Bhavana, an Ayurvedic Pharmaceutical Method and a Versatile Drug Delivery Platform to Prepare Potentiated Micro-Nano-Sized Drugs: Core Concept and Its Current Relevance.

Scholars of ancient Ayurveda (Indian system of medicine) were extremely reasonable and had strong scientific rationality in fundamental concepts, which are also applied to drug manufacture and therapy. Bhavana is a unique traditional method of transformation of raw material/substances into the drug by levigation or wet grinding of powdered drugs with juice/decoction/solution of plant, animal, or mineral origin. This method adds the unique capability of affecting the physicochemical and biological properties of a drug, making the drug quicker, augmented, and persistent action with minimal dose. Despite the fact that Bhavana has a wide range of applications in Ayurvedic pharmaceutics, there is only a limited amount of knowledge of its fundamental notions. A comprehensive review was performed on the core concepts of Bhavana, alongside its possible pharmacotherapeutic effects and relevance in drug development, by probing Ayurvedic claims in light of published pharmaceutical, analytical, and pharmacological reports. Various processes, such as thermo- and photochemistry, physicochemical reactions, and mechanic chemical changes, appear to occur during Bhavana.

1. Introduction

Ayurveda is the most ancient (dates to 5000 years BC), widely recognized, practiced, and flourished recognized traditional system of medicine in India, with strong logical and philosophical roots and rich literature in the Sanskrit language [1]. Ayurveda has a distinct branch of pharmaceutics (aka Rasa Shastra evam Bhaishajya Kalpana) dealing with drug manufacturing, standards, and quality control. It has established a drug regulatory system (chapter IVA in Drugs & Cosmetic Act, 1940), pharmacopoeia, and formularies as authoritative official publications. In Ayurveda, medicinal plants, processed metals and minerals, purified poisonous drugs, animal-origin materials, and several other natural products are being used traditionally for therapeutic purposes [2].

Bhavana (levigation or wet grinding of single/compound powdered drugs with liquid media (i.e., juice/decoction/solution of plant, animal, or mineral origin)) is a unique process and probably the most extensively used pharmaceutical procedure of Ayurveda. Bhavana is also known as Samskara in Sanskrit, that is, transformation (Samskaro hi Gunantaradhanamuchyate) of the inherent attributes of a substance which leads to the addition of new properties or qualitative improvement. Bhavana carries the qualities and action (Guna-Karma) of liquid media with powdered drugs to be levigated; thus, in simple words, Bhavana corresponds to the impregnation of the properties of liquid media to the Bhavita material (drug material undergone Bhavana process). Thus, it presumably regulates the quality/potency (Guna) level by change in potency (Gunantara), addition of new properties (Gunadhana), augmentation (Gunotkarsha), or reduction or removal of properties (Gunahani) [2, 3]. In the present scenario of globalization, all rational skeptics are engrossed in understanding this traditional pharmaceutical process of transformation. Ancient Indian sage Charaka in the context of describing the principles of pharmaceutics advocates Bhavana by expressing herbal juice (Svarasa) or herbal decoction (Kwatha) of the same drug or drugs with similar properties, and its uses are explained as quicker, augmented action with possible reduction in the required therapeutic dose of the drug under process [4]. Ayurveda literature is used as an authoritative search engine highlighting the importance of Bhavana in herbal and herbomineral drug possessing with multidimensional pharmaceutical and therapeutic implications (Figure 1). Likewise, in the Siddha system of Indian medicine, Bhavana with herbal juices is advocated to prepare highly potent, microfine, metal-based formulations named “Chunnam” akin to Ayurvedic metallomineral Bhasma (an Ayurvedic dosage form of incinerated ash/calx of metals/minerals) preparations [5].

Figure 1

Pharmaceutical implications of Bhavana in Ayurvedic pharmaceutics.

At least a total of 39 (plant origin-15, animal origin-21, mineral origin-3) varieties of liquid media are found mentioned in classical texts to be used in Bhavana [6]. In Bhavana, the drugs of herbal or mineral origin are powdered, or different powders are thoroughly mixed with the specified liquid media, like urine, milk, juice, or decoction of herbs, among others, and staged intermittent trituration followed by drying in sunlight. The process is continued to attain the Subhavita Lakshana (confirmatory test for completion of the process with desired characteristics). Finally, the complete absorption of liquids into the powder and drying of the mixture yields the product [7]. It mixes the drug homogeneously, and it involves numerous physicochemical and biological changes, such as the extraction of soluble chemicals or liberation of valuable chemicals from their matrices, exchange with intra/extra cell chemicals of the mixture (in case of herbs), chemical interaction with coexisting chemicals, and secondary or newly generated chemical moieties in the mixture [6, 8]. The chemical nature of thus formed mixture might be constantly changing during operation. This process can give newer directions in evolving new medicinal molecules with improved strength that would be surely the win-win situation for healthcare [9].

