MEDICAL APPLICATIONS OF PVP
PVP is available in various forms such as tablets, granules, pellets , several kinds of hydrogels [93-100], powders, syrups, oral solutions, coatings in medical applications [101-103], etc. PVP has a wide range of properties and hence can be used in biomaterial applications. PVP polymer is extensively used in medical sectors. It is used as a blood plasma expander and binder substance in tablets. When use it orally, or the substance abusers injected, autopsies shown that crospovidone can contribute much larger in pulmonary vascular injury. Besides all these characteristics, the povidone- iodine complex has disinfectant properties and can be used widely in the ointment, pessaries, liquid soaps, and surgical scrubs.
Poly(vinylpyrrolidone) has better film formation ability and affinity towards amphiphilic surfaces. It has excellent sorption behavior and is generally used as a base substrate against toxins and viruses.
PVP is frequently used in drugs and chewable tablets due to the small shape and size of particles [104, 105].
This polymer exhibits a unique holding capacity to grasp all components together and finally rapid releasing the medicinal component. On transdermal deliveries, PVP is considered as an additive which reduces the crystallization behavior in drugs [105, 107]. Patel et al. gave explanations in the case of solid drugs, PVP act as a membrane coat and a drug capsule with controlled release, but when PVP coated in antidepressant drug system, discharge of venlafaxine is normally delayed .
PVP is also used for ophthalmic applications also and the major function is to reduce severe eye imitation. It generally acts as a pore former in drug release controlling membranes and layers .
PVP-based bio-adhesive films can be extensively used in buccal release of fentanyl  and preferred surface area was only 1-2 cm: equivalent to a 10 cm2 transdermal patch afford a healing effect . Nanofibrous PVP is used for wound healing applications, developed by electrospinning method. Other types of nanofibrous membranes for potential applications such as enhanced wound healing and drug release include PVP blended emodin . An optimum combination of PVP-Alginate with nanoparticles of silver plays a vital role in wound dressings , vascular, nervous system, cartilage, bone, and ligament regeneration [114-116].
Silver nanoparticles bounded PVP polymers shows superior effect on angiogenesis . This study was proposed by Kang et al. Silver nanoparticle dopped PVP-Chitosan have remarkable property of reducing serious infections in connection with medical tools. Cancer treatments are widely earned out using PVP grafted carbon nanotubes; it can also used as dentistry, orthopedics, as well as controlled drug delivery. PVP-Hypericin complex [118-121] is widely used for anti-cancer photodynamic analysis and treatments. Due to its superior properties such as nontoxic, nonantigenic, and biocompatible nature, it is widely used in the delivery of genes/drugs.
Graphene-based materials are used in various fields such as biomedical, drug, and vaccine delivery shows exciting properties. Nanocomposite of graphene, PVP, and polyaniline can be used for measuring cholesterol levels in medical diagnosis. Both graphene oxides coated as well as non-coated PVP on human immune cells describes outstanding immune enhancement properties and such kinds of studies were carried out by Zhi et al. PVP coated nanostructured cobalt ferrite shows extremely different properties such as biocompatibility, magnetic, and antioxidant property and this excellent antioxidant property help them to use in cancer treatments. Co-polymers of PVP have extensive use in various fields.
Veeran et al. explained polycaprolacone-PVP co-polymers are used in antituberculosis drug carriers and antitumor drug encapsulation. Kodaira et al. and Kamada et al. proposed PVP copolymerized with dimethyl maleic anhydride nowadays used for renal and various kinds of other drug delivery systems. PVP-Iodine complex shows disinfectant properties and it is used during surgery, antibacterial, and antimicrobial agent in medical devices. Apt et al. ; Benevento et al. ; Ciulla, Yanai, et al. proved PVP-Iodine can be used as an antiseptic agent in intraocular surgery and can have a capacity to diminish the effect of conjunctival bacterial flora. Jones et al. suggested the use in urinary catheters, ureteral stents.
These types of devices can be used in cardiovascular diseases which will help a free motion thr ough the vasculature.
