Introduction Rheology and Viscosity Rheology in Pharmaceuticals • Pharmaceutical formulation • Pharmaceutical manufacturing • Dispensing pharmacy • Pharmaceutical technology • Physical pharmacy • Pharmaceutical jurisprudence Scope of rheology Applications: Examples Conclusion  Rheology has applications in materials science engineering, geophysics, physiology, human biology and pharmaceutics. Materials science is utilized in the production of many industrially important substances, such as cement, paint, and chocolate, which have complex flow characteristics. In addition, plasticity theory has been similarly important for the design of metal forming processes. The science of rheology and the characterization of viscoelastic properties in the production and use of polymeric materials has been critical for the production of many products for use in both the industrial and military sectors. Study of flow properties of liquids is important for pharmacists working in the manufacture of several dosage forms, such as simple liquids, ointments, creams, pastes etc. The flow behavior of liquids under applied stress is of great relevance in the field of pharmacy. Flow properties are used as important quality control tools to maintain the superiority of the product and reduce batch to batch variations

1. RHEOLOGY
MD. MYNUL HASAN
SOUTHEAST UNIVERSITY

2. Introduction:
Rheology: The study of materials with both solid and fluid characteristics. The study of
the flow of matter, primarily in a liquid state, but also as 'soft solids' or solids under conditions in
which they respond with plastic flow rather than deforming elastically in response to an applied
force.
It applies to substances which have a complex microstructure, such as muds, sludges, suspensions,
polymers and other glass formers (e.g., silicates), as well as many foods and additives, bodily fluids
(e.g., blood) and other biological materials or other materials which belong to the class of soft
matter.
The term rheology was coined by Eugene C. Bingham, a professor at Lafayette College, in 1920,
from a suggestion by a colleague, Markus Reiner. The term was inspired by the aphorism of
Simplicius (often attributed to Heraclitus), panta rhei, "everything flows.
Rheology generally accounts for the behavior of non-Newtonian fluids, by characterizing the
minimum number of functions that are needed to relate stresses with rate of change of strain or
strain rates. For example, ketchup can have its viscosity reduced by shaking but water cannot.
Ketchup is a shear thinning material, like yoghurt and emulsion paint exhibiting thixotropic, where
an increase in relative flow velocity will cause a reduction in viscosity, for example, by stirring.
Some other non-Newtonian materials show the opposite behavior, rheopecty: viscosity going up
with relative deformation, and are called shear thickening or dilatant materials. Since Sir Isaac
Newton originated the concept of viscosity, the study of liquids with strain rate dependent viscosity
is also often called Non-Newtonian fluid mechanics.
Rheology and Viscosity: Rheometers for measuring viscosity and viscoelasticity - from
formulation to product use
Rheology is the study of flow and deformation of materials under applied forces which is
routinely measured using a rheometer. The measurement of rheological properties is
applicable to all materials – from fluids such as dilute solutions of polymers and surfactants
through to concentrated protein formulations, to semi-solids such as pastes and creams, to
molten or solid polymers as well as asphalt. Rheological properties can be measured from
bulk sample deformation using a mechanical rheometer, or on a micro-scale by using a
microcapillary viscometer or an optical technique such as Microrheology.
Many commonly-used materials and formulations exhibit complex rheological properties,
whose viscosity and viscoelasticity can vary depending upon the external conditions applied,