Despite the wider applications of Bhavana in Ayurvedic pharmaceutics, information on its basic concepts is still lacking. Thus, the present report attempts to cover in-depth information on the holistic formulation process perspectives and core concepts of Bhavana, with a view to shedding light on future research and implications in the field of pharmaceutics and medicine. The available data were analyzed and represented for the current review.

2. Methodology

The approach consisted of searching several resources, including Ayurvedic treatises, books, theses, technical reports, conference proceedings, and web-based scientific databases, such as publications on PubMed, MEDLINE, Science Direct, Springer, Google scholar, MEDSCAPE, BMC, SCOPEMED, and other allied databases covering pharmaceutics, pharmacology, and biomedicine fields. The searches were performed using keywords such as Bhavana, Samskara, Shodhana, Marana, Bhasma, nanomedicine, nanoparticle, liquid media for Bhavana, levigation, wet-grinding, wet trituration, crystal defects, chelation, trace elements, metal absorption and biocompatibility, herbal drying and packing, and quality assurance with their corresponding MeSH terms in a combination of OR/AND. The search criteria were restricted to throw light on the pharmacotherapeutic effects of Bhavana by probing Ayurvedic claims in light of published pharmaceutical, analytical, and pharmacological outcomes. A total of 495 published articles were retrieved, of which nonrelevant articles were excluded from the final analysis. This search was undertaken from June 2018 to March 2022, and articles only in English were included.

3. Results

3.1. Modus Operandi of Bhavana

Materials needed for Bhavana are (1) single/compound powdered drug and (2) liquid media. Liquid media is an essential component, contributing to a major role in the outcome of Bhavana apart from mechanical procedures, like grinding and so on. Bhavana can be carried out by adopting two processes: (1) staged levigation [10] or (2) Nimajjana (saturating with a specified liquid) [11]. The amount of liquid added should be sufficient to generate a soft mass and keep the material moist during the grinding process [12, 13]. To prepare the extracted juice or decoction (as liquid media) for Bhavana, classical guidelines for extraction should be adopted [7, 13, 14]. If the nature of liquids for Bhavana is not specified, it should be equal or similar in properties to powdered drugs and are chosen as per the desired therapeutic indications [4, 15]. When Bhavana duration is not specified, then it should be carried out for 7 days [12]. Subhavita Lakshana should be carefully watched to ensure the completion of the process of successive cycles of levigations. At the end stage of levigation, the amalgam should become soft and fine consistency and, on pressing between fingers, should turn into a flat cake, and pills can be made easily without sticking to the fingers. These characteristics are indicative of properly triturated drugs and are suitable to be used for medicinal purposes [7]. The whole unit operating process of traditional Bhavana preparation is depicted in Figure 2.

Figure 2

Unit operating process of traditional Bhavana preparation. (a) (1) Fresh medicinal plants and (2) copped/crushed, (b) (1) expressed herbal juice and (2) or herbal decoction is prepared, (c) (1) wet grinding of powdered drug with liquid media in pestle and mortar (for small-scale manufacturing) (2) or wet grinding in edge-runner (for large-scale manufacturing), (d) soft and fine mass formed during grinding, (e) observation of Subhavita Lakshana (confirmatory tests for completion of levigation), (f) wet granulation, (g) hot air oven drying, (h) dry granules, and (i) preparation of tablets.

3.2. Bhavana: Equipment Required and General Precautions

Pestle and mortar are used for small-scale manufacturing at the level of physicians. Edge runners, end runners, and wet grinders are used for large-scale production by pharmacies. Continuous grinding is imperative, as interrupted grinding causes dryness of the material, which needs more liquid in levigation. Some precautionary measures must be taken, such as (i) contact parts of pestle and mortar should be of inert material, (ii) levigation should be continued until the attainment of Subhavita Lakshana and the liquid media must be mixed well, (iii) after levigation, the material should be allowed for complete drying to remove/evaporate moisture content and to prevent the multiplication of microbes as a quality control measure [16].

3.3. Drying and Storage

Drying is said to be done in sunlight or may be done in the shade, in mass form, or after making pellets. Although the chief desired characteristics of levigation are perceived after grinding, the complete drying of the levigated material must also be ensured. Any fraction of retained moisture interferes in the therapeutic properties and stability of the drug. Finished product should be stored in airtight, dry, and sterile conditions. Containers should be nonreactive, especially with the content being stored in them [17].

3.4. Factors Affecting the Bhavana Process and Regulating Measures

Some factors affect Bhavana process, may have a significant effect on the final product, and hence must be strictly monitored for process standardization, such as batch size, ingredient proportion, nature, and form of drugs (particle size, stickiness, hygroscopic nature (water absorption, imbibition, or retention capacity)), apparatus (material makeup and capacity), rotations per minute, duration of Bhavana, and environmental factors (temperature, humidity, airflow, and sunlight). Environmental variables are most vulnerable to changes that can be regulated through (a) temperature: air conditioner/room heater, (b) humidity: dehumidifier, and airflow: fan/blower [18, 19].

