Design, in-silico testing and fabrication of hydrogel patches for skeletal muscle defects

There are several types of skeletal muscle defect. A first example is volumetric muscle loss (VML), which is currently treated by grafting a muscle flap obtained from a patient healthy muscle. However, this approach is very invasive and often unsuccessful. Another cause of skeletal muscle defects are the malformations, such as congenital diaphragmatic hernia (CDH), a neonatal condition in which the diaphragm is incorrectly formed, leaving a hole through which abdominal organs can herniate into the chest cavity. Traditional therapeutic solution consist of closing the defect with synthetic patches, but these are unable to follow the patient's growth. The proposed solution for the treatment of skeletal muscle defects involves engineered patches based on an extracellular matrix derived hydrogel. The hydrogel is obtained through decellularization of porcine diaphragm. Muscle cells are added to the patches, that should integrate and grow with the patient, in line with the tissue engineering approach. To optimize the alignment of the collagen fibres within the hydrogel patches, the patches are mechanically stressed during cross-linking in a specially designed bioreactor. The aim is to impose a deformation ramp up to physiological values of 5-10%. In this work, two patches were designed, one for muscles with linearly arranged fibres and one for the diaphragm with radially arranged fibres. A finite element computational model of the system was created and validated, with which the deformation field was studied to derive the parameters to be imposed in the bioreactor to impart the desired deformations to the patches. The designed patches were fabricated using the micro-molding technique. A preliminary analysis of the influence of mechanical stimulation on the orientation of the collagen fibres in the patches was carried out, and finally it was verified that the stimulation system used was also suitable for mid-term cell cultures.