You can tailor the composition of biocopolyester mixes for extrusion-based printing that is dimensionally exact.

FFF can be implemented in the medical industry by using thermoplastic Biopolymers. Medical instruments such as surgical guides and medical instruments for single usage can be customized, and the simplified manufacturing method allows for easier handling for the practitioner.²¹. If biopolymers are made from renewable sources, they can have a positive effect on the environment. PLA, PBAT and PHA can also be biodegradable under certain conditions. This allows them to counter uncontrolled littering as well as landfill.²². FFF is still a challenge when used in the medical profession. FFF objects must be stable in dimensions and can be autoclavable according to a protocol that allows for use in a sterile environment. This study examined the dimensions of biocopolyester mixtures following extrusion-based printing, analing, steam sterilization.

As the test specimen, a square specimen was chosen, as it is more susceptible to warpage. The longitudinal orientation of the hair strands enhances the contraction of straight sections. This results in increased pulling forces on the corners of warpage specimens. This design was already used for previous studies to evaluate the warpage in FFF printable polypropylene.^20,23To approximate the size of a surgical manual, the side lengths were shortened in this current study. A previous study measured the height of one corner and fixed it with a particular force. The warpage was then quantified.²⁰. To achieve greater accuracy in measurement, the present study determined warpage after digitization. After determining the enclosed volume below the squares, the volume from the original STL dataset was subtracted.

All the materials evaluated were biocopolyester-blends containing PLA, PHA, and PBAT. It was found that the composition of the materials, including the ratio of fillers, nucleating agent and melt stabilizers, had significant impacts on the accuracy and reproducibility of the specimens. While there was no visual warpage, it was evident that significant differences existed between the groups printed with the same standard parameters. Material D, which was based on a different basis composition compared to materials A–C, showed the highest warpage after sterilization.

The mechanical properties of extrusion printed parts can be improved with thermal annealing. Commonly, annealing is performed approximately 20 °C below the polymer melt temperature, where amorphous and poorly organized crystalline regions can reorganize²⁴. This is often a result of a decrease in stress.²⁵It is performed with higher thermal stability and mechanical stability²⁶. Annealing can also reduce the impact of changing printing conditions on dimensional accuracy²⁰. The annealing process must be extended for lower temperatures. This results in limits on practical application. The thermal post-processing results of the square printed specimens showed different effects on their dimensional accuracy. Materials A and B, which contained a higher amount of mineral fillers (21–32 wt%) as well as nucleating agents, showed no significant dimensional change due to annealing. The steam sterilization that followed did not cause significant warpage. However, both the steam sterilization and subsequent annealing caused small warpages that resulted in substantial warpage. However, the deviation overall was much lower than that of sterilized specimens without prior annealing.

Mineral fillers are responsible for the fact that annealing did not result in significantly higher warpage in test specimens in groups B and A. Increased nucleation rates during crystallization of polymers can be attributed to nucleating agents. This will lead to faster crystallization. This is done by lowering the surface energy barrier to nucleation and allowing polymers crystallize at higher temperatures.²⁷. DSC analyses did not detect any influence of the nucleating agents on the total crystallinity and polymer portions of the samples. However, the addition of the Nucleating Agent may have led to a reduction in the size and associated lower tendency of warp. Further research is needed to investigate this issue. Material R that contained a lower amount of filler showed higher warpage following annealing. This suggests that nucleating agents and a higher content of filler could help to reduce warpage during annealing. Group R annealed showed a greater increase in warpage than samples that had been steam sterilized directly after printing, suggesting no benefit to thermal annealing.

Qualitatively, warpage following sterilization is related to an increase in crystallization. Due to the increased temperatures of 134 °C during sterilization, crystallization of the PLA occurred. Warpage resulted from the associated volume shrinkage. Warpage was especially evident in filler-free groups D and C. The presence of crystalline PLA in sterilized specimens was more apparent in those without fillers. A growing number of mineral fillers counteracted the post-crystallization and stiffened the material at high temperatures. The fillers had a positive effect on warpage. However, they also caused an accelerated aging of the material or degrading it at higher temperatures during sterilization. This could limit repeat sterilization. For other polymers, the significant effect of filler contents on dimensional stability was also described.²⁸. Additional fillers are beneficial for materials with a higher crystalline content such as polyolefins.²³. Smaller fillers may be more effective in decreasing shrinkage and warpage. PLA-based biopolymers can also be affected by their material properties by changing the types and sizes of fillers.²⁹. After solidification of PLA-based filaments, the addition of fillers has been shown to increase flexural stiffness as well as improve dimensional stability.⁹. It was demonstrated that increased thermal stability of PLA can be achieved by adding calcium carbonate to materials A and B.³⁰Particularly when combined with talc³¹. The use of fillers may also have drawbacks such as decreased tensile strengths, brittleness, or increased density. Plastic processing machines can also be subject to greater wear due to the use of mineral fillers.⁹. Mineral fillers can limit the materials’ biodegradability. Natural fibers (e.g. It is also possible to use natural fibers such as pulp in biodegradable material.

