More particularly this invention relates to a process for the preparation of multifunctional, pH sensitive, resorbable, non-toxic, 100% biocompatible and biodegradable hydro gel. The hydro gels, in general, find application as biomaterial & super absorbent materials in agro industry and biomedical engineering. Particularly they exhibit potential use as controlled/ regulated delivery systems, artificial skin, sutures, membranes for transfusion purposes, and implants. They are also used in the treatment of osteomyelitis as implants for localized site-specific delivery of drugs, and as contact lenses but not limited to only these applications
The hydro gels are cross linked polymeric networks capable of absorbing large amount of water and drastically increasing in volume. Their ability to absorb water is due to the presence of hydrophilic groups such as -OH, -CONH2, -COOH, and -SO3H. Hydro gels are hydrophilic natured three-dimensional network held together by chemical or physical bonds. If enough interstitial space exists within the network water molecules can become trapped and immobilised filling the available free volume.
The properties and characteristics of the hydro gels can be designed
and tailored by using appropriate polymers to form Interpenetrating
Polymer Networks (IPNs). IPNs make it possible to combine partially compatible or incompatible polymers to achieve the desired phisico-chemical properties. IPNs have several advantages over simple hydro gel because the synthesis and cross linking of two or more different polymers is done in the immediate presence of each other so that the cross linked chains are intermingled, resulting in considerable phase mixing, thereby restricting the domain size.
The properties of IPNs are influenced by the manner of synthesis, composition (type & proportion of polymers and cross linking agents employed), degree of cross-linking and compatibility.
The types of polymers used to prepare IPNs are: (1) Natural biodegradable such as polysaccharides that include starch, chitosan, cellulose; polypeptides of natural origin which include gelatin and bacterial polyesters, (2) Polymer with hydrolysable backbones that may cover polyesters, polycaprolactone, polyamides, polyurethanes, & polyanhydrides and (3) Polymers with carbon backbones which can be exemplified by vinyl polymers like polyvinyl alcohol and acrylates.
The IPNs can be classified as simultaneous IPNs and sequential IPNs based on polymerisation method. Simultaneous IPNs are composed of highly incompatible polymer pairs such as polystyrene and polyurethanes.
Thus, variations in the composition of polymers and manner of synthesis adopted can lead to the formation of hydro gels / IPNs that are pH sensitive; temperature sensitive; hydrophilic; hydrophobic; biodegradable; non-biodegradable; bio-compatible; non-biocompatible; having varied i) water sorption ability, ii) substance loading & releasing potential, & ability to monitor flow of fluids/substances; non toxic and without undesirable by products/ free of leach able impurities, with minimum undesired aging and chemically inert.
To monitor the loading, releasing property, and regulating the degradation rate of the IPN, a polymer with appropriate geometry need to be developed using right length of cross links. Increase in cross link helps in getting a polymer with increased porosity that helps in loading and mobility of substance in addition to improvement in compatibility and degradation property of the polymer. However, this property needs to be balanced judiciously.
The hydro gels find potential application in large number of areas such as medicine, industry, & environmental clean up. Applications of such materials include surface coating, uptake and release of heavy metal ions, drug delivery, controlled regulated release systems, opto -electronic switches, Agriculture, and consumer packaging.
In the field of medicine hydrogel can be applied as an interface between bone and an implant, as artificial skin, as contact lenses, as blood
contact materials and in controlled site-specific delivery systems due to their permeability to small molecules, soft consistency, low interfacial tension, facility for purification and mainly high equilibrium water content which make them similar to the physical properties of living tissues. In addition to this, they have the ability to mimic the functions of living system.
Currently, many hydro gels are being developed and are in use as biomaterials and super-absorbent materials in bio-medical engineering. Some of them are illustrated below: 1. Thermo sensitive and pH sensitive PVA / PAAC Polymer composed of poly (vinyl alcohol) and poly (acrylic acid). The hydro gels are synthesized by sequential method by which PVA hydro gel networks were formed inside of cross linked PAAC chains due to UV radiation for 1 hour followed by repetitive freezing and thawing process for 8 cycles each of 2 hours. 2-2 dimethyl-2 phenyl acetone (DMPAP 0.2 wt%) was used as photo initiator and Methylene Bis Acryl amide (MBAAm) 0.5 mol% was employed as cross-linking agent. PVA: Acrylic ratio used is 6:4, 5:5 and 4:6. The gel having higher content of PAAC has better swelling property and thus better capability to deliver drug. It exhibits high release rate at higher temperature (45°C) due to temperature dependent swelling behaviours. They are basically used as sensors and non-degradable sutures. Due to non-degradable property, tissue does not find space to grow during the process of healing. Drug is generally loaded using solvent sorption method. The
solvents employed may result in side effects.
