Introduction

Biomimetic peptides used as skincare ingredients are typically synthetic peptides designed on the basis of natural human proteins, extracellular matrix fragments, receptor ligands, or protein–protein interaction regions. Through specific amino acid sequences and spatial conformations, they mimic the molecular recognition information of natural molecules and may thereby influence receptor signaling, enzyme activity, metal-ion coordination, or protein–protein interactions.

Activity observed for a peptide in a cell culture experiment only indicates that it may affect a particular biological process at the tested concentration and under the specified experimental conditions. Its efficacy in topical skincare also depends on whether the peptide can be released from the formulation, reach the skin layer containing its target, resist degradation, and contact the relevant cells in an intact and biologically active form.

The action process of biomimetic peptides can be summarized as follows:

Sequence and conformation establish recognition information → the intact peptide is released from the formulation → the peptide enters the target skin layer → the peptide resists chemical and enzymatic degradation → the peptide contacts the relevant cells and molecular targets → cellular signaling or enzyme activity changes → measurable skin outcomes are produced.

Sequence design determines what a peptide may recognize, skin delivery determines where it can reach, molecular stability determines how long it can persist, and target matching determines whether it can produce the intended effect after reaching the relevant site.[1]

The topical activity of biomimetic peptides is not determined solely by sequence-related activity, but also depends on formulation release, skin delivery, molecular stability, and target accessibility, as illustrated by the key steps shown below. The sequence and conformation of a peptide provide candidate recognition information, while formulation release, stratum corneum delivery, and molecular stability collectively affect the exposure of the intact peptide within the target skin layer. Delivery depth, intact-peptide exposure, and the degree of correspondence with the location of the target jointly influence the likelihood that the peptide will contact its target and elicit the corresponding cellular response. The figure presents a conceptual pathway and does not imply that all peptides can reach the viable epidermis or dermis; the listed skin effects must still be evaluated separately according to the specific peptide, formulation, and supporting evidence from human studies.

Keywords: biomimetic peptides; sequence mimicry; signaling peptides; stratum corneum delivery; lipidation; proteolytic stability; cell-penetrating peptides; liposomes; cellular target matching; extracellular matrix regulation

1 What Are Biomimetic Peptides?

1.1 Biomimetic Peptides Primarily Consist of Short Amino Acid Sequences

Peptides are formed by amino acids linked through peptide bonds. Biomimetic peptides used in skincare products are generally oligopeptides containing only several to slightly more than ten amino acid residues.

A short-chain structure facilitates control over sequence, purity, and chemical modification, but chain length alone does not determine biological activity. An ordinary dipeptide or tripeptide without a clearly defined molecule to mimic or a defined recognition target cannot be classified as a biomimetic peptide merely because of its small molecular size.

Biomimetic peptides used as skincare ingredients generally have the following characteristics:

① A clearly defined amino acid sequence;

② Measurable molecular weight and purity;

③ A relatively clear design origin or molecule being mimicked;

④ Candidate receptors, enzymes, metal ions, or protein-binding partners;

⑤ Properties that can be adjusted through lipidation, terminal protection, cyclization, or amino acid substitution.

The defining feature of a biomimetic peptide is its use of a limited amino acid sequence to reproduce a local structural element involved in the biological recognition of a natural molecule.[1]

1.2 How Amino Acid Sequences Encode Biological Information

Amino acid side chains differ in charge, polarity, hydrophobicity, volume, and chemical reactivity. In aqueous environments, at membrane interfaces, or within protein-binding pockets, a peptide chain adopts certain conformations that orient these side chains in specific spatial arrangements.

Receptors, enzymes, and other proteins primarily recognize the following structural features:

① The spatial distribution of positive and negative charges;

② Contact regions formed by hydrophobic side chains;

③ The positions of hydrogen-bond donors and acceptors;

④ Aromatic rings, sulfur atoms, or metal-coordinating groups;

⑤ Turns, helices, or extended conformations formed by the peptide chain.

The sequence determines which side chains are present in the peptide, whereas the conformation determines their relative spatial positions. Amino acid substitution, lipidation, or cyclization may alter the conformation and consequently affect target binding.

1.3 Differences Between Biomimetic Peptides and Protein Hydrolysates

Ingredients such as hydrolyzed collagen and hydrolyzed elastin are obtained from natural proteins through enzymatic or chemical hydrolysis and generally consist of mixtures of peptides with different chain lengths and sequences. Their effects may involve film formation on the skin surface, moisture absorption, and improvement of skin feel, and they may also contain biologically active fragments.

