我是文本块。单击“编辑”按钮来更改此文本.
Preface
Polydimethylsiloxane (PDMS) has become the most widely used substrate in the fields of biological microfluidics, organ-on-a-chip, microdroplet generation and cell analysis, benefiting from its excellent properties including high light transmittance, superior biocompatibility, gas permeability, elasticity and low processing cost. The SU-8 silicon master mold soft lithography process is the mainstream and mature fabrication solution in the industry. With over a decade of in-depth experience in microfluidic processing, Suzhou Wenhao owns a complete production line covering lithography, PDMS molding and plasma bonding. Based on the standardized process flow diagram, this article comprehensively elaborates on the working principles, key technical parameters and practical troubleshooting tips for every procedure from mold replication to finished chip production.
1. Overview of the Full Process Flow (With Illustrated Procedure Correlation)
The diagram below illustrates six core procedures applicable to both laboratory research and mass production:
SU-8 silicon master mold preparation → PDMS pouring → Thermal curing → Demolding → Inlet/outlet punching → Oxygen plasma activation cleaning → Irreversible PDMS-glass bonding
Legend of Material Colors
-
Blue: PDMS chip substrate
-
Reddish-brown: Silicon (Si) wafer substrate
-
Yellow: SU-8 photoresist (raised microchannel mold structure)
-
Gray: Glass cover slide (chip sealing substrate)
2. Step-by-Step Process Principles and Operational Standards (Mass Production Specifications of Suzhou Wenhao)
2.1 PDMS Pouring: The First Step of Microchannel Replication
Pre-preparation: A silicon wafer is processed via spin coating, photolithography and development to fabricate a SU-8 master mold with raised microchannel structures. The PDMS prepolymer and curing agent are fully mixed at a mass ratio of 10:1, followed by 30 minutes of vacuum defoaming to eliminate air bubbles generated during stirring.
Operation Process: The defoamed liquid PDMS is slowly poured onto the surface of the SU-8 silicon master mold. A secondary vacuum pumping process is performed to remove tiny air bubbles introduced during pouring, ensuring no void defects inside the microchannels.
Industry Pain Points & Solutions: Air bubbles directly cause channel blockage and fluid shunting. Equipped with fully automatic integrated vacuum defoaming equipment, Suzhou Wenhao’s production line eliminates micron-scale bubble defects in batch processing.
2.2 Thermal Curing: Crosslinking for Elastic Substrate Formation
Curing Mechanism: The hydrosilylation crosslinking reaction occurs between the PDMS prepolymer and hydrogen-containing siloxane curing agent, transforming liquid PDMS into a solid elastic body.
Standard Process Parameters (Wenhao General Specification)
-
Conventional laboratory processing: Curing in an oven at 65~80℃ for 2~4 hours
-
High-speed batch processing: Constant-temperature curing at 120℃ for 20~30 minutes
Precautions: Abrupt temperature fluctuations are prohibited during curing, as they induce internal thermal stress and cause chip warpage after demolding. The PDMS must be cooled to room temperature before demolding to prevent tensile deformation of microchannel structures.
2.3 Demolding: Complete Peeling of Replicated Microchannel Chips
After full cooling, the entire PDMS sheet is slowly peeled off along the edge of the silicon mold. The raised SU-8 structures accurately replicate recessed microchannels on the inner surface of PDMS.
Mass Production Optimization: Reusable SU-8 silicon molds require prior silanization treatment to reduce adhesion between PDMS and photoresist, avoiding microchannel tearing during demolding. The standardized silanization process in Wenhao’s mold workshop significantly extends the service life of master molds and reduces customers’ mold replacement costs.
2.4 Punching: Fabrication of Fluid Inlets and Outlets
According to the experimental microchannel layout, standard punches are used to drill upstream sample inlets and downstream waste liquid outlets on PDMS chips.
Operational Details: Vertical punching is required to ensure smooth, burr-free hole walls. The hole diameter is precisely matched with the outer diameter of connecting capillaries and hoses to prevent high-pressure fluid leakage. A chip thickness of ≥3mm is recommended to avoid cracking during punching, suitable for high-pressure micro-pump fluid experiments.
2.5 Oxygen Plasma Cleaning: Core Procedure for Surface Activation
The native PDMS surface is covered with methyl groups (-CH₃), exhibiting strong hydrophobicity and poor adhesion to glass. After oxygen plasma bombardment and oxidation, a large number of hydrophilic silanol groups (-Si-OH) are generated on the PDMS surface. This process simultaneously removes organic contaminants and demolding residues from the chip surface, achieving dual effects.
