Exploring the Versatile Role of PEG and Carboxylic Acid PEGs in Biomedical Applications

Polymers play an important role in the biomedical field, and polyethylene glycol (PEG) and its derivatives are among the multifunctional polymers that have attracted much attention. PEG is a synthetic macromolecule with a linear structure consisting of glycol units (-CH₂CH₂O-) repeatedly linked. Its unique properties give PEG a wide range of applications.

PEG is soluble in organic solvents and water has excellent physicochemical and physiological properties, and is non-toxic, non-antigenic, and non-immunogenic. PEG is biocompatible and exhibits low protein and platelet adsorption in vivo as well as low cellular adherence, which are features that have led to a wide range of applications in biomedical fields.

Linking PEG to proteins, peptide analogs (e.g. Hamburger pentapeptide analog, Cys-gly-tyr-gly-pro-lys-lys-lys-arg-lys-val-gly-gly), and small molecules can alter the pharmacokinetic and physiological properties of these substances in vivo, thereby imparting some of the properties of PEG to these compounds. There are many ways to connect PEG with proteins and peptide compounds. Due to the presence of amino groups, a commonly used method is to introduce carbonyl groups into the PEG molecule, so that it can form sec-ammonia or acyl-ammonia with proteins or peptide compounds. The most commonly used at present are PEG carboxylic acids.

Carboxylic acid PEGs

Lysine, cysteine, histidine, arginine, aspartic acid, glutamic acid, serine, threonine, tyrosine, and ε-amino acids are most commonly conjugated to PEGs during the PEGylation of proteins. To conjugate with lysine residues, PEGs terminated with carboxylic acids are most commonly used. The synthesis process consists of the reaction of PEG with catalytic amounts of 2,2,6,6-tetramethyl-1-piperidinyloxy (TEMPO) and KBr as a regenerative oxidant in water.

Carboxylic acid functional groups endow PEGs with more chemical reactivity and functionalization possibilities. For example, through carboxylic acid functional groups, PEGs can covalently bind to drugs, targeting ligands, or other biologically active molecules, thus enabling drug-targeted delivery and controlled release. In addition, carboxylic acid PEGs can be involved in regulating interactions with cells, such as fusion with cell membranes and cellular uptake, providing effective carriers for cell therapy and gene delivery.

Applications of PEGs and Carboxylic Acid PEGs

• Drug Delivery

PEG and its carboxylic acid derivatives have important applications in drug delivery. PEG-modified nanoparticles can enhance drug bioavailability and targeting by increasing particle stability, improving drug solubility, and reducing recognition by the immune system. Carboxylic acid PEGs can achieve targeted delivery and controlled release of drugs by covalently binding them. In addition, carboxylic acid PEGs can be used as surface modifiers for drug carriers to increase drug circulation time and improve drug stability.

• Bioimaging

PEGs and carboxylic acid PEGs also have a wide range of applications in bioimaging. PEG-modified nanoparticles can be used as biomarkers for detecting and imaging biomolecules. Carboxylic acid PEGs can be combined with markers such as fluorescent dyes or radionuclides to achieve high-resolution imaging and fluorescent labeling in vivo. In addition, carboxylic acid PEGs can be used to construct imaging probes with specific biological activities, such as pH-responsive probes, temperature-sensitive probes, etc., for disease diagnosis and treatment monitoring.

• Biomaterials

PEGs and their carboxylic acid derivatives also play an important role in biomaterials. PEGs have excellent biocompatibility and tunable physical properties and thus are widely used in artificial joints, tissue engineering, biosensors, and other fields. Carboxylic acid PEGs can be used to construct biologically active material surfaces such as cell adhesion and proliferation for tissue engineering and regenerative medicine.