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With the objective of developing a biodegradable ureteric stent, various polylactides were analyzed and grafted with a clinically adapted surface. Stent moulding was performed by CESP technology (Controlled Expansion of Saturated Polymers), which is not based on high temperature but gas-loading under high pressure which induces a foamy bulk structure. The hydrolytically biodegradable, synthetic homo- and copolymers poly(D,L-lactide) (PDLLA), poly(D,L-lactide-co-trimethylene-carbonate) (PDLLA-co-TMC), poly(D,L-lactide-co-glycolide) (PDLLA-co-Gly) as derivatives of lactic acid or glycolic acid and surface modifications with hydroxyethylene-methacrylate (HEMA) and oligoethyleneoxidemonomethacrylate (OEOMA) were analyzed with regard to cytotoxicity and cell adhesion. Methacrylates have minimized protein and cell adhesion and degradation of non-toxic products. All polymers exhibited a high degree of biocompatibility and cell adhesion was markedly reduced following HEMA grafting. A 3 cm and 7 Charrière prototype of the stent was moulded from PDLLA-co-TMC by CESP-technology, and grafted with HEMA by means of plasma-induced polymerization. Finally, the stents were implanted into female sheep, following unilateral ureterotomy. Regular blood and urine analysis as well as ultrasound and the final autopsy revealed no pathological findings. Histopathological analysis exhibited a regular epithelium without any changes being determined by contact to the stent, and a good regeneration of all layers in the area of anastomosis.

The renal pelvis and the ureter represent a functional system with myogenic excitation generation and conduction. The activity of this system is modulated by the autonomic nervous system: alpha-adrenergic and cholinergic substances stimulate, beta-adrenergic drugs inhibit the pyeloureteral activity. Besides the sympathetic nervous system with adrenergic postganglionic excitation conduction and the parasympathetic nervous system with cholinergic transmission, non-adrenergic, non-cholinergic systems appear to exist. Vasoactive intestinal peptide (VIP), e.g., markably decreases the frequency and amplitude of the ureteral activity. Calcium antagonists (e.g. nifedipin) lead to a direct inhibition of the ureteral activity: the quick phasic contractions are selectively oppressed without any influence on the tonic activity of the pyeloureter. A direct therapeutic modulation of the ureteral activity, however, e.g. to treat a colic or to accelerate the spontaneous discharge of stones, seems to be only rarely possible: Glucagone shows a markable decrease of ureteral peristalsis in animal experiments. Antagonists of prostaglandine proved to have not only an antiinflammatory and central analgetic effect but they also influence the pyeloureter directly by relaxing the muscular layer.

Ureteral peristalsis originates in the most proximal parts of the caliceal system. It is then conducted to the ureter by way of myogenic excitation conduction. In the pyeloureteral region, however, there seems to be some sort of physiological blockade and modulation of activity. It depends on the level of diuresis whether only a few or all contractions of the renal pelvis reach the ureter. Morphological and functional investigations show that the pathophysiological disturbance in cases of primary stenosis of the pyeloureteral junction seems to be a complete blockade of myogenic excitation conduction. The principle of open surgical corrections (dismembered pyeloureteroplasty) is not only to create a widely open connection between renal pelvis and ureter but also to remove the misfunctioning pyeloureteral segment and to substitute it by a region of improved myogenic excitation conduction.