# Poly(\(\alpha\)-hydroxy Acids)-Based Cell Microcarriers
###### Abstract  
Biodegradable poly(\(\alpha\)-hydroxyacids) have gained increasing interest in the biomedical field for their use as cell microcarriers thanks to their biodegradability, biocompatibility, tunable mechanical properties/degradation rates and processability. The synthesis of these poly(\(\alpha\)-hydroxyacids) can be finely controlled to yield (co)polymers of desired mechanical properties and degradation rates. On the other hand, by simple emulsion-solvent evaporation techniques, microspheres of controlled size and size distribution can be fabricated. The resulting microspheres can be further surface-modified to enhance cell adhesion and proliferation. As a result of this process, biodegradable microccarriers with advanced functionalities and surface properties that can be directly employed as injectable cell microcarriers are obtained. polylactide; poly(\(\alpha\)-hydroxyacids); cell microcarriers; microparticles; tissue engineering 2016  
(Oct4, Sox2, Nanog, Rex1) and enhanced pro-angiogenic properties, determined by the tubular network formation ability of human umbilical vein endothelial cells (HUVECs) in the presence of hADSCs seeded on microcarriers when cultured on gelatin microspheres with respect to hADSCs cultured in a monolayer [8]. Several studies compared the performance of cells in commercially available microcarriers [9; 10], and these are summarized in Table 1. Since each cell type responds differently to different microcarriers, the choice of the microcarrier will be directly determined by the particular application under consideration. Apart from the aforementioned commercially available microcarriers, research has also focused on the development of other kinds of microcarriers with improved performance and advanced functionalities [11; 12; 13; 14; 15; 16; 17]. For the present review, microcarriers that are made out of biodegradable and biocompatible poly(\(\alpha\)-hydroxy acids) will be considered. These materials have attracted increasing interest for their use as microcarriers due to their biodegradability, biocompatibility, tunable mechanical properties/degradation rates and possibility of being employed directly as injectable cell microcarriers in cell-based therapies. For the regeneration of several tissues cell-based therapies have been studied, particularly for those that show limited capacity to spontaneously regenerate, for example, intervertebral discs [18], cartilage [19] and the nervous system [20], among others. The direct injection of living cells in the absence of supporting biomaterials has shown limited efficacy in clinical trials because of poor cell survival, uncontrolled differentiation, low retention/integration into the host tissue, etc. Therefore, a combination of cells with biomaterials has been proposed as a strategy to overcome the aforementioned obstacles. Among these, injectable systems such as hydrogels [21] or microcarriers have shown promising results. The present review first considers the current strategies that have been adopted for the synthesis of biodegradable and biocompatible poly(\(\alpha\)-hydroxy acids) with tunable mechanical properties and degradation rates. Then, the fabrication methods that yield micron-sized particles are briefly summarized. Finally, how these microparticles have been applied as cell microcarriers in biomedical applications are considered. \begin{table}
\begin{tabular}{l l l l l l l l} \hline \hline
**Commercial Name** & **Shape** & **Dimensions** & **Matrix** & **Surface** & **Surface** & **Manufacturer** & **Performance of Cells** \\
**Value** & & & & & & & & \\ \hline \hline \multirow{2}{*}{_Cylate 1_} & \multirow{2}{*}{Spherical} & \multirow{2}{*}{-190 μm} & Cross-linked & Hydrophilic & \multirow{2}{*}{0.44} & GE Healthcare & Study by [PERSON] et al.