Biologische vaskularisierte Matrix (BioVaM)

Lacrimal gland regeneration: The unmet challenges and promise for dry eye therapy

DED (Dry eye disease) is a common multifactorial disease of the ocular surface and the tear film. DED has gained attention globally, with millions of people affected.. Although treatment strategies for DED have shifted towards Tear Film Oriented Therapy (TFOT), all the existing strategies fall under standard palliative care when addressed as a long-term goal. Therefore, different approaches have been explored by various groups to uncover alternative treatment strategies that can contribute to a full regeneration of the damaged lacrimal gland. For this, multiple groups have investigated the role of lacrimal gland (LG) cells in DED based on their regenerating, homing, and differentiating capabilities. In this review, we discuss in detail therapeutic mechanisms and regenerative strategies that can potentially be applied for lacrimal gland regeneration as well as their therapeutic applications. This review mainly focuses on Aqueous Deficiency Dry Eye Disease (ADDE) caused by lacrimal gland dysfunction and possible future treatment strategies. The current key findings from cell and tissue-based regenerative therapy modalities that could be utilised to achieve lacrimal gland tissue regeneration are summarized. In addition, this review summarises the available literature from in vitro to in vivo animal studies, their limitations in relation to lacrimal gland regeneration and the possible clinical applications. Finally, current issues and unmet needs of cell-based therapies in providing complete lacrimal gland tissue regeneration are discussed.

In vitro maturation of large-scale cardiac patches based on a perfusable starter matrix by cyclic mechanical stimulation

The ultimate goal of tissue engineering is the generation of implants similar to native tissue. Thus, it is essential to utilize physiological stimuli to improve the quality of engineered constructs. Numerous publications reported that mechanical stimulation of small-sized, non-perfusable, tissue engineered cardiac constructs leads to a maturation of immature cardiomyocytes like neonatal rat cardiomyocytes or induced pluripotent stem cells/embryonic stem cells derived self-contracting cells. The aim of this study was to investigate the impact of mechanical stimulation and perfusion on the maturation process of large-scale (2.5×4.5cm), implantable cardiac patches based on decellularized porcine small intestinal submucosa (SIS) or Biological Vascularized Matrix (BioVaM) and a 3-dimensional construct containing neonatal rat heart cells. Application of cyclic mechanical stretch improved contractile function, cardiomyocyte alignment along the stretch axis and gene expression of cardiomyocyte markers. The development of a complex network formed by endothelial cells within the cardiac construct was enhanced by cyclic stretch. Finally, the utilization of BioVaM enabled the perfusion of the matrix during stimulation, augmenting the beneficial influence of cyclic stretch. Thus, this study demonstrates the maturation of cardiac constructs with clinically relevant dimensions by the application of cyclic mechanical stretch and perfusion of the starter matrix.

STATEMENT OF SIGNIFICANCE

Considering the poor endogenous regeneration of the heart, engineering of bioartificial cardiac tissue for the replacement of infarcted myocardium is an exciting strategy. Most techniques for the generation of cardiac tissue result in relative small-sized constructs insufficient for clinical applications. Another issue is to achieve cardiomyocytes and tissue maturation in culture. Here we report, for the first time, the effect of mechanical stimulation and simultaneous perfusion on the maturation of cardiac constructs of clinical relevant dimensions, which are based on a perfusable starter matrix derived from porcine small intestine. In response to these stimuli superior organization of cardiomyocytes and vascular networks was observed in contrast to untreated controls. The study provides substantial progress towards the generation of implantable cardiac patches.

Generation of bioartificial heart tissue by combining a three-dimensional gel-based cardiac construct with decellularized small intestinal submucosa

