Lecture 9 Bioengineering and Immune System

Types of stem cells

Embryonic, induced pluripotent stem cell, and adult stem cells (multi-potent but still limited and derived from tissue).

Secondary Germ

Can only differentiate into the cells near it

Relationship between basal cells and stem cells

Some basal cells act like stem cells

Hair Follicle in wound healing

Keratinocytes leave the follicle to repopulate the wounded skin.

Follicle Neogenesis

New follicles form in wounded regions during re-epithelialization. (might be because of the secondary germ cells)

Inflammation Overview

Immune cell infiltration, growth factors, and blood clotting factors (which helps with the provisional matrix).

Tissue Formation Overview

New tissue, re-epithelialization of the outer surface, granulation tissue formation, and neovascularization (reforming blood vessels).

Tissue Remodeling Overview

Break down damaged tissue and ECM, remodel and deposit new ECM, contraction of wound by fibroblasts.

Blood Clot

Created from the blood coagulating and platelet deposition. The provisional matrix starts to form afterward and there’s the growth factor reservoir.

Immune Cell Invasion

First neutrophils (calls other immune cells and activates fibroblasts), then monocytes/macrophages. Cytokines are released to promote cell integration and break down damaged tissue.

Re-epithelialization

Epidermal cells move under the fibrin clot but above the provisional matrix.

Granulation Tissue

Growth factors stimulate the fibroblasts and new ECM is put down.

Chronic Wound

Can lead to loss of tissue viability and elevated/sustained inflammation.

Scar Tissue in Dermis

Results in less permeability, fewer neurons, and less blood flow.

Autograft

Graft from self and can collect the epidermis and part of the dermis.

Allograft

Graft from someone else. There’s risk of rejection

Xenograft

Graft from an animal. Modern grafts like this are decellularized, include the dermal skin, and provide collagen & ECM that supports new dermis growth.

Graft Benefits

It fulfills the re-epithelialization step so that granulation tissue can form. Some grafts are meshed so that the wound can exude (otherwise build up and infection might occur).

(Modern) Acellular Skin Substitutes

This could be a decellularized xenograft or autograft. It’s a synthetic mesh or collagen from the dermis up.

(Modern) Allogenic Skin Substitutes

Fibroblasts grown with a matrix (could be synthetic) so that they make ECM

(Modern) Autologous Skin Subs

Fibroblasts/keratinocytes from the patient are cultured and then used.

Apligraf

Neonatal foreskin fibroblasts/keratinocytes w/bovine collagen matrix. Expensive w/ a short shelf life

Integra Dermal Regeneration Template

Good long term outcomes, prone to infection, acellular shark bovine collagen. Two stages: dermal regrowth then skin graft

Dermagraft

Synthetic, absorbable, prone to infection.

Cell Spray

From patient, no new ECM, infection risk.