PVP is considered as a water-soluble matrix and have excellent applications in drug delivery [122, 123]. It has been observed that the rate of cytotoxicity of pharmaceutical ingredients reduces generally due to the solid diffusion structure of polymer  and shows defensive properties towards macrophage action [125, 126]. Due to the nontoxic nature of PVP, it has superior application in plasma replacement and describes a clear solution [127-129].
PVP has the ability to bind chemically with dyes, insulin, and all types of other drugs . The rate of aggregation of erythrocytes  normally increases on adding PVP by intravenously and also diminishes the count of platelet adhesiveness in human blood by both in vivo and in vitro types of patterns  and even in high concentrations, PVP functions in human erythrocytes in frozen storage. At this stage, PVP induce plasma proteins
 , fibrinogen, and antihemophilic factor VIII and coagulation factors
 . The excellent nature of PVP functioning on embryonic development in humans is the other most significant area to be concerned. It is firstly considered as the substitute for blood plasma and other extensive areas of use such as cosmetics, pharma, and industry, PVP is selected as an apt polymer.
PVP is the main part of therapeutic systems; namely wound dressing and prostaglandin release devices. PVP shows distinctive sorption behavior and acts as a matrix for agents removing viruses from blood. When it is used as a tablet, polymers remain in the body, it did not metabolize and veiy little amount of high molecular fractions will exist within the body. Generally accessible in an extensive range of molecular weights, i.e., 2500-3,000,000 g mol-1, hence it is used for pharmaceutical applications. Universal solubility in water and other organic solvents are the essential property of PVP .
The presence of polar lactam group makes it highly hydrophilic in nature and nonpolar methylene group attributed the lipophilic character. These excellent features have led to the extensive application in pharmaceutical field. Wet granulation method is applicable in the production of tablets, syrups, drops, injectables, and in film coatings . PVP exhibits film forming capacity and are applicable in tablets, transdermal systems, and therapeutic sprays. PVP and its copolymers are also widely useful in biomedical areas [137-142]. N-vinyl pyrrolidone and its copolymers based hydrogels used in wound healing applications. PVP modified materials have been widely used in medical devices, in polyurethane (PU) central venous catheters have superior properties when covered with PVP polymer .
PVP bounded PU catheters were highly hydrophilic in nature and can absorb less amounts. PVP exhibits the film-forming capability thus it can be used in tablets, transdermal systems, and therapeutic sprays of fibrinogen and fibronectin. Minimum amount of protein adsorption is related to a reduction of Staphylococcus aureus and Staphylococcus epidermidis. Blending of PVP with suitable materials led to outstanding applications. If PVP is considered as an additive, BSA adsorption capacity is comparatively less and the blood compatibility of PES membrane becomes better. Wang et al. reported the significance of this work  in their research on PVP. PVP polymer has numerous applications and it can be tested in artificial cartilage , artificial skin, drug vehicle, and cardiovascular devices [146,147]. PVP hydrogel systems are used in nasal release of acyclovir (ACV) and these are completely harmless and safe materials. PVP-ethylcellulose composite was used for coating pellets for topiramate delivery . The role of PVP extended in wide way, it can also act as a pore-former and increases the rate of drug delivery fiom 23% to 29%. PVP-poloxamer 407 combined to form a thermally reversible in situ gel as drug release matrix for human growth hormone and can be applied in pediatric hypopituitary dwarfism . PVP hydrogels are also used for skin regeneration and wound dressing uses and the membrane prepared has excellent characteristic properties such as transparency, fast pain-relieving property, and compatibility [150-162]. PVP bounded paracetamol tablets release the drug veiy rapidly compared to others such as tablets with gelatine or hydroxypropyl cellulose. The function of PVP as a binder and the tablets containing povidone were usually veiy harder . PVP shows unique stability to the conditions of Phenytoin tablet formulations  and when combined with triesters of citric acid, get a soft gelatine capsule that contains insoluble drugs  and the pharma based applications of PVP is shown in Table 4.1.