Biomimetic peptides are generally single peptides or a small number of defined peptides with fixed sequences and clearly specified modifications. Their structures, contents, and candidate targets are comparatively easier to quantify.

The principal differences between the two lie in whether their structural composition is clearly defined and whether a relationship can be established between a specific sequence and a specific effect.

1.4 Differences Between Biomimetic Peptides and Signaling Peptides

Biomimetic peptides primarily emphasize the mimicry of natural sequences, conformations, or functional motifs, whereas signaling peptides used in skincare are mainly named according to their proposed modes of action. Some signaling peptides may be classified as biomimetic peptides, but the two terms are not strictly synonymous.

In molecular biology, the term “signal peptide” generally refers to an N-terminal sequence in a nascent protein that directs the protein into the endoplasmic reticulum or secretory pathway. This differs from the meaning of signaling bioactive peptides used in skincare products.

2 Why the Stratum Corneum Restricts the Delivery of Biomimetic Peptides

2.1 Barrier Structure of the Stratum Corneum

The stratum corneum consists of keratin-rich corneocytes and intercellular lipids. The intercellular lipids are composed primarily of ceramides, cholesterol, and free fatty acids and form ordered lamellar structures. These structures limit water loss from within the skin while also restricting the entry of exogenous molecules.[2]

Most peptides contain multiple peptide bonds and polar side chains and form stable hydration shells in water. Residues such as lysine, arginine, aspartic acid, and glutamic acid also affect the net charge of the peptide. Highly polar, charged, and extensively hydrated molecules have difficulty entering the lipid regions of the stratum corneum.

Peptide entry into the stratum corneum is mainly limited by two types of resistance:

① Partitioning resistance: peptides have limited ability to partition from the aqueous phase of a formulation into stratum corneum lipids;

② Diffusion resistance: after entering the stratum corneum, the hydrated volume, number of hydrogen-bonding groups, and conformational flexibility of the peptide reduce its diffusion rate.

Molecular weight is only one factor affecting skin delivery. Charge, lipophilicity, polar surface area, conformation, aggregation state, and release from the formulation collectively determine peptide distribution within the skin. Most anti-wrinkle peptides are hydrophilic and contain ionizable groups, and their skin penetration is therefore generally limited.[3]

2.2 Main Routes by Which Peptides Enter the Skin

Biomimetic peptides may enter the skin through three principal routes.

① Intercellular Route

Peptides diffuse through the lipid regions between corneocytes. This route requires the peptide to partition from the formulation into the intercellular lipids and retain sufficient diffusivity within the lipid layers.

② Transcellular Route

Peptides pass through keratin-rich corneocyte regions and repeatedly partition between hydrophilic regions and intercellular lipid regions. Hydrophilic peptides may use part of this route but remain restricted by the cornified envelope, the keratin network, and adjacent intercellular lipid regions.

③ Skin Appendage Route

The pilosebaceous unit and openings of sweat ducts may provide local deposition sites or shunt pathways. Hair follicles occupy only a small proportion of the skin surface but may accommodate certain hydrophilic molecules, charged molecules, and particulate carriers. Follicular deposition primarily reflects local retention and does not mean that the peptide has entered the dermis uniformly.

2.3 Delivery Depth Must Correspond to the Site of Action

The appropriate delivery endpoint for a topical peptide is determined by the location of its target.

A peptide intended to act directly on keratinocytes must reach the viable epidermis. If a peptide is claimed to act directly on dermal fibroblasts, an intact and biologically active form of the peptide must be detected in the dermis. The cumulative amount detected in receptor fluid mainly reflects full-thickness permeation and does not indicate the effectiveness of local delivery within the skin.

3 How Formulations and Carriers Can Improve Peptide Delivery into the Skin

3.1 Lipidation

Attaching a fatty chain, such as a palmitoyl group, to the terminus of a peptide chain can increase the peptide’s affinity for stratum corneum lipids, cell membranes, and phospholipid-based carriers.

Palmitoyl pentapeptide-4, or Pal-KTTKS, consists of a palmitoyl group linked to the lysine–threonine–threonine–lysine–serine sequence, abbreviated KTTKS. KTTKS is derived from a type I procollagen-related fragment. Human topical studies have been conducted with Pal-KTTKS, and improvements in certain visible parameters of photoaged skin were observed.[4]

Increasing the lipid-chain content enhances hydrophobicity but may also promote the formation of micelles, fibers, or other aggregated structures. C16-KTTKS can form ordered nanostructures, and its salt form and assembly state may also affect the associated biological activity.[5]

Lipidation design must balance solubility, aggregation state, skin partitioning, and release rate. Excessive aggregation or excessively strong binding to the carrier may reduce the concentration of free peptide.