3.5. Probable Changes during Bhavana Process

In pharmaceutics, microparticles and nanoparticles are generally produced by size reduction of larger particles under a top-down approach [20], although little is known to understand the kinetics, breakage mechanisms, and possible aggregation during the traditional wet grinding process of Bhavana. The conventional wet grinding in Bhavana involving successive processes, such as hydration (or soaking), adding additional liquids during grinding, interaction with organic/inorganic liquids, drying, and duration of the process, may lead to unique and suitable physicochemical-biological changes in the drug [21].

Reduction in hardness: constant wet grinding in liquid media turns the hard material soft [21].

Role as an excipient in formulation: (1) as a binding agent, in wet grinding process during Bhavana, liquid media act as a binding agent, and pills/tablets can be made easily; (2) as suspension stabilizer, after consumption, liquid media used for Bhavana may contribute to the formation of stable suspension; (3) as a disintegrant, in some cases, it may play a role in drug disintegration.

Increase in weight: liquid media may contribute to the bulk of the formulation and thereby may act as a diluent.

Particle size reduction (PSR): continuous and repeated grinding during Bhavana helps in PSR, which may influence the extraction of chemical components of the drug and absorption of its constituents (site, percent, and rate of absorption and metabolism) in the gastrointestinal tract (if administered orally). PSR in Bhavana can be explained by “Griffith theory,” which states that all solids contain flaws (structural weakness) that may develop into a microscopic crack under stress/strain-like pressure applied during Bhavana [22]. As per “Attrition theory,” rubbing of the materials between liquid media and the surfaces of pestle and mortar results in PSR [23, 24]. During Bhavana, drug particles are subjected to various stresses, leading to breaking of chemical bonds to create new surfaces and retard rejoining of the broken surfaces [25]. These stress-induced cracks or fractures could be intragranular (within the particle) or intergranular (along the grain boundaries), leading to PSR and liberation. The addition of liquid media in Bhavana is suggested to further amplify the size reduction process [26-29]. Wet grinding involves two simultaneous processes, that is, pulp flow and stress application, which helps in the transport of drug material between grinding surfaces, subsequent propagation, and initiation of cracks followed by PSR. The pulp flow process greatly relies on the nature of interactions between the particles and the grinding liquid media [30].

3.5.1. Physical Changes

PSR is proposed to have the following effects: (i) uniform mixing-uniform dose; (ii) more changes in active principles upon exposure to environmental conditions like humidity, airflow, temperature through hydrolysis, oxidation, and so on; (iii) extraction of extractable principles in liquid media and their interactions with constituents of liquid media and other constituents of formulation; (iv) increased interparticle collisions thereby augmenting the rate of reactions and neoformation of chemicals (theory of collision) [31]; (v) random dispersion in liquid media; (vi) facilitation of impregnation; (vii) increased particle surface area and thus enhanced dissolution rate (Noyes–Whitney equation or Ostwald–Freundlich equation) [32, 33] and absorption and bioavailability of the drug.

In a study, GR showed more PSR and suggested the possibility of uniform overlapping of liquid media contents with sulphur particles (in the core) in a sample prepared by 88 Bhavana in a comparison of 11 Bhavana samples and a sample prepared by mixing dry aqueous extract of liquid media [34]. Wet grinding of drug powder with liquid media facilitates PSR [21] and homogenization leading to modification of the properties (Gunantaradhana) of the end product [2]. PSR and uniform particle distribution effect of Bhavana were also substantiated by a microscopic study on a medicated enema formulation preparation, which involves a wet grinding process [35].

3.5.2. Chemical Changes

Bhavana brings fine particles of material in contact with liquid media, facilitates the impregnation of organic/inorganic contents and inherent specific properties of the media with material, and provides favorable circumstances to accelerate the chemical reactions. Grinding (friction between particles and particles alongside particles and the liquid media) during Bhavana is an energy-consuming process. Out of the total energy input to the grinding mill, only a minimal (<1%) energy is required for fracture and further formation of new surface area, while a major portion of energy (>75%) is released in the form of mild heat, which may lead to the degradation of thermolabile compounds in the drug materials [8, 30]. Liquid-assisted grinding in Bhavana helps to maintain the temperature during wet grinding and further facilitates mechanochemical reactions.

Mild heat produced during grinding may also initiate chemical reactions between material and media, and thus new and desired chemical changes in the final product can be obtained; for example, in Kajjali (a compound of mercury and sulphur) preparation, during levigation of mercury (Hg) and sulphur (S), the juice of aerial roots of Ficusbenghalensis acts as acidic media, which along with mild heat produced during grinding helps in the formation of mercury sulphide (HgS) [36]. The increased temperature is said to evaporate the volatile impurities.

