RESOMER® RG 752 H is a poly(D,L-lactide-co-glycolide) 75:25 acid-terminated bioresorbable polymer supplied under the RESOMER drug delivery grade portfolio. The designation encodes a nominal D,L-lactide:glycolide molar ratio of 75:25 and a nominal inherent viscosity of approximately 0.2 dL/g; the H suffix identifies free carboxylic acid end groups rather than an ester-terminated equivalent. The material is a white to off-white powder intended for parenteral drug delivery processes, including solvent-based microparticle formation, in situ forming depots, extruded implants, and nanoparticle precipitation. Each batch is released against product-specific specifications covering residual monomer content, residual solvent content, molar mass distribution, and water content.

Specification Envelope and Analytical Certification for Acid-Terminated PLGA

The primary release property is inherent viscosity measured according to ISO 1628-1:2021 using a 0.1% w/v solution in chloroform at 25°C. The typical specification window for RESOMER RG 752 H is 0.16–0.24 dL/g. Glass transition temperature is determined by differential scanning calorimetry at a controlled heating rate of 10 K/min under nitrogen; the observed glass transition for a 75:25 PLGA of this molar mass typically falls between 42°C and 50°C, but the batch certificate of analysis should be consulted for the exact acceptance interval. Molecular weight is reported by gel permeation chromatography against polystyrene calibrators; results are method-dependent and are not directly comparable to absolute values from multi-angle light scattering.

Residual organic solvents are controlled by headspace gas chromatography against product-specific acceptance limits derived from ICH Q3C concepts. The drug delivery grade is not a finished drug product; suitability as an excipient in a parenteral formulation is assessed under 21 CFR 211.84 and 21 CFR 211.94. When the polymer is incorporated into a finished device, biocompatibility testing is typically performed on the final device according to ISO 10993-5 for in vitro cytotoxicity and ISO 10993-1 for device categorization. The manufacturer supplies batch documentation with certificate of analysis, and change control is maintained under a pharmaceutical quality system aligned with ICH Q7.

What Processing Conditions Apply to Low-Viscosity Acid-Terminated PLGA?

Solvent-based microencapsulation of RESOMER RG 752 H is typically performed in a jacketed reactor equipped with an overhead rotor-stator disperser. The polymer is dissolved in dichloromethane or ethyl acetate at concentrations between 5% and 30% w/w, depending on target particle porosity and drug loading. The low solution viscosity of the acid-terminated 0.2 dL/g grade reduces the shear stress required for droplet break-up in oil-in-water emulsification. Rotor tip speeds in the range of 3 m/s to 8 m/s are used in development equipment, but median particle size is also governed by continuous-phase surfactant concentration, dispersed-phase volume fraction, and solvent removal rate. Batch-to-batch inherent viscosity shifts of ±0.03 dL/g can alter the dispersed-phase Reynolds number and displace the median particle size by several micrometres when disperser speed and polyvinyl alcohol concentration are held constant. An in-process viscosity check after dissolution and before emulsification is therefore required for reproducible scale-up.

Droplet stability during solvent removal is influenced by Ostwald ripening and coalescence. In aqueous continuous phases containing 0.5–2.0% w/v polyvinyl alcohol, the acid-terminated PLGA produces a lower interfacial tension than the corresponding ester-terminated grade because the carboxylic acid chain ends increase hydrophilicity at the droplet interface. This modifies drug encapsulation efficiency, especially for cationic peptide drugs that can ion-pair with the polymer chain ends. Solvent removal is commonly controlled by ramping the jacket temperature from 25°C to 40°C over 2–4 h, but the ramp must be tuned to the selected solvent and particle size target. Rapid solvent extraction can freeze porosity into the particle surface and increase initial burst release.

