RESULTS AND DISCUSSION

The research work was dealing with the preparation of different hydrogels for biomedical and technological purposes. The research studies and results obtained can be reported in the following items:

 Preparation and Characterization of Supported Hydrogels as Biocompatible Materials Interfaced with Blood and Tissue.

 Use of Radiation Grafted Membrane in the Dialysis of Low Molecular Weight Metabolites.

 Stimuli-Responsive Hydrogels for Possible Use in Drug Delivery Systems.

 Hydrophilic/Hydrophobic Materials for Protein Adsorption.

 Immobilization of Enzyme by Radiation Grafted Hydrogels.

The results obtained for the above items can be summarized, as follows.

2.1. Preparation and characterization of supported hydrogels

The graft co-polymers were prepared by direct radiation grafting of Sty/MAn binary monomers system onto PE films using Co-60 J-rays. Attention was focused on the selection of the reaction parameters suitable for the commercial production of such supported hydrogels.

The factors which affect the preparation process and grafting yield are; type of solvent, dose and dose rate, co-monomer composition and their concentrations in the diluents. The structure and composition of the grafted chains were also investigated

2.1.1. Effect of solvent

Table I shows the influence of different solvents on the graft co-polymerization of Sty/MAn binary monomers onto HDPE and LDPE. It can be seen that the higher degrees of grafting of such binary monomers/solvent-mixture are obtained in presence of acetone and ethyl methyl ketone as compared with those obtained in other solvents investigated here. It is expected that appropriate solvent that swells the surface grafted layer initially formed, enhance the diffusivity of Sty/MAn into the interior regions of the polymer substrate.

2.1.2. Effect of co-monomer composition

Some attention on enhancing grafting efficiencies has involved the use of mixed monomers systems, particularly with regard to synergistic effects leading to more efficient grafting processes. Therefore, the grafting of Sty/MAn binary system of various relative compositions is investigated at overall co-monomer concentration 20 mol%, at a dose rate of 0.7 and 1.38 Gy/s. The obtained results are illustrated in (Figs 1, 2). It is clear that the grafting yield initially increases with increasing the styrene content in the co-monomer feed solution to

reach a maximum degree of grafting at (Sty/MAn) composition of (70/30 mol%) and (60/40 mol%) for HDPE and LDPE, respectively. Synergism could be taken place for the grafting of MAn in all co-monomer compositions. However, such synergism was observed only in styrene-rich co-monomer composition. It was also observed that the grafting process is dependent on the dose rate; the higher the dose rate, the lower the degree of grafting is obtained when the MAn-rich co-monomer feed solution is used. However, using a styrene-rich co-monomer feed solution, it resulted in increasing the degree of grafting as the dose rate decreases.

TABLE I. EFFECT OF DIFFERENT SOLVENTS ON THE GRAFTING PROCESS OF THE STY/MAN BINARY MONOMERS (50/50 MOL%) SYSTEM UNTO LDPE AND HDPE FILMS.

TOTAL IRRADIATION DOSE; 10 K GY, DOSE RATE; 1.4 GY S ^-1, CO-MONOMER CONCENTRATION; 20 MOL%

Degree of Grafting (%) Solvent

LDPE HDPE

Acetone 404.25 120

Butanone 97.9 75

Ethyl acetate 122.8 55

Dioxane 14 5

Benzene 73 45

DMF 70.5 20

FIG. 1. Effect of Sty/Man co-monomer composition on the degree of grafting onto HDPE films at different irradiation dose rate (Gy/s); ( ) 1.4 and ( ) 0.8. co-monomer concentration in acetone; (20 mol%) and irradiation dose ; 7.5 k Gy.

FIG. 2. Effect of Sty/Man co-monomer composition on the degree of grafting onto LDPE films at different irradiation dose rate (Gy/s); ( ) 1.4 and ( ) 0.8. co-monomer concentration in acetone;

(20 mol%) and irradiation dose ; 7.5 k Gy.

Results suggested that the relative participation of charge transfer complex in the graft co-polymer depends on the composition of co-monomer feed solution and the concentration of CTC in feed solution reach its maximum when Sty-rich co-monomer composition of 70 mol%

was used. Also the molar ratio of Sty/MAn on the graft co-polymer support such assumption that the CTC participated in graft co-polymerization processing. The molar ratio of Sty/MAn in all graft co-polymer chains of different co-monomer compositions, specially these containing excess Sty which give high percent graft, was formed to be 1: 1 in the first stage of grafting [Table II].

