Shared Flashcard Set


Biomaterials Ch 11
Wound Healing
Undergraduate 2

Additional Engineering Flashcards




3 phases of normal skin wound healing

1. Inflammation

2. Proliferation

3. Remodeling


24hrs: a clot begins to form around the wound; neutrophils gather at the wound site


1-7d: The tissue around the wound begins to re-epithelialize (triggered by macrophage-released factors); granulation tissue forms; a new capillary is formed to connect the healing tissue and an adjacent blood vessel (angiogenesis)


>1 wk: Regeneration is basically finished; the wound site contracts

Skin Repair/Scar Formation

1) Dermal wound

2) Granulation Tissue Formation

3) Random orientation of collagen III around the wound

4) Collagen III is replaced with Collagen I

5) Angiogenesis

6) Collagen accumulates for 2-3 mos.

7) Some blood vessels resorb, scab becomes pale (prim. composed of fibroblasts, ECM. collagen

Skin Regeneration

1) Epidermal wound

2) Epithelial cells flatten, release from ECM, and migrate towards center of wound, contacting other epithelial cells

3) ECM reattaches, regains cuboidal shape with the same mechanical properties as before

Granulation Tissue
Dut to cell death and removal following injury, there is a local decreased tissue mass; fibroblasts and vascular endothelial cells are rectruited to the site, begin to form granulation tissue (ECM and new blood vessels)

1) Endothelial cells activate and survive due to VEGF (vascular-endothelial growth factor)

2) MMPs break down basement membrane, ECM

3) VEGFs cause endothelial cells to proliferate and migrate

4) Integrins form, elongate, and remodel tubes

5) Ang-1 TGF alpha causes maturation of pericytes and smooth muscle vasculature cells


Vasculogenesis: No pre-existing cells (likely differentiated from bone marrow stem cells)


Angiogenesis: Sprouting of new blood vessels from pre-existing vessels

Foreign Body Reaction

FBGCs - fused macrophages attempting to phagocytose the matl; undergo frustrated phagocytosis


Formation affected by surface topography/chemistry, surface area/volume ratio


More roughness, porosity = higher FBGC formation (higher SA:V ratio)

Fibrous Encapsulation

End stage of healing response in non-degradable biomatls (~4wks post-implantation)


An acellular fibrous capsule (spindle-shaped fibroblasts, a small number of macrophages) forms around the material


Presence of neutrophils suggests persisting inflammation


Presence of FBGCs suggests production of small particles by corrosion, dissolution, wear (unresolved active inflammation/ attempted degradation)


Capsule thickness enhanced by: injury during implant, particulates, motion, edges, current

Chronic Inflammation

Can result in granulomas (layer of FBGCs surrounded by modified macrophages and lymphocytes)


Caused by motion around implant and physiochemical implant properties


Can trigger an aquired immune response


After normal wound healing, myofibroblasts disappear by apoptosis


Continuous collagen secretion, remodeling and contraction leads to connective tissue contraction


Examples: hypertrophic scars, keloids, fibrotic diseases

4 Types of Implant-Caused Wound Resolution

1) Extrustion - formation of a pouch contiguous with the newly formed epithelium; pouch forces material out of the body


2) Resorption - Only occurs with biodegradable materials; the fibrous capsule is collapsed or replaced by appropriate tissue; success for tissue engineering


3) Integration - Relatively rare; material is directly in contact with host material (electrode in the brain, bone implant); success for tissue engineering


4) Encapsulation - Formation of a fibrous capsule around the material; does not resolve, but can reach a steady state; failure for tissue engineering, typical response for non-degradable biomaterials

Considerations for Assaying in vivo immune response

1) Animal choice (start small, use animals comparable to humans)


2) Implant site


3) Study length: Acute (0-24h), Subacute (14-28d), Subchronic (<90d), Chronic (>90d)


3) Dose and administration


4) Controls (sham surgery)


5) Assesment - visual, histology, electron microscopy, mechanical testing

Factors related to an implant that affect in vivo response

1) Materials used


2) Intended additives, procces contamination, residues from fabrication


3) Leachable substances


4) Degradation products (designed to degrade, enter body environment)


5) Properties, characteristics of 'final product'


6) Alternation in load or strain in the area surrounding the implant

Supporting users have an ad free experience!