## 1 Introduction  
As we have outlined in our previous work [1], neurons play a crucial role in receiving and sending electrochemical information within the peripheral nervous system of vertebrates. Here, the neurons are essentially supported and protected by glial cells. Among these, Schwann cells are particularly significant. They are responsible for forming myelin sheaths, which insulate and protect neuronal axons [2], and are indispensable for axon regeneration following injury [3]. Peripheral axons regenerate within regeneration tracks, which consist in principle of parallelly aligned glial cells [4]. While small gaps in axons can regenerate independently, larger gaps typically require the assistance of a nerve graft. Peripheral nerve injuries often leave life-long disabilities affecting millions of people worldwide. In Europe alone, the typical annual number of nerve repair procedures exceeds 300,000, and this is projected to increase over time. The global peripheral nerve injury market size was estimated at USD 1.65 billion in 2024 and is expected to grow at a compound annual growth rate (CAGR) of 7.80% from 2025 to 2030 [5]. The current gold standard for treating nerve injuries involving large gaps is the use of autografts. However, this approach has notable limitations, such as donor site morbidity and the requirement of a second surgical procedure, highlighting the need for improved alternatives. One such alternative is nerve allografts, which circumvent the drawbacks of autografts but necessitate approximately 18 months of immunotherapy to prevent graft rejection [6]. A third option for addressing large nerve injuries is the use of synthetic neuronal implants. These commercially available implants are typically hollow tubular channels that connect the two severed nerve ends, aiming to enhance the growth of newly formed axons, i.e., more axons growing longer and faster [6]. To be effective, nerve conduits must possess key properties such as biocompatibility, biodegradability and appropriate mechanical and biochemical characteristics. However, significant challenges remain, including issues like incorrect target innervation and axonal dispersion. Additionally, the repair length in humans achievable with current implants has its limitations. Gaps of more than 3 cm are considered to be critical [6]. For larger nerve gaps spanning several centimeters, the success rates of artificial nerve grafts remain insufficient. A critical factor here is the stimulation of the Schwann cells from their surrounding environment, such as the extracellular matrix (ECM) or, in the case of artificial implants, the supporting material, which can influence their elongated alignment and therefore the regeneration of the axons [3; 7]. One potential approach to guiding Schwann cells is the employment of silk materials from nature. For example, the studies reported in [8; 9] highlight promising advancements in utilizing natural silk fathoms produced by spiders for guiding newly formed neuronal axons. However, collecting spider silk fathoms is expensive and requires a lot of time. As an alternative, synthetic electrospun fibers with sub-um diameters offer a more practical solution. Early research efforts in this direction have been documented in [10]. Recently, it has been shown that Schwann cells grow significantly faster and with better directionality on spider silk with parallel grooves, with periodicities and heights in the dimensions of a few micrometers, compared to smooth spider silk fibers without grooves [11]. An interesting material in this aspect is cellulose acetate butyrate (CAB). CAB is a biocompatible and biodegradable polymer, its main part being the biomaterial cellulose with attached acetyl and acyl rests. It is used as artificial silk and can be prepared in fiber form by electrospinningning. Electrospun CAB nanofibers with longitudinal nano-grooves on the fiber surface were used for the regeneration of nerves in rats [12].