TABLE 4.1 Functions and Medicinal Grades of Poly(Vinylpyrrolidone)
For cartilage replacement, Shi, and Xiong performed research based on PVP-PVA hyrogel and these manufactured by F/T method, F/T cycles, and also 60Co gamma-irradiation [166, 167]. For the treatment of oral squamous cell carcinoma, the buccoadhesive PVA patches of 5-fluorouracil and its general nature as well as properties by the effects of PVP were studied by Ghareeb and Mohammad  and the patches were analyzed by the mucoadhesive mechanical properties. For steroid release, PVP coatings were employed for beclomethasone dipropionate microparticles within a hydrofluoroalkane propellant  from high pressure metered inhaler. The addition of PVP into a system decreases the nature of aggregation of microparticles and hence obtains somewhat stable suspensions.
The substitution of opacified natural lens by a polymeric intraocular one in Cataract surgeiy is also carried out using PVP like polymeric materials. Conventional methods used PMMA, silicon, and acrylic-based polymers but due to the high stiffness, they cannot perform in normal way. PVP-PVA hydrogel overcomes this difficulty and is used widely in ophthalmology related applications  and on further studies as well as research shows, the nature of hydrogel is completely related to human lens. The wide use of PVP copolymers in various kinds of drugs such as indomethacin, tolbutamide, nifedipine improves its water solubility and bioavailability . These polymers with drugs are normally applicable to hot melt extrusion process and the extrudates have excellent dissolution capacity. Topiramate drug carries PVP in the form of a binder and has very high efficiency in drug layering technique and it also changes the drug delivery, solubility, etc. PVP based films are used widely for the buccal release of fentanyl and these systems are much more beneficial in therapeutic treatments.
Most significant role of precipitation agents is its use as drug excipient. The unfavorable consequence of most of the drugs is its low solubility in water, reduced bioavailability, etc. When on adding PVP composites with these drugs, the rate of dissolution and drug solubility is remarkably increases. If we are considering the insoluble drugs, PVP is widely applicable as a precipitating agent. The remarkable property of this polymer is that, used for extension of agonist and the drug release method in capsule shell as well as membranes and disintegrating agents in solid drugs. PVP coated Membrane with the capsule shell in a dry condition is not easily release. Insoluble Polyvinylpyrrolidone is known as Crospovidone and prepared by the physical crosslinking reaction of PVP with a monomer containing bi-functional unit in presence of alkali at 100°C. This is also used as a perfect disintegrant tablet formulation and forms complexes with other substrates. In ophthalmic solutions, role of PVP termed as a demulcent or moisturizer and on blended with polyethylene glycol (PEG) 400 and dextran 70, it is usefiil for slight irritations, eye diyness, wind, and sun . Discussing the nature of PVP, it is physiologically inert but hard, transparent, oxygen-permeable material and on crosslinking reactions, PVP forms various crosslinked networks .
This polymer is comparatively stable at normal conditions and can form complexes with various other compounds such as dyes, organic substartes, etc. Complexes of PVP can remove by filtration process.
Based on the application of PVP as a binder, it can form hard granules with high flow property but very low friability . PVP when combined with germicidal compounds such as bisphenols and chlorinated phenols shows low toxicity and side effects of skin reactions. One of the most important points to be remembered is that chemicals like nicotine, formamide, and potassium cyanide show little oral toxic nature in PVP solutions. Copolymers of PVP are used to enhance the bioavailability nature of less soluble tolbutamide, indomethacin, and nifedipine [175-178] drugs.
PVP-heparins composite have superior properties compared to other molecules and this complex have anticoagulant activities due to heparin nature and mostly soluble in all types of organic solvents. This polymer has widely used in oral liquid dosage forms and the role of PVP in such solutions is as dispersing agents. Crosslinked PVP can be used to treat diarrhea and based on research, an excellent capacity to treat burns and completely removes toxins. When PVP combines Phenobarbitals and secobarbitals, the renal emission of barbityrates and the toxic effects of ameliorate. Hence from all the experimental records, surely state that polyvinylpyrrolidone polymer has higher effect on reducing the pharmacological actions of drugs include sulfathiazole, sodium salicylate, cholramphenicol insulin, Phenobarbital, procaines, and p-amino benzoicacid. PVP based hydrogels are widely used in controlled drug delivery systems and sustainable release is the main benefit for drug release investigations and the medicinal constituent emitted has been used for extended time intervals. This results in adding high concentrations of medicinal components to a desired location for a longer period of time.