2, PGA PLA (Poly glycolic acid / Poly lactic acid) both homo and copolymers. These semi inter penetrating polymers are biodegradable and are used in surgery. They are well suited to implantation as they can serve as a temporary scaffold to be replaced by host tissue, & degrading by hydrolysis to non-toxic products, which are excreted. However, the IPNs, thus produced, are cost extensive due to costly monomers used in the production of IPN. Further the IPNs exhibit poor shelf life.
Ref: D.K. Gilding and A.M. Reed, "Biodegradable polymers for use in surgery: poly glycolic acid / poly lactic acid homo and copolymers", Polymer 20, 1459-1464 (1979)
I.O. Hollinger, "Preliminary report on the osteogenic potential of a biodegradable copolymers of Poly lactide (PLA) & Poly glycolide (PGA)", Biomed.Mater.Res. 17, 71-82 (1983).
Greater than 50% of the drug is released rapidly as the burst effect. The IPN continue to release drug for over 4 months and release more than 60% of their load. They are quite biocompatible and do not require subsequent surgical removal. The release pattern depends on the drug-loading ratio and could be monophasic for higher level and biphasic for lower levels.
3. PS-PHEMA (polystyrene (cross linked) and poly 2 hydroxyethyl metha crylate) - synthesized by sequential IPN method and show micro phase-separated structure. It has potential applicability as
biomedical materials, particularly as extra corporal material, & membranes for separation or selective absorbent. There is no report of its being used as implant. It's a blend of incompatible components. Cross- linked (Polystyrene) was prepared using Azobisisobutyronitride (AIBN) as initiator and Divinyl Benzene (DVB) as cross- linking agent. Cross linked PHEMA was prepared using ethyleneglycol dimethacrylate (0 - 0.1 mol%) as initiator. The use of initiator is optional. For preparation of IPN, DMF was used as a common solvent. The IPN is non biodegradable and toxic in nature. Thus it cannot be used for food and biomedical applications.
4. Cross linked chitosan and poly ether semi IPN (CV-CS / PE semi
IPN) hydro gels are pH sensitive and are widely used in biomedical
engineering due to its peculiar character. The gel undergoes sharp
swelling change from a hydrophobic state to a swollen one as pH of
swelling medium becomes acidic'. Glutaraldehyde was used as a cross-
linking agent. IPN has restricted applicability due to specific pH
requirement for release of drug. These IPNs find applicability in
gastrointestinal tract.
5. pH sensitive biodegradable PGA / PL [ poly (y glutamic acid) and
poly (e lysine)]. The cross linking was carried out by using y
irradiation. Polymers used are naturally occurring polymers; can absorb
over 1400 times of its weight in water; find application in drug delivery
system. No data is available on loading, release, & toxicity property.
6. Starch based biodegradable hydro gels. Gels were prepared by free radical polymerization of Acryl amide (Aam) and acrylic acid (AA) and some formulations with bis-acryl amide in the presence of corn starch / ethylene co vinyl alcohol copolymer blend (SEVA-C). The radical initiator used was benzoyl peroxide (BPO) and N-dimethyl amino benzyl alcohol (DMOH) as an activator. The hydro gels are also pH sensitive as well as degradable. They show improvement over conventionally used Aams/AA for (i) insulin release (ii) to improve osteoblast adhesion and (iii) super absorbent property. However, their suitability for biomedical application is not proven.
A new family of nanoscale materials on the basis of dispersed networks of cross-linked ionic and non-ionic, hydrophilic polymers for drug delivery applications have been reported. Poly (ethylene oxide) (PEO) and polyethylene imines (PEI) [PEO-CL-PEI] can be quoted as one example. In situ forming hydro gels through photo-polymerization is reported to be a substitute to mercury amalgam fillings in bone cementing. Cyanoacrylate materials also have been used as bone cements because they are capable of polymerizing in situ. However, while they provide reasonably strong adhesion, they have proven to be brittle.
7. Another conventional bone cement, Polymethyl methacrylate
(PMMA) is applied by mixing polymerized methyl methacrylate in
combination with benzyl peroxide and liquid methyl methacrylate
monomer. Hydroquinone is added to inhibit spontaneous free
radical polymerization. Dimethyl toluidine is also added to reduce
threshold temperature for the polymerization. However, PMMA is not biodegradable and is less than an ideal biologic implant.
PMMA beads impregnated with antibiotics have been successfully used as local drug delivery agents in the treatment of osteomyelitis since 1970. However, there are some disadvantages associated with this therapy.
a. PMMA, being inert, acts as a foreign body. As a result a second
surgical procedure is required for its removal.
b. Only 20% of the drug loaded is released from the PMMA implant
beads.
c. Drug release lasts for only four weeks.