Bhavana is carried out as a pretreatment of Marana (a classical method to prepare calx formulation of metals/minerals), and it helps metal or mineral drugs to change their chemical actions, which are expected during Marana [37]. It is also evident that Bhavana of different drugs is likely to give different colors to the Bhasma of the same substance [38, 39]. For example, in Mrigshringa Bhasma (deer horn calx) preparation, Bhavana with latex of Calotropis procera gives black-colored Bhasma, while Bhavana of Aloe vera juice imparts white color [40].

3.5.3. Biological Changes

During the Bhavana of Rasaushadhi, bioactive compounds of the liquid media are transferred to the material. This facilitates Nirendriyadravya (inorganic material) conversion to Sendriyadravya (organometallic/organomineral compound form) [41], which is easily assimilable and biologically favorable to the body. The human body is unable to absorb most minerals in their natural (inorganic) form. Once the organometallic/organomineral complex gets formed, the body accepts it [39]. Furthermore, the trace elements from liquid media could supply micronutrients to our body [42]. In general, the probable changes in drugs imparted by Bhavana process are summarized in Figure 3. Illustration of probable physicochemical changes undergoing herbal/mineral/metal-based drugs during Bhavana is portrayed in Figure 4.

Figure 3

Probable changes and proposed benefits apropos Bhavana.

Figure 4

Illustration of probable physicochemical changes undergoing herbal/mineral/metal-based drugs during Bhavana.

3.6. Importance of Wet Grinding Process in Bhavana

It is evident that the presence of some amount of appropriate solvents helps to significantly improve the rate of product formation [43]. Moreover, wet grinding with organic liquids is reported to be more efficient than that with plain water [44, 45]. This is suggestive of more efficacy of medicinal preparations prepared by wet grinding than dry grinding. Therefore, the wet grinding process adopted in Ayurvedic formulations could produce better PSR alongside potentiation of the drug under processing. Relative importance of the wet grinding process of Bhavana than merely dry trituration may be ascribed as follows: (i) it facilitates easy and smooth grinding, (ii) it prevents health hazards of dust produced during grinding, (iii) finer particles can be obtained by dry and wet grinding [28, 29], (iv) it may act as preservative or buffers for chemical interaction in the process of Bhavana [46], (v) wet grinding has several applications in ancient and modern pharmaceutics, such as Malahara (ointment/liniment/gel/lotion/creams preparation), Lepa (medicated herbal/herbomineral paste for topical application), and Kharaliya Rasayana.

3.7. Probable Role of Sunlight in Bhavana

(i) Bhavita herbal formulations may be shade dried, as hot sun rays may reduce volatile oil content and aromatic substances, and changes in color may occur. (ii) Some chemicals may also undergo photodegradation by UV rays in sunlight and thereby the formation of new chemicals. (iii) Sunlight causes sterilization by UV rays. (iv) During Bhavana of metals/minerals in Marana, sun drying is advocated. When sunlight falls on the surface of metals, free unpaired electrons in their outer shells absorb photons, start oscillating, and emit radiation of frequency equivalent to that of the incident light, and these electrons can be reacted and get neutralized easily. This process is nothing but a light-induced electron transfer reaction and is more likely applicable to minerals and metals. UV rays from sunlight are responsible for initiating photochemical reactions, in which photosensitizers are essential. Many studies have reported the probable role of liquid media as photosensitizers [47]. The ability of liquid media to absorb UV radiation is also substantiated by electronic spectra studied [46]. Ayurvedic texts also advocate the sunlight exposure of metal and mineral-based drugs after the completion of Bhavana. With a few exceptions, for example, in Pishti preparations (levigated and powdered gems/minerals), Bhavana is indicated at night, probably to avoid the photochemical effect [48].

3.8. Bhavana vis-a-vis Churnakriya

Churnakriya is a pharmacological procedure in which Bhavana is mixed with the juice or decoction of the same drug with the goal of enhancing the drug's characteristics and, as a result, potentiating the therapeutic action. Churnakriya involves the levigation of juice/decoction of one drug to the other having similar attributes, which not only will yield a combined effect of all ingredients but can change the effect of the finished drug (may be due to synergistic, antagonistic, or change in action or addition of new action). Charaka has laid out the original concept of Churnakriya; however, the term was coined by ancient sage Sushruta [15]. Several Ayurveda formulations are known to be prepared by the Churnakriya process, namely, Salasaradi Churna [15], Amalaki Rasayana [10, 49], Gokshuraka Rasayana [50], Alambusha Kalpa [51], Krimihara Yoga [52], and Vidari Churna Kalpa [11].

3.9. Importance and Applications of Bhavana

3.9.1. Bhavana for Changing the Therapeutic Efficacy of Drug

To increase or control any pharmacological activity, one should skillfully handle the pharmaceutical process of combination and elimination. This principle can be applied to change the therapeutic efficacy of the drug through Bhawana acknowledged by Charaka [4]:

Combination/addition of ingredients usually having similar characteristics or being known to increase certain effects or in general possess Yogavahitva (effect augmenting property) (aka Samyoga).

