Physico-mechanical characterization of 3D-printed PLGA for patient-specific resorbable implants in craniofacial surgery

Abstract

Patient-specific implant (PSI) has optimized the management for a wide range of complex craniofacial deformity over the past years by increasing the accuracy of surgical procedures and lowering the operating time. In hypertelorism (HTO) surgery particularly, the orbital bone repositioning is nowadays guided by patient-specific bone fixation plates that are usually made from non-resorbable alloplastic material (e.g., titanium). Developing resorbable personalized plates could be a relevant alternative to overcome the well-known drawbacks of titanium plates such as infection, exposure or even the lack of bone growth which is detrimental in pediatric patients. This study investigated the mechanical and structural characteristics of poly(lactic-co-glycolic acid) (PLGA) PSI as resorbable materials for HTO surgery. We assessed the feasibility of printing PLGA PSI by Fused Deposition Modeling additive manufacturing (FDM). The geometrical and the mechanical properties of the 3D-printed device were compared with standard resorbable plates and analyzed after sterilization process (i.e., hydrogen peroxide gas plasma). The Young's modulus was greater than the standard resorbable plates while a decrease of 36% (p = 0.004) after the sterilization was observed. The sterilization also induced a plate deformation with an increase of 0.27 mm in Z-axis and a decrease of 0.8 mm in Y-axis due to annealing effect. Compared to the design, the PLGA PSI were successfully 3D-printed with a maximum deviation of 0.1 mm, making our custom-made plate promising for personalized craniofacial applications. Further investigations on the sterilization process must be considered in view of its mechanical and structural impact on resorbable PSI.

Fig. 1

Stages of Custom Plate Design. (a) 3D bone reconstruction of a patient with hypertelorism. (b) 3D simulation of box osteotomy surgery. (c) The red objects represent the modeled plates, with the upper one for the fronto-temporal area and the lower one for the zygomatic bone. (d) Illustration showing the zygomatic plate on the left, and the fronto-temporal plate on the right. The blue supports are used exclusively in the pin holes, providing support for the overhang and stabilizing the piece to limit wobbling.

Fig. 2

Diagram illustrating the overall research methodology, from the initial surgery planning to the mechanical evaluation of the manufactured plates. The process begins with the custom plate design, incorporating parameters such as localization on the bone, geometry, thickness… The designed plate is then manufactured using 3D printing, where biomaterial selection, printing speed, and layer height are critical factors. After fabrication, the plates undergo sterilization, with parameters such as temperature, gas type, pressure, and exposure time considered. Subsequently, the PLGA structure and geometry are analyzed using thermogravimetric analysis (TGA), attenuated total reflection-Fourier transform infrared (FTIR) spectrometer, the differential scanning calorimetry (DSC), and micro-CT scan to assess material properties and potential alterations. The mechanical response of the plates is then evaluated through tensile tests and compared to a standard resorbable plate. The iterative nature of the process allows adjustments at various stages to optimize the final design.

Fig. 3

( a) TGA curves of PLGA filament, printed PLGA, and printed and sterilized PLGA. (b) First derivative thermogravimetric curves focusing on the decomposition phase of PLGA.

Fig. 4

DSC curves for PLGA as a filament, after printing, and after printing followed by sterilization.

Fig. 5

ATR - FTIR spectra of PLGA filament, after printing, and after printing and sterilization. ν, stretching; δ, bending; τ, twisting; s, symmetric; as, anti-symmetric.

Fig. 6

Representative tensile test curves of PLGA with standardized specimens, before and after sterilization, according to orientation. The black dots indicate tests stopped after reaching maximum stress, while the arrows indicate tests stopped after rupture.

Fig. 7

Colormap Comparison of the Fronto-Temporal Plate. Panels a and b illustrate the comparison between the PLGA-printed plate and its 3D model across different orientations. Panels c and d show the comparison between the same PLGA-printed plate after sterilization and the 3D model.

Fig. 8

Micro-CT scans of the fronto-temporal piece, before (a) and after sterilization (b), using the same scale and reconstruction plane. The red arrows indicate examples of under-extrusion, and the asterisk (*) marks the residual brim.