Prof. Sohee Kim’s research team has successfully developed an ultrasoft and flexible balloon-type implantable device for long-term drug delivery at the target site of implantation. (Credit: DGIST)

Implants that steadily release the right dose of a drug directly to the target part of the body have been a major advance in drug delivery. However, they still face some key challenges, such as ensuring that the drug is released at a constant rate from the moment it is implanted and ensuring that the implant is soft and flexible enough to avoid tissue damage but tough enough not to rupture. One particular challenge is to avoid triggering the foreign body response, which is when the patient’s body encloses the implant in a tight capsule of tough connective tissue which can slow the drug’s release or prevent it from diffusing out.

In a paper published in Biomaterials Research, a team led by researchers from the Daegu Gyeongbuk Institute of Science and Technology (DGIST) in the Republic of Korea present data on their nonbiodegradable, ultrasoft, and flexible balloon implant for drug delivery. Their findings demonstrate the balloon’s effectiveness in delivering a model drug both in the laboratory setting and in animal models.

The balloon consists of two halves. One is made of a single-layer of a rubbery silicone-based polymer called polydimethylsiloxane, and the other is a two-layer combination of polydimethylsiloxane on the outside and the non-permeable polymer parylene C lining the inside. That ensures that the drug only diffuses out from one side of the balloon, making it easier to control the direction of drug delivery.

The team experimented with polymer membranes of different thicknesses and compositions to study how that affected drug diffusion and membrane strength. “We were able to achieve a sustained drug release for more than five months, and all the devices remained intact for this duration despite the ultrasoft mechanical properties,” explains corresponding author Sohee Kim, a professor at DGIST.

The balloons were filled with a fluorescent dye to serve as a drug model and then implanted into rats and mice. The dye was released at a steady rate of 1.16 micrograms per day, without any significant variation in dose for 30 days and with very little variation for 58 days.

“Most importantly, the ultrasoft mechanical properties of the device ensured less foreign body responses than previously developed reservoir-type devices, with relatively thin fibrotic encapsulation,” says Tausif Muhammad, the first author of the study.

Such a device could have implications for long-term drug delivery for a wide range of diseases and conditions, including diabetes, epilepsy, heart disease and cancer. They could also include sensors to allow ongoing, real-time monitoring of disease and physiological markers. The researchers are now planning to study the balloon’s effectiveness in delivering anticancer drugs in a brain cancer model.

For more information, contact Sohee Kim at This email address is being protected from spambots. You need JavaScript enabled to view it. or visit here  .

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An Ultrasoft and Flexible PDMS-Based Balloon-Type Implantable Device for Controlled Drug Delivery

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    Medical Design Briefs Magazine

    This article first appeared in the August, 2024 issue of Medical Design Briefs Magazine (Vol. 14 No. 8).

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    Overview

    The document presents research on an innovative ultrasoft balloon-type device (USBD) designed for controlled drug delivery, addressing significant challenges associated with non-biodegradable implants. The USBD is fabricated using polydimethylsiloxane (PDMS) and poly(p-xylylene) (parylene C) through selective bonding via plasma treatment. This design aims to minimize foreign body responses, a common issue with traditional implants, while enhancing drug delivery efficiency.

    The study highlights the limitations of existing implantable devices, which often suffer from high initial burst release, risk of membrane rupture due to in vivo degradation, and excessive foreign body responses. These issues hinder the accurate control of drug delivery, making it difficult to achieve targeted therapeutic effects. Previous soft devices embedded with micro-channels have been reported, but they often lack flexibility and can lead to off-target toxicity due to their design.

    In contrast, the USBD demonstrates superior characteristics, including a nearly zero-order release profile, maintaining a consistent release rate of 4.87 μg/day over an extended period. The device was evaluated in vivo, showing a total release of 60.4% of the drug (RB) over 28 days, consistent with in vitro results. The study also details the histological assessment of tissue response, revealing a significantly reduced fibrotic capsule thickness around the USBD compared to traditional rigid devices, indicating a lower foreign body response.

    The document includes methodologies for assessing the device's performance, such as IVIS imaging to visualize drug release and Masson’s trichrome staining to evaluate tissue inflammation and capsule thickness. The findings suggest that the USBD not only improves drug delivery efficiency but also enhances biocompatibility, making it a promising candidate for long-term implantation in clinical settings.

    Overall, the research underscores the potential of the USBD to revolutionize localized drug delivery systems, offering a solution to the challenges faced by current implantable devices. The combination of soft materials and innovative design principles positions the USBD as a significant advancement in the field of biomedical engineering, with implications for personalized medicine and improved patient outcomes.