RESOMER R 202 H is a bioresorbable poly(D,L-lactide) homopolymer supplied as a drug delivery grade with an acid-terminated chain architecture. The manufacturer specification for inherent viscosity is 0.16–0.24 dL/g measured as a 0.1% w/v solution in chloroform at 25 °C, with residual monomer below 1.0%, water content below 0.5%, and residual tin below 200 ppm. Unlike semicrystalline poly(L-lactide), the D,L-lactide backbone is amorphous; no melting endotherm is observed, and the glass transition is typically reported near 40–50 °C for moderate-molecular-weight PDLLA, with additional depression possible in this low-viscosity acid-terminated grade. The product is intended for solvent-based microspheres, nanoparticles, in situ forming depots, and melt-extruded implants in which low melt viscosity, rapid hydrolytic chain scission, and dissolution in organic solvents are critical formulation attributes.

R 202 H Compared with Ester-Terminated PDLLA and 50:50 PLGA Grades

The “H” designation indicates free carboxylic acid end groups. In an aqueous environment these end groups ionize, increase water uptake, and catalyze backbone ester hydrolysis. The ester-terminated analogue R 202 S has a similar inherent viscosity range but lacks the additional acidic chain ends; it is therefore less hydrophilic and typically exhibits slower degradation under otherwise identical geometry. Compared with RG 502 H, a 50:50 poly(D,L-lactide-co-glycolide) of similar IV, R 202 H contains no glycolide units. The absence of glycolate ester linkages lowers the degradation rate relative to 50:50 PLGA and changes the solubility profile; R 202 H dissolves readily in dichloromethane, acetone, ethyl acetate, and tetrahydrofuran, whereas high-glycolide PLGA grades are more restricted in solvent choice. These differences are not cosmetic: for a peptide or protein with pH-sensitive stability, the ester-terminated or higher-IV homopolymer may be preferred, while for a short-duration depot requiring rapid mass loss, R 202 H is selected.

In solvent-extraction microsphere manufacture, R 202 H is dissolved in dichloromethane or ethyl acetate at polymer concentrations of 10–25% w/w. The low inherent viscosity reduces organic-phase viscosity, allowing a rotor-stator homogenizer to operate in the 10,000–24,000 rpm range or a Silverson L5M-A batch mixer to reach target droplet size with lower energy input than higher-IV grades. For water-in-oil-in-water double emulsions, a primary water-in-oil emulsion is dispersed into an aqueous poly(vinyl alcohol) continuous phase at 1–2% w/v, and the solvent is extracted under controlled temperature. Residual dichloromethane must be reduced below the ICH Q3C Class 2 limit of 600 ppm; vacuum drying at 25–35 °C and <10 mbar for 12–24 h is commonly used when particle size and drug stability permit. Because inherent viscosity influences the droplet breakup and coalescence balance, a lot-to-lot shift from 0.16 dL/g to 0.24 dL/g can narrow the operating window for target mean particle size; the certificate of analysis should be reviewed before each campaign.

For microspheres, the main process conflicts are residual solvent and particle size control. Under-drying leaves dichloromethane above the ICH Q3C limit and can plasticize the matrix, lowering the glass transition below ambient storage temperature. Over-drying after hardening can cause agglomeration if the polymer is held above its glass transition in the presence of residual solvent. When spray-drying is used as an alternative, a low inlet temperature and high-velocity cyclone collection are required because the low glass transition of this grade reduces the temperature margin before particle adhesion. Residual dichloromethane from spray-drying must likewise meet the 600 ppm limit.

Rheological measurement of R 202 H in solution is typically performed with a Brookfield or Anton Paar rheometer; intrinsic viscosity in chloroform is the primary release specification because it tracks molecular weight. A change of 0.02 dL/g in inherent viscosity is often within lot-to-lot variability, but can alter microsphere release. For melt processing, small-amplitude oscillatory shear at 1 Hz can be used to determine the crossover from elastic to viscous behavior; this crossover approaches the glass transition.

When Melt Processing Is Required, How Does Low-Molecular-Weight Acid-Terminated PDLLA Behave?

Hot-melt extrusion of R 202 H is conducted in a co-rotating twin-screw extruder with an L/D ratio of 25:1–40:1 and zone temperatures from feed to die in the 80–110 °C range. The amorphous homopolymer softens rather than melts, and its low molecular weight produces low melt pressure; controlling specific mechanical energy is therefore more important than melt temperature alone. Acid-terminated chains are hydrolytically labile, so the feedstock should be vacuum-dried at 35–40 °C and <50 mbar for at least 12 h if water content exceeds 0.25%. Residual moisture above 0.5% can reduce inherent viscosity during compounding and produce bubbles or torque instability. Shear heating above 130 °C should be avoided because thermal degradation of PDLLA can begin well below the apparent 250 °C decomposition onset. Terminal sterilization of extruded implants is usually performed with ethylene oxide or gamma radiation; gamma dose mapping per ISO 11137-2 is required if radiation is selected, and product-specific data should be reviewed because ionizing radiation can cause chain scission and alter release kinetics.

