PolyHEMA hydrogel

Diffusion through polymers is influenced not only by the polymer s structure, but also by the molecular structure of the solute. The solute structure may also influence the rate of partitioning into the elution medium. However, there is only a low relationship between these factors. The influence of gel structure on the diffusion characteristics of solutes through polyHEMA hydrogels has been reported [146]. 

In our experiments the donors were selected to be excitable with a S43 nm HeNe laser. The donors and acceptor were dissolved at concentrations listed in Figure 4 in a 40 mM NaHCOs solution and mixed with a polyHEMA hydrogel (66). The equilibrated hydrogels were sandwiched between silicone rubber membranes, and sealed to retain the indicator solutions. 

Figure 4 Dependence of donors fluorescence phase angles on pC02. The donor-acceptor pairs were in polyHEMA hydrogel, 25 C, =543...

Seidel JM, Malmonge SM (2000) Synthesis of polyHEMA hydrogels for using as hiomaterials. 

M. Halpenny, M. Genevieve, M. Olmstead and P. K. Mascharak. Incorporation of a designed ruthenium nitrosyl in polyhema hydrogel and light-activated delivery of NO to myoglobin. Inorg. Chem. 46, 2007, 6601—6606. 

The two matrices in these cements are of a different nature an ionomer salt hydrogel and polyHEMA. For thermodynamic reasons, they do not interpenetrate but phase-separate as they are formed. In order to prevent phase separation, another version of resin glass polyalkenoate cement has been formulated by Mitra (1989). This is marketed as VitraBond, which we term a class II material. In these materials poly(acrylic acid), PAA, is replaced by modified PAAs. In these modified PAAs a small fraction of the pendant -COOH groups are converted to unsaturated groups by condensation reaction with a methacrylate containing a reactive terminal group. These methacrylates can be represented by the formula ... 

Applications of hydrogels include highly absorbent diapers based on poly(sodium acrylate), contact lenses based on poly(2-hydroxyethyl methacrylate) (polyHEMA), and switches based on variations of swelling of the hydrogels. A number of drug delivery systems have also been based on hydrogels. 

On-wafer membrane deposition and patterning is an important aspect of the fabrication of planar, silicon based (bio)chemical sensors. Three examples are presented in this paper amperometric glucose and free chlorine sensors and a potentiometric ISRET based calcium sensitive device. For the membrane modified ISFET, photolithographic definition of both inner hydrogel-type membrane (polyHEMA) and outer siloxane-based ion sensitive membrane, of total thickness of 80 pm, has been performed. An identical approach has been used for the polyHEMA deposition on the free chlorine sensor. On the other hand, the enzymatic membrane deposition for a glucose electrode has been performed by either a lift-off technique or by an on-chip casting. 

The same transducers covered with the polyHEMA membranes can serve as a basis for several other amperometric sensors. The optimum trade-off between rapid response (thin membrane) and stirring independency (thicker membranes) should be found for each particular application (77). In many cases, the hydrogel membrane... 

Tighe, B. and Corkhill, P. Hydrogels in biomaterials design Is there life after polyHEMA ... 

Process Analysis - Diffusion. - Water diffusion in methacrylate based copolymer hydrogels and incorporaion of vitamin B12, aspirin or chlorhexidine Diacetate into such copolymer hydrogels were investigated." The diffusion of water into cylinders of poly-2-hydroxyethyl methacrylate (PHEMA) and copolymers of (HEMA) with tetrahydrofurfuryl methacrylate (THFMA), butyl- methacrylate (BMA), and cyclohexyl methacrylate (CHMA) were studied over a range of copolymer compounds." The diffusion of water into the polymers was found to follow a Fickian, or case 1 mechanism. The diffusion coefficients of water were determined from mass measurements and NMR imaging studies. They were found to vary from 1.7 0.2 x 10 " m s for polyHEMA at 37°C to lower values for the copolymers. The mass of water absorbed at equilibrium relative to the mass of dry polymer varied from 52-58 wt% for polyHEMA to lower values for the copolymers. 

Poly(2-hydroxyethyl methacrylate) (polyHEMA) is used for soft contact lenses and is a representative medical use hydrogel. Encapsulation of cells into polyHEMA or poly(2-hydroxyethyl methacrylate-co-methyl methacrylate) (polyHEMA-co-MMA)) will be introduced in the following. 

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