Division/removal of ingredients usually having opposite characteristics (aka Vishlesha).

Effect of duration of levigation, drying time of day, and season (aka Kala).

Pharmaceutical processing, for example, operative methodology of micronization, type of equipment used, aeration, method of addition of liquid immersion, levigation, and drying (aka Samskara).

Intelligence/logical thinking to organize multicausal phenomenon, titrating, and combining the above-cited variables to form different sets of Bhavana procedures keeping in view specified objectives, predominantly the therapeutic aspect of the final drug (aka Yukti).

Samyoga refers to the addition of new properties to the drug, thereby widening the therapeutic utility. The majority of Kharaliya Rasayana (formulations prepared in pestle and mortar by wet grinding) are multicomponent and have a wide spectrum of therapeutics too; for example, a classical sulphur-based formulation Gandhaka Rasayana (GR) has Bhavana of 11 different liquids so that therapeutic efficacy and spectrum of Bhavita sulphur increase [53]. Thus, Bhavana can be utilized to improve therapeutic action, palatability, and dose reduction by logical selection of liquid media. In Kharaliya Rasayana, various liquids of plant materials may induce organic quality in the final product, enhance the original properties of the main drug, increase therapeutic efficacy, and minimize adverse effects. It may also help in drug delivery to the target-specific action or target organ, although further investigations are warranted in this direction. The shelf life of the finished products may also increase by Bhavana [54]. Vishlesha infers the elimination of unwanted constituents; for instance, Chausatha Prahari Pippali (CPP), a classical formulation prepared by Bhavana of Pippali (Piper longum), is to be consumed for a long time to attain the qualities of Rasayana (rejuvenating drug). At the same time, it is advised to avoid excessive and long-term use of Pippali. In the pharmaceutical preparation of CPP, with the number of Bhavana with Pippali decoction on Pippali powder, quantitative differences between “Pippali powder” and “CPP” were observed [55], along with the reduction of piperine content [56]. Similarly, a decrease in gallic acid percentage [57] and an increase in phenolic contents [58] were noted during successive Bhavanain Amalaki Rasayana (Bhavana-based formulation of Indian gooseberry). Thus, from this, inference can be drawn that piperine and gallic acid reduction is anticipated in the respective formulations, justifying the significance of the Bhavana process. By logically modifying all the above-described variables of Bhavana, a formulation (processed through Bhavana) with desired attributes can be obtained, which is termed by ancient seers as Yukti.

Bhavana drugs are chosen judiciously according to the disease so that they can synergize the ultimate effect of the final product. Even less amount of a drug will exert multiple actions if it undergoes proper Bhavana. In this process, one should process drugs with their own juice (Churnakriya) or the juice of the drugs similar in potency [4]. Multiple application of Bhavana is reported to alter the physicochemical properties of the same drug [59]. When an herbal drug is levigated with the expressed juice of the same drug or has similar attributes, the inherent properties of that drug are fortified [2], for example, classical formulations such as Guduchi Churnakriya, Amalaki Rasayana, and CPP. Guduchi Churnakriya prepared by 7 Bhavana on powder of Tinospora cordifolia with its own extracted juice showed significant antimicrobial activity than that without Bhavana sample of T. cordifolia powder [60]. In a recent study, Guduchi Churnakriya samples exhibited significant in vitro α-amylase, α-glucosidase inhibitory activities, and in vivo antihyperglycemic effects, ascertaining a definite role of Bhavana in the improvement of the bioefficacy of drugs. Further chromatographic quantification also showed increased berberine level in Bhavita Guduchi samples, which confirms the role of Bhavana in increasing the concentration of phytoconstituents [61]. In another study, Amalaki Rasayana prepared by 21 Bhavana showed a better activity profile in terms of both immune stimulants and a cytoprotective activity than Amalaki Rasayana prepared by 7 Bhavana [57]. It signifies an augmentation in drug potency with increasing numbers of respective Bhavana. A recent study on mice also validated the therapeutic augmentation effects of Bhavana with a nootropic herbal combination [62].

3.9.2. Bhavana for Purification/Detoxification of Poisonous and Herbomineral-Based Drugs

Bhavana is also advocated for Shodhana (purification/detoxification) of metals/minerals, aiming to minimize the toxic effects of a drug besides changes in attributes and the addition of new desired qualities. Raw Vatsanabha (Aconite) is cardiotoxic, which is principally due to the alkaloid aconitine. Upon Shodhana by immersion in cow urine for three days in sunlight, aconitine level becomes negligible/absent, and the drug becomes safe and cardioprotective in the mentioned doses. Shodhita Vatsanabha has a wide range of therapeutic utility, and it is used for Rasayana too [63]. Aconitine percentage before Shodhana with cow urine was 0.113, and after Shodhana, it was 0.089 [64]. Researches show that even simple immersion of aconite species in water reduces its toxicity [65]. Likewise, during Shodhana of Kupeelu (nux vomica), immersion in cow's urine lessens toxicity and improves the drug's intrinsic properties by hydrolyzing the active components that cause toxicity [66, 67]. Hence, it can be presumed that immersion in liquid media as a part of Bhavana has large importance and future scope in the purification of poisonous herbs. The toxic constituents of the drug are transferred into the media, making the drug nontoxic, according to studies [68]. The acidic/alkaline organic liquids and animal byproducts used for Bhavana can enhance the cation exchange capacity and solubility of metals/minerals. Furthermore, these natural compounds facilitate the removal of toxic elements in the structure [69]; therefore, the drug is needed to be analyzed before and after Bhavana.