For in situ forming depots, R 202 H is dissolved at 20–50% w/w in N-methyl-2-pyrrolidone or dimethyl sulfoxide. Injection into an aqueous medium drives phase inversion; the low-viscosity grade exchanges solvent more rapidly than R 203 H or R 205 H, producing a more immediate depot skin and shorter lag phase. The depot releases drug and water-soluble acidic oligomers; in confined implant geometries, autocatalytic hydrolysis can depress the internal pH below 4. Formulation screening therefore includes in vitro release testing in phosphate-buffered saline at 37 °C and local pH measurement with a microelectrode or pH-sensitive dye. Published data for this specific grade in large-animal confined depot geometries is limited, so internal pH should be verified for each implant size rather than extrapolated from microsphere data.

Because R 202 H carries free carboxylic acid end groups, basic drugs can form ionic associations during microsphere hardening. This interaction may improve encapsulation of amine-containing small molecules but can also delay release or create a pH-dependent release profile when the drug is protonated. Neutral or acid-sensitive drugs do not interact with the chain ends to the same degree; the ester-terminated R 202 S may then be a cleaner comparator. The effect should be characterized by differential scanning calorimetry for glass transition shifts and by release testing in media at pH 7.4 and pH 5.5 to detect pH-dependent liberation.

For solvent-displacement nanoprecipitation, R 202 H is typically dissolved in acetone or tetrahydrofuran and added dropwise to an aqueous stabilizer solution such as poly(vinyl alcohol) or poloxamer. The low IV is advantageous because chain diffusion during solvent exchange is rapid, producing smaller mean particle diameters at a given stirring condition. The absence of crystalline domains prevents crystallite-induced instability in aqueous dispersion.

Residual Monomer, Tin Content, and the Regulatory Data Package

Batch release data for R 202 H should be checked against the manufacturer specification for residual lactide, water, tin, and heavy metals. These values are relevant because the polymer is intended for parenteral products, and residual lactide can contribute to local acidity while water drives early hydrolysis during storage and processing. Typical acceptance limits are shown in the table below; the test methods correspond to pharmacopoeial or ISO procedures where applicable.

Because no USP-NF or Ph. Eur. monograph for poly(D,L-lactide) drug delivery grades is defined, the material is not released against a compendial monograph as an excipient. Instead, the certificate of analysis and regulatory technical file are used in combination with finished-product controls under 21 CFR 210/211 for drug product manufacturing. For injectable dosage forms, the manufacturer’s statement on residual solvents should be checked against ICH Q3C, and the finished device or depot should be evaluated for biocompatibility under ISO 10993-1.

Why Acid Termination Accelerates Hydrolytic Degradation in Phosphate-Buffered Saline

Within the acid-terminated R H homopolymer series, R 202 H represents the lowest IV grade, R 203 H occupies the intermediate range at 0.25–0.35 dL/g, and R 205 H provides a higher-viscosity option at 0.5–0.7 dL/g. A higher IV increases chain entanglement and prolongs mass loss but also raises solvent viscosity and melt processing temperature. In phosphate-buffered saline at pH 7.4 and 37 °C, low-IV PDLLA loses molecular weight before substantial mass loss; the acid-terminated end groups accelerate this first stage relative to ester-terminated grades. Complete resorption in vivo depends on implant size, vascularity, and drug loading, and published data for this specific configuration is limited. R 202 H is therefore preferred where rapid molecular weight decay and short-duration release are required, but it is not appropriate for load-bearing implants or devices requiring mechanical integrity beyond a few weeks.

Cold storage at 2–8 °C in sealed, desiccated containers is recommended. Containers should be equilibrated to room temperature before opening to avoid condensation on granules. Once opened, the polymer should be re-dried and used within a validated holding period; exposure to ambient relative humidity above 60% can increase water content above 0.5% and reduce the processing window. The grade is supplied as granules or milled powder depending on order form, and milling introduces shear history that can slightly reduce inherent viscosity; particle size reduction should be performed under cryogenic conditions and verified by post-mill IV testing.

R 202 H cannot be steam-sterilized because the amorphous polymer softens near 40–50 °C and hydrolyzes in saturated steam. Ethylene oxide is the most common terminal sterilization route for preformed microspheres and implants; if ethylene oxide is used, residual ethylene oxide and ethylene chlorohydrin must meet ISO 10993-7 limits. Aseptic processing is required when terminal sterilization is not feasible, and all aqueous media used after particle formation should be sterile-filtered to avoid endotoxin contamination.