Sheep, pig and human platelet- material interactions with model - - PowerPoint PPT Presentation

Sheep, pig and human platelet- material interactions with model cardiovascular biomaterials

Steven L. Goodman Center for Biomaterials, University of Connecticut Health Center

Presented by Andrew Thistle, Brian Choi, John Bocchino, Philip Kemp, and Timothy Hersey

Dr Steven L. Goodman

• Professor of Biomaterials,

Physiology, Biomedical Engineering and microscopy at University of Connecticut

• Founded 10H Technology

– Assists small company in

• btaining governmental

research funding

Journal of Biomedical Materials Research

Key Terms

• Thrombus - Also known as a blood clot, a thrombus is the final product of

the blood coagulation step in hemostasis. It is achieved via the aggregation of platelets that form the platelet plug.

• Hemocompatibility - Tests the effects of blood contacting the bio-

materials, products, compounds, and on blood or blood components to see if they are compatible with an organism’s body.

• Pyrolytic Carbon - A material similar to graphite. Pyrolytic carbon is used

for biomedical applications because of its bio-compatibility and is thromboresistant.

• Rheological - The study of the flow of matter, primarily in liquid state, but

also as “soft solids” where the material responds with plastic flow rather than deforming elastically in response to an applied force.

• Topography -The study of surface shape and features
• Elution - A term used in chemistry to describe the process of extracting
• ne material from another by washing with a solvent
• Pseudopodia - Temporary projections that extend and contract by the

reversible assembly of actin subunits into microfilaments. These projections allow a cell to move.

Introduction

• Why did the researchers use sheep and pig in

their experiments?

Animal Experimentation

Pros:

– No human deaths through experimentation – Can find cures for diseases/problems without risking human life

Cons:

• Nonhuman species

differ from humans in their responses to cardiovascular devices

• Need to fully

understand the species to fully evaluate their predictive ability

Blood-Material Interaction

• Focus: Sheep and Pig platelet adsorption to

biomaterials compared to human platelet adhesion

– See how different animal models spread and grow thrombi on different biomaterials

• Platelet-mediated thrombosis may determine

the success or failure of mechanical heart valves and other vascular prosthetics used in high-shear-rate locations

Biocompatibility

• In Vitro studies have

shown that human platelets attach and become extremely well spread on PYC

• This indicates that PYC

may not be as passive to platelets as previously described

• Pyrolytic carbon (PYC)

– Used in mechanical heart valves – Topography is much rougher at the submicron scale – which directly influences platelet adhesion

Purpose of the Study

• Study the platelet responses of the two most
• ften used large animals in cardiac valvular

prosthetics: sheep and pigs

– Shape of the platelet – Platelet adhesion – # of platelet cells per area

Materials

Formvar Pyrolytic Carbon Polyethelene Silicone Rubber

Discussion Question 1

Why would you want to use 4 different materials that elicit different platelet responses?

Experimental Animal Species

Methods

• Platelet response from the three different species were

tested on the four materials

• Wanted to determine which animals platelet response was most like

humans

• Platelet suspensions were purified and test materials were

hydrated

• Platelets were applied to each material and allowed to

adhere for 45 min

• The excess platelets were removed and the adhered

platelets were incubated for another 45 min

• This allowed the platelets to for the surface of the material
• Electron microscopy was used to analyze platelet response

Discussion Question 2

The study used blood from adult humans and adult sheep, but juvenile pigs. Do you think this could have skewed the data? How so?

Results: Human Platelets

PYC and PE

• Almost completely covered

by spread platelets

• Platelets in direct material

contact with PYC were spread to a greater extent than those with PE

• Both produced similar low

levels of focal centers FVR and SIL

• FVR were extensively

clustered into aggregates and minimally shape- changed

• SIL induced minimal

spreading with dendritic forms (cohesion was essentially zero)

Results: Sheep Platelets

PYC and PE

• PYC: mostly round and

dendritic

• PE: similar to PYC with

fewer spreading shapes FVR and SIL

• SIL induced greatest

percentage of dendritic forms.

• FVR induced NO dendritic

spread. **Overall, level of response of sheep platelets was considerably less than humans

Results: Porcine Platelets

PYC and PE

• PYC: platelets reached fully

spread and spreading morphologies

• PE: Even distribution over

material with dendritic and spread-dendritic shapes

• **The extent of most

porcine platelet responses was comparable to that of human platelets FVR and SIL

• SIL:Platelets were of round
• r dendritic shapes.
• Lower deposition on SIL and

FVR than PYC and PE

Human Ovine Porcine

Discussion Question 3

Based on the adhesion properties of the different species of platelets, why were sheep, pig and human platelets used? Also, baboons were said to have similar properties – because they are most closely related to humans, why weren’t they used?

Discussion: Sheep

• Large difference between the response of sheep and

human platelets

– Major difference: sheep platelets do not attach or spread to the same extent – Other differences:

• Lower surface coverage
• Less platelet interaction
• Discussion Question: Using Figures 3-5 and other

content within the article, what are some explanations for why there was such a minimal response of sheep platelets compared to human platelets for all measures (adherent platelets, cohesion, surface coverage, and focal centers)?

Discussion: Pigs

• Pigs

– Porcine platelets may be more similar to human platelets – More extensive “human- like” coverage and spreading observed on PYC – Results correspond closely to that of human platelets – More studies to be done using pig platelets

Discussion: Summary

• Rank of material performance similar among

all species:

– Spreading: PYC greatest, slightly less for PE and FVR, and minimal responses to SIL (Table 1)

Major Conclusions

• Sheep platelets are attenuated in response to

biomaterials when compared to humans

• Human platelets extremely spread on PYC

– Based on in vitro studies, full spreading and surface coverage of human platelets may be important in the clinical biocompatability of PYC.

• Porcine platelets had a similar response to human

platelets

– In vivo, porcine platelets may more closely model human responses – Porcine platelets on PYC in vivo can be used in future studies as a suitable model for examining platelet attachment and thrombosis on cardiovascular biomaterials

Questions?

This guy does