Hot-melt extrusion of RG 752 H is possible but presents a narrow thermal processing window because the low molar mass material has low melt viscosity and undergoes thermal degradation at elevated temperature. For a corotating twin-screw extruder with L/D 25:1, barrel set points between 140°C and 170°C are typically evaluated. A set-point deviation of ±5°C can shift melt viscosity sufficiently to alter fill pressure and residence time distribution. Pre-drying under vacuum at 25–35°C for a minimum of 12 h is recommended when the powder has been exposed to relative humidity above 60%. Water uptake before processing increases hydrolytic chain scission during extrusion and can produce a measurable loss in molecular weight even before the implant is sterilized.

The acid-terminated polymer should not be combined with amine-based additives at elevated temperature. Free carboxylic acid end groups can react with primary amines to form amides or salts, causing localized viscosity shifts and possible drug degradation. Steam sterilization is not applied to bulk PLGA because moisture and heat accelerate hydrolysis. Gamma irradiation induces dose-dependent chain scission; the magnitude should be characterized for the specific packaging, dose rate, and initial water content. Published data for this specific configuration is limited, so irradiation mapping studies are required before routine use.

End-group functionality rather than comonomer ratio alone controls several processing and degradation properties. RESOMER RG 752 H differs from the corresponding ester-terminated 75:25 grade of similar nominal viscosity by the presence of free carboxylic acid end groups. This difference increases initial water uptake during the first phase of hydrolytic degradation, shifts autocatalytic mass loss to an earlier time point, and provides reactive sites for covalent conjugation of amine-bearing drugs, targeting ligands, or surface modifiers. Because the acid-terminated polymer can ion-pair with cationic peptides, formulations containing basic peptide drugs may show higher encapsulation efficiency but also a greater risk of pH-driven peptide acylation during long-term storage.

Compared with 50:50 PLGA grades, the 75:25 copolymer degrades more slowly. The higher lactide content reduces the density of glycolate linkages and extends the diffusion-dominated release phase in monolithic implants. A direct substitution of RG 752 H for a 50:50 ester-terminated PLGA in a long-acting depot could alter the release lag phase, the initial burst, and the terminal erosion period. Substitution should not be performed without matching the inherent viscosity, end-group specification, and residual monomer profile to the existing design of experiments.

When a 75:25 Acid-Terminated PLGA Is Substituted for 50:50 Ester-Terminated Grades in Long-Acting Depot Formulations

Substitution analysis requires comparative degradation data generated under identical conditions. In phosphate-buffered saline at pH 7.4 and 37°C, 75:25 PLGA degrades more slowly than 50:50 PLGA because the increased lactic acid content reduces the number of hydrolytically labile glycolate-rich sequences along the backbone. The release profile shifts from a shorter erosional phase toward a longer diffusion-controlled phase. In an in situ forming depot, where the polymer is dissolved in a water-miscible solvent such as N-methyl-2-pyrrolidone or dimethyl sulfoxide at 10–40% w/w and precipitates after injection, the higher lactide content prolongs the depot solidification period and moderates the acidic microenvironment.

For a depot containing a small-molecule drug with a pKa above 6, the free acid end groups of RG 752 H may depress local pH within the implant and alter drug solubility gradient. An ester-terminated 50:50 grade of similar viscosity would exhibit faster water ingression and a shorter induction period. The choice of RG 752 H is justified when a longer release interval, lower initial burst, or slower acidic degradation is required, provided the formulation is re-optimized for the changed polymer hydrophilicity. Parallel design-of-experiment batches are recommended because published data for this specific configuration is limited.

Operational boundaries include storage below 2–8°C in sealed containers, avoidance of high relative humidity during weighing, and exclusion of amine-containing processing aids at elevated temperature. For microsphere manufacturing, in-process drying after particle hardening should reduce residual moisture below 0.5% w/w before terminal packaging to suppress premature degradation during shelf life. For implant extrusion, start-up purging with a sacrificial batch of the same polymer is advisable to displace adsorbed moisture from the barrel before processing the drug-loaded formulation.