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International Journal of Bioprinting 3D-printing silicone patient-specific soft-tissue expander

4. Discussion expander expansion. Based on the relationship between
5,6
the average expanded volume and time of the expansion
A soft-tissue expander should expand gradually within the test, a fourth-degree polynomial function was obtained
necessary treatment timeframe, with maximum expansion with an R-squared value of 0.99. This result was notably
volume post-expansion compared to pre-expansion. 2–4,7 superior to commercial expanders as its volume over time
The expander material must be nontoxic, nonirritating, exhibited an almost linear expansion. The fourth-degree
and should not provoke sensitivity reactions. The final polynomial curve indicated a gradual expansion in the
product should have rounded edges to prevent damaging first 2 weeks, followed by an accelerated expansion from
the soft tissues and should be easy to repair when clinically the second to fifth week. Thereafter, the expansion rate
required. The surface contact area between the expander decreased from the fifth to the sixth week. These results
and the hard bone should be maximized and adaptable revealed a relatively modest expansion trend in the initial
to the shape and size of the underlying hard tissue. 2 weeks, aligning with the approximate 2-week healing
Furthermore, it should efficiently distribute pressure on the time of wounds in clinical scenarios. Furthermore, the
soft-tissue structure to minimize localized high pressure tapering expansion between the fifth and sixth weeks
and prevent tissue necrosis, perforation, or underlying indicated the suitable period for the expander to be placed
bone resorption. in the soft tissues to promote growth. Researchers have
However, current self-inflating soft-tissue expanders demonstrated successful tissue expansion 4–5 weeks after
are mostly capsule-shaped with an expansion volume of implantation. 4,10,11 The gingiva tissue expansion rate was
less than 1 mL (1000 mm ). The expansion ratio before determined as 0.5–1 mm/day according to the distraction
3
and after expansion is approximately tenfold and can osteogenesis protocol, in which gingival tissue expanded
11
only provide partial soft-tissue space restoration for some alone with bone distraction. To ensure the maturation
patients. These capsule-shaped expanders cannot provide of the gingival tissue growth and enhance the strength of
complete and sufficient space for patients with complex the tissue after inflation, we added one additional week
and extensive bone defects. Considering the clinical to our study. Nonetheless, the findings from our study
requirements for soft-tissue expanders described above, could be verified in the future with additional animal and
silicone would be suitable as the enveloping membrane human studies.
for the swellable tablets, owing to its high deformation This study utilized CT-reconstructed image data to
ability and strain capacity. However, understanding construct a CAD model of large patient-specific soft-tissue
the fundamental tablet expansion rate is crucial before expanders. This approach accounted for the significant
preparation, considering variations in volume dependent variations in the geometric shapes of mandibular bone
on patient-specific factors. For example, the expansion defects among individual patients and our aims of (i)
agent dosages should be tailored specifically to the clinical maximizing the contact surface area between the expander
requirements of different patients. This study selected and the hard bone and (ii) ensuring a rounded-edge
Carbopol 940 NF as the material, whose characteristics product to prevent soft-tissue damage and enable easy
conform to FDA ISO10993-5 standards. Our findings fixation. The 3D-silicone printing technology enabled
revealed that without silicone membranes, the expansion convenient, rapid, and accurate production of complex
volume could reach approximately 64 times the original structures without the need for additional molds.
volume within 24 h. After placing the tablets into a Furthermore, the material was tested for biocompatibility
perforated silicone membrane, the expected expansion (FDA ISO10993) and complied with the requirement for
volume of 1960 mm (1.96 mL) was achieved after 6 weeks maximum expansion volume post-expansion compared
3
in PBS. Consequently, the exact quantity of swellable to pre-expansion. This study also evaluated the feasibility
tablets could be calculated based on different patient- of the expander on two patients with extensive left/right
specific volume requirements. mandibular bone defects, involving at least two teeth
The slot-shaped silicone expander designed with missing. The test findings revealed that after 6 weeks of
perforated silicone membranes was used to evaluate the expansion, the average volume deviation between the
expansion volume of the silicone membrane. The original obtained soft tissue silicone expander and the original CAD
silicone membrane design was 28 mm in length, 14 mm model was less than 2%. Additionally, the expander’s cross-
in width, and 0.8 mm in height. The average expanded sectional shape and height met the required specifications,
height reached approximately 5.72 mm, indicating an collectively demonstrating the feasibility of the novel soft-
expansion in surface area of less than 200%. The silicone’s tissue silicone expander.
tensile strength used in this study was 1.861 MPa, with When sealing the comma- and heart-shaped
an elongation rate of 300%, meeting the requirements for expanders, one end was sealed first to allow insertion of the

Volume 10 Issue 4 (2024) 577 doi: 10.36922/ijb.2918