8. Polymers based on poly (acrylic acid) and gelatin are also in use due to their swelling properties and sensitivity to pH and temperature. The IPNS (AAC and GX) are prepared by sequential polymerization using NN'-methylene bisacrylamide (BSA) (0.5 mol%) and glutaraldehyde (4% w/v) as cross-linking agents for poly acrylic acid &gelatin respectively. Free radical polymerization and cross-linking of AAC was carried out by using ammonium persulfate and sodium metabisulfite as redox initiator. The gel thus formed was immersed in Glutaraldehyde to cross link the gelatin chain. For semi IPN either PAAC or GE was cross-linked. The BSA having molecular weight of 154 was used as cross linker resulting in to the production of IPN that is nondegradable up to 6 months in vivo. Due to basic hydrolytic
character, it was less degradable in vitro. The ratios of AAC:GE used were 1:1, 3:1 and 5:1 swelling ratio of full IPNs increases with pH from 5 to 8.4.
It can be seen that the hydro gels or IPNs have received much attention for applications in biomedical engineering as implants in vascular and orthopedic surgery, controlled drug delivery system, absorbable sutures and super absorbent. They are uni-functional or bi - functional. Biodegradable hydro gels have more promising potential over nonbiodegradable ones, the reasons for which have been outlined above. Biodegradable gels are generally used for:
a) to replace tissues that are diseased or otherwise nonfunctional, as in-
joint replacements, artificial heart valves and arteries, tooth
reconstruction and intraocular lenses;
b) to assist in the repair of tissue, including the obvious sutures but also bone fracture plates, ligament and tendon repair devices;
c) to replace all or part of the function of the major organs, such as in haemodialysis (replacing the function of the kidney), oxygenation (lungs), left ventricular or whole heart assistance (heart), perfusion (liver), and insulin delivery (pancreas);
d) to deliver drugs to the body, either to targeted sites (e.g. directly to a tumors) or sustained delivery rates (insulin, pilocarpin, contraceptives).
The hydro gels of stimuli responsive polymers have added advantage
for its application. pH and temperature are the factors most available
environments inside the human body. Biocompatibility will be an additional feather to the gel particularly when used as implants or sutures.
Biocompatibility is better if the implant polymer is hydrophilic. Hydrophilic surface lubricity is the common phenomenon found on marine life and living tissues in animals and human bodies. This surface lubricity serves to reduce friction in motion or protect tissues from damage or both. Hydrophilic materials with surfaces having low coefficients of friction when in contact with an aqueous fluid, such as a body fluid facilitate insertion or removal of a medical device into or out of a patient, and would minimize injury or inflammation of mucous membranes as well as aid patient comfort. For ease of handling, it is even more desirable if the surface exhibits a normal plastic feel when dry, but becomes slippery only upon exposure to an aqueous fluid.
Every orthopedic surgical procedure carries the risk of bacterial infection of the bone termed osteomyelitis.
1. Microorganisms infect soft tissue of the bone.
2. Microbes enter the bone either directly through physical injury or indirectly through the hematogenous route as secondary infection.
3. Once they reach inside the bone, the microbes elicit immune response resulting in inflammation of the infected soft tissue.
4. Depending on the pathophysiology of the disease osteomyelitis could be either Acute osteomyelitis or Chronic osteomyelitis.
5. The acute osteomyelitis is associated with the initial acute exudative inflammation leading to edema, increased vascularity and accumulation of immune response cells. This eventually leads to bone necrosis.
6. The chronic phase sets in with the granulation of the highly vascular tissue, surrounding the exudative pus forming necrotic tissue, forming an impenetrable avascular scar separating the infected tissue from the healthy tissue. The infected region is further isolated by the formation of bone over the avascular scar.
7. The disease can spread to other regions of the same bone or to other bones during the severe acute exudative inflammatory stage due to the circulatory disturbances caused by the pressure exerted by the exuded pus and infected fluids.
Hence, there is a great need to develop novel hydro gel, which is biocompatible, biodegradable, resorbable, pH sensitive, and nontoxic. Further the hydro gel should be permeable to biologically active molecules, biologically active substances, pharmaceutically and therapeutically active compounds. The occurrence of inflammation in case of osteomyelitis should be exploited to enhance the degradation of the gel while designing the gel.
It is therefore an object of the present invention is to provide a
process for the preparation of a novel hydro gel with multifarious properties.
Another object of this invention is to provide a process to develop a hydro gel that can act as an intelligent drug delivery system and is able to release drug in response to the external chemical, physical and biological stimuli.
Still another object is having a process to design the hydro gel that is fully biocompatible and biodegradable resulting in to non-toxic metabolites.
