Date of Award

12-2022

Degree Type

Dissertation

Degree Name

Doctor of Philosophy in Applied Biomedical Engineering

Department

Chemical and Biomedical Engineering

First Advisor

Joanne M Belovich

Second Advisor

Ronald J Midura

Third Advisor

Lutful I Khan

Abstract

In healthy osteonal bone, embedded osteocytes form an intercellular communication network through overlapping cell membrane extensions, possibly defining an overlooked and clinically relevant lipid-mediated transport pathway for nonpolar molecules. Previous techniques evaluating solute transport in cortical bone limit tissue analysis to microscale areas (less than 1 mm2) using tracers and assumptions that diminish clinical relevance, presenting the need for an improved method to evaluate solute diffusion in macroscale areas (greater than 1 mm2) of osteonal bone. A new diffusion system - constructed of glass and polytetrafluoroethylene - was designed and validated for this purpose, exhibiting minimal adsorption of solutes and resistance to leaking. A detailed protocol was also developed and validated for delipidizing experimental bone specimens.

We measured the partition coefficient and effective diffusivity of 3H-estradiol and 14C-sucrose (polar control) through macroscale osteonal bone areas in native and delipidized tissue states, at physiological estradiol concentrations (sub-nanomolar). Delipidization resulted in a 30% reduction in the estradiol partition coefficient (n=6, p=0.028) and a 280% increase in the sucrose partition coefficient (n=6, p=0.0003). Likewise, delipidization resulted in a 69% decrease of the effective diffusivity of estradiol (1.02 x 10-8 cm2/s versus 3.18 x 10-9 cm2/s, n=18, p=0.007), while increasing the effective diffusivity of sucrose by 346% (n=19, p=0.047). The data reveal an unrecognized lipophilic transport medium in osteonal bone.

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