated application. Hence, it was decided to modify the original network architecture by the introduction of dithiol chain transfer agents which are able to coreact with the acrylates and reduce the crosslink density.6 The base monomer was a commercially available urethane diacrylate. In combination with reactive diluents and dithiols the properties of the final photopolymers were tailored and degradability could be introduced. The optimized photoelastomers were in good mechanical accordance with native blood vessels. Moreover, they also showed good biocompatibility in in-vitro tests, degraded similar to poly(lactic acid) and could successfully be manufactured with lithography-based AMTs.
