A Minimally-Invasive 3D-Printed Microneedle Array Applicator System (μNAAS) for Delivery of Therapeutics to Citrus Leaf Tissue

Abstract

mal growth environment, which causes reproduction to occur at a fast and steady rate. As the disease progresses, the bacteria slowly obstruct the systemic phloem and block the sugar transport to the roots, ultimately killing the tree within a decade of initial symptom development (Bové, 2006). Unfortunately, there is still a lack of treatment options that are technically feasible, sustainable, and environmentally safe, since C. Las cannot be cultured, making lab work extremely challenging (Grafton-Cardwell et al., 2013). HLB has spread to nearly all major citrus-producing regions around the world (Chen et al., 2018). In Florida alone, the estimated damage over the last five years amounts to over $1 billion per year and around 5000 jobs are lost yearly (Li et al., 2020).Younger seedlings are extremely susceptible to C. Las. Once they are infected, their health slowly declines, reducing the productivity and quality of the fruit. HLB-affected fruit are lopsided, bitter, hard, and green when ripe (Burrow and Dewdney, 2019). All infected trees will eventually succumb to HLB unless an effective treatment methodology is developed.Citrus growers are currently using bactericides such as streptomycin and oxytetracycline as an attempt to kill the bacteria in the tree, but they have provided no significant improvements (Li et al., 2020). Growers currently utilize two main therapeutic application methods: soil drench and foliar application (Eveland and Brown, 2019). Although soil drench, where treatments are added to the base of the plant