# Poly(lactic acid)-Based Blends: A Comprehensive Review
## 3 Composites of Poly(lactic acid) with Poly(glycolic acid)  
Poly(glycolic acid) (PGA) (Figure 5) has a glass transition temperature of 35-40 \({}^{\circ}\)C, a melting point of 220-230 \({}^{\circ}\)C, and a density of 1.53 g/mL [45]. PGA also has an increased degree of crystallinity, about 45-55%, which leads to insolubility in water. The solubility of this polyester varies from the molecular weight and the degree of crystallinity. Its high-molecular form is insoluble in almost all common organic solvents (acetone, dichloromethane, chloroform, ethyl acetate, tetrahydrofuran) with the exception of highly fluorinated organic compounds such as hexafluoroisopropanol [46], while low-molecular oligomers are quite different in their physical properties and are more soluble. The mechanical properties of PGA are much higher than those of other biodegradable plastics and the most traditional plastics. It has a tensile strength of about 115 MPa and a Young's modulus of about 7 GPa. The flexural strength and elastic modulus of PGA are about 222 MPa and 7.8 GPa, correspondingly. The molecular structure of PGA has a flat zigzag conformation, which may be the reason for high mechanical properties compared to other biopolymers [47]. Poly(glycolic acid) is widely used in medicine, as well as in the fields of packaging and the oil and gas industry [48]. The presence of hydrolysate ester bonds in the structure of macromolecules makes the polymer capable of enzymatic hydrolysis during composite. According to the studies, the duration of biodegradation for PGA is 1.5-3 months [49]. Therefore, PGA has better mechanical properties and faster degradation than PLA that provides appealing to develop materials based on PLA/PGA blends. Due to the widespread use of PGA for medical purposes, special attention is paid to nonwovens based on PLA/PGA blends. [PERSON] et al. [50] have obtained the matrices from ultrafine PLA/PGA fibers by an electrospinning method. Figure 6 shows SEM images of the developed nonwoven materials of different compositions. All ultrathin fibers of the matrices were characterized by a round shape and an average diameter from 200 to 500 nm. By varying the ratio of PLA/PGA in the blend, it is possible to control the rate of biodegradation [51], as well as the mechanical properties of the materials obtained by an electrospinning method [52]. An acceptable level of physical and mechanical characteristics of PLA/PGA nonwovens allows us to create natural soft tissues, in particular the stretching of blood vessels on their basis. PLA/PGA scaffolds have shown effectiveness in the proliferation and stability of epithelial cells in the intestinal epithelium, and in the treatment  
Figure 5: The chemical structure of poly(glycolic acid). of short bowel syndrome [53]. In addition, such materials have shown an increase in the ability to pass the blood-brain barrier [54]. [PERSON] et al. [55] have studied PLA/PGA blends in orthopaedic applications such as tissue growth implants and fracture fixation devices. Bioabsorbable fixing devices and ultrahigh-strength implants consist of PLA and/or PGA are widely used in orthopaedic and craniofacial surgery. The main areas of application of such materials are stabilizing frames for fractures, bone grafting, reattaching ligaments and tendons, etc. It has been shown that the application of PLA/PGA blends reduces the risks during preimplantation osteoporosis and the risks arising from infections, as well as showing promise for the slow release of bioactive agents in the field of orthopaedics. [PERSON] et al. [56] have created a wound-healing dressing based on PLA/PGA composites, which provides a temporary basis for cell migration in the wound, while simultaneously delivering ibuprofen as an anti-inflammatory and analgesic agent. This material collapses in 6 days, which avoids the need to remove this bandage. The flexibility of the electrospinning method allows combining fibre production to support cell attachment and migration with simultaneous drug release.