3.2 Chemical Penetration Enhancement

Ethanol, polyols, fatty acids, certain surfactants, and terpenes can alter the stratum corneum environment and increase the opportunity for active substances to enter the skin.

Molecular simulation studies have shown that terpene compounds such as terpineol, 1,8-cineole, and limonene can alter the organization of model stratum corneum lipids in a concentration-dependent manner and disrupt cholesterol-associated regions.[6]

Chemical penetration enhancement may also increase lipid extraction, irritation, and transepidermal water loss. Formulation evaluation should therefore include measurements of peptide distribution within the skin, skin irritation, and barrier recovery.

3.3 Cell-Penetrating Peptides and Skin-Penetrating Peptides

Cell-penetrating peptides (CPPs) usually contain relatively high numbers of arginine or lysine residues. They can interact with anionic components on the cell-membrane surface and promote cellular uptake through endocytosis or direct membrane translocation.

The stratum corneum and the membranes of living cells have different structures. Conventional cell-penetrating peptides primarily improve uptake by living cells, and their effects on intact stratum corneum must be evaluated separately.

The skin-penetrating and cell-entering peptide, known as the SPACE peptide, is a skin-delivery peptide identified through phage-display screening. Relevant studies have shown that the SPACE peptide can increase the accumulation of cyclosporine A in the viable epidermis of porcine skin.[7]

For a peptide to act on an intracellular target, it must sequentially complete the following steps:

Entry through the stratum corneum → uptake by living cells → endosomal escape → arrival in the cytosol or a specific organelle.

Peptides or peptide–cargo complexes taken up through endocytosis may remain trapped in endosomes and lysosomes. Increased cellular uptake does not directly indicate a corresponding increase in the concentration of active peptide in the cytosol.

3.4 Liposomes and Deformable Vesicles

Liposomes consist of phospholipid bilayers. Hydrophilic peptides can be encapsulated in the internal aqueous phase, whereas lipidated peptides may associate with or become embedded in the phospholipid membrane.

The principal behaviors of conventional liposomes on intact skin include surface adsorption, vesicle rupture, lipid exchange, release of encapsulated contents, and follicular deposition. Liposome particle size, membrane flexibility, phospholipid composition, surface charge, and the location of the encapsulated substance all influence delivery outcomes.[8]

Deformable vesicles, such as transfersomes, contain membrane-softening components and exhibit a relatively high capacity for deformation. They may increase the deposition and diffusion depth of certain active substances within the skin. Whether a carrier reaches deeper skin layers and whether the intact peptide reaches the same location are two distinct analytical questions and must be verified separately.

3.5 Total Formulation Content and Effective Exposure

The labeled amount of peptide added to a product does not directly represent its concentration near the target. Actual activity involves the following sequential processes:

Total peptide content in the formulation → amount of peptide released from the formulation → amount of intact peptide entering the target skin layer → amount of peptide retaining target-binding activity.

A high encapsulation efficiency indicates that a relatively large amount of peptide has entered the carrier, but it does not mean that the peptide will be adequately released at the target site. A high total peptide content in the skin may also include degradation products, aggregates, or fractions irreversibly bound to the stratum corneum.

Key parameters for evaluating a delivery system include the proportion of intact peptide, release rate, distribution across different skin layers, and bioavailable concentration near the target.

4 How Biomimetic Peptides Resist Proteolytic Degradation

4.1 Enzymatic Degradation of Peptide Chains

Aminopeptidases and carboxypeptidases can sequentially remove amino acids from the N-terminus or C-terminus of a peptide chain, whereas endopeptidases recognize specific internal residues and conformations and cleave peptide bonds within the chain.

Critical recognition sequences in short peptides are often highly concentrated. A single enzymatic cleavage may alter the charge, conformation, or arrangement of key side chains, causing the peptide to lose its original target affinity.

Stabilization strategies must extend the persistence of the intact peptide while preserving the structural features required for target binding.

4.2 D-Amino Acid Substitution

Natural human proteins are composed primarily of L-amino acids, and the binding sites of most proteases are also adapted to the stereochemical structure of L-peptide chains.