Bhavana is claimed to make Rasoushadhi (herbo-metallo-mineral-based drugs) relatively nontoxic and thus may have a role in preventing Adverse Drug Reactions. Toxic metals/minerals are triturated with the juice/paste of certain herbs under the heading of the Shodhana process, for example, for Manahshila (realgar): ginger juice, Parada (mercury): garlic paste, Kasisa (green vitriol): lemon juice, Hingula (cinnabar): ginger juice, and Kamkushtha (rhubarb): dry ginger decoction. For instance, in Manahshila Shodhana in ginger juice, the sulphur-based amino acids cysteine and methionine act as phytochelatins, which are heavy metal-binding peptides and are suggested to detoxify heavy metals by chelation. Besides, cysteine, a methyl-donor peptide, helps in the process of methylation of arsenic present in Manahshila. The study also suggests that the alkalinity of Manahshila is neutralized by the acidic nature of ginger juice due to acid-base reactions. Under these reactions, Manahshila becomes nontoxic and safer for therapeutic use [70, 71]. The grinding of herbs and minerals may initiate some acidic/alkaline reactions or facilitate the transfer of soluble impurities from the mineral to herbs and add useful materials to the drug. This could be detected with chromatographic studies. The toxic constituent presumably gets converted to nontoxic complexes [72-78]. Nevertheless, more scientific and evidence-based validation of these Ayurvedic principles is needed.

Bhavana combats the untoward effects of certain constituents and adds desirable attributes to the formulation; for example, in Laghumalini Vasanta (zinc-based herbometallic formulation), Bhavana of clarified butter is given to reduce Rukshatva (dryness of human tissues) of zinc calx and then Bhavana with lemon juice to reduce excessive Snigdhansha (unctuousness) and enhance Deepana (stomachic property) in drug [79].

3.9.3. Possible Effects of Bhavana in terms of Current Assumptions of Science

Scientific analysis of chemical reactions occurring during Bhavana process is difficult to interpret because (i) a metal/mineral may be a single entity, but Bhavita metal mineral (that has undergone levigation with organic liquid media) is a complex mixture of various chemicals, (ii) the action of Bhavita drug is also driven by the combined action of its several ingredients, (iii) many of the active chemicals in both herbal and mineral compounds are still unknown; therefore, specific action is difficult to assess.

An uncertainty arises. Whether “liquid media for Bhavana” is a mere liquid? No, the liquids used for Bhavana contain one or many of the following qualities or substances such as weak/strong acids, weak/strong bases, enzymes, solvents, inorganic contents, and herbomineral entities, some of them having specific Prabhava (special action/unexpected pharmacodynamics of an herb or drug). The probable changes that the material may undergo during Bhavana can be enlisted as extraction, micronization/nanonization, structural changes at the molecular level, oxidation, reduction, hydrolysis, dehydration, formation of hydroxides (alkaline earth metals) or salts of ingredients of powdered drugs, microbial growth, fermentation, enzymatic catalysis/autolysis/photolysis, and so on.

Bhavana involves chemical reactions as well as physical interactions between solid and liquid phases (heterogeneous kinetics). As a general rule, it is most likely that the rate of such an interaction/reaction is proportional to the surface area of the solid phase available for interaction. The ancient Ayurvedic drug manufacturers were cognizant of these points and surmounted this riddle firstly by increasing the primary surface area and secondly by removing the chemical layer formed on the metal particles and thus exposing new metallic surfaces [80]. This could be achieved by various means like through intermitted grinding and/or along with Bhavana (grinding and levigation with some organic liquids), thermal cracking of the metal particles, and immersion of particles in liquid during Nirvapana (heating and quenching in prescribed organic liquids) [80].

Wet micronization treatment in Bhavana is a versatile drug delivery platform and a proven formulation approach that can also enhance the bioavailability of poorly water-soluble drugs [81]. Bhavana may cause amorphization of treated materials, as well as changes in the microstructure, size, and form of particles, among other things [82], for example, the change of crystalline mica into an amorphous state upon grinding and thus enhanced bioavailability [83, 84].

