The document proposes a tissue engineering approach to treating pressure ulcers using a chitosan-gelatin scaffold embedded with growth factors, stem cells, and antimicrobials. The scaffold would be modified for pressure ulcer healing through inhibiting human neutrophil elastase, stimulating perfusion, and PEGylating basic fibroblast growth factor for faster wound healing. Pressure ulcers would be monitored by enhancing transdermal delivery of growth factors using sonophoresis or deferroxamine, and through fluorescence observation of growth factor levels in serum samples. This tissue engineering approach aims to address the major health issue of pressure ulcers through a multifaceted scaffold designed specifically for pressure ulcer healing.

1. Treating Pressure Ulcers
A potential tissue engineering-based approach
By
Nuruddin Bahar
MSc Student (Biomedical Engineering)

2. Background
• Pressure ulcers (PU) / pressure sores / bedsores are injuries to the skin and
underlying tissue, primarily caused by prolonged pressure on the skin. This pressure
causes decreased circulation and skin breakdown. (NHS Definition)
• Causes :
 Extrinsic – immobilization, decreased sensation, poorly fitted medical devices
 Intrinsic – diabetes, malnutrition, smoking
• Affects bony areas - heels, elbows, hips and base of the spine
• National Pressure Ulcer Advisory Panel (NPUAP) categorizes it into 4 stages –
1. Non-
blanchable
erythema
2. Partial
thickness
skin loss
3. Full
thickness
skin loss
4. Full
thickness
tissue loss
Figure 1. Four stages of pressure ulcer. [1]

3. Rationale for Study
• Most vulnerable group >75 years,
disabled and under wound care
• May develop blood poisoning or
gangrene if untreated
• 1 of 4 common patient harms
• >1,300 new ulcers per month (NHS
Digital)
• 200,000 new cases in 2017/18 (Guest
et al 2017)
• Treatment cost / day - £1.4 million
(Guest et al 2017)
Figure 2. Rate of hospitalized patients with pressure
ulcers across all age groups in the United States from
2008 to 2012 (National Inpatient Sample). [2]

4. Potential Solution
• 3 pillars approach – scaffold , cells and environmental conditions
• Porous chitosan (CS) [3] scaffold embedded with
1. Basic fibroblast growth factors (bFGF) in gelatin (GE)
microparticles
2. Exhaustive amounts of antimicrobials (pre/post implantation)
3. Human neutrophil elastase (HNE) inhibitors
4. Perfusion stimulators (human serum albumin (HSA) and
antihypotensive agents)
5. Stem cells and/or fibroblasts (with senescence control)
Scaffold Design
Scaffold
Modification
PU-specific
Modification
Monitoring
of PU
Figure 3. SEM of a typical
chitosan scaffold.
Figure 4. SEM of GE
microparticles embedded
in a biopolymer.

5. Scaffold Design
Design Requirements : [Absolute | Needed | Preferential | Optional]
Biocompatibility Biodegradability Bioabsorbability Haemostasis 2-D Porosity 3-D Porosity
Pro-coagulation Wound sealing Anti-bacterial Anti-fungal Non-cytotoxicity
Water adsorption Proliferation Compressive strength Tensile strength Water/fluid retention
Material Constituents Useful Characteristics Ref
Sponges CS, GE Cell proliferation, non-cytotoxicity, bacteriostatic, biodegradability. [4]
Films
CS, GE,
ibuprofen
Water/fluid retention, antibacterial, non-cytotoxicity, wound sealing [5]
Hydrogel
CS, GE,
PVA
pH-sensitivity, water/fluid retention, adhesion [6]
Fibers CS, GE High porosity, wettability, rapid blood absorption, pro-coagulation [7]
Table 1. A few suggested CS-GE based scaffolds for current design.
Scaffold Design
Scaffold
Modification
PU-specific
Modification
Monitoring
of PU

