tested on smaller tissue models of lungs. the company organovo, which designed one of the initial commercial bioprinters in 2009, has displayed that biodegradable 3d tissue models can be used to research and develop new drugs, including those to treat cancer. an additional impact of organ printing includes the ability to rapidly create tissue models, therefore increasing productivity. challenges one of the challenges of 3d printing organs is to recreate the vasculature required to keep the organs alive. designing a correct vasculature is necessary for the transport of nutrients, oxygen, and waste. blood vessels, especially capillaries, are difficult due to the small diameter. progress has been made in this area at rice university, where researchers designed a 3d printer to make vessels in biocompatible hydrogels and designed a model of lungs that can oxygenate blood. however, accompanied with this technique is the challenge of replicating the other minute details of organs. it is difficult to replicate the entangled networks of airways, blood vessels, and bile ducts and complex geometry of organs. the challenges faced in the organ printing field extends beyond the research and development of techniques to solve the issues of multivascularization and difficult geometries. before organ printing can become widely available, a source for sustainable cell sources must be found and large-scale manufacturing processes need to be developed. additional challenges include designing clinical trials to test the long-term viability and biocompatibility of synthetic organs. while many developments have been made in the field of organ printing, more research must be conducted.