The in vitro generation of a bioartificial cardiac construct (CC) represents a promising tool for the repair of ischemic heart tissue. Several approaches to engineer cardiac tissue in vitro have been conducted. The main drawback of these studies is the insufficient size of the resulting construct for clinical applications. The focus of this study was the generation of an artificial three-dimensional (3D), contractile, and suturable myocardial patch by combining a gel-based CC with decellularized porcine small intestinal submucosa (SIS), thereby engineering an artificial tissue of 11 cm² in size. The alignment and morphology of rat neonatal cardiomyocytes (rCMs) in SIS-CC complexes were investigated as well as the re-organization of primary endothelial cells which were co-isolated in the rCM preparation. The ability of a rat heart endothelial cell line (RHE-A) to re-cellularize pre-existing vessel structures within the SIS or a biological vascularized matrix (BioVaM) was determined. SIS-CC contracted spontaneously, uniformly, and rhythmically with an average rate of 200 beats/min in contrast to undirected contractions observed in CC without SIS support. rCM exhibited an elongated morphology with well-defined sarcomeric structures oriented along the longitudinal axis in the SIS-CC, whereas round-shaped and random-arranged rCM were observed in CC. Electric coupling of rCM was demonstrated by microelectrode array measurements. A dense network of CD31⁺/eNOS⁺ cells was detected as permeating the whole construct. Superficial supplementation of RHE-A cells to SIS-CC led to the migration of these cells through the CC, resulting in the re-population of pre-existing vessel structures within the decelluarized SIS. By infusion of RHE-A cells into the BioVaM venous and arterial pedicles, a re-population of the BioVaM vessel bed as well as distribution of RHE-A cells throughout the CC was achieved. Rat endothelial cells within the CC were in contact with RHE-A cells. Ingrowth and formation of a network by endothelial cells infused through the BioVaM represent a promising step toward engineering a functional perfusion system, enabling the engineering of vascularized and well-nourished 3D CC of dimensions relevant for therapeutic heart repair.

Long-term functional reconstruction of segmental tracheal defect by pedicled tissue-engineered trachea in rabbits

Due to lack of satisfactory tracheal substitutes, reconstruction of long segmental tracheal defects (>6 cm) is always a major challenge in trachea surgery. Tissue-engineered trachea (TET) provides a promising approach to address this challenge, but no breakthrough has been achieved yet in repairing segmental tracheal defect. The longest survival time only reached 60 days. The leading reasons for the failure of segmental tracheal defect reconstruction were mainly related to airway stenosis (caused by the overgrowth of granulation tissue), airway collapse (caused by cartilage softening) and mucous impaction (mainly caused by lack of epithelium). To address these problems, the current study proposed an improved strategy, which involved in vitro pre-culture, in vivo maturation, and pre-vascularization of TET grafts as well as the use of silicone stent. The results demonstrated that the two-step strategy of in vitro pre-culture plus in vivo implantation could successfully regenerate tubular cartilage with a mechanical strength similar to native trachea in immunocompetent animals. The use of silicone stents effectively depressed granulation overgrowth, prevented airway stenosis, and thus dramatically enhanced the survival rate at the early stage post-operation. Most importantly, through intramuscular implantation and transplantation with pedicled muscular flap, the TET grafts established stable blood supply, which guaranteed maintenance of tubular cartilage structure and function, accelerated epithelialization of TET grafts, and thus realized long-term functional reconstruction of segmental tracheal defects. The integration of all these improved strategies finally realized long-term survival of animals: 60% of rabbits survived over 6 months. The current improved strategy provided a promising approach for long-term functional reconstruction of long segmental tracheal defect.

Small intestinal submucosa segments as matrix for tissue engineering: review

Tissue engineering (TE) is an emerging interdisciplinary field aiming at the restoration or improvement of impaired tissue function. A combination of cells, scaffold materials, engineering methods, and biochemical and physiological factors is employed to generate the desired tissue substitute. Scaffolds often play a pivotal role in the engineering process supporting a three-dimensional tissue formation. The ideal scaffold should mimic the native extracellular environment providing mechanical and biological properties to allow cell attachment, migration, and differentiation, as well as remodeling by the host organism. The scaffold should be nonimmunogenic and should ideally be resorbed by the host over time, leaving behind only the regenerated tissue. More than 40 years ago, a preparation of the small intestine was introduced for the replacement of vascular structures. Since then the small intestinal submucosa (SIS) has gained a lot of interest in TE and subsequent clinical applications, as this material exhibits key features of a highly supportive scaffold. This review will focus on the general properties of the SIS and its applications in therapeutical approaches as well as in generating tissue substitutes in vitro. Furthermore, the main problem of TE, which is the insufficient nourishment of cells within three-dimensional, artificial tissues exceeding certain dimensions is addressed. To solve this issue the implementation of another small intestine-derived preparation, the biological vascularized matrix (BioVaM), could be a feasible option. The BioVaM comprises in addition to SIS the arterial and venous mesenteric pedicles and exhibits thereby a perfusable vessel bed that is preserved after decellularization.