Table 1 Comprehensive outline of mechanisms, available human trials data as well as limitations of the here proposed studies

Regulatory T cells (T-regs)

Not applicable (N/A)

Pre-clinical evidence suggests that T-regs may act as a therapeutic for non-healing wounds by helping terminate the inflammatory phase. This would allow for the wound healing sequence to progress and tissue recovery and homeostasis to be achieved

Pre-clinical murine model

N/A

The functional application of T-reg-based therapies has only been explored in vitro and pre-clinical models. Extensive research is still required to determine their use in humans

[11,12,13]

Induced pluripotent stem cells (iPSCs)

N/A

The clinical application of iPSCs lies in their ability to transform into fibroblasts, keratinocytes, endothelial cells, dermal stem cells, and a variety of different cell types. iPSCs may be used to culture and then transplant depleted cell types within chronic wounds, or potentially be directly applied to wound beds and behave as a source of growth factors, depleted cell types, and as orchestrators of inflammation-resolving programs

Pre-clinical murine model

N/A

The major concern with the clinical application of iPSCs is their safety profile, especially regarding their tumorigenic/teratogenic potential

[14, 15]

iPSC-derived smooth muscle cells

N/A

One specific study evaluated human iPSC-derived smooth muscle cells. The group found that application accelerates diabetic wound healing to a greater extent than acellular and adipose-derived stem cell-containing scaffolds

Pre-clinical murine model

N/A

In the specific iPSC-derived smooth muscle cell study, the authors mention the streptozotocin model of diabetes approximating type 1 diabetes more than type 2 diabetes, which is the patient demographic that mostly suffers from chronic, non-healing wounds. Moreover, only male mice were used for the study

[14, 15]

Stem cell-based therapies

Grafix

Grafix is a cryopreserved amniotic membrane with a 3D-extracellular matrix (ECM) scaffold that contains growth factors, fibroblasts, endothelial cells, and mesenchymal stem cells (MSCs). The use of MSCs is unique to Grafix and although the authors acknowledge that the mechanism remains to be elucidated, they cite data that suggests MSCs may play an important role in all phases of wound healing and complete tissue recovery

Human trials

Food and Drug Administration (FDA)-approved with indications for chronic wounds

Clinical trials of Grafix have not been updated since 2016. Moreover, although one of the studies was a robust randomized controlled trial (RCT), the other was a retrospective study that lacked a proper control group. Finally, there may have been variability in data reporting amongst the participating clinics

[16]

Pharmaceutical macrophage therapy

Infliximab

Infliximab is a monoclonal, neutralizing antibody of tumor necrosis factor-α (TNF-α). Studies have shown that inhibition of TNF-α prevents M1 macrophage polarization and activity. This suppresses the inflammatory microenvironment and allows for normal wound healing progression to continue

Human trials

Infliximab is FDA-approved with indications for a variety of autoimmune diseases, including Crohn’s disease, ulcerative colitis, rheumatoid arthritis, psoriatic arthritis, and plaque psoriasis, among others. However, it is not FDA-approved nor indicated for the treatment of chronic wounds

The study referenced is from 2006. Moreover, the study design was not completely robust, as it was unblinded and contained a small sample size

[17]

GQ-11

GQ-11 is a partial/dual peroxisome proliferator-activated receptor α/γ (PPARα/γ) agonist. Activation of PPARα is postulated to promote anti-inflammatory phenotypes in activated M1 macrophages by repressing pro-inflammatory gene expression and inducing anti-inflammatory gene expression

Pre-clinical murine model

N/A

Although there was an overall benefit with GQ-11 treatment, effect sizes were statistically significant but modest. Moreover, treatment with GQ-11 did not show any effect in non-diabetic mice

[18]

Growth factor therapy

Beclapermin

Beclapermin is a topical formulation of recombinant human platelet-derived growth factor subunit B (PDGF-BB). It promotes the recruitment and proliferation of fibroblasts and immune cells to the wound bed, promoting granulation tissue formation

Human trials

FDA-approved with indications for diabetic, chronic wounds

The original clinical study is from 1999. No updated study was found. Moreover, its use has not been established in pressure or venous stasis ulcers

[19]

Combined cellular therapies

Dermagraft

Dermagraft is a sterile, cryopreserved, human fibroblast-derived dermal substitute. It is generated from cultured neonatal dermal fibroblasts onto a mesh scaffold. It does not contain any other cell type. It is thought to work by serving as a source of cytokines, growth factors, and living cells, which can then migrate into the wound bed and promote granulation tissue formation

Human trials

FDA-approved with indications for chronic wounds

The RCT was designed using Dermagraft in conjunction with, and not as a replacement for, the standard of care (SOC) of debridement, disinfection, and bandaging

[20]

Apligraf

Apligraf is a bi-layered bioengineered skin substitute constructed from neonatal fibroblasts and keratinocytes derived from human foreskin. Although its exact mechanism is unknown, it is thought to provide cytokines and growth factors to aid in wound healing

Human trials

FDA-approved with indications for chronic wounds

The RCT was designed using Apligraf in conjunction with, and not as a replacement for, the SOC of debridement, disinfection, and bandaging. Moreover, there may have been variability in data reporting amongst the participating clinics. However, 17/33 (51.5%) of Apligraf-treated patients did report full wound closure compared to 10/38 (26.3%) of control patients

[21]

TheraSkin

TheraSkin is an all-human, split-thickness, skin allograft that is procured from human skin donors. It is thought to work by serving as a source of endogenous growth factors and cells in addition to providing a native ECM. Moreover, TheraSkin can be vascularized by the recipient following transplantation to support the development of granulation tissue, which aids in epithelialization to support wound closure

