Targeting microspheres and cells to polyethylene glycol-modified biological surfaces

Optimizing the Porohyperelastic Response of a Layered Compliance Matched Vascular Graft to Promote Luminal Self-Cleaning

Thrombosis and intimal hyperplasia have remained the major failure mechanisms of small-diameter vascular grafts used in bypass procedures. While most efforts to reduce thrombogenicity have used a biochemical surface modification approach, the use of local mechanical phenomena to aid in this goal has received somewhat less attention. In this work, the mechanical, fluid transport, and geometrical properties of a layered and porous vascular graft are optimized within a porohyperelastic finite element framework to maximize self-cleaning via luminal reversal fluid velocity (into the lumen). This is expected to repel platelets as well as inhibit the formation of and/or destabilize adsorbed protein layers thereby reducing thrombogenic potential. A particle swarm optimization algorithm was utilized to maximize luminal reversal fluid velocity while also compliance matching our graft to a target artery (rat aorta). The maximum achievable luminal reversal fluid velocity was approximately 246 μm/s without simultaneously optimizing for host compliance. Simultaneous optimization of reversal flow and compliance resulted in a luminal reversal fluid velocity of 59 μm/s. Results indicate that a thick highly permeable compressible inner layer and a thin low permeability incompressible outer layer promote intraluminal reversal fluid velocity. Future research is needed to determine the feasibility of fabricating such a layered and optimized graft and verify its ability to improve hemocompatibility.

Assembly and Function of a Bioengineered Human Liver for Transplantation Generated Solely from Induced Pluripotent Stem Cells

The availability of an autologous transplantable auxiliary liver would dramatically affect the treatment of liver disease. Assembly and function in vivo of a bioengineered human liver derived from induced pluripotent stem cells (iPSCs) has not been previously described. By improving methods for liver decellularization, recellularization, and differentiation of different liver cellular lineages of human iPSCs in an organ-like environment, we generated functional engineered human mini livers and performed transplantation in a rat model. Whereas previous studies recellularized liver scaffolds largely with rodent hepatocytes, we repopulated not only the parenchyma with human iPSC-hepatocytes but also the vascular system with human iPS-endothelial cells, and the bile duct network with human iPSC-biliary epithelial cells. The regenerated human iPSC-derived mini liver containing multiple cell types was tested in vivo and remained functional for 4 days after auxiliary liver transplantation in immunocompromised, engineered (IL2rg^-/-) rats.

In vivo PEG modification of vascular surfaces for targeted delivery

OBJECTIVE

Thrombosis and restenosis remain problematic for many intravascular procedures. Previously, it has been demonstrated that modifying an injured vascular surface with a protein-reactive polymer could block undesirable platelet deposition. As an added benefit, it would be advantageous if one could target therapeutics to the injured site. This study investigates a site-specific delivery system to target microspheres to vascular surfaces modified with a reactive polyethylene glycol tagged with biotin.

METHODS

Rabbit femoral arteries were injured with a 2F embolectomy catheter. Modification of the vascular surface was achieved using a channeled balloon catheter or small-diameter tube. Microspheres were injected intravenously through catheterization of the ear vein. Polymer modification on the injured surface and delivery of microspheres was quantified using epifluorescence microscopy at 0, 24, 48, and 72 hours.

RESULTS

Polymer modification of the vascular surface could be achieved using a channeled drug delivery catheter or small-diameter tube with similar results. Maximum polymer coverage occurred at 0 hours and decreased to 85% maximal at 24 hours, 72% at 48 hours, and 67% at 72 hours. The initial number of microspheres per mm(2) binding to modified, injured arteries was 304 versus 141 for the unmodified, damaged control (P < .01). At subsequent times, the number of adherent microspheres to modified, injured arteries decreased by 50%, 70%, and 84% at 24, 48, and 72 hours, respectively; while nonspecific binding to unmodified, injured arteries quickly decreased by 93%. Initial microsphere binding to modified, healthy arteries was 153 microspheres/mm(2) as opposed to 26 microspheres/mm(2) for the unmodified, healthy controls (P < .01).

CONCLUSIONS

Chemical modification of injured vessels following intravascular procedures can be readily accomplished in vivo to create a substrate for targeted delivery systems. As a proof of concept, targeted microspheres preferentially adhered to polymer-modified surfaces as opposed to injured, unmodified, or healthy vascular surfaces.