iCVD PHEMA Hydrogel Films Crosslink Density Control
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Solution Overview
Problem
Current methods for producing PHEMA thin films lack control over crosslink density, which is crucial for their gel properties and applications such as drug release, and involve wet processes that require solvents and post-treatments, limiting their efficiency and environmental sustainability.
Innovation Solution
Initiated Chemical Vapor Deposition (iCVD) is used to deposit linear and crosslinked PHEMA thin films by feeding a mixture of a monomer, a methacrylate or acrylate crosslinker, and a radical initiator into a vacuum chemical vapor deposition reactor, allowing control of crosslink density through partial pressure adjustments and eliminating the need for solvents.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If wet processes are used to produce PHEMA thin films, then film formation is achieved, but solvents and post-treatments are required which reduces efficiency and environmental sustainability
Solution Approach 1:
The patent replaces wet chemical processes with a vacuum-based chemical vapor deposition process. Instead of using solvents and performing multiple post-treatment steps, the invention uses vacuum CVD to directly deposit crosslinked PHEMA films in a single step, eliminating the need for solvent evaporation and curing operations.
Solution Approach 2:
The invention changes the process parameters from liquid-phase wet chemistry to gas-phase vacuum deposition. By controlling the vacuum pressure, monomer flow rates, and substrate temperature, the process achieves direct formation of crosslinked films without requiring separate solvent removal and curing steps.
2Manufacturing precision
If conventional CVD is used, then film deposition is achieved, but crosslink density cannot be controlled which limits gel property optimization
Solution Approach 1:
The patent implements feedback control by monitoring and adjusting monomer flow rates and vacuum pressure during deposition. This allows real-time control of polymerization kinetics and crosslink density, enabling precise optimization of gel properties for specific applications.
Solution Approach 2:
The invention controls crosslink density by adjusting the ratio of crosslinking agent to monomer in the gas phase, controlling vacuum pressure levels, and optimizing substrate temperature. These parameter changes enable precise control over the degree of crosslinking and resulting gel properties.
3Manufacturing precision
If PECVD is used to produce PHEMA thin films, then film deposition is achieved, but systematic control of crosslink density has not been demonstrated
Solution Approach 1:
The patent replaces plasma-based chemistry with vacuum chemical vapor deposition using resistively heated filament wires. This substitution allows for controlled radical generation without the complex plasma chemistry, enabling systematic control of crosslink density through straightforward parameter adjustment.
Solution Approach 2:
The invention uses resistive heating to control the temperature of filament wires, which generates radicals for polymerization. By controlling filament temperature and monomer flow rates, the process achieves systematic control of crosslink density that was not possible with PECVD.
4Manufacturing precision
If HFCVD is used, then film deposition is achieved, but multiple steps and high energy input are required which reduces efficiency
Solution Approach 1:
The patent incorporates an initiator into the monomer stream before deposition, so that polymerization and crosslinking begin immediately upon contact with the heated filament. This preliminary preparation eliminates the need for separate initiation steps and reduces total energy input compared to conventional HFCVD.
Solution Approach 2:
The invention merges the polymerization, crosslinking, and film deposition steps into a single vacuum CVD process. By combining these operations that would traditionally require separate steps, the process reduces total energy input and improves efficiency.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
iCVD enables the production of films with specific crosslink densities, thermal stabilities, and hydrophilic properties, enhancing mechanical properties and enabling controlled drug release while avoiding solvent use and post-treatments, thus improving film quality and environmental sustainability.
Implementation Method 1
resistively-heated filament wires... selective thermal decomposition of species is achieved using resistively-heated filament wires... very low filament temperatures (180-250° C.) are required to generate radicals for initiation
Implementation Method 2
generate radicals for initiation... These radicals serve as starters of polymer chains
Implementation Method 3
Chemical vapor deposition (CVD) is a one-step, vacuum process... Initiated CVD (iCVD) can be positioned as a complementary method to PECVD in depositing films with control of crosslink density
Implementation Method 4
In another embodiment, iCVD is used to form crosslinked thin films by the addition of a crosslinking agent (e.g., a diacrylate or a dimethyacrylate)... The incorporation of a crosslinking agent into the thin films is shown to increase systematically with its partial pressure
Implementation Method 5
PHEMA-based hydrogels have been widely researched and used in biomedical applications because of their non-toxicity, non-antigenic properties, and biocompatibility... The unique swelling properties of these films are also disclosed, establishing that certain inventive films function as hydrogels when soaked in water
Data Source
AI summary
In one embodiment of the invention, iCVD is used to form linear thin films using a radical initiator and an alkene. In another embodiment, iCVD is used to form crosslinked thin films by the addition of a crosslinking agent (e.g., a diacrylate or a dimethyacrylate). The incorporation of a crosslinking agent into the thin films is shown to increase systematically with its partial pressure. In one embodiment, when the crosslinker is EDGA and the monomer is HEMA it results in crosslinked P(HEMA-co-EGDA) copolymer. In another embodiment, when the crosslinker is EDGA and the monomer is VP, it results in crosslinked P(VP-co-EGDA). Disclosed are the effects of crosslinker incorporation on the thermal and the wetting properties of the polymers. The unique swelling properties of these films are also described; certain films of the present invention are hydrogels when soaked in water.