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Hygroscopic Behaviour and Diffusion Characteristics of Flexible TPU Materials Fabricated by FDM for Potential Biomedical Applications.

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Title: Hygroscopic Behaviour and Diffusion Characteristics of Flexible TPU Materials Fabricated by FDM for Potential Biomedical Applications.
Authors: Šimunić, Nikola1 (AUTHOR) nikola.simunic@vuka.hr, Kostadin, Tihana1 (AUTHOR), Hoster, Josip1 (AUTHOR), Obranović, Dino1 (AUTHOR)
Source: Polymers (20734360). Jun2026, Vol. 18 Issue 11, p1392. 17p.
Subjects: Fused deposition modeling, Polyurethane elastomers, Hardness, Diffusion measurements, Moisture, Mechanical behavior of materials, Biomedical engineering
Abstract: Flexible thermoplastic polyurethane (TPU) materials fabricated using fused deposition modeling (FDM) are increasingly used in engineering and biomedical applications where exposure to moisture is unavoidable. However, the relationship between material hardness, water absorption, diffusion behaviour, and dimensional stability remains insufficiently understood and investigated. In this study, the hygroscopic behaviour of eight commercially available TPU filaments (60A–98A Shore hardness) was systematically investigated. Specimens were produced using an FDM 3D printer under controlled processing conditions and immersed in physiological solution (0.9% NaCl) for up to 96 h. Water absorption, dimensional changes, and diffusion characteristics were analyzed. Diffusion coefficients were determined using the Fickian diffusion model based on the initial stage of water uptake. The results suggest a transition in behaviour between lower- and higher-hardness materials. Softer TPU materials (60A–85A) exhibited higher water absorption (up to ~1.80%) and an apparent linear trend between hardness and absorption within the investigated material group (R2 = 0.999). In contrast, higher-hardness materials (89A–98A) showed lower absorption (~1.18–1.42%) and a weaker apparent relationship with hardness (R2 = 0.4214). Diffusion coefficients ranged from 1.40 × 10−13 to 3.40 × 10−12 m2 s−1, with no monotonic dependence on hardness. Additionally, no clear correlation between diffusion kinetics and equilibrium absorption or volumetric expansion was observed. These findings indicate that hygroscopic behaviour of FDM-printed TPU materials cannot be reliably predicted based solely on hardness, and that diffusion, absorption, and swelling may be influenced by different mechanisms. The identified transition from hardness-dependent to behaviour potentially influenced by material structure provides new insight for the design and selection of flexible polymer components in moisture-exposed environments, particularly in biomedical applications. [ABSTRACT FROM AUTHOR]
Copyright of Polymers (20734360) is the property of MDPI and its content may not be copied or emailed to multiple sites without the copyright holder's express written permission. Additionally, content may not be used with any artificial intelligence tools or machine learning technologies. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)
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  Data: Hygroscopic Behaviour and Diffusion Characteristics of Flexible TPU Materials Fabricated by FDM for Potential Biomedical Applications.
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  Data: <searchLink fieldCode="AR" term="%22Šimunić%2C+Nikola%22">Šimunić, Nikola</searchLink><relatesTo>1</relatesTo> (AUTHOR)<i> nikola.simunic@vuka.hr</i><br /><searchLink fieldCode="AR" term="%22Kostadin%2C+Tihana%22">Kostadin, Tihana</searchLink><relatesTo>1</relatesTo> (AUTHOR)<br /><searchLink fieldCode="AR" term="%22Hoster%2C+Josip%22">Hoster, Josip</searchLink><relatesTo>1</relatesTo> (AUTHOR)<br /><searchLink fieldCode="AR" term="%22Obranović%2C+Dino%22">Obranović, Dino</searchLink><relatesTo>1</relatesTo> (AUTHOR)
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  Data: <searchLink fieldCode="JN" term="%22Polymers+%2820734360%29%22">Polymers (20734360)</searchLink>. Jun2026, Vol. 18 Issue 11, p1392. 17p.