Human trials

FDA-approved with indications for chronic wounds

The study was designed using TheraSkin in conjunction with, and not as a replacement for, the SOC of debridement, disinfection, and bandaging. There also may have been variability in data reporting amongst the participating clinics. Finally, it was a retrospective-matched cohort study which could have overlooked potential confounders

[22]

Platelet-rich fibrin (PRF)

Leukocyte-rich fibrin and PRF

PRF is a biodegradable fibrin scaffold embedded with large numbers of leukocytes and platelets. The entrapment of cells within a scaffold is thought to be superior to platelet-rich plasma due to prolonged and regulated release of growth factors that aid in wound healing

Human trials

Does not require FDA-approved as it is derived from a patient’s blood with only physical modifications. Use on chronic wounds is dependent on the provider’s discretion

The study referenced was self-controlled with limited strength. However, a systemic review shows that 18 of 31 clinical studies reported positive wound healing outcomes compared to control

[23, 24]

Platelet extracellular vesicles (PEVs)

N/A

PEVs are released from platelets once activated. They contain stores of growth factors, cytokines, and ECM modulators. Studies have demonstrated how PEVs are able to aid in wound recovery by stimulating proliferation and angiogenesis

Human trials

N/A

Unfortunately, this study only focused on safety and not specific outcomes. The PRF control had better wound healing outcomes than the PEV treatment group. However, the authors noted that further research into the most effective dose is warranted

[25]

Polyclonal antibodies

N/A

Polyclonal antibodies are used, for example, to target the N-terminal of Pseudomonas aeruginosa (P. aeruginosa) type b flagellin in infected burn wounds and also to inactivate pathogenic toxins

Pre-clinical murine model

N/A

The study was only pre-clinical and had a small sample size. It should be noted that there was no difference in mortality and wound healing time between anti-P. aeruginosa antibody treatment and imipenem antibiotic treatment

[26]

Monoclonal antibodies

N/A

Topical programmed death-ligand 1 (PD-L1) is a checkpoint inhibitor that can, applied as a gel, support re-epithelialization and attenuating prolonged inflammation

Pre-clinical murine model

N/A

The study was only pre-clinical and had a small sample size

[27]

Wnt inhibitor

Pyrvinium

Pyrvinium, at least in pre-clinical studies, may enhance MSC proliferation, engraftment, and stemness in an in-vitro and in-vivo wound healing model. Pyrvinium was separately found to increase vascularity, cellular proliferation, and general organization of granulation tissue in a polyvinyl alcohol (PVA) sponge model. These results suggest it may be used as an ancillary therapy to stem cell-based therapies

Pre-clinical murine model

Pyrvinium pamoate is FDA-approved with indications as an anthelmintic. A single ongoing phase I trial is being conducted to evaluate its utility in pancreatic cancer (PMID: 34,413,127). It is not currently indicated for the treatment of chronic wounds

Only in vitro and pre-clinical data is available which demonstrates statistically significant but relatively small effect sizes. Moreover, our search found only one group that has researched its potential therapeutic use in wound healing

[28, 29]

Hypoxia inducible factor-1α (HIF-1α)

Deferoxamine (DFO)

DFO is an iron chelator. HIF-1-prolyl hydroxylase (PHD), an enzyme responsible for HIF-1 degradation, requires iron as a cofactor. Chelation of iron then indirectly inhibits HIF-1-PHD, increasing the abundance of HIF-1 which leads to increased vascular endothelial growth factor (VEGF) expression

Pre-clinical murine model

DFO is FDA-approved with indications for iron overload and is not currently indicated for the treatment of chronic wounds

The study was only pre-clinical and had a small sample size. Moreover, effect sizes were statistically significant but relatively small

[30, 31]

Cyclometalated iridium (III) metal complex 1a

Cyclometalated iridium (III) metal complex 1a functions as a stabilizer of HIF-1α. It does so by disrupting the von Hippel-Lindau-HIF-1α protein interaction, allowing for the accumulation of HIF-1 in cellulose. Wild-type and diabetic mice with excisional wounds treated with cyclometalated iridium (III) metal complex 1a showed an accelerated rate of wound healing accompanied by increased skin thickness, collagen deposition, and, evidence of neovascularization

Pre-clinical murine model

N/A

We only found the recent study by Li et al. [32] that used cyclometalated iridium (III) metal complex 1a to accelerate diabetic wound healing. Moreover, the authors report that their murine models all have limitations and cannot fully replicate the human diabetic pathological state

[32]

Antibiofilm therapies

Antibody-mitomycin C conjugate

Antibody-antibiotic conjugates have become important objects of research due to their specificity and increased bacterial killing compared to standalone antibiotic treatment. Mitomycin C is an antibiotic used as an anti-neoplastic agent. In vitro, however, mitomycin C is also a potent anti-bacterial and biofilm eradicator

Pre-clinical murine model

Mitomycin C is FDA-approved with indications for gastric and pancreatic adenocarcinoma as well as urothelial cancer. It is not currently indicated for use as an anti-biofilm antibacterial

The study did not find a significant difference in bactericidal effect between antibody-conjugated mitomycin C and mitomycin C alone. However, two counter points were proposed by the authors. First, toxicity was lower in conjugate treatment. Second, the maximum effective dose of the antibody-antibiotic conjugate was not explored, suggesting a higher dose may be more effective

[33]

Rifampicin-containing nanoparticles

Polymeric nanoparticles loaded with rifampicin and covalently bound to a Staphylococcus aureus (S. aureus)-specific antibody was demonstrated to accumulate in S. aureus biofilms and have significantly increased bactericidal effects against both planktonic and biofilm bacteria compared to free-form rifampicin

Pre-clinical murine model

N/A

The study only used 3 mice per treatment group (n = 12 total), although the effect sizes of the antibody-conjugate treatments were considerably large

[34]