Aqueous liquid media facilitate drug-drug interactions (chemical/physical (adsorption)). Equilibrium dialysis, electrometric techniques (target organ delivery of cationic, neutral, and anionic surfactants in equilibrium and nonequilibrium states) [85], and extent of binding (drug release) are determined, and thermodynamic treatments of the data are studied. Such recent extensive developments in the past years revealed possible applications of Bhavana for industrial applications, understanding of biological processes, and the basis for usage of different aqueous-based media for desirable changes in the material for medicinal use [86, 87].

Organic materials have basic properties to interact and form metal complexes with some specific minerals and metals [88]. Polysaccharide templates are capable of penetrating nanoparticles of iron oxide. The interaction between iron sulphate and template has been carried out in an aqueous phase to obtain the narrow distribution of particle size after selective removal of the template [89]. In Lauha Bhasma (iron calx) preparation, Bhavana between two Puta (successive heat treatments) involves very intricate processes in which exposure of many herbal materials containing various disaccharides and polysaccharides occurs along with the heating pattern of Lauha (iron) for its conversion into medicinal form, which is a combination of oxides of iron [90].

3.9.4. Uniqueness of Bhavana Biocompatibility

Bhavana makes the drug “biocompatible” by converting it into an organometallic complex, especially in the preparation of Ayurvedic dosage form, Bhasma [91-94]. It combines organic elements and reactive substances, which may lead to the formation of metallic salts, metallic oxides, sulphates, and herbomineral compounds. It is reported that the elemental form of metals is not absorbable and may produce toxic effects [95]. Plants have the capacity to transfer them into a readily absorbable form. During the processing of metals with herbal liquid extracts in Bhavana, organometallic complexes are formed that aid in the assimilation and transport of the ingredient into the human tissues. Induction of organic molecules in the free lattice space during Bhavana can change the properties of the drug [96, 97].

Nonabsorbed and nonexcreted inorganic metals, minerals are said to be toxic in raw form, may get bioaccumulated in organs, and produce biocidal or cytotoxic effects [98]. As organic chemical moieties are easily assimilable, there are fewer chances of deposition of such organometallic complexes. Metabolism, distribution, target organ/receptor delivery, and excretion of such organoinorganic complexes could be different in both of these subcomponents of complexion. Most of the other Ayurvedic purification procedures (like Nirvapana, Swedana, Dhalana, etc.) are carried out mainly to convert the surface particles into organic material. However, Bhavana is a method in which more number and surface area of particles are likely subjected to the formation of organoinorganic chemicals.

Many of the liquids used for Bhavana act as reducing agents. All plant extracts primarily possess carbon in one or the other form, and carbon is considered the best reducing agent, for example, Kumari (Aloe vera), Guduchi (Tinospora cordifolia), and Triphala (equal parts of fruits (without seed) of Terminalia chebula, Terminalia bellirica, and Emblica officinalis). With their antioxidants, free radical scavenging properties may help in converting the drug chemically free from free radicals, thus preventing tissue damage due to oxidation [99]. The trace elements present may act as oxidizing agents, eventually converting into a shape of an acceptable, reducible molecule. A study has shown that the coalition of Bhasma with organic macromolecules shows enhanced superoxide dismutase and catalase activity, thereby lessening the free radical concentration [100].

Bhasmas such as Swarna Bhasma (Au nanoparticles) is biogenic traditionally prepared nanoparticles with quick and targeted action. This nanoparticle, at 27 ± 3 nm size, has been found efficient in the treatment of arthritis [101], while at the size of 4 nm, it was found to relieve the increased apoptosis in B-Chronic Lymphocytic Leukemia [102]. Swarna Bhasma assay by FTIR and XRD shows that pure Au is in a zero valency state [91]. Rasa-Sindoor (sublimed mercury compound, structurally mercury sulphide, and 25–50 nm size) is coupled with several organic macromolecules derived from herbal extract used during Bhavana of the drug, which are bioavailable and responsible for adding to the bioefficacy of Rasa-Sindoor. One more significant possibility is debated is that the organic molecules act as coating materials on the surface of the metallic compounds present in the drug, and the metal compounds act as the carrier of the organic matter (akin to the theory of novel drug delivery in contemporary medicine) obtained from botanicals [103]. It is reported that when Bhasma nanoparticles are integrated with biological molecules (in organic liquid media), their stability, functionality, bioavailability, biocompatibility, and bioefficacy are improved [104-108].

3.9.5. Bhavana May Correct the Crystal Defects

Raw metals and minerals have inborn defects [109]. During Bhavana, cited crystal defects in their atomic arrangements may be produced or corrected, thereby changing the chemical composition of the formulation. Impurities, Vacancy, Frenkel defect, and Schottky defect in crystalline arrangement of metals/minerals are corrected by displacement, pushing, or filling of an atom by the flux of organic/inorganic matter from the powdered drugs. In metal excess defects (nonstoichiometric defects) and metal deficient defects, the deficit between one or more anions/cations might be corrected by diffusing those anions/cations present in the liquid material used for Bhavana. Apart from micronization during mechanical grinding of Bhavana, spontaneous aggregation, adsorption, or recrystallization may result in mechanochemical changes in a series of physical and chemical transformations, namely, altered partial crystal structure and size, lattice deformation/rearrangements, reshuffling of interlaced structures, or other composite metastable forms with new and useful properties [8, 110–113].