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  Data: <searchLink fieldCode="DE" term="%22Fused+deposition+modeling%22">Fused deposition modeling</searchLink><br /><searchLink fieldCode="DE" term="%22Polyurethane+elastomers%22">Polyurethane elastomers</searchLink><br /><searchLink fieldCode="DE" term="%22Hardness%22">Hardness</searchLink><br /><searchLink fieldCode="DE" term="%22Diffusion+measurements%22">Diffusion measurements</searchLink><br /><searchLink fieldCode="DE" term="%22Moisture%22">Moisture</searchLink><br /><searchLink fieldCode="DE" term="%22Mechanical+behavior+of+materials%22">Mechanical behavior of materials</searchLink><br /><searchLink fieldCode="DE" term="%22Biomedical+engineering%22">Biomedical engineering</searchLink>
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  Label: Abstract
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  Data: Flexible thermoplastic polyurethane (TPU) materials fabricated using fused deposition modeling (FDM) are increasingly used in engineering and biomedical applications where exposure to moisture is unavoidable. However, the relationship between material hardness, water absorption, diffusion behaviour, and dimensional stability remains insufficiently understood and investigated. In this study, the hygroscopic behaviour of eight commercially available TPU filaments (60A–98A Shore hardness) was systematically investigated. Specimens were produced using an FDM 3D printer under controlled processing conditions and immersed in physiological solution (0.9% NaCl) for up to 96 h. Water absorption, dimensional changes, and diffusion characteristics were analyzed. Diffusion coefficients were determined using the Fickian diffusion model based on the initial stage of water uptake. The results suggest a transition in behaviour between lower- and higher-hardness materials. Softer TPU materials (60A–85A) exhibited higher water absorption (up to ~1.80%) and an apparent linear trend between hardness and absorption within the investigated material group (R2 = 0.999). In contrast, higher-hardness materials (89A–98A) showed lower absorption (~1.18–1.42%) and a weaker apparent relationship with hardness (R2 = 0.4214). Diffusion coefficients ranged from 1.40 × 10−13 to 3.40 × 10−12 m2 s−1, with no monotonic dependence on hardness. Additionally, no clear correlation between diffusion kinetics and equilibrium absorption or volumetric expansion was observed. These findings indicate that hygroscopic behaviour of FDM-printed TPU materials cannot be reliably predicted based solely on hardness, and that diffusion, absorption, and swelling may be influenced by different mechanisms. The identified transition from hardness-dependent to behaviour potentially influenced by material structure provides new insight for the design and selection of flexible polymer components in moisture-exposed environments, particularly in biomedical applications. [ABSTRACT FROM AUTHOR]
– Name: AbstractSuppliedCopyright
  Label:
  Group: Ab
  Data: <i>Copyright of Polymers (20734360) is the property of MDPI and its content may not be copied or emailed to multiple sites without the copyright holder's express written permission. Additionally, content may not be used with any artificial intelligence tools or machine learning technologies. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract.</i> (Copyright applies to all Abstracts.)
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        Value: 10.3390/polym18111392
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      – Code: eng
        Text: English
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        PageCount: 17
        StartPage: 1392
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      – SubjectFull: Fused deposition modeling
        Type: general
      – SubjectFull: Polyurethane elastomers
        Type: general
      – SubjectFull: Hardness
        Type: general
      – SubjectFull: Diffusion measurements
        Type: general
      – SubjectFull: Moisture
        Type: general
      – SubjectFull: Mechanical behavior of materials
        Type: general
      – SubjectFull: Biomedical engineering
        Type: general
    Titles:
      – TitleFull: Hygroscopic Behaviour and Diffusion Characteristics of Flexible TPU Materials Fabricated by FDM for Potential Biomedical Applications.
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            NameFull: Šimunić, Nikola
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            NameFull: Kostadin, Tihana
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            NameFull: Hoster, Josip
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            – D: 01
              M: 06
              Text: Jun2026
              Type: published
              Y: 2026
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