Yet another object of the invention is that the process be able to design the hydro gel capable of delivering drug at specific site and in a specific manner eliminating the potential for both under and overdosing.
Further, the gel prepared by the process of the present invention should be capable of getting loaded with varied types of biologically active substances, agrochemicals, bioactive molecules, pharmaceutically and therapeutically active substances.
The gel thus produced also should be free of impurities such as monomers, initiators and other ingredients used for the production of the gel.
The hydro gel produced using the process of this invention should be able to maintain effective drug concentration in the blood over longer periods, maximize efficacy and minimize side effects.
The hydro gel produced by the process of this invention should have proper geometry and porosity for desired loading releasing & degrading capability.
Accordingly the present invention provides a process for the preparation of a novel hydro gel, which comprises: polymerizing polymer with carbon back bones such as herein described using a mixture of conventional redox initiator and a divinyl ester prepared by reacting poly (caprolactone diol) followed by cross linking with the polypeptide of natural origin using glutaraldehyde as a cross linking agent, then converting it to desired shapes by conventional methods.
One of the embodiment of the present invention is that the natural polypeptide used may be albumin, chitosan, gelatin preferably gelatin.
Another embodiment of the present invention is that the polymer with the carbon backbone used may be such as vinyl polymers exemplified by poly vinyl alcohols, acrylates, & Poly Acrylic Acid but not limited to.
Yet another embodiment of the invention is that the gel may contain poly acrylic acid as backbone cross-linked with gelatin and divinyl ester- a poly caprolactone based diol having molecular weight ranging from 530 to 2015 & glutaraldehyde as cross linkers.
Still another embodiment is that the PAAC and GE may be in the ratio of 1:5 to 5:1
The hydro gel optionally may contain biologically active molecules such as proteins, vaccines, antigens, antibiotics, any component of cell;
biologically active substances like fertilizers, hormones, pesticides other agrochemicals; conventional therapeutically and pharmaceutical^ active substances that includes drugs, formulations.
The loading of the molecules or substances may be effected by soaking hydro gel in distilled water or buffer solution (pH-7.4) containing desired loading material at ambient temperature. Further the loading may be carried out under nitrogen atmosphere.
The gel may be produced in the geometrical forms such as cylinders, cubes, slabs, blocks, or sheets. They may be produced as tablets or capsules and skin patch. The hydro gel may be stored in an airtight container at ambient temperature.
The gel produced by the process of the present invention may be full IPNs or semi IPNs. In case of full IPNs the gel may be prepared by radical polymerization of cross linked PAAC and crossed linked Gelatin. In case of semi IPNs either PAAC or Gelatin used may be crossed linked. The molecular weight of cross linkers used in the present invention ranges from 600 to about 2000 as against 154 in the prior art.
The novel hydro gel is made a subject matter of our co-pending application filed under Mailbox provision.
The following examples are set forth to illustrate the process for the preparation of hydro gel. The examples are provided for the purpose of illustration only and are not intended to be limiting the scope of the present invention in any sense.
Example 1
Synthesis of divinyl ester
Divinyl ester (DVE) was obtained by reacting poly(caprolactone diol) (PCLd), (Mw. 530
to 2000), with excess of acryloyl chloride according to the following reaction scheme:
(Scheme Removed)
The monomers were taken in the ratio of 1:3 (mole ratio). The reaction was carried out in chloroform at 40 to 60°C for 4 hours, with continuous stirring. Excess acryloyl chloride was removed by repeated washing with chloroform and water. The washed DVE was dried under vacuum at 40°C.
Characterization of the divinyl ester
DVE was characterized by FTIR and 'H-NMR spectroscopic techniques. FTIR
spectrum was recorded as liquid film on KBr disc using Nicolet 5PC FTIR
spectrophotometer. 'H-NMR spectrum was recorded on a Bruker Spectrospin DPX 300
spectrometer using CDCI3 as solvent and tetramethyl silane as internal standard.Figures
la & b accompanying this specification show the FTIR spectra of PCLd and DVE
respectively. In the FTIR spectrum of the DVE Figure lb, exhibits the a doublet
at 1620 and 1635 cm"1 confirming the formation of DVE.
Figures 2a & b accompanying this specification show the 'H-NMR spectra of PCLd and DVE. In PCLd no signal was observed in the range of 8 5-7 ppm. The signal due to -OH was observed at 5 3.70
ppm. In the lH-NMR spectrum of DVE, signal due to acryloyl appeared in the range of 8 5.69-6.25 ppm. The signal due to methine proton was observed at 8 6.01-6.05 ppm. The two vinyl protons (terminal) are different and were observed at 8 5.69-5.73 ppm and 8 6.24-6.25 ppm. All other signals present in the 'H-NMR spectrum of PCLd were seen in the spectrum of DVE except hydroxyl group thereby confirming the structure of DVE.