TABLE II. EFFECT OF CO-MONOMER COMPOSITION ON THE MOLAR RATIO OF GRAFTED P-STY AND P-MAN GRAFT CHAINS IN THE OVERALL GRAFT CO-POLYMER AT DOSE RATE OF 1.38 GY/S AND 0.8 GY/S., USING UV SPECTROPHOTOMETRIC AND TITRATION METHOD AT DIFFERENT DEGREES OF GRAFTING

Degree of

2.1.3 Thermal and mechanical properties

It is very important that the grafted films must show a good tensile strength, especially for the use in biomaterials. The change in tensile strength and percent elongation at break with degree of grafting was determined and shown in (Figs 3 and 4), respectively. It can be seen that the tensile strength increases gradually with degree of grafting, however, the percent elongation decreases as the degree of grafting increases.

FIG. 3. Change in tensile strength with degree of grafting for LDPE-g-P(Sty/MAn) films.

FIG. 4. Change in elongation percent with degree of grafting for LDPE-g-P(Sty/MAn) films.

The knowledge on the changes in thermal properties and crystallinity of LDPE-g (Sty/MAn) system is important for its application. Diffusion is generally limited to the amorphous regions of a polymer so that applications that really depend on the diffusion characteristics of films such as those used for separation processing require careful control of crystallinity. The change in Tm and 'Hm for the grafted co-polymer at the first and second heating runs with degree of grafting is investigated (Table IV). It can be seen that no remarkable change in Tm by grafting is observed. Also, a slight decrease in (Trc) and a decrease in ('Hrc) are observed (Table III). This is good evidence that such grafted co-polymer is not highly crosslinked.

TABLE III. EFFECT OF DEGREE OF GRAFTING ON THE THERMAL PARAMETERS OF LDPE-G-P(STY/MAN)

2.2. Biocompatible materials interfaced with blood and tissue

Since the major problems for application of biomaterials that contact occur at the blood and for tissue material surface, an attempt has been made to gain insight into the biomedical uses of polypropylene-g-poly (vinyl acetate/maleic anhydride) mode system, that prepared by radiation grafting method, and its treated one with sodium hydroxide and ammonia solutions and tested as biocompatible materials interfaced with blood and tissue. Investigations on the biomedical and histopathological changes which might be caused in the tissue due to muscle implantation of (PP) and PP-g-P (VAc/MAn) graft co-polymer of film having 100% graft were investigated. Histopathological studies of the dorsal muscle of the rabbits surrounded the implanted polymer was investigated. Results showed that no sign of degradation in the tested polymers occurred and much materials seem to be inert. Consequently, they might be used as biocompatible materials.

To investigate the suitable percent grafting that minimize the thickness of capsule which may be formed around the implanted films, PP-g-poly (VAc/sodium maleiate) graft co-polymer film having degree of grafting varied from 0 to 100% are implanted subcutaneously in rabbits. After 4 weeks, capsules with different thickness were formed around the implanted polymer materials.

The thickness of capsules depends on the percent graft of the grafted films under investigation as shown in Table IV. The thick capsules were formed around ungrafted PP and for the grafted films having 5% and 10% grafting. However, the implantation of grafted films having higher percent grafting films resulted in forming thin capsules.

The results indicate that the graft co-polymer of succinate and VAc supported into PP films enables to present biocompatible materials at low percentage of grafting.

TABLE IV. GRADE OF THE ENCAPSULATION OF PP-G-P(VAC/SODIUM SUCCINATE) IMPLANTED SUBCUTANEOUSLY FOR FOUR WEEKS. (+) IS PROPORTIONAL TO THE THICKNESS OF CAPSULE

Degree of Grafting of implanted polymer

2.2.1. Evaluation of blood compatibility

The main obstacles in the use of non-biological materials in cardiovascular implants are surface induced thromboses. In the present work, series of PP-g-P (VAc/MAn) graft co-polymer films with different percent grafts which treated with various reagents such as diluted HCl, NaOH at 30qC, NH4OH and NaOH at 100qC were prepared. The whole blood clotting technique was used to evaluate the blood compatibility of such films.

Fig. 5 shows the effect of the percent grafting of treated films that having different functional groups; free –COOH, -COONa, -CONH2, -COONa, -COO-NH4+, –COONa, and -OH groups, on the time required for clotting the blood adherent to those films. It is found that for most grafted co-polymer films investigated, the lower the percent grafting, the shorter the time required for clotting the blood is noticed, especially those films containing free carboxylic acid groups. However, for the films containing both –COOH, and –OH groups, and treated with NaOH at 100qC, it was found that the lower the percentage of grafting, the longer the time required for clotting the blood adherent to such film. However, at all high degrees of grafting, it was noticed that the time needed to clot the blood, increases as the degree of grafting increases. But in case of graft co-polymers containing both –COONa and –OH groups, the shorter time for clotting the blood is observed at high degrees of grafting. Also, it can be seen that the time required to clot the blood contacted with films containing –CONH4, -COONa, and -COONH4+ gave almost the lowest time in comparison with those containing – COOH or –COONa groups.

3. Use of radiation grafted membrane in dialysis of low molecular weight metabolites