3. such as stress, strain, timescale and temperature. Internal sample variations such as protein
concentration and stability, and formulation type for biopharmaceuticals, are also key factors
that determine rheological properties.
Rheological properties impact at all stages of material use across multiple industries – from
formulation development and stability to processing and product performance. The type of
rheometer required for measuring these properties is often dependent on the relevant shear
rates and timescales as well as sample size and viscosity.
Examples of rheological measurements include:
 Viscosity profiling for non-Newtonian shear-dependent behavior to simulate
processing or in-use conditions.
 Viscoelastic fingerprinting for material classification to determine extent of solid-like
or liquid-like behavior.
 Optimising and assessing dispersion stability.
 Determination of thixotropy of paints and coatings for product application and final
finish quality.
 Impact of molecular architecture of polymers on viscoelasticity for processing and
end-use performance.
 Benchmarking Food and Personal Care products for ability to pump or spread.
 Full cure profiling for bonding or gelling systems.
 Pre-formulation screening for therapeutics, particularly biopharmaceuticals.
Rheology in Pharmaceuticals: Pharmaceutics is the discipline of pharmacy that deals with the
process of turning a new chemical entity (NCE) or old drugs into a medication to be used safely
and effectively by patients. It is also called the science of dosage form design. There are many
chemicals with pharmacological properties, but need special measures to help them achieve
therapeutically relevant amounts at their sites of action. Pharmaceutics helps relate the formulation
of drugs to their delivery and disposition in the body.[1]
Pharmaceutics deals with the formulation
of a pure drug substance into a dosage form. Branches of pharmaceutics include:
 Pharmaceutical formulation
 Pharmaceutical manufacturing
 Dispensing pharmacy
 Pharmaceutical technology
 Physical pharmacy
 Pharmaceutical jurisprudence

4. Pure drug substances are usually white crystalline or amorphous powders. Historically before the
advent of medicine as a science it was common for pharmacists to dispense drugs as is, most drugs
today are administered as parts of a dosage form. The clinical performance of drugs depends on
their form of presentation to the patient.
Scope of rheology:
 rheology is principally concerned with extending continuum mechanics to characterize
flow of materials, that exhibits a combination of elastic, viscous and plastic behavior by
properly combining elasticity and (Newtonian) fluid mechanics. It is also concerned
with establishing predictions for mechanical behavior (on the continuum mechanical
scale) based on the micro- or nanostructure of the material, e.g. the molecular size and
architecture of polymers in solution or the particle size distribution in a solid suspension.
Materials with the characteristics of a fluid will flow when subjected to a stress which
is defined as the force per area. There are different sorts of stress (e.g. shear, torsional,
etc.) and materials can respond differently for different stresses. Much of theoretical
rheology is concerned with associating external forces and torques with internal stresses
and internal strain gradients and flow velocities.
 Rheology unites the seemingly unrelated fields of plasticity and non-Newtonian fluid
dynamics by recognizing that materials undergoing these types of deformation are unable
to support a stress (particularly a shear stress, since it is easier to analyze shear deformation)
in static equilibrium. In this sense, a solid undergoing plastic deformation is a fluid,
although no viscosity coefficient is associated with this flow. Granular rheology refers to
the continuum mechanical description of granular materials.
 One of the major tasks of rheology is to empirically establish the relationships between
deformations (or rates of deformation) and stresses, by adequate measurements, although
a number of theoretical developments (such as assuring frame invariants) are also required
before using the empirical data. These experimental techniques are known as rheometry
and are concerned with the determination with well-defined rheological material functions.
Such relationships are then amenable to mathematical treatment by the established methods
of continuum mechanics.
 The characterization of flow or deformation originating from a simple shear stress field is
called shear rheometry (or shear rheology). The study of extensional flows is called
extensional rheology. Shear flows are much easier to study and thus much more
experimental data are available for shear flows than for extensional flows.