Example 2: Synthesis of full interpenetrating polymer networks
Sequential full interpenetrating polymer networks based on acrylic acid (AAc) and gelatin (Ge), crosslinked with divinyl ester (DVE) and glutaraldehyde (GA) respectively, were synthesized by first crosslinking acrylic acid with divinyl ester in the presence of gelatin, followed by the addition of glutaraldehyde to crosslink gelatin. The ratios (w/w) of acrylic acid to gelatin in the initial feed were varied. The sample designations and the initial feed ratios are given in the Table I.
Table I: Sample Designation and Monomer Ratios in the Preparation of Full IPNs

(Table Removed)
For cross linking of acrylic acid, divinyl ester of different molecular weights (680 to 2150) was used. The DVE concentration was varied from 0.1 to 2 mole %. For cross-linking of gelatin, 0.5 to 4% (w/v) of glutaraldehyde was used.
For example, for the synthesis of Kl, acrylic acid crosslinked with DVE (molecular weight 680) and cross linking densities of 0.5 mol % for acrylic acid and 4% for gelatin was employed. 0.089g of divinyl ester, dissolved in 2g of AAc, was added to the Ge solution obtained by dissolving 2g of Ge in 20 ml of oxygen free distilled water. Free radical polymeriization of AAc was carried out in nitrogen atmosphere using redox initiator (a mixture of ammonium persulfate and sodium metabisulfite). The reaction was allowed to proceed overnight at room temperature, which resulted in the formation of firm gels. The gels, after carefully separating from the walls of container, were immersed overnight in 25 ml of 4% GA solution to cross link Ge. The samples were washed extensively with water to remove the unreacted monomers as well as water-soluble moieties and then dried in vacuum to constant weight.
Example 3 Synthesis of semi interpenetrating polymer networks where
acrylic acid is crosslinked with divinyl ester and gelatin is not crosslinked
Semi interpenetrating polymer networks based on acrylic acid (AAc) and gelatin (Ge), where acrylic acid is crosslinked with divinyl ester (DVE) and gelatin is not crosslinked, were synthesized by crosslinking acrylic acid with divinyl ester in the presence of gelatin. The ratios (w/w) of acrylic acid to gelatin in the initial feed were varied. The sample designations and the initial feed ratios are given in the Table II.
Table II: Sample Designation and Monomer Ratios in the Preparation of Semi IPNs where only acrylic acid is crosslinked and gelatin is not.

(Table Removed)
For crosslinking of acrylic acid, divinyl ester of different molecular weights (680 to 2150) was used. The DVE concentration was varied from 0.1 to 2 mole %. For example, for the synthesis of Bl, acrylic acid was crosslinked with DVE (molecular weight 680), and crosslinking density of 0.5 mol % for acrylic acid, 0.089g of divinyl ester, dissolved in 2g of AAc, was added to the Ge solution obtained by dissolving 2g of Ge in 20 ml of oxygen free distilled water. Free radical polymerization of AAc was carried out in nitrogen atmosphere using redox initiator (a mixture of ammonium
persulfate and sodium metabisulfite). The reaction was allowed to proceed overnight at room temperature, which resulted in the formation of firm gels. The gels were washed extensively with water to remove the unreacted monomers as well as water-soluble moieties and then dried in vacuum to constant weight.
Example 4 Synthesis of semi interpenetrating polymer networks where gelatin is cross linked with glutaraldehyde and acrylic acid is not cross linked.
Sequential semi interpenetrating polymer networks based on acrylic acid
(AAC) and gelatin (Ge), where gelatin was crosslinked with glutaraldehyde and acrylic acid was not crosslinked, were synthesized by first homo-polymerizing acrylic acid in the presence of gelatin, followed by the addition of glutaraldehyde to crosslink gelatin. The ratios (w/w) of a acrylic acid to gelatin in the initial feed were varied. The sample designations and the initial feed ratios are given in the Table III. Table III: Sample Designation and Monomer Ratios in the Preparation of Full IPNs

(Table Removed)
For cross-linking of gelatin, 0.5 to 4% (w/v) of glutaraldehyde was used.
(Scheme Removed)
or example, the synthesis of B6 with cross-linking density of 4% for gelatin was carried out in the following manner. 2g of AAc was added to the Ge solution obtained by dissolving 2g of Ge in 20 ml of oxygen free distilled water. Free radical homo-polymerization of AAc was carried out in nitrogen atmosphere using redox initiator (a mixture of ammonium persulfate and sodium metabisulfite). The reaction was allowed to proceed overnight at room temperature, which resulted in the formation of firm gels. The gels, after carefully separating from the walls of container, were immersed overnight in 25 ml of 4% GA solution to crosslink Ge. The samples were washed extensively with water to remove the unreacted monomers as well as water-soluble moieties and then dried in vacuum to constant weight.