PLA has a disadvantage: the Vicat melting temperature/softening temperature is lower than thermoplastics that have crystalline content. PLA’s processing temperature is also close to its melting temperature. The composition, however, could increase the softening temp with other biopolymers as well as additives. In the case of the examined reference material, the Vicat softening temperature was around 160 °C, which was significantly higher than the typical Vicat softening temperature starting at approximately 60 °C for PLA³². However, these biocopolyesters showed greater resistance to higher temperatures than polymers with higher crystalline contents, such as those used for steam sterilization.³³. In the present study, a steam sterilization protocol with a temperature of 134 °C was selected, representing a frequently applied protocol in dental offices. Similar studies investigating the capability to sterilize various 3D printable materials often used solely a temperature of 121 °C^34,35. In previous studies, the reference material R was found to have acceptable dimensional stability under steam sterilization at 121 °C^17,36. Thus, it can be assumed that sterilizing the printed biocopolyester specimens at a temperature of 121 °C would have amounted to a reduced warpage, whereas H₂O₂ Plasma sterilization may be another option. The disadvantages of this method include the low availability and high costs, which could make it difficult to achieve a low-budget workflow.³⁷.

The dimensional accuracy of FFF-printed parts can be affected by many factors, including the material composition (fillers and nucleating agents), as well as the printing parameters. On the basis of the dimension accuracy, there were significant differences in the nozzle temperature, outershells and infill. The printed parts were less stable when there was a reduced number of shells. This was especially evident during sterilization, where there was more warpage. Dong et. al. found that a higher number of shells is beneficial for mechanical strengths. PLA³⁸. Although the present study revealed a reduced deviation of printed samples at 230 °C compared to the original file, further research is necessary to evaluate the influence of high nozzle temperatures on the mechanical parameters such as strength and stiffness³⁹. You might find solutions to many of the drawbacks using the different printing parameters. This can often require trial and error.⁹. Even though the parameters were the same, there are still other factors that could influence the results, especially when the goal is to achieve a low budget workflow. This study was designed to evaluate an affordable and easy workflow. We used a desktop extrusion-based printer that didn’t require any additional equipment. Because the printer doesn’t have a chamber, ambient conditions, such as temperature and humidity, may have affected the printing quality.⁸. It was done with extreme care to ensure that the filaments were kept in a dry, cool place. However, there might be slight differences in humidity between the two printing batches.

Dimensional printability is also affected by the geometry of the object. Although square specimens are more susceptible to warpage and have significant differences, surgical guides show fewer differences. Only group B showed significantly more warpage after sterilization and Annealing than other groups. The heatmaps revealed that even after steam sterilization, most regions only showed deviations of up to 0.2 mm. Preclinical studies showed that implant placements with printed surgical manuals made of material R did not show significant differences to those using SLA printed surgical guide.¹⁷. The fact that surgical guides show less distortion than squares is due to their thicker and more stiffer nature. Because the stiffer areas of the molten polymer are strong enough to resist deformation, additional layers can shrink. The stress must be relieved by the last strand that is deposited. The fact that surgical guides had the highest warpage in the molar region is similar to squares’ warpage tendency. Warpage was higher at the end the longest printed axis.²⁰. It is important to determine for each application if a slight distortion has any impact on the respective clinical application. These surgical guides are made from novel biocopolyester mixtures. The implant position after placement should be compared with the plan position in vitro.¹⁷. It is also important to test the biocompatibility and safety of the biocopolmers. Recent studies have shown that the used reference material was non-cytotoxic to oral cells. It may also be more biocompatible than a popular photopolymer used for surgical guides.⁴⁰. In different studies, it has been shown that cytotoxic results can result from vat polymerizations light-curing compounds.^41,42. The promising results for R’s biocompatibility suggest that similar results can be expected for other extrusion materials. These will need to be evaluated in further research.