6. Scaffold Modification
Stem Cells
• Bone marrow mononuclear cells (BM-MNCs) [8]
• Adipose-derived stem cells (ADSC) [9] – better proliferative capability than BM-MNCs
Fibroblasts
• Quick senescence at PU site – prolongs healing process
• Senescence control is a good option
(1) microRNA controls [10] (2) signaling pathway control [11]
Anti-microbials
• Administered pre-implantation in situ or as a part of scaffold in vitro
• Apply cocktail of antiseptics – povidone iodine, silver sulfadiazine, hydrogen peroxide and Dakin’s
solution (sodium hypochlorite) [12] (dosage must be low and exhaustive to reduce healing time)
• Check for viability of fibroblasts in the cocktail of antiseptics in vitro.
Scaffold Design
Scaffold
Modification
PU-specific
Modification
Monitoring
of PU

7. PU-specific Modification
Protection of bFGF and inhibition of HNE
• Can use derivatized dextrans (DxD) containing carboxymethyl and its derivatives. [13]
• One DxD, RGT 11 displayed maximum efficacy. [13]
Perfusion Stimulation
• Electrical stimulation post implantation [14]
• Regulation of tissue perfusion around PU is affected by (a) hypotension (b) lack of serum albumin
(c) hyponatremia [15]
o Use human serum albumin (HSA) – maintains colloid osmotic blood pressure and degrades
to amino acids (nutrients to cells and tissues)
o Use antihypotensive agents to increase cardiac output but not vasoconstrict (e.g. Midodrine).
o Using sodium salts will control hyponatremia.
PEGylation of bFGF
• Evidence of faster wound healing in diabetic rat [16]
Scaffold Design
Scaffold
Modification
PU-specific
Modification
Monitoring
of PU

8. Monitoring of PU
Enhancing Transdermal Delivery
• Deferoxamine (DFO) can enhance neovascularization, angiogenesis and subcutaneous
penetration [17]
• Low-frequency sonophoresis (LFSO) for transdermal delivery of bFGF and hydrophilic drugs
[18]
Site Monitoring
• bFGF can be derivatized with Texas Red (TR) for fluorescence observation of serum sample [19]
• Perform abscess drainage and debridement to check ‘unstageable’ ulcers and suspected deep
tissue injury (SDTI)
Risks and Issues
• Cytotoxicity and senescence of fibroblasts due to antiseptic end-products
• Sonophoresis may rupture weak epidermis or dermis layers [20]
• Aluminium toxicity due to DFO in dialysis patients [21]
Scaffold Design
Scaffold
Modification
PU-based
Modification
Monitoring
of PU

9. Summary
Scaffold Design
Scaffold
Modification
PU-based
Modification
Monitoring
of PU
Fibroblasts with senescence control
via
MicroRNA
or
Modified signalling pathway
Stem Cells
(BM-MNCs or ADSCs)
HSA
bFGF (PEGylated)
and
Gelatin (GE) microspheres
having
Chitosan-GE scaffold
(sponge, film,
hydrogel or fiber)
Enhancing transdermal delivery
using
DFO
and/or
LFSO
Pressure
Ulcer
Epidermis
Dermis
Subcutaneous Fat
Muscle
Bone
Surface monitoring
via
Infection control
(antiseptic cocktail,
abscess drainage & debridement)
HNE
Recruitment
of pro-
coagulation
factors
DxD (RGT11)
bFGF
HSA
Artery
Vein
Capillaries
Artery
Osmotic Pressure
Maintenance

