The document proposes a tissue engineering approach to treat pressure ulcers using a chitosan-gelatin scaffold embedded with growth factors, stem cells, and antimicrobials. The scaffold would be modified for pressure ulcer-specific needs like inhibiting human neutrophil elastase and stimulating perfusion. Pressure ulcers would be monitored by enhancing transdermal delivery of drugs and fluorescence imaging of growth factors. This multi-pronged regenerative approach aims to address the complex etiology of pressure ulcers and high treatment costs.

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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