5. Applications:
 Rheology has applications in materials science engineering, geophysics,
physiology, human biology and pharmaceutics. Materials science is utilized in the
production of many industrially important substances, such as cement, paint, and
chocolate, which have complex flow characteristics. In addition, plasticity theory
has been similarly important for the design of metal forming processes. The science
of rheology and the characterization of viscoelastic properties in the production and
use of polymeric materials has been critical for the production of many products
for use in both the industrial and military sectors. Study of flow properties of liquids
is important for pharmacists working in the manufacture of several dosage forms,
such as simple liquids, ointments, creams, pastes etc. The flow behavior of liquids
under applied stress is of great relevance in the field of pharmacy. Flow properties
are used as important quality control tools to maintain the superiority of the product
and reduce batch to batch variations
Examples:
a. Industrial rheology with particular reference to foods,
pharmaceuticals, and cosmetics.
b. Rheology of End-Tethered Polymer Layered Silicate Nanocomposites:
The rheology of end-tethered polymer layered silicate nanocomposites is investigated using linear
viscoelastic measurements in oscillatory shear with small strain amplitudes. Two systems
consisting of poly(ε-caprolactone) and nylon-6 with varying amounts of layered silicate
(montmorillonite) are examined. The storage (G‘) and loss (G‘‘) moduli increase at all frequencies
with increasing silicate loading, consistent with previous findings with conventionally filled
polymer systems. However, the power-law dependence of G‘ and G‘‘ in the terminal zone is
different from that observed in homopolymers and decreases with increasing silicate loading. At
low frequencies the rheological response becomes almost invariant with frequency, suggestive of
a solid-like response. Comparisons are drawn with rheology of other intrinsically anisotropic
materials, and an attempt is made to explain phenomenologically their rich-rheological behavior
c. The rheology of microcrystalline cellulose powder/water mixes —
measurement using a mixer torque rheometer: Microvascular rheology of Definity
microbubbles after intra-arterial and intravenous administration: The microvascular
rheology and extent of pulmonary retention of second-generation microbubble ultrasound
contrast agents has not previously been well characterized. After intravenous injection and
pulmonary passage, the microvascular rheology of Definity microbubbles is similar to that
of red blood cells. Microbubble entrapment within the pulmonary microcirculation after

6. venous injection should be negligible and transient. These findings are important for
establishing the safety of this agent.
d. Dynamic Rheology of Renneted Milk Gels Containing Fat Globules
Stabilized with Different Surfactants: Anhydrous milk fat was emulsified with
αs1-CN (casein), αs2-CN, β-CN, κ-CN, α-lactalbumin, β-lactoglobulin, Tween 80, or
phosphatidylcholine to produce a 30% fat cream in a 0.1 M imidazole pH 7 buffer.
Recombined milk containing globules coated with the more amphipathic and
phosphorylated αs2-CN and β-CN clotted faster but gel firmness increased more slowly and
weaker gels were formed. Gel firmness increased more rapidly for milks containing
globules coated with of αs1-CN and κ-CN that possess more uniformly distributed
hydrophobic domains.
e. Rheology, oxygen transfer, and molecular weight characteristics of poly
(glutamic acid) fermentation by Bacillus subtilis:
Poly (glutamic acid) (PGA) is a water-soluble, biodegradable biopolymer that is produced
by microbial fermentation. Recent research has shown that PGA can be used in drug delivery
applications for the controlled release of paclitaxel (Taxol) in cancer treatment. A fundamental
understanding of the key fermentation parameters is necessary to optimize the production and
molecular weight characteristics of poly (glutamic acid) by Bacillus subtilis for paclitaxel and
other applications of pharmaceuticals for controlled release. Because of its high molecular weight,
PGA fermentation broths exhibit non-Newtonian rheology. In this article we present experimental
results on the batch fermentation kinetics of PGA production, mass transfer of oxygen, specific
oxygen uptake rate, broth rheology, and molecular weight characterization of the PGA biopolymer.
Conclusion: Rheology covers the science of the deformation and flow of soft matter, with
special interest in experimental and computational advances in the characterization and
understanding of complex fluids, including their nonequilibrium dynamic and structural behaviors.

7. References:
1. James Freeman Steffe (1 January 1996). Rheological Methods in Food Process
Engineering. Freeman Press. ISBN 978-0-9632036-1-8.
2. The Deborah Number
3. Barnes, Jonathan (1982). The presocratic philosophers. ISBN 978-0-415-05079-1.
4. Beris, A. N.; Giacomin, A. J. (2014). "πάντα ῥεῖ : Everything Flows". Applied Rheology
24: 52918. doi:10.3933/ApplRheol-24-52918.
5. R. B. Bird, W. E. Stewart, E. N. Lightfoot (1960), Transport Phenomena, John Wiley &
Sons, ISBN 0-471-07392-X
6. R. Byrin Bird, Charles F. Curtiss, Robert C. Armstrong (1989), Dynamics of Polymeric
Liquids, Vol 1 &2 , Wiley Interscience, ISBN 0-471-51844-1 and 978-0471518440
7. J Am Soc Echocardiogr 2002; 15:396-403.)
8. 2003 Wiley Periodicals, Inc. Biotechnol Bioeng 82: 299–305, 2003