Schematic representation of the synthesis of full and semi IPNs
Characterization of Hydrogels
The gel prepared by the process of the present invention has been characterized for its physico chemical property and its behaviour to asses its suitability for bio medical and other applications.
Swelling Studies Weighed amounts of full and semi IPN samples were dipped in distilled water of varying pH (pH adjusted with acid/alkali) or buffers (citrate-phosphate-borate-barbitone buffer). At intervals, the swollen gels were lifted, blotted dry and weighed. The swelling studies were carried out for a maximum period of 48 hours.
Effect of pH
In full-IPNs, Kl toK5, and all semi-IPNs (Bl to B8) increase in pH from 1 to 10 in distilled water depicted no noticeable effect on % swelling. All IPNs showed a drastic increase in swelling above pH 10. This could be due to the shear bulk of the -COOH groups of the Ax chains of the IPNs. With increase in concentration of AAc network from Kl to K5, increase in water uptake is due to the ionization of-COOH groups. K6 to K9 also show higher swelling above pH 10 but not as high as observed in the case of samples rich in AAc.
The effect of buffer pH, on the percent swelling of above-mentioned polymers in buffers of varying pH, ranging from 2 to 10, illustrate drastic increase in % swelling between pH 4 and 5 and above 8 was observed. The swelling of hydrogels in buffer solutions was quite different from that observed in distilled water. This difference in behavior could be explained on the basis of charged species, which are present in the buffers. These charged species i.e., cations and anions lead to swelling, because they change from neutral state to ionized state and vice versa, in response to the change of pH.
Effect of Temperature
The swelling characteristics of hydrogels, full and semi-IPNs in buffer solutions, at pH 3, 5, 7.4 and 8.4 are tabulated in tables IV and V. The experiment was conducted at a temperature of 25°C, 35°C and 45°C. The percentage swelling of Ax increased with increasing temperature at pH 3 and 5.In case of full-IPNs, all the samples showed an increase in swelling with increase in temperature. In semi-IPNs, percentage swelling was higher as compared to full IPNs and samples showed an increase with increasing temperature.
Effect of Composition Percent swelling increased with increasing AAc content in full IPNs over a wide range of pH, i.e., 3.0 to 8.4 (Table IV&V). However in case of semi-IPN, it was found to decrease with increasing Ax content. In case of samples having crosslinked AAc (Table V) (Bl to B3), this behavior was more evident at higher pH. At higher pH these semi-IPNs imbibed water at a faster rate. Presumably, there could be the leaching out of the free Ge chains from these IPNs. In addition, the ester linkages of the DVE could break up, giving way to a loose texture, enabling higher uptake of water resulting in the early onset of degradation in the Bl and B2, i.e., within 48 hours.
Table IV: Results of % Swelling as a Function of pH and Temperature for Full IPNs
(Table Removed)
Table V: Results of % Swelling as a Function of pH and Temperature for Semi IPNs

(Table Removed)
In vitro degradation
Percentage weight changed Figures 3a-c and 4a-c accompanying this specification show the effect of composition on the rate of degradation of various hydro gels in distilled water (pH ~5.8) and phosphate buffer pH (7.4) respectively at 37±0.1°. Rate of the degradation depends upon the composition of the hydro gel. As the acrylic acid content increases in the hydro gel rate of the degradation decreases in full IPNs as well as semi IPNs. Gelatin rich hydro gel degraded faster in comparison rich to acrylic acid hydro gel.
In vivo degradation of the hydrogel depends upon the feed composition as well as the crosslinker concentration of the hydrogel. It has been observed that the rate of degradation in vivo is very slow as compared to that in vitro. Hydrogels Kl, K9,
B6, degrade within 40 days in vitro in phosphate buffer (pH 7.4) at 37°C. However, they do not degrade in vivo (model, Wister rats) even after 6 months at 0.5 (AAc) and 4 (Ge) mole percent crosslinking density. We reduced the crosslink density of poly(acrylic acid) chain as well as of gelatin chain of the hydrogels. It has been observed that at lower crosslinking density (0.3 AAc and 1 Ge mole % ) polymers degraded within 45 days.