10. References
[1] https://npuap.org
[2] https://www.o-wm.com/article/pressure-ulcers-united-states-inpatient-population-2008-2012-results-retrospective
[3] Park, C. J., Clark, S. G., Lichtensteiger, C. A., Jamison, R. D., & Johnson, A. J. W. (2009). Accelerated wound closure of pressure ulcers
in aged mice by chitosan scaffolds with and without bFGF. Acta Biomaterialia, 5(6), 1926–1936.
[4] Lan G., Lu B., Wang T., Wang L., Chen J., Yu K., Liu J., Dai F., Wu D. Chitosan/gelatin composite sponge is an absorbable surgical
hemostatic agent. Colloid. Surface. B. 2015;136:1026–1034.
[5] Li H., Cheng F., Gao S., Wu Z., Dong L., Lin S., Luo Z., Li X. Preparation, characterization, antibacterial properties, and hemostatic
evaluation of ibuprofen-loaded chitosan/gelatin composite films. J. Appl. Polym. Sci. 2017;134:1–9.
[6] Fan L., Yang H., Yang J., Peng M., Hu J. Preparation and characterization of chitosan/gelatin/PVA hydrogel for wound
dressings. Carbohydr. Polym. 2016;146:427–434.
[7] Gu B.K., Park S.J., Kim M.S., Lee Y.J., Kim J.I., Kim C.H. Gelatin blending and sonication of chitosan nanofiber mats produce
synergistic effects on hemostatic functions. Int. J. Biol. Macromol. 2016;82:89–96.
[8] Sarasúa JG, López SP, Viejo MA, et al. Treatment of pressure ulcers with autologous bone marrow nuclear cells in patients with
spinal cord injury. J Spinal Cord Med. 2011;34(3):301–307.
[9] Holm, J. S., Toyserkani, N. M., & Sorensen, J. A. (2018). Adipose-derived stem cells for treatment of chronic ulcers: Current status.
Stem Cell Research and Therapy, 9(1), 142.
[10] Suh, N. (2018). MicroRNA controls of cellular senescence. BMB Reports, 51(10), 493–499.
[11] Wang, E., Lee, M. ‐J, & Pandey, S. (1994). Control of fibroblast senescence and activation of programmed cell death. Journal of
Cellular Biochemistry, 54(4), 432–439.
[12] Boyko, T. V., Longaker, M. T., & Yang, G. P. (2016). Review of the Current Management of Pressure Ulcers. Advances in Wound Care,
7(2), 57–67.

11. References
[13] Meddahi, A., Lemdjabar, H., Caruelle, J. P., Barritault, D., & Hornebeck, W. (1996). FGF protection and inhibition of human neutrophil
elastase by carboxymethyl benzylamide sulfonate dextran derivatives. International Journal of Biological Macromolecules, 18(1–2),
141–145.
[14] Thakral G, Lafontaine J, Najafi B, Talal TK, Kim P, Lavery LA. Electrical stimulation to accelerate wound healing. Diabet Foot Ankle.
Published 2013 Sep 16.
[15] Wywialowski, E. F. (1999). Tissue perfusion as a key underlying concept of pressure ulcer development and treatment. Journal of
Vascular Nursing, 17(1), 12–16.
[16] Huang Z, Lu M, Zhu G, Gao H, Xie L, Zhang X, Ye C, Wang Y, Sun C, Li X. Acceleration of diabetic-wound healing with PEGylated
rhaFGF in healing-impaired streptozocin diabetic rats. Wound Repair Regen. 2011;19(5):633–644.
[17] Bonham, C. A., Rodrigues, M., Galvez, M., Trotsyuk, A., Stern-Buchbinder, Z., Inayathullah, M.,Gurtner, G. C. (2018). Deferoxamine can
prevent pressure ulcers and accelerate healing in aged mice. Wound Repair and Regeneration, 26(3), 300–305.
[18] Zhou, Z., Fan, W., Lang, M., & Wang, Y. (2015). Transdermal bFGF delivery using low-frequency sonophoresis: An innovative
potential therapy for osteoradionecrosis of jaws. Journal of Medical Hypotheses and Ideas, 9(1), 9–12.
[19] Healy, A. M., & Herman, I. M. (1992). Preparation of fluorescent basic fibroblast growth factor: localization in living retinal
microvascular endothelial cells. Experimental Eye Research, 55(5), 663–669.
[20] Polat BE, Blankschtein D, Langer R. Low-frequency sonophoresis: application to the transdermal delivery of macromolecules and
hydrophilic drugs. Expert Opin Drug Deliv. 2010;7(12):1415–1432.
[21] McCarthy, J. T., Milliner, D. S., & Johnson, W. J. (1990). Clinical experience with desferrioxamine in dialysis patients with aluminium
toxicity. The Quarterly Journal of Medicine, 74(275), 257–276.

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