Replacing a residue at or near a proteolytic cleavage site with a D-amino acid can alter the local direction of the peptide backbone and the spatial arrangement of side chains, thereby reducing protease recognition and cleavage efficiency.

D-amino acid substitution may also alter receptor binding, membrane interactions, and peptide conformation. During design, major cleavage sites are generally identified first, followed by localized substitution and reassessment of target affinity and cellular activity. The combined use of D-amino acid substitution and peptide cyclization has been shown to improve proteolytic stability in multiple classes of experimental peptides.[9]

4.3 Peptide Cyclization

Head-to-tail cyclization, side-chain lactam bridges, disulfide bonds, and other covalent bridges can restrict the conformational freedom of a peptide chain.

Cyclization primarily improves stability through the following mechanisms:

① Masking or eliminating free termini;

② Reducing the likelihood that the peptide chain will adopt a protease-binding conformation;

③ Decreasing the spatial accessibility of cleavage sites;

④ Fixing the peptide in a conformation close to its target-bound state.

Inappropriate selection of bridging positions may obscure critical side chains or lock the peptide into a conformation with lower target affinity. Proteolytic stability, skin partitioning, and target binding after cyclization must therefore be measured separately.

4.4 Terminal Protection

N-terminal acetylation, N-terminal fatty acylation, and C-terminal amidation can reduce the recognition of peptide termini by certain exopeptidases.

Terminal protection may also alter:

① The net charge of the peptide;

② Hydrogen-bonding properties;

③ Aqueous solubility;

④ Membrane affinity;

⑤ The mode of target binding.

A free N-terminus or C-terminus may sometimes participate in receptor or enzyme binding. The biological activity of such peptides must therefore be reassessed after terminal modification.

4.5 Carrier-Mediated Protection

Carrier encapsulation can reduce direct contact between a peptide and proteases in the formulation or on the skin surface. After release, however, the peptide remains exposed to the enzymatic environment of the skin; carrier-mediated protection therefore mainly serves to delay degradation.

If carrier release is too rapid, the duration of protection is shortened. If release is too slow, the concentration of free peptide in the target region is reduced. Molecular stabilization and carrier release must therefore be designed in coordination.

5 How Biomimetic Peptides Match Target Cells

5.1 Target Expression Determines the Range of Cellular Responses

Keratinocytes, fibroblasts, melanocytes, sebaceous gland cells, and immune cells in the skin differ in their expression patterns of receptors, enzymes, and cell-surface molecules.

Binding of a peptide to a particular receptor indicates a certain degree of target affinity. If the same receptor is distributed across multiple cell types, the peptide may also act on more than one type of cell.

Cellular matching involves three levels:

① Molecular matching: the peptide can bind to a specific receptor, enzyme, or protein;

② Cellular matching: the target cell expresses a sufficient number of accessible targets;

③ Tissue-level matching: the peptide forms effective exposure within the skin layer containing the target cell.

High affinity cannot compensate for insufficient delivery depth. Detection of a peptide within the skin also does not directly demonstrate that it has contacted the target receptor.

5.2 Cell-Surface Targets and Intracellular Targets

Cell-surface receptors are located on the extracellular side of the plasma membrane. Once a peptide reaches the surface of the target cell, it can bind to the receptor and initiate intracellular signal transduction.

Intracellular targets are located in the cytoplasm, nucleus, or other organelles. The peptide must first be taken up by the cell, escape from the endosome, and enter the relevant subcellular compartment.

Acetyl hexapeptide-8, Ac-EEMQRR-NH₂, is frequently discussed in relation to skincare mechanisms involving neurotransmitter release. Its proposed activity is associated with interactions involving proteins related to the soluble N-ethylmaleimide-sensitive factor attachment protein receptor (SNARE) complex and therefore requires intracellular accessibility.

An in vitro human skin penetration study showed that most of the applied acetyl hexapeptide-8 was washed off the skin surface. The fraction that entered the skin was located primarily in the stratum corneum, and intact peptide was not detected in the receptor fluid.[10]

5.3 Screening of Cell-Targeting Sequences

Cell-targeting peptides may be identified from natural ligand sequences, structural calculations, or peptide-library screening. Phage display enables large numbers of peptide sequences to be displayed on the surfaces of bacteriophages and subsequently screened for binding to target cells.

Whole-cell screening preserves membrane proteins within their native membrane environment. Counter-screening with non-target cells can reduce the selection of sequences that adhere broadly and nonspecifically to cell membranes.[11]

Candidate peptides obtained through screening must also be evaluated for the following:

① The specific receptor to which they bind;

② Binding affinity;

③ Whether cellular internalization occurs;

④ The location of target expression in human skin;

⑤ The extent of binding to non-target cells.