Gentamicin sulphate loading in hydrogels Drug loading was carried out by swelling the known weight of polymer sample in gentamicin sulphate solution in phosphate buffer (pH 7.4) at 37±0.1°C under nitrogen atmosphere. It was seen that nitrogen atmosphere prevented the fungal contamination on polymer during loading of the drug. For the observation of leaching of polymer component from polymer network, the Xero gels was immersed in phosphate buffer (pH 7.4) under nitrogen atmosphere at 37°C. After immersing the polymer sample for 24 hours, it was taken out, dried and reweighed. The increase in the weight of the polymer was taken as the amount of drug loaded, whereas no weight change of the polymer was observed in phosphate buffer. Furthermore, for the confirmation of percentage of drug loading in hydro gels, the amount of gentamicin sulphate left in the loading medium, was determined by measuring the optical density at 333 nm using UV-Vis spectrophotometer.
In vitro drug release The pattern of gentamicin sulphate release in distilled water (pH -5.8) as well as phosphate buffer (pH 7.4) showed an initial burst followed by a constant release until the polymers start disintegrating. Composition of the polymer samples also played an important role in the release of gentamicin.
Figures 5 and 6 accompanying this specification represent the kinetics of gentamicin release in distilled water and phosphate buffer respectively at 37°C. The pattern of

release from all the polymers irrespective of composition was found to be identical. All the polymers showed initial burst effect and a biphasic release pattern in water.
In vivo drug release Blood samples of the implants loaded with gentamicin sulphate were collected at 4 hour, 12 hour, 1,5,7, 15, 30 and 50 days and the sera were stored at -70°C. The concentration of the drug in the serum is determined by disc diffusion method (efficacy 1 ug/ml). It has been found that, plasma level concentration of the antibiotics was 2 µg/ml after 4 hour of implantation and afterwards, no antibiotic was found in the serum samples. It shows that current drug delivery system dose not produce any systematic toxic effect.
Toxicity
The local tissue response of the biomaterial is the most important criteria for determination of biocompatibility. In the present invention, full and semi interpenetrating polymer networks (IPN) based on poly acrylic acid (AAc) and gelatin (Ge) cross linked using divinyl ester (DVE) and glutaraldehyde respectively, were evaluated for tissue response after subcutaneous implantation in rats. Twenty-two different IPNs with varying ratios of crosslinked acrylic acid (Ax) and crosslinked gelatin (Gx) were studied in different doses. These polymers were loaded with gentamicin sulphate and were also implanted for studying tissue reaction. The samples were implanted in groups of 5 rats each and they were sacrificed at the end of up to 9 months in predetermine time intervals. The site of implantation was biopsied and processed for light microscopy (LM) for assessment of tissue reaction. The degree of neutrophil,
lymphocyte and macrophage infiltration, fibrosis, granuloma formation, integration with extracellular matrix, vascular proliferation, and damage of adjacent structures were assessed. All the IPNs showed mild local inflammation without doing damage to the adjacent structures. No significant fibrosis is seen. Increased cross link density (>0.5) showed prolonged chronic inflammation. Majority of the polymers showed integration with extra cellular matrix and growth of capillaries in the polymer (Figure 7 accompanying this specification). No systemic toxicity due to the polymer was observed (Figure 8 accompanying this specification).
Phagocytosis The polymers attract macrophages, which engulf the polymers after degradation by the process of phagocytosis (Figure 9 accompanying this specification). They remove the degraded polymers from the site of implantation. The macrophage infiltration decreases with time and leaving little residue after an interval of 3 to 12 weeks, depending upon the composition of the polymer. Thus polymers play an active role in activation of macrophages.
Treatment of Osteomyelitis
A patient isolate of S. aureus (obtained from Department of Microbiology, AIIMS) was used. 30 rabbits were used to induce osteomyelitis. Out of 30, five animals died due to endemic infections in the animal house. Using patient isolate, chronic osteomyelitis was
developed in 25 rabbits within 2 to 3 weeks. These rabbits were equally divided into five categories and each category five rabbits were chosen for the studies . Development of osteomyelitis was confirmed by X- rays and Histopathology.
♦ Group A - Control - 5 rabbits
♦ Group B - Treated with 16 mg of 40% drug loaded hydro gels
♦ Group C - Treated with 16 mg of 75% drug loaded hydro gels
♦ Group D - Treated with 16mg of 100% drug loaded hydro gel
♦ Group E- Treated with 12 mg of 100% drug loaded hydro gel
The infected rabbits developed painful swelling with discharging sinuses. The infection was confirmed by microbial culture and serial X-ray. At the same time 2 ml of venous blood was drawn from ear vain of each animal. Blood sample were taken before the implantation of drug-loaded hydro gels and at 15, 30, 45, 60 and 90 days after implantation to determine the blood urea and serum creatinine. One each of four group of animal was sacrificed at 15, 30, 45, 60 and 90 days after implantation of drug loaded polymer for histopathological observation. The femur along with its surrounding tissue was taken and fixed in 10 % formalin for histological examination. In addition, other organs were sampled for histological evaluation. There was no evidence of increase in blood urea nitrogen and serum creatinine after implantation of drug loaded polymer.
