## 4 Discussion  
PLGA is the most widely used synthetic biodegradable material due to its excellent biocompatibility, non-toxicity, and non-immunogenicity [63]. Indeed, PLGA is generally recognized as safe for use in particular pharmaceutical products such as degradable sutures, stents, screws, bone plates, and wound dressing by international regulatory agencies, such as the United States Food and Drug Administration (FDA) and the European Medicines Agency (EMA). PLGA is considered the \"material of choice\" to manufacture biodegradable MCs or scaffolds since its degradation products are quickly metabolized in the body via the Krebs cycle [44; 45]. PLGA has also been used as a core polymer to manufacture MCs to culture anchorage-dependent cells, which require large surface areas for attachment and growth. However, pure PLGA carriers do not inherently possess cell-adhesion  
Figure 11: Comparison of the secretome profiles of ASC52 telo cells cultured in standard cell culture vessels (2D) or dynamic conditions (spinner flask, 3D). In this latter case, the cells were cultured either on _BR44_ MC or commercial ProNectin-F MC. The calculated levels are expressed as a percentage relative to the reference spot present on the membrane. Remarkably, the secretion profile depends on the three culture conditions (2D, 3D spinner ProNectin-F, and 3D spinner _BR44_) tested in this study. \begin{table}
\begin{tabular}{c c c c} \hline \hline \multirow{2}{*}{**Analyte/Control**} & **2D** & **3D** & **3D** \\  & **ASCs 52 telo** & **ASCs 52 telo _BR44_ & **ASCs 52 telo ProNectin-F** \\ \hline IL-6 & X & & \\ CXCL8/IL-8 & X & X & X \\ CCL2/MCP-1 & X & & X \\ MIF & X & X & X \\ CCL5/RANTES & X & & \\ Pentraxin-3/TSG-14 & X & & X \\ \hline Sorption E1/PAI-1 & X & X & \\ \hline TIMP-1 & X & X & X \\ Endocan & X & & \\ HGF & X & & \\ ICAM-I/CD54 & X & & \\ Nidogen-1/Entactin & X & & X \\ \hline \hline \end{tabular}
\end{table} 
Table 5: _Cont._motifs. Different approaches have been proposed to functionalize the MC surface and allow efficient attachment and proliferation of anchorage-dependent cells [21]. Therefore, it was decided to synthesize gelatin-PLGAA composite MCs by emulsifying gelatin in a PLGA/dichloromethane solution, followed by a modified water-in-oil-in-water double emulsion solvent evaporation method [25]. Gelatin is a naturally derived polymer, has a chemical structure similar to collagen, thus mimicking the natural extracellular environment [64]. However, it is a product of animal origin and, therefore, potentially able to initiate an immunological response or transmit zoonotic diseases is a drawback. Nevertheless, gelatin has a long history of clinical use, with few adverse outcomes [65; 66]. Moreover, bovine gelatin was replaced by porcine gelatin to avoid Bovine Spongiform Encephalopathy (BSE) related issues. For the orthopedic application of stem cells, it is realistic to plan for ex-vivo cultivation, a manufacturing period of approximately two months. Three to four weeks are needed to amplify the stem cells and as many weeks again to differentiate them into chondrocytes or osteocytes. It is known that during differentiation, the extracellular matrix (ECM) is replaced with one more suited to their new role as mature cells [67]. We estimate that porcine gelatin makes up approximately 10% of the MC. Thus, it is very likely that there will be very little residual porcine gelatin remaining at the time of implantation of the engineered tissue, reducing the risk of an immunological reaction. Nevertheless, further steps are planned to replace porcine gelatin with recombinant human ECM proteins or biomimetic peptides [68]. This is also a necessary step toward respecting the ethical or religious convictions of a considerable number of human beings who do not allow the consumption or use of products of porcine or bovine origin. Several types of MCs were manufactured and examined.