###### Abstract  
Tendon injuries still pose a challenge to reconstructive surgeons. Tendon tissue is a bradytrophic tissue and has a poor tendency to heal. Autologous tendon grafts are, therefore, still the gold standard in restorative operations but are associated with significant donor side morbidity. The experimental approach of the present study focused on the use of the biomaterial spider silk as a biocompatible and very stable carrier matrix in combination with a collagen type I hydrogel and adipose-derived stromal cells. The constructs were differentiated by axial strain to tendon-like tissue using a custom-made bioreactor. Macroscopically, tendon-like tissue could be detected which histologically showed high cell vitality even in long-term cultivation. In addition, cell morphology comparable to tenocytes could be detected in the bioreactor-stimulated tendon-like constructs compared to the controls. Immunohistochemistry-disochemically, tendon tissue-specific markers could be detected. Therefore, the developed tendon-like construct represents a promising approach towards patient specific tendon reconstruction, but further studies are needed. t 19 December 202022 January 20212 January 20  
injuries are still a challenge for reconstructive surgery and, therefore, either restorative operations or versatile grafts are needed to fully replace their function. High failure and recurrence rates have implicated the usage of autograft, allograft and xenograft in tissue replacement [7]. Therefore tissue engineering of tendon tissue might play a significant role for future therapeutic strategies and clinical applications. Choosing the most favorable biomaterial as scaffold for tendon tissue engineering is still challenging as it has to have several features that could translate it into functional tendon tissue [8]. For tendon tissue engineering, mechanical stimulation by means of strain seemed to induce further differentiation in terms of cell shape, production of extracellular matrix (ECM) and expression of tissue-specific markers [9; 10; 11; 12]. Applied strain results in straightening, realignment and sliding of tendon and, therefore, collagen fibers, ultimately subjecting tenocyte nuclei under strain [13; 14]. This consecutively leads to interference of their mechanotransduction pathways and fibril alignment [15]. Studies focusing on bioreactor-based systems led to insights in engineering tendon-like constructs (TLC). Loading amplitudes affect cell and tissue properties with physiological loads leading to overall anabolic response and increased strength of the construct. In contrast, no mechanical stimulation or high amplitude loads lead to a catabolic response [16]. Probably the most favorable approaches are those based on functional tissue engineering with special regard to in vitro-to-in vivo strategies, which ultimately aim to allow early implantation while at the same time tolerate substantial in vivo forces early postoperatively and even larger forces once patients resume to normal activities of daily living [16]. Many biomaterials have been investigated as scaffold for tendon tissue engineering purposes including collagen, silk, alginate, chitosan, polycaprolactone, polyglycolic acid and polylactic acid. In addition, several techniques have been investigated, such as electrospinning, electrochemical alignment, knitting and freeze-drying to create tendon-like constructs [17]. However, current tendon tissue engineering approaches showed promising short-term results but failed over time. The ideal scaffold material should be biodegradable and biocompatible as well as providing sufficient mechanical properties [7; 18]. The stability of the biomaterial chosen depends on mechanical strength, elasticity and biodegradation. Therefore, matching the mechanical properties of a scaffold to those of native ECM is important to ensure that tissue growth is not limited by mechanical failure of the scaffold [7].