6 How Biomimetic Peptides Produce Skincare Effects

6.1 Mimicking Extracellular Matrix Signals

The extracellular matrix (ECM) is composed of collagen, elastin, fibronectin, proteoglycans, and other components. It not only provides structural support for tissues but also regulates cellular behavior through cell-surface receptors and mechanical signaling.

During the processing or degradation of collagen and other matrix proteins, short peptide fragments with regulatory activity may be generated. These matrix-derived bioactive peptides may influence extracellular matrix synthesis and remodeling by fibroblasts.

Signaling biomimetic peptides regulate cells through similar recognition mechanisms. They act by modulating biological information rather than by being directly incorporated into the dermis as structural materials.

The tetrapeptide GEKG, consisting of glycine–glutamic acid–lysine–glycine, was developed through molecular design. Relevant studies have observed that GEKG regulates processes associated with collagen, fibronectin, and hyaluronic acid in human dermal fibroblasts, and a double-blind human evaluation has also been conducted.[12]

Increased collagen expression represents only one component of matrix renewal. Procollagen must also undergo hydroxylation, triple-helix formation, secretion, propeptide cleavage, fibril assembly, and cross-linking. Matrix metalloproteinase-mediated degradation, cellular mechanical tension, and glycation-related damage also influence the final condition of the tissue.

6.2 Coordinating and Regulating Metal Ions

Glycyl-L-histidyl-L-lysine (GHK) can form the coordination complex GHK-Cu with divalent copper ions.

Copper participates in multiple enzymatic and tissue-repair processes. GHK may alter the coordination state and local bioavailability of copper ions and influence copper exchange among extracellular proteins, cell membranes, and other ligands. Cellular, animal, and tissue studies have reported associations between GHK or GHK-Cu and fibroblast function, collagen-related processes, and wound repair.[13]

Wounds or invasive administration methods alter or bypass the stratum corneum. Such studies can support the biological activity of GHK-Cu, but conventional topical formulations still require separate verification of delivery depth in intact skin.

6.3 Regulating Protein–Protein Interactions

Some biomimetic peptides are designed from local binding sequences within larger proteins and influence protein-complex formation through competitive mechanisms.

This type of action requires the peptide to maintain the correct conformation and reach a sufficient concentration in the region containing the target protein. Peptides targeting intracellular protein–protein interactions must also undergo cellular uptake and endosomal escape.

Cell-free protein-binding assays can demonstrate interactions between a peptide and its target protein, but they cannot independently establish that the same effect will occur after topical application. Evidence of skin distribution and intracellular localization is also required to support a topical mechanism.

6.4 Regulating Enzyme Activity

Peptides can mimic enzyme substrates or binding sequences and regulate enzyme activity through competitive binding, noncompetitive binding, or allosteric mechanisms.

Peptides designed around pigmentation, matrix degradation, inflammatory mediator formation, or oxidative processes may act through such mechanisms.

Direct enzyme regulation must be distinguished from indirect regulation of enzyme expression:

① Reproducible kinetic changes in a purified enzyme system can support a direct effect of the peptide on the enzyme;

② Changes in enzyme expression in cells may result from upstream signaling regulation;

③ If the target enzyme is intracellular, it must also be confirmed that the peptide can reach the corresponding cellular compartment.

6.5 Regulating Inflammation- and Barrier-Related Signaling

Some peptides may regulate inflammatory mediator release, oxidative stress, and repair responses through cell-surface receptors, membrane interactions, or intracellular signaling.

Changes in cytokine levels may result from direct receptor regulation, but they may also arise from reduced cellular injury, antioxidant activity, or changes in membrane status. Mechanistic studies generally combine receptor blockade, signaling-protein phosphorylation, transcriptional changes, cell viability, and skin-barrier indicators to determine the underlying mechanism.

The evaluation of biomimetic peptides can focus on five key questions.

In vitro skin permeation testing can be conducted using Franz diffusion cells, with the skin-surface wash, stratum corneum, epidermis, dermis, and receptor fluid analyzed separately. Following targeted method development and validation, liquid chromatography–tandem mass spectrometry (LC–MS/MS) can be used to distinguish and quantify intact peptides and specific degradation products.

