Molecular engineering is transforming essential medical devices to improve patient outcomes and reduce complications
For the millions of people who need a ureteral stent each year, this small, flexible tube is a medical necessity that often comes with a host of uncomfortable problems. Placed to drain urine from kidney to bladder, conventional stents can cause pain, infection, and blockages from mineral buildup. But what if a stent could be designed to resist these complications? The answer lies in cutting-edge surface modifications—invisible shields engineered at the molecular level that are transforming this essential medical device.
Ureteral stents are indispensable in urology, used to treat conditions ranging from kidney stones to tumors. Over 1.5 million are implanted globally each year, creating a market valued to exceed $564 million 6 . Despite their widespread use, over 80% of patients experience stent-related complications, with rates approaching 100% for long-term indwelling beyond four weeks 6 .
Stents implanted globally each year
Patients experiencing complications
Market value exceeding this amount
The urinary system presents a uniquely challenging environment for any foreign object. Stents must withstand constant urine flow, pH fluctuations, and exposure to microorganisms, proteins, and mineral salts 6 . This leads to several common problems:
Mineral crystals from urine accumulate on the stent surface, potentially causing blockages
Bacteria colonize the stent, leading to infections that are resistant to antibiotics
Friction and irritation cause pain, hematuria (blood in urine), and urinary symptoms
These complications not only affect patients' quality of life but may also necessitate early stent replacement, requiring additional surgical procedures 2 8 . Surface modification technologies aim to address these very issues by creating stents that actively resist these biological challenges.
Researchers have developed various surface modification strategies, which can be broadly classified into two main categories: coated stents and drug-eluting stents 1 .
Creating Passive Barriers
Coated stents work by creating a physical or chemical barrier between the stent material and the urinary environment.
Active Therapeutic Delivery
Unlike passive coatings, drug-eluting stents actively release therapeutic agents.
| Technique | Mechanism | Key Advantages | Limitations |
|---|---|---|---|
| Plasma-enhanced Chemical Vapor Deposition | Forms thin polymer films through gas plasma | Creates uniform, durable coatings; excellent for inner surfaces | Requires specialized equipment 2 |
| Impregnation | Infuses therapeutic agents into stent material | Provides sustained drug release | Potential alteration of mechanical properties 4 |
| Spraying | Applies coating solution as fine mist | Simple process; suitable for mass production | May create uneven coating thickness 4 |
| Chemical Grafting | Covalently bonds molecules to surface | Creates permanent, stable modification | Complex chemical processes 4 |
| Electrospinning | Creates nanofiber mats on surface | High surface area for drug delivery | Limited mechanical durability 4 |
To understand how these technologies work in practice, let's examine a landmark experiment that demonstrates the promise of surface modification.
In 2023, Korean researchers conducted a rigorous study to evaluate a novel plasma-enhanced chemical vapor deposition (PECVD) technology for modifying the inner surface of polyurethane ureteral stents 2 8 . Their approach was methodical:
Five Yorkshire pigs were implanted with stents on both sides—a conventional "bare" stent on one side, and the plasma-modified stent on the other 2
Using a specialized PECVD system, the researchers treated the inner surface with acetylene gas after pre-activation with helium gas 2
The stents remained in place for two weeks, after which they were harvested and analyzed using sophisticated imaging techniques 2
The results demonstrated striking differences between the modified and conventional stents:
| Assessment Method | Bare Stent Findings | Modified Stent Findings |
|---|---|---|
| Physical Examination | Hard, palpable materials in 4 of 5 models | No palpable hard materials in any model |
| Component Analysis (FT-IR) | Calcium oxalate/uric acid stones in 2 models | Only proteinaceous materials, no stone formation |
| Microscopy (SEM/EDS) | Significant biofilm and calcium deposition | Minimal biofilm, largely intact surface |
Hard, palpable materials were found in four out of five bare stents, but no such materials were identified in any of the modified stents 2
Fourier-transform infrared spectroscopy revealed that two of the bare stents had developed actual stones composed of calcium oxalate dihydrate and uric acid, while the modified stents showed only minimal protein deposits 2
Scanning electron microscopy with energy-dispersive X-ray spectroscopy confirmed severe biofilm formation and calcium salt deposition on the bare stents, while the modified stents showed significantly less biofilm and larger intact surface areas 2
The success of surface modification relies on a sophisticated arsenal of technologies and materials. Here are the key tools revolutionizing ureteral stent development:
| Tool/Technology | Function | Application in Stent Development |
|---|---|---|
| Scanning Electron Microscopy (SEM) | Provides high-resolution surface imaging | Visualizes biofilm formation and encrustation at microscopic level 2 |
| Energy-Dispersive X-ray Spectroscopy (EDS) | Identifies elemental composition | Analyzes mineral components of encrustation 2 |
| Fourier-Transform Infrared Spectroscopy (FT-IR) | Determines chemical bonds and functional groups | Identifies specific stone compositions (e.g., calcium oxalate vs. uric acid) 2 |
| Mass Flow Controller | Precisely regulates gas flow during deposition | Ensures uniform coating thickness in plasma modification 2 |
| Polyurethane Substrate | Serves as base material for most conventional stents | Provides mechanical strength; platform for various coatings 3 |
| Biodegradable Polymers (PLA, PCL) | Materials that safely break down in body | Enables development of temporary stents that don't require removal 5 |
The future of ureteral stents lies in increasingly sophisticated approaches that address multiple challenges simultaneously.
Next-generation stents are being designed with coatings that combine lubricity, antifouling, antibacterial, and anti-encrustation properties all in one 6 . This integrated approach recognizes that complications in the urinary system are interconnected—bacterial infections can promote encrustation, while encrustation provides binding sites for bacteria 6 .
A particularly promising development is the emergence of biodegradable ureteral stents (BUS) made from materials that safely dissolve in the body after serving their purpose 5 . These stents eliminate the need for a second removal procedure, potentially revolutionizing patient care. Materials being investigated include natural polymers (alginate, gelatin, silk fibroin, chitosan), synthetic polymers, and even specially treated metals 5 .
The ultimate goal is developing "smart" stents that can respond to their environment—for instance, releasing antibiotics only when bacteria are detected or dissolving at a precisely controlled rate 6 . While still largely in experimental stages, these technologies represent the cutting edge of ureteral stent innovation.
First generation of ureteral stents introduced
Basic FunctionIntroduction of coated stents with hydrophilic surfaces
Surface ModificationDevelopment of drug-eluting stents with active therapeutic delivery
Active ReleaseAdvanced plasma modification and multifunctional coatings
MultifunctionalBiodegradable and smart responsive systems
Smart StentsThe surface modification of ureteral stents demonstrates how molecular engineering can dramatically improve medical devices and patient outcomes. What appears as a simple plastic tube to the naked eye becomes, under the microscope, a sophisticated platform for therapeutic intervention.
As research continues to combine multiple functions into stable, durable coatings, we move closer to the ideal stent—one that provides essential drainage while remaining virtually invisible to the patient's body. This progress in surface science doesn't just represent technical achievement; it promises tangible improvements in quality of life for the millions who depend on these devices each year.
The invisible shield on modern ureteral stents exemplifies how the smallest modifications, at the nanoscale, can make the biggest difference in human health.