Use of SPM to Measure Adhesion Forces: Some Pharmaceutical Applications Frank M. Etzler
Particle Adhesion in Pharmaceutical Science Particle adhesion important to a number of areas of interest. Adhesion science has received relatively little attention by pharmaceutical scientists. Particle adhesion related to: Powder flow Powder mixing Powder dispersion in Dry Powder aerosol devices Tablet hardness
Powder Dispersion in Dry Powder Inhalation Devices Problem: Dry powders can inhaled directly for pulmonary delivery of drugs. A constant amount of particles in the range of 2-5μm must be delivered to the lung. Variable adhesion between components results in variable drug delivery.
Principles of Adhesion W a =γ 1 + γ 2 - γ 12 W a =W a LW +W a AB vogc W a AB =2 (γ 1 + γ 2- ) 1/2 + 2 (γ 1 - γ 2+ ) ½ Fowkes W = f N ΔH AB a f = 1 lnwa lnt AB 1 AB a AB * H KDN a KAN d Δ = +
Particle Size and Adhesion For sphere-sphere and sphere-plane interactions: London - van der Waals Forces: Fr () r Electrical: Fr () r 2 3 1 Fr () Coulomb: 2 r Capillary: F() r r(1 r x ) x> 1 Zimon, A.D. Adhesion of Dust and Powder, 2 nd ed. 1982.
SPM to Measure Adhesion Forces Colloidal Probe
Adhesion Force Curve approach Cantilever Deflection (a.u.) Δz Δz retraction Distance(a.u.)
Adhesion Mapping Gelatin Capsules a b Adhesion maps (10 x 10 μm scan): (a) adhesion and (b) adhesion area map of a capsule. c d (c) adhesion and (d) adhesion area map of capsule after extraction process.
vocg Acid Base Parameters of Gelatin Capsules 2.5 Surface Free Energy (mn/m) 2 1.5 1 0.5 Gamma B Gamma A Extracted 0 c12363 24465 27984 27985 27986 27987 c94840 51301 51501 351A51 BOR1 CMR BOR2 PEG 2 Capsugel Su Heung PEG Plasticized Gamma B Normal Surface Free Energy (mn/m) 1.5 1 0.5 Gamma A 0 c12363 24465 27985 27986 27987 51301 Capsule Lot
Contamination of Capsule Affects Adhesion F ad / d particle (nn/μm) 60 40 20 72601 Pyrole Acrylic Acid acetylene C6F14 Mother Lot 29625 ext TOF-SIMS shows surface contamination of capsules with SDS. Some mold release components are unextractable 0 29623 29625 0.6 0.7 0.8 0.9 1 1.1 % S+P
Lactose Surface Imaging SPM phase image of a surface of a single particle of lactose (1x1μm). Dark area represents a thin layer of contaminating material. White specks are another surface contaminant.
Lactose Surface Chemistry and Capsule Adhesion
Surface Contamination of Lactose CH vs OCO ESCA suggests partial coverage of lactose with aliphatic containing materials. SIMS confirms ESCA results. Acidic surfaces are more contaminated
Lactose Gelatin Adhesion Adhesion Force (nn) 500 400 300 200 100 0 Pext 29625ext 72601 29623 P 29625 0 4 8 12 16 Particle diameter (μm) Adhesion force of Pharmatose 200M vs colloidal probe diameter. Linear relation indicates that interaction is primarily via London - van der Waals forces.
Relative Adhesion of Drug and Lactose on Capsules Lactose Adhesion Force (nn) 240 200 160 120 80 PEGext 29625ext 72601 29625 PEG 160 200 240 280 320 360 400 IBr Adhesion Force (nn) 29623 Normalized Adhesion Force (nn/μm) 100 80 60 40 20 0 Drug-Drug Lact-Lact Lact-Drug Drug-Cap Lact-Cap Drug-CC Lact-CC F N = F exp d
SPM in Tablet Making Punch Sticking 80 Fe Coated Tip Drug Interactions Adhesion Force (nn) 60 40 20 Iboprofen Ketoprofen Fe Flubiprofen 0 Wang et al. J. Pharm Sci 92(4) 798 2003 Wang et al. J. Pharm Sci. 92(4),798 (2003) 0 2000 4000 6000 8000 W AD (nn/nm)
Effect of Humidity on Particle Adhesion Force measurements taken using blank AFM tips against compressed disks of SEDS and micronized salbutamol. (a) Flexible contact tip against micronised salbutamol (b) Flexible contact tip against SEDS salbutamol (c) Stiffer tapping tip against micronized salbutamol (d) Stiffer tapping tip against SEDS salbutamol Pharmaceutical Research, Vol. 21, No. 6, June 2004 ( 2004)
Friction on Steel J. Lee / International Journal of Pharmaceutics 340 (2007) 191 197
Take Home Message SPM can be a useful tool in pharmaceutical applications. Several applications to inhalation formulations have been published. SPM can help determine the surface chemical purity of surfaces. SPM can be used to understand the relative adhesion between materials. Other surface chemical methods (e.g. IGC) can be used successfully with SPM to enhance understanding. Further application to pharmaceutical science appears to be promising.