The concept of closed-loop insulin delivery was proposed by Kadish over five decades ago [47]. The Biostator, the first commercially available device, was introduced in the late 1970s utilising intravenous glucose sampling and intravenous insulin infusion. With advances in subcutaneous insulin pump therapy and sensor technology, the focus moved to combining body-worn and not implantable devices to deliver insulin and measure glucose in the subcutaneous tissue. Current closed-loop systems consist of three components: a real-time CGM, an insulin pump and a control algorithm (Fig. 14.1).

Two main categories of control algorithm have been employed, the proportional-integral-derivative (PID) controller [48, 49], a classic feedback control mechanism, and the model predictive controller (MPC) [50]. Other clinically evaluated approaches include controllers based on fuzzy logic [51] or a combination of MPC and PID for insulin and glucagon co-delivery [52]. Apart from the insulin-only systems, bi-hormonal systems have evolved which deliver both insulin and glucagon [44].

Initial single- or multiday/night studies in children and adolescents under controlled laboratory settings suggested improved glycaemic control during overnight closed loop [50, 53–55] and day-and-night closed loop [56, 57] and an unchanged [56, 57] or reduced [50, 53, 54] risk of hypoglycaemia when compared to sensor-augmented pump therapy.

Investigations in transitional settings, incorporating remote monitoring and supervision by research staff on-site in hotels [58] or at diabetes camps [59–61] demonstrated promising results in children and adolescents with regard to improved glucose control and hypoglycaemia reduction using insulin-only [59, 61] and bi-hormonal systems [60].

Recently, first short- to midterm at-home studies have been performed. In adolescents, three- [62] to six-week [63] home use of overnight closed-loop systems with remote monitoring [63] or unsupervised [62] was shown to be feasible, safe and effective. The time glucose was in the target range was significantly increased compared to sensor-augmented pump therapy [62, 63], including fewer nights with glucose levels in the hypoglycaemic range [62] and reduced time spent in hypoglycaemia [63]. In a 7-day free-living evaluation of a 24/7 closed-loop system with manual prandial insulin in suboptimally controlled children and adolescents, closed loop significantly reduced mean glucose and increased time in target without increasing the risk of hypoglycaemia [64].

In a quantitative and qualitative psychosocial analysis of experiences of closed-loop trial participants, adolescents and their parents reported positive themes such as reassurance/peace of mind, ‘time off’ from diabetes demands, improved overnight control leading to improved daily functioning and diabetes control and improved sleep. The key negative themes are related mainly to technical difficulties, intrusiveness of alarms and size of the devices. Overall, for adolescents, benefits of a closed-loop system seemed to outweigh practical challenges [65].