Histological findings
The rabbits with osteomyelitis without any treatment or with implantation of hydro gel without antibiotic, showed development of bone infection with multiple discharging sinus (Figure 10 accompanying this specification) and radiological evidence (Figure 12 a-c accompanying this specification) of bony deformity within 3 to 4 weeks. The histological section from the site of infection (Figure 10) shows areas of necrosis, acute inflammatory exudates, dead bone, and bacterial colonies. The lesions were healed after implantation of antibiotic loaded hydro gel. The effective healing could be documented both radiologically (Figure 12c) and histologically (Figure 11). Four weeks after the implantation of 16 mg of 100% drug-loaded hydro gel (Kl), there is mild fibrosis (Figure 11). Focal aggregates of lymphocytes, plasma cells and occasional multinucleated giant cells were seen. No granuloma formation is seen. Adjacent bone marrow and bony trabaeculae away from the implantation site were histologically unremarkable after healing of infection. Rate of osteomyelitis depends upon the amount of the drug loaded in the polymer. It has been observed that for effective treatment, the amount of drug in the drug loaded hydro gel to the implanted should be more than 7 mg. No residual hydro gel is seen after 2 months. The organs were all within normal histological limits.
ADVANTAGES:
a) The process makes use of cross linkers having higher molecular
weight there by capable of producing hydro gel with higher porosity &
appropriate geometry resulting in attributing unique properties of
swelling de-swelling, loading & releasing of loaded substances,
degradation into metabolites which can be absorbed and used in the site of application, non-toxicity and phagocytosis.
b) The hydro gel is completely biodegradable, biocompatible, non
toxic, resorbable and thus does not require subsequent surgery for
removal.
c) It is pH sensitive.
d) It can be synthesized and stored at room temperature.
e) It is capable of providing site specific and pattern specific delivery of active molecules
f) It has a potential for loading of varied substances like biological active molecules (harmones, antigens cytokines DNA,) & substances, agrochemicals, pharmaceutically and therapeutically components
g) Has a wide application in the area of bio-medical engineering as drug delivery system, tissue engineering, implants particularly in the treatment of osteomyelitis.
h) Can be used as a controlled release device having zero order release rate.

We claim:
1. A process for the preparation of a novel hydro gel, which comprises: polymerizing polymer with carbon back bones such as herein described using a mixture of conventional redox initiator and a divinyl ester prepared by reacting poly (caprolactone diol) followed by cross linking with the polypeptide of natural origin using glutaraldehyde as a cross linking agent then converting in to desired shapes by conventional methods.
2. A process as claimed in claim 1 wherein the natural polypeptide used is albumin, chitosan, gelatin preferably gelatin.
3. A process as claimed in claim 1 wherein, the polymer with he carbon backbone used is vinyl polymers exemplified by poly vinyl alcohols, acrylates, & Poly Acrylic Acid.
4. A process as claimed in claim 1 wherein the poly acrylic acid is used as back bone cross linked with gelatin.

5. A process as claimed in claim 1 wherein, divinyl ester-a poly caprolactone based diol having molecular weight ranging from 530 to about 2015 & glutaraldehyde are used as cross linkers.
6. A process as claimed in claim 1 wherein the Poly Acrylic Acid (PAAC) and Gelatin (GE) are in the ration of 1:5 to 5:1
7. A process as claimed in claim 1 wherein, the hydro gel thus produced optionally contains biologically active molecules such as proteins, vaccines, antigens, antibiotics, any component of cell; biologically
active substances like fertilizers, hormones, pesticides other agrochemicals; conventional therapeutically and pharmaceutical^ active substances that includes drugs, formulations.
8. A process as claimed in claim 7 wherein, the loading of the molecules
or substances into hydro gel is effected by soaking hydro gel in
distilled water or buffer solution containing desired loading material.
9. A process as claimed in claims 7 & 8 wherein, the loading may be carried out in nitrogen atmosphere.
10. A process as claimed in claims 7 & 8 wherein, the buffer of pH 7.4 is used for loading purposes.
11.A process as claimed in claim 1 wherein, the gel is converted to geometrical forms such as cylinders, cubes, slabs, blocks, or sheets.
12.A process as claimed in claim 1 wherein, the gel is produced as tablets or capsules or skin patch.
13.A process as claimed in claim 1 wherein, the hydro gel thus produced is stored in an airtight container at ambient temperature.
14.A process for the preparation of a novel hydro gels substantially as herein described.