3.9.6. Liquid Media for Bhavana: As Chelating Agent

“Liquid media” are organic moieties and probably act as chelating agents and form a bonding with metals to reduce the untoward effect of absorption of the metal, help in its safe elimination from the body, and possibly provide some synergistic effects in therapeutics [39]. This is the reason for the choice of liquid media for Bhavana. In Lauha, Bhasma preparation, during treatment of purified metallic iron with Triphala decoction (ellagic acid, chebulagic acid, and corilagin) chelates with iron to preserve the same in a biocompatible form. These organic ligands generally convert to gallic acid, which exhibit hepatoprotective functions [46]. The organic moieties of Triphala possess laxative properties and hence may avert constipation induced by the side effects of iron [46]. In another study, three Bhavana with left juice of Sesbania grandiflora in Gandhakadi Yoga (a sulphur-based Ayurvedic formulation) has proven to reduce iron sorbitol-induced iron overload in experimental studies. Bhavita formulation prevented iron deposition and promoted chelation of excess iron from the body, thus preventing iron overload-induced organ injury, inflammatory changes, and weight loss [114].

Bhasmas are a structurally multielemental cocktail wherein the major constituent elements are at % level; several other essential microelements (Na, K, Ca, Mg, Cu, Fe, Zn, Au, etc.) have also been found in trace (μg/g) or ultratrace (ng/g) levels. These might remain chelated with organic ligands derived from Bhavana in herbal liquids [97, 115]. Human body enzymes and many organic drugs require traces of metallic ions for proper biological actions. Owing to the wide variety of coordination spheres, ligand design, oxidation states, and redox potential, coordination and organometallic complexes are believed to exert their effects by enhancing lipophilicity, inhibition of enzymes, alteration of cell membrane functions, and so on [116].

3.10. Scope of Bhavana

Bhavana plays an important role in the alteration of properties, incorporation of additional bioactive attributes to the drugs, and thus changing the therapeutic value of them. Although these changes can be perceived at pharmacognostical as well as phytochemical levels [59, 117–122], more studies are required on the fundamental understanding of the Bhavana process (mechanochemistry), the complex interplay between particle breakage kinetics and possible aggregation, overlapping of liquid media contents on solid particles, and the physical stability of the wet-grinded microparticles.

Same Bhasma prepared with different liquid media may act distinctly on different target tissues. Studies are warranted and focused on the use of radiolabelled metallic compounds in these differently prepared Bhasma, and subsequently, their distribution and disposition should be tracked down [123]. Owing to multiple affecting factors of Bhavana, it is advisable to adhere strictly to its specific standardized operating procedure with uniform grinding intensity so as to avoid product variability and regulate and monitor the effect by sophisticated tools such as particle size distribution and analysis, scanning electron microscopy, and so on.

PSR during Bhavana is of great importance in Ayurvedic pharmaceutics. Properties of metals get changed at microparticle size level, and thus levigating them with organic moieties as done in many Ayurvedic formulations may give a lead to the invention of newer molecules with evident bioefficacies. It may provide the basis for the invention of products of effects of new chemical moieties obtained after Bhavana due to processes like oxidation, hydrolysis, extractable ingredients, and so on. Furthermore, these nanoparticles possess biodegradable, biocompatible, and nonantigenic properties, which in general could be used to provide selective/targeted/controlled delivery of drugs to target action sites even across the blood-brain barrier. This may also help in reducing the chance of any peripheral side effects of drugs by trimming down the general drug dose requirement in the human body [124]. In the coming era of nanomedicine, Bhasma prepared via the Bhavana technique might be very useful [125, 126].

4. Conclusion and Future Perspective

This review provides in-depth knowledge of Bhavana, coupled with available contemporary evidence. Bhavana is a type of Ayurvedic pharmaceutical processing that has a wide range of medicinal and therapeutic applications. It is a process with high impact during drug processing, influencing the physicochemical properties and biological actions of a dosage form. Various processes, such as thermo- and photochemistry, physicochemical reactions, and mechanochemical changes, appear to occur during wet grinding and thus should be addressed and highlighted while understanding the kinetic chemistry of Bhavana. This review can provide new insights into modern drug discovery and development on the base of traditional medicinal knowledge.

Although the theories proposed in the present review to understand the kinetic chemistry of Bhavana are not adequately supported by experimental studies and the specified biological roles of Bhavana are not very clear, further extensive in vivo and in vitro researches might explain the complete pharmacokinetics of Bhavita drugs on the human system. This is a revolutionary concept, and major pharmaceutical corporations need to renew their strategies on how it can be utilized in identifying chemical moieties with improved bioefficacy for drug discovery and development. Apart from medical and pharmacy, Bhavana could contribute to the field of chemistry too.