The healing potential of individual polymer implants for the reconstruction of extensive craniofacial defects after cancer resection is largely determined by the internal architecture of the implant. The architecture of an implant during polymer crystallization could affect the structure and shape of the implant at the micro and macro levels. In this study, the relationship between the internal architecture (triply periodic minimum surface structure (gyroid), cube, grid, and honeycomb) and shape changes of individual implants by 3D printing with a vinylidene fluoride-tetrafluoroethylene copolymer after crystallization is examined at a filling density of 70%. Using the method of differential scanning calorimetry, it is established that crystallization leads to the rearrangement of the crystalline structure of the implant into electrically active (ferroelectric) crystalline phases. Moreover, the type of internal architecture affects the change in the shape of the implant after crystallization. The results of the computed tomography show that structures with a triply periodic minimum surface (gyroid) provide the minimal deformation of the implant during crystallization, which makes such structures optimal for manufacturing implants for replacing bone defects in the zygomatic-orbital complex.

Surgical intervention for the treatment of oncological pathologies requires the use of individual implants to replace the affected tissues. This article presents the results of studies on the use of a Russian-originated polymer material — a copolymer of vinylidene fluoride with tetrafluoroethylene (VDF-TeFE) - for the manufacture of individual implants by 3D printing using layer-by-layer deposition technology (fused deposition modeling, FDM). The influences of the steam sterilization process on the crystal structure, geometric dimensions, and cytotoxicity of implants were studied. Sterilization was found to lead to an increase in crystallite size in the electrically active (ferroelectric) crystalline phase in the polymer material from which the implant is made but not to produce significant changes in implant shape, while maintaining high implant functionality. Studies using 3T3L1 fibroblast cell cultures showed that the steam sterilization process did not cause the formation of toxic compounds and can be used to sterilize individual implants made from VDF-TeFE copolymer by FDM 3D printing.

The healing potential of individual polymer implants for the reconstruction of extensive craniofacialdefects after cancer resection is largely determined by the internal architecture of the implant. The architectureof an implant during polymer crystallization could affect the structure and shape of the implant at themicro and macro levels. In this study, the relationship between the internal architecture (triply periodic minimumsurface structure (gyroid), cube, grid, and honeycomb) and shape changes of individual implants by3D printing with a vinylidene fluoride-tetrafluoroethylene copolymer after crystallization is examined at afilling density of 70%. Using the method of differential scanning calorimetry, it is established that crystallizationleads to the rearrangement of the crystalline structure of the implant into electrically active (ferroelectric)crystalline phases. Moreover, the type of internal architecture affects the change in the shape of theimplant after crystallization. The results of the computed tomography show that structures with a triply periodicminimum surface (gyroid) provide the minimal deformation of the implant during crystallization, whichmakes such structures optimal for manufacturing implants for replacing bone defects in the zygomatic-orbitalcomplex.

Introduction Assessment of biological characteristics of polylactide/hydroxyapatite (PLLA/HA) biodegradable materials is requiered to specify indications for the use of PLLA/HA composite implants in clinical practice. The present study was aimed to measure the kinetics of calcium and phosphate release from PLLA and its dependence on polymer structure crystallinity. Material and methods Four types of biodegradable materials were studied in vitro. Samples of type 1 and type 3 made of crystalline PLLA after annealing contained 25 % and 50 % of HA mass fraction, respectively. Samples of type 2 and type 4 made of amorphous PLLA (without annealing) contained 25 % and 50 % of HA mass fraction, respectively. In every group, 6 samples were tested. The samples were incubated in an aqueous medium at 37 °C for 52 weeks. The rate of PLLA degradation was assessed by the accumulation of lactate monomer in the hydrolysate. The concentrations of calcium ions and phosphate ions were determined for assessment the HA hydrolysis rate. The degree of crystallinity of the polymer matrix was evaluated by scanning calorimetry. Results The hydrolysis of PLLA and HA in the samples was not simultaneous. The PLLA was hydrolyzed first followed by HA hydrolysis. By the moment of complete hydrolysis of PLLA, there was only 15 % of hydrolyzed HA. The release of calcium ions occurred from the sixth week of incubation for all tested samples, that of phosphate ions from the third week. The total amount of the released calcium ions and phosphate ions decreased in the line: material 3 > material 4 > material 1 > material 2. Calcium ions in the hydrolysates were detected up to 42 weeks of incubation, phosphate ions up to the 52nd week. Conclusion Higher crystallinity of PLLA achieved by annealing results in increased rate of hydrolysis of HA from PLLA matrix. Biological activity of PLLA/HA implants can be determined by degree of polymer crystallinity and saturation with HA.

We studied the features of hydrolytic degradation of polylactic acid (PLLA) implants depending on their structural filling with hydroxyapatite (HA). The resistance to in vitro hydrolysis was tested for the following samples: PLLA without HA (control; group 1), PLLA/HA 25 wt% (group 2), and PLLA/HA 50 wt% (group 3). Samples were incubated at 37°C. In the hydrolysate, lactate, calcium ions, and inorganic phosphate were determined. Additionally, the time of appearance of visual deformation and sample disintegration was recorded. PLLA degradation was higher in samples saturated with HA. The highest resistance to deformation was noted for samples without HA. Samples with a PLLA/HA 50 wt% demonstrated the maximum degradation of PLLA in combination with lower resistance to deformation and the highest bioavailability of calcium and phosphate. Group 2 samples are most promising for clinical use.

In this work, effect of additional annealing on mechanical and morphological properties of 3D-printed PLLA/HAp composite scaffolds of three compositions (12.5, 25, and 50 wt.% of HAp) was investigated. Morphology and Young's modulus of 3D-printed scaffolds were investigated by scanning electron microscopy and nanoindentation. It has been shown that additional annealing does not have an effect on the homogeneous distribution of HAp powder in the PLLA-matrix. Results of nanoindentation showed growth of Young's modulus after annealing. The maximum value of 9393 ± 709 MPa Young's modulus was reached for the annealed composite with 50 wt.% of HAp.

Synthesis of new biodegradable materials is one of the most promising area of reconstructive and regenerative orthopedy development. The implant made of biodegradable material serves as a temporary scaffold in the process of new tissues growth and fully dissolves during osteosynthesis [1]. Poly(L-lactic acid) (PLLA) is highly attractive polymer for biodegradable implants fabrication due to its ability to degrade to non-toxic lactic acid monomers [2]. However, poor mechanical and bioactive properties restrict applying of PLLA as a material for orthopedic implants [3]. In this research biological mineral hydroxyapatite (HAp) was used to obtain biodegradable PLLA-based composite with enhanced mechanical and bioactive properties. Composites were produced from PLLA and biological HAp at different wt.% HAp content (12.5, 25, 50 wt.%). To produce PLLA-HAp filaments, PLLA pellets were dissolved in chloroform and mixed with HAp powder, then composite mixtures were granulated and extruded through 1.75 mm nozzle. In addition, 100% PLLA filament was prepared for printing control samples. Samples were obtained using FDM 3D-printing technology. Samples were divided into two groups, and then samples from one of the groups were annealed at 110 ̊C for 12 hours to increase PLLA matrix crystallinity degree.