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<p>The long-term clinical translation of implantable micro-light-emitting diode (micro-LED) systems is dependent on the biocompatibility and chemical stability of encapsulation materials at the tissue–device interface. While short-term studies have demonstrated encouraging preliminary results, the scope of long-term evaluations remains restricted. In this study, an 8-week biocompatibility assessment was conducted on three representative encapsulation materials—polydimethylsiloxane (PDMS), Ecoflex, and Kapton—using a subcutaneous rat implantation model. Bare micro-LEDs and material-only samples were included for comparison. A multimodal evaluation strategy was employed, including extract-based MTS cytotoxicity testing in L-929 fibroblasts, arsenic elution analysis by inductively coupled plasma mass spectrometry (ICP-MS), histological examination with ISO 10993-6–based scoring, and immunohistochemistry analysis (IHC) of CD68 and myeloperoxidase (MPO). All of the groups that were subjected to testing exhibited non-cytotoxic cell viability, with values that exceeded the commonly accepted 70% threshold. The release of arsenic was undetectable in the groups related to PDMS-, Ecoflex-, PDMS-encapsulated micro-LED-, and Ecoflex-encapsulated micro-LED. However, trace amounts of arsenic were detected in the groups related to bare micro-LEDs, Kapton, and Kapton-encapsulated micro-LEDs. These levels were found to be within acceptable limits. Histological analysis revealed minimal to slight local tissue reactions, with no evidence of necrosis or severe inflammatory changes. IHC analysis demonstrated low percentages of CD68- and MPO-positive area across the study groups. Among the materials that were tested, PDMS and Ecoflex demonstrated the most favorable overall biocompatibility profiles, while Kapton exhibited slightly higher but still acceptable chronic tissue responses. These findings underscore the significance of long-term, multimodal evaluation in guiding the selection of encapsulation materials for chronic implantable optoelectronic devices.</p>

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Long-term in vitro and in vivo biocompatibility evaluation of encapsulation materials for micro-LEDs using a multimodal assessment strategy

  • 期刊论文

  • 发表日期：

    2026年7月28日

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  • Jaewoo Baek,
  • Hyeryun Jeong,
  • Duk-Jo Kong,
  • Jae Gwan Kim

摘要

The long-term clinical translation of implantable micro-light-emitting diode (micro-LED) systems is dependent on the biocompatibility and chemical stability of encapsulation materials at the tissue–device interface. While short-term studies have demonstrated encouraging preliminary results, the scope of long-term evaluations remains restricted. In this study, an 8-week biocompatibility assessment was conducted on three representative encapsulation materials—polydimethylsiloxane (PDMS), Ecoflex, and Kapton—using a subcutaneous rat implantation model. Bare micro-LEDs and material-only samples were included for comparison. A multimodal evaluation strategy was employed, including extract-based MTS cytotoxicity testing in L-929 fibroblasts, arsenic elution analysis by inductively coupled plasma mass spectrometry (ICP-MS), histological examination with ISO 10993-6–based scoring, and immunohistochemistry analysis (IHC) of CD68 and myeloperoxidase (MPO). All of the groups that were subjected to testing exhibited non-cytotoxic cell viability, with values that exceeded the commonly accepted 70% threshold. The release of arsenic was undetectable in the groups related to PDMS-, Ecoflex-, PDMS-encapsulated micro-LED-, and Ecoflex-encapsulated micro-LED. However, trace amounts of arsenic were detected in the groups related to bare micro-LEDs, Kapton, and Kapton-encapsulated micro-LEDs. These levels were found to be within acceptable limits. Histological analysis revealed minimal to slight local tissue reactions, with no evidence of necrosis or severe inflammatory changes. IHC analysis demonstrated low percentages of CD68- and MPO-positive area across the study groups. Among the materials that were tested, PDMS and Ecoflex demonstrated the most favorable overall biocompatibility profiles, while Kapton exhibited slightly higher but still acceptable chronic tissue responses. These findings underscore the significance of long-term, multimodal evaluation in guiding the selection of encapsulation materials for chronic implantable optoelectronic devices.