Synchronous Substrate Treatment: The glass slides for chip sealing are placed in the plasma cleaner for synchronous treatment to generate surface silanol groups, providing a chemical foundation for irreversible covalent bonding.
2.6 Bonding: Permanent Sealing of PDMS and Glass
Immediately after plasma treatment, the activated PDMS microchannel surface is precisely aligned and bonded to the glass slide. Gentle pressure is applied to expel interfacial air, followed by baking at 60~80℃ for 15~30 minutes to accelerate dehydration and condensation of interfacial silanol groups, forming stable irreversible Si-O-Si covalent bonds.
Process Advantages: Compared with temporary tape lamination, plasma-bonded chips withstand fluid pressure of hundreds of kPa without leakage. The inner channel walls maintain high hydrophilicity, enabling direct cell and aqueous solution experiments without additional surface modification. This process is widely applied in microdroplet generation, single-cell capture, long-term organ-on-a-chip culture and other scenarios.
3. Core Advantages of the Process (Suitable for Scientific Research and Small-Batch Production)
3.1 High Precision of Microstructure Replication
SU-8 photoresist enables the fabrication of high-precision microchannels ranging from 1μm to 1000μm. Soft lithography replication achieves zero dimensional loss, meeting the precision structural requirements of micromixing, microsorting, microreactors and other microfluidic devices.
3.2 Excellent Biocompatibility
PDMS is non-cytotoxic and gas-permeable, ideal for long-term living cell culture, organoid construction, drug penetration testing and other life science experiments.
3.3 Accessible Processing and Scalable Replication
A single silicon master mold can replicate hundreds of PDMS chips. Suzhou Wenhao provides two delivery modes: research prototyping and pilot-scale batch production, catering to small-batch customization for university laboratories and small-volume production for enterprises.
3.4 High Light Transmittance for Easy Observation
With high transmittance for visible light and fluorescence, PDMS chips are compatible with microscopes, confocal microscopes and high-content imaging systems for real-time observation of microscale reactions.
4. Common Process Failures and Standardized Solutions (Wenhao Technical Experience)
4.1 Fluid Leakage and Delamination After Bonding
Causes: Insufficient plasma treatment time, excessive exposure time after activation (silanol group deactivation), and dust/oil contamination on the bonding interface.
Solutions: Adopt unified oxygen plasma parameters (30~50W power, 60~120s treatment time); complete bonding within 3 minutes after activation; operate in a fully dust-free environment.
4.2 Broken or Incomplete Microchannels After Demolding
Causes: Unsilanized molds, incomplete PDMS curing, and demolding at high temperatures.
Solutions: Implement regular silanization maintenance for silicon molds, strictly follow complete curing and cooling procedures, and increase PDMS substrate thickness for thin-walled microchannels.
4.3 Bubbles and White Spots in Microchannels
Causes: Incomplete defoaming during PDMS mixing and air entrapment from excessive pouring speed.
Solutions: Adopt fully automatic integrated stirring and defoaming equipment, perform slow layered pouring, and conduct secondary vacuum defoaming.
5. One-Stop Microfluidic Processing Services by Suzhou Wenhao
As a professional microfluidic enterprise with a complete soft lithography production line in China, Suzhou Wenhao provides full-chain PDMS chip manufacturing services:
-
Upstream: Mask fabrication and SU-8 photolithography processing of silicon wafers;
-
Midstream: Standardized processing including PDMS batching, pouring & curing, cutting & punching, and plasma bonding;
-
Downstream: Supporting experimental hardware including syringe pumps, microfluidic chip fixtures and fluid pipelines.
We also support customized services, including multi-layer PDMS lamination & bonding, modified PDMS (high hardness / low non-specific adsorption), and large-size microfluidic chip batch processing. Our clients cover university laboratories, biomedicine, environmental detection, microchemical engineering and other fields.
6. Conclusion
Soft lithography for PDMS chip fabrication is the most classic and versatile standardized technology in the microfluidic industry. Precise parameter control of each procedure directly determines the stability of chip-based experiments. If you have demands for microfluidic chip customization, process debugging or experimental scheme design, welcome to communicate with the technical team of Suzhou Wenhao.
