BME 208
Biomaterials Sessional
Lab 2
Biomaterials solution preparation (PBS, PVA)
Department of Biomedical Engineering
BUET
Preparation of Solution
• We know, a solution has two parts : solvent and a solute
• Solvent: The substance which does the dissolving (typically a liquid,
such as water or alcohol). Must be greater than 50% of the solution.
• Solute: The substance which is dissolved, or has gone into solution
(typically a solid
• Before preparation of a solution, we have to get an idea about
concentration
1
Concentration
• Concentration can be expressed in many units, more common ones
are:
1. Molarity number of moles per unit volume of solution (L)
2. Percentage (w/v) : mass of solute (gm) per unit volume of solution
(mL)
3. Percentage (w/w) : mass of solute (gm) per unit mass of solution
(gm)
4. Percentage (v/v) : volume of solute (mL) per unit volume of
solution (mL) [This is for liquid solutes]
1
Making a solution
• We want to make a 20 mL solution with concentration 10% (w/v),
where the solute is a solid
• For most solid solutes, we can consider, the volume of solvent =
volume of total solution (volume of solute is negligible)
• 10% w/v conc means,
• 100 mL solvent requires 10 gm solute
• So, 20 mL solvent requires : (10/100*20) = 2 gm solute
1
Making a solution
• We want to make a 20 mL solution with concentration 10% (w/v),
where the solute is a liquid
• For liquid solutes, the volume of solvent + the volume of solute =
volume of total solution (volume of solute is not negligible)
• 10% v/v conc means,
• 100 mL solution requires 10 mL solute, 90 mL solvent
• 20 mL solution requires : (10/100)*20 = 2 mL solute, and (20-2)=18
mL solvent
1
PVA (Polyvinyl Alcohol)
• PVA is a hydrophilic polymer, due to the OH functional group in its
monomeric unit, so PVA can dissolve in water, water can be a solvent
for PVA
• Heating Is needed for dissolution of PVA (70-90 degree Celsius), at
low temperatures, PVA tends to aggregate together and form PVA
clumps due to their tendency to hydrogen bond with each other
1
PBS (Phosphate Buffer Saline)
• Phosphate-buffered saline (PBS) is a buffer solution (pH ~ 7.4)
commonly used in biological research
• It is used to mimic the biological condition of the human body, by
mimicking body fluid
• Two important properties are mimicked : Osmolarity/Ion
concentration and Buffering capacity (the ability to maintain pH)
1
PBS composition
• It is an aqueous solution with 4 main ionic salts :
1
Buffer capacity
• The buffer capacity is maintained by mainly 2 salts, Disodium
Phosphate (Na2HPO4) and monopotassium phosphate (KH2PO4)
• We know, a buffer is a solution with a weak acid and its conjugate
base (and vice versa)
• Here, the weak acid is H2PO4- ion and its conjugate base is HPO42- ion
1
Why is maintaining osmolarity important
• Matching the osmolarity of body is important for cell culture
applications
• A cell, kept in mismatched osmolar condition will be damaged, in
hyperosmolar condition, will shrink and in hyposmolar condition will
swell up
• But, a cell kept in PBS will retain its shape and properties, because,
the osmolarity of PBS matches the osmolarity of the cellular
environment.
1
Other uses of PBS
• PBS has a wide variety of uses
• For example, to get an idea about how any drug/agent behaves
inside the human body, PBS can be used as a dissolving media
• Pharmaceutical company often use PBS to determine the release
kinetics of drugs
• As mentioned before, in cell culture PBS is used
• Common laboratory protocol often requires PBS, as we go forward in
the 208 sessional, we can see its examples.
1
Let’s move on to the Lab!
1