## 3 Discussion
### Sterilization  
A fundamental step in the manufacturing process of biomaterials is sterilization in order to avoid any complications such as infections or rejections [31]. The intensive progress on development of biofunctional materials have been continuously growing over the last years, but the sterilization methods remained mainly unchanged. Besides the three most industrially used methods such as ethylene oxide treatment, gamma irradiation and steam sterilization, there are, furthermore, dry heat sterilization, peracetic acid treatment, electron beam (E-beam) or H\({}_{2}\)O\({}_{2}\) gas plasma sterilization. Both heat methods (i.e., steam and dry heat) are not suitable for heat sensitive materials. In chemical treatments, ethylene oxide and peracetic acid might be either toxic and cause carcinogenic outputs. Application of H\({}_{2}\)O\({}_{2}\) gas plasma might cause not only changes in chemical and mechanical properties of polymers but, furthermore, might induce formation of the reactive residuals. The irradiation techniques such as gamma and E-beam, offer a low temperature and short processing time with a range of penetration ability. The gamma radiation uses high-energy photons emitted by a \({}^{60}\)Co source and have no mass or charge, whereas the E-beam sterilization uses fast electrons (with both mass and charge) that has a lower penetration ability compare to gamma treatment [32]. However, in practice, the gamma irradiators deliver dose rate between 2 and 10 kGy per hour, while the E-beam accelerators can deliver dose rates more effectively by a factor of 1000 [20]. Therefore, greater dosing rate of E-beam causes less expose time and reduced potential degradation of polymers. One of the main advantages is the high-energy power of E-beam can sterilize in seconds. Although the gamma radiation conditions with a dose level of 25 kGy became recommended by the International Organization for Standardization (ISO) for health care products, some research showed that this condition can, furthermore, cause degradation of polymers. A study by [PERSON] et al. [33] examined the influence of gamma sterilization on PLA and found a reduction in \(M_{\mathrm{w}}\) by 26-35% compared to the untreated sample. Thus, the selection of treatment parameters is of great importance. The impact of irradiation method on biomaterials is affected by the exposure time, penetration depth and dose rate. As PLA is a thermal and hydrolytic sensitive material, conventional sterilization methods may cause the physical and molecular degradation of the polymer. In the current study, we selected the E-beam radiation within the irradiation methods in order to ensure short exposure time and test the effect of this type of sterilization on the properties of PLA composites. However, in our examined samples, the \(M_{\rm w}\) of both polymers substantially reduced when the E-beam irradiation was applied, compared to their preparation counterparts. Despite of the advantages of this type of sterilization, literature, furthermore, mentioned that the E-beam might lead to degradation of polymers by cross-linking, chain scission or a combination of both, depending on type of polymer tested [21; 22]. The chain scission might occur as random rupturing in weak bonds of polymer that results in a reduction of its molecular weight and formation of shorter chains, which might go further reduction in molecular size [34]. The mechanism of crosslinking can undergo towards the formation of large three-dimensional network that further might translate into cracking, discolouration, brittleness or intensive polymer degradation [35] but, furthermore, might improve the mechanical properties of composite. The examined samples in this publication showed a slightly greater compression strength after sterilization irrespectively to the HA inclusion or its morphology/metal doping, which might be a result of occurrence of crosslinking. The porosity of PLA composites might, furthermore, be affected by the sterilization conditions. A study by [PERSON] et al.