Fluorescent labeling is suitable for visualizing spatial distribution, but the fluorophore may alter the molecular weight, charge, and lipophilicity of the peptide. Free fluorescence or detachment of the label may also introduce bias. Fluorescence imaging is therefore generally used together with structure-specific quantitative methods.[14]

Human studies should use a formulation consistent with the final product and include a vehicle control with the same composition but without the target peptide. When a formulation also contains humectants, retinol, niacinamide, or other active ingredients, its overall efficacy cannot be attributed independently to a single peptide.

8 Classification and Scientific Applications of Representative Chemicals Related to Biomimetic Peptide Sequence Design, Stabilization, Skin Delivery, and Cellular Target Research

Table 1 Core Biomimetic Peptide Ingredients and Functional Sequences

Table 2 Products Related to Peptide Stabilization, Cyclization, and Terminal Modification

Table 3 Products Related to Stratum Corneum Penetration Enhancement and the Construction of Liposomes, Niosomes, and Deformable Vesicles

Table 4 Products Related to Proteolytic Stability, Peptide Degradation, and Analytical Detection

Note: The products listed above are representative Aladdin products related to scientific research and formulation studies. The trypsin, Lys-C, and α-chymotrypsin products in Table 4 are primarily used for standardized enzymatic digestion, degradation mapping, and mass-spectrometric analysis and do not represent the complete composition of proteases present in human skin in situ. Additional product specifications, grades, and certificate of analysis information can be retrieved from the Aladdin website using the product name, CAS number, or catalog number.

References

[1] Pintea A, et al. Peptides: Emerging Candidates for the Prevention and Treatment of Skin Senescence: A Review. Biomolecules. 2025;15(1):88. doi:10.3390/biom15010088.

[2] Školová B, et al. The Role of Ceramides in Skin Barrier Function and the Importance of Their Correct Formulation for Skincare Applications. International Journal of Cosmetic Science. 2024.

[3] Aghaei H, et al. Skin Permeability, a Dismissed Necessity for Anti-Wrinkle Peptide Performance. International Journal of Cosmetic Science. 2022.

[4] Robinson LR, et al. Topical Palmitoyl Pentapeptide Provides Improvement in Photoaged Human Facial Skin. International Journal of Cosmetic Science. 2005;27(3):155–160.

[5] Hamley IW, et al. Nanostructure and Collagen-Stimulating Activity of Cationic Pentapeptide Lipopeptides. Journal of Peptide Science. 2026:e70111. doi:10.1002/psc.70111.

[6] Yu X, Liu S, Li Y, Yuan S. Molecular Insights into the Penetration Enhancement Mechanism of Terpenes to Skin. The Journal of Physical Chemistry B. 2024;128(50):12507–12516. doi:10.1021/acs.jpcb.4c05910.

[7] Kumar S, et al. Topical Delivery of Cyclosporine A into the Skin Using SPACE-Peptide. Journal of Controlled Release. 2015;199:190–197.

[8] Bouwstra JA, Honeywell-Nguyen PL. Liposomes and Niosomes as Topical Drug Delivery Systems. Dermatologic Therapy. 2005;18(1):23–30.

[9] Overcoming Proteolytic Instability in a β-Turn Antimicrobial Peptide via Cyclization and Stereochemical Inversion to Combat MDR Bacteria. Journal of Medicinal Chemistry. 2026. doi:10.1021/acs.jmedchem.5c03372.

[10] Kraeling MEK, Zhou W, Wang P, Ogunsola OA. In Vitro Skin Penetration of Acetyl Hexapeptide-8 from a Cosmetic Formulation. Cutaneous and Ocular Toxicology. 2015;34(1):46–52.

[11] Hsu T, Mitragotri S. Delivery of siRNA and Other Macromolecules into Skin and Cells Using a Peptide Enhancer. Proceedings of the National Academy of Sciences of the United States of America. 2011;108(38):15816–15821. doi:10.1073/pnas.1016152108.

[12] Farwick M, et al. Bioactive Tetrapeptide GEKG Boosts Extracellular Matrix Formation: In Vitro, In Vivo and Clinical Evidence. Experimental Dermatology. 2011;20(7):602–604.

[13] Pickart L, Margolina A. Regenerative and Protective Actions of the GHK-Cu Peptide in the Light of the New Gene Data. International Journal of Molecular Sciences. 2018;19(7):1987. doi:10.3390/ijms19071987.

[14] Lane ME. In Vitro Permeation Testing for the Evaluation of Drug Delivery to the Skin. European Journal of Pharmaceutical Sciences. 2024:106873. doi:10.1016/j.ejps.2024.106873.

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