## 3 Results and Discussion
It indicated that the degradations of PLGA for samples (C) and (D) were a little fast compared to those for samples (A) and (D) due to the high number of acidic groups in these samples. The same results can be also found at the ampicillin release profiles for samples (B)-(E) in the buffer solution, as shown in Figure S4 II. Figure 4I shows the variations of the total amount of antibiotic agents released from the samples as a function of time. Total concentrations of antibiotic agents released from samples (C) and (D) were in the range of values for MIC 90 on _S. aureus_ for ampicillin and vancomycin on the 27 th-30 th day tests. The cumulative release profiles for the total amount of antibiotic agents from samples (A)-(E) into the buffer solutions are given in Figure 4 II. The released percentages of antibiotic agents from sample (D) into buffer solution approached 100% at around the 24 th day test due to the faster degradation of PLGA. It indicated that the antibacterial property of sample (D) only remained around 24 days and cannot approach the clinical requirement (around one month). Total percentages of antibiotic agents released from samples (A)-(C) and (E) were still lower than 100%, which indicated that their antibacterial properties may be higher than one month. Samples (A)-(C) and (E) can meet the antibacterial requirements of orthopedic surgery. Therefore, we tested the antibacterial performances for samples (A)-(E) using the disk-diffusion method. Figure 5 shows the bioactivity and the estimation of drug release distributions of antibiotic agents in the Petri disks as a function of time using the calibration curve for the inhibition of _S. aureus_. From the results shown in Figure 5I-V, the bioactivity of sample (A) (only vancomycin/PLGA coated on the PEEK disk) on _S. aureus_ was kept at 80% on the first 15 days and decreased to around 20% for the 15 th to 20 th days. After that, the bioactivity of samples increased to 90%. The results showed the good bioactivity of sample (A) on the first 15 day tests due to the release of vancomycin that weakly absorbed or coated the surface of the PLGA layer. For the period of the 15 th-20 th day tests, the vancomycin at the sample surface ran out and made a fast decrease in the value of bioactivity of sample (A) on _S. aureus_. After that, the degradation of the PLGA layer continued and the concentration of vancomycin also increased and maintained its bioactivity on _S. aureus_ up to 30 days. However, the unstable drug-release profile for sample (A) would increase the possibility of infection. For sample (B), a bioactivity of the sample higher than 80% was observed at the first 20 days and decreased quickly to 10%. For the application of orthopedic surgery, the recovery time of an orthopedic patient is around 28 days. It indicates that its antibacterial property is not enough to meet the antibacterial requirement of orthopedic surgery. However, sample (B) may have good application if the recovery time of a patient is less than 20 days. The drug release behavior and the bioactivity of sample (C) were similar to those of sample (A), but its bioactivity was still higher than sample (A), which indicated that sample (C) had better antibacterial property than sample (A). For samples (D) and (E), their bioactivities could remain at least 18 days and decrease to around 30% from the 18 th day to the 30 th day. It seems that the antibacterial properties of samples (D) and (E) were not good enough to meet the long-term antibacterial property of orthopedic surgery. For the above results, the 3D-printing PEEK sample with the coating of vancomycin (50%) + ampicillin (50%) using the PLGA as the control-release unit is good for application in orthopedic surgery. Figure 5: \(Cont.\)