In the manufacture of long-acting injectable microspheres intended for intramuscular or subcutaneous administration, PURASORB PDLG 5002A is used as the biodegradable matrix former in an oil-in-water emulsification–solvent extraction process. The polymer, with a specification of 0.16–0.24 dL/g inherent viscosity (0.1% w/v in chloroform, 25 °C; ISO 1628-1:2021) and an acid-terminated 50:50 DL-lactide/glycolide architecture, is dissolved in dichloromethane at 10–20% w/w, while the active pharmaceutical ingredient is dissolved or dispersed at a drug-to-polymer ratio of 1:5 to 1:20. The organic phase is emulsified into a continuous aqueous phase containing 0.5–2.0% w/v polyvinyl alcohol with 87–89% hydrolysis and 4–30 mPa·s viscosity at 4% w/v, 25 °C, under high-shear rotor–stator agitation at 8,000–15,000 rpm using a Silverson L5M-A or equivalent fitted with a square-hole high-shear screen. The resulting primary emulsion is transferred to a hardening bath of 2–5 L aqueous 0.5–1.0% w/v polyvinyl alcohol maintained at 25–30 °C; extraction of dichloromethane into the continuous phase is driven by the difference between the solvent vapor pressure and the controlled bath temperature, not by aggressive vacuum stripping. Residual dichloromethane must fall below the ICH Q3C(R8) limit of 600 ppm with a permitted daily exposure of 6.0 mg/day before lyophilization; residual solvent analysis is performed by headspace GC according to USP <467> or an equivalent compendial method. Microsphere particle size is controlled by the ratio of rotor diameter to vessel diameter, with a d50 target of 30–80 µm for injectability through a 19–21 gauge thin-wall needle; particles below 10 µm are minimized because they exhibit faster drug release and contribute to phagocytic uptake. Sterility and bioburden are controlled to USP <71> and USP <85>; if terminal gamma irradiation is used, the absorbed dose is typically 25–40 kGy on frozen product, while aseptic filtration of the polymer solution through a 0.22 µm hydrophobic membrane is the alternative for radiation-sensitive drugs. The acid-terminated chain ends accelerate autocatalytic hydrolysis once the matrix absorbs water, producing a pH drop within the microsphere core; this accelerates release after an initial lag phase, but basic drugs with pKa > 7 may form ion pairs with the terminal carboxylic acid groups, reducing initial burst and slowing diffusion. The terminal dosage form is a sterile lyophilized single-dose vial or a prefilled dual-chamber syringe containing microsphere powder and aqueous diluent for constitution before intramuscular or subcutaneous injection. Process conflicts arise when polymer loading exceeds 20% w/w: continuous-phase viscosity rises to a point where satellite droplets form during high-shear mixing, broadening the particle size distribution beyond a span of 0.8–1.2; conversely, polymer loading below 5% w/w reduces encapsulation efficiency below 30% for low-molecular-weight peptides because the polymer precipitates too slowly during solvent extraction. Batch-to-batch variance is most often traced to differences in polyvinyl alcohol grade, dichloromethane evaporation rate, and the acid number of the PLGA, because acid-terminated PDLG 5002A has a higher free carboxyl content than ester-terminated grades of the same inherent viscosity, increasing the sensitivity of the primary emulsion to pH and divalent cation levels in the continuous phase.

In Situ Forming Depot Precipitation Boundaries in N-Methyl-2-Pyrrolidone Systems

A 40% w/w solution of PURASORB PDLG 5002A in N-methyl-2-pyrrolidone (NMP) is used to produce an injectable in situ forming implant for subcutaneous or periodontal delivery of hydrophobic small molecules and peptides. The formulation addition ratio ranges from 20–50% w/w polymer, with the acid-terminated grade selected at the higher end because its low inherent viscosity of 0.16–0.24 dL/g keeps the solution injectable through a 21–23 gauge needle. Drug loading is typically 5–15% w/w, with the drug dissolved or suspended in the polymer–NMP vehicle; for water-soluble peptides, a cosolvent such as dimethyl sulfoxide at 5–10% w/w may be used, but this increases the solvent burden and must be accounted for under ICH Q3C(R8), where dimethyl sulfoxide is a Class 3 solvent with a permitted daily exposure of 50 mg/day and NMP is Class 2 with a permitted daily exposure of 5.3 mg/day. The production process consists of dissolving the polymer and drug in anhydrous NMP under low-shear overhead stirring at 25–40 °C, filtering the solution through a 0.22 µm membrane, and filling glass or cyclic olefin copolymer syringes under nitrogen. Upon injection into aqueous tissue fluid, the water-miscible NMP exchanges with water; the PLGA, being insoluble in water, precipitates as a porous depot with entrapped drug. The critical process window is the demixing rate: if NMP content remains above 20% w/w in the depot core for more than 24 h, initial release may be suppressed but residual solvent extraction can be delayed beyond the 3–7 day tissue residence of NMP; if polymer concentration is below 20% w/w, the depot forms as a fragmented or gelled mass with poor mechanical integrity and uncontrolled burst release above 40% in 24 h. The apparent viscosity of a 40% w/w solution of PDLG 5002A in NMP at 25 °C is typically 0.8–2.5 Pa·s at a shear rate of 10 s⁻¹ on a Brookfield viscometer with an SC4-18 spindle; below 0.5 Pa·s the solution may leak from the injection site, and above 3.0 Pa·s the force required to extrude through a 21 gauge needle can exceed 25 N or become too variable across batches. Sterility and pyrogenicity are controlled according to USP <71> and USP <85>; terminal sterilization by moist heat is generally not applicable because PLGA hydrolyzes in the presence of water at high temperature, so aseptic processing under ISO 13485:2016 and current good manufacturing practice is mandatory. The terminal product is a prefilled syringe or a vial with luer adapter for subcutaneous, intratumoral, or periodontal administration; after injection, the depot delivers drug over 1 week to 6 months depending on drug lipophilicity, polymer molecular weight, and the initial NMP demixing rate. The acid-terminated end groups create a local acidic microclimate within the depot, which can degrade acid-labile peptides; therefore, the formulation must be screened by dissolution testing under pH 7.4 phosphate-buffered saline at 37 °C using USP apparatus 4 or USP apparatus 7 to quantify burst release and confirm that the depot does not shed visible particles larger than 10 µm as required by USP <788>.

What Limits Encapsulation Efficiency in Acid-Terminated PLGA Nanoprecipitation?

At a solvent-to-antisolvent ratio of 1:5 to 1:10, the antisolvent precipitation of PURASORB PDLG 5002A into poly(D,L-lactide-co-glycolide) nanoparticles is performed by dissolving the polymer at 1–5% w/v in acetone or tetrahydrofuran and injecting the organic phase into an aqueous antisolvent phase containing 0.1–1.0% w/v poloxamer 188 or polyvinyl alcohol. The drug-to-polymer ratio is kept between 1:10 and 1:5 for hydrophobic small molecules with log P > 3; higher drug loadings above 20% w/w with respect to polymer reduce the yield of sub-200 nm particles because the drug acts as a plasticizer and lowers the glass transition temperature of the polymer matrix below 37 °C, leading to coalescence during solvent removal. Processing equipment includes a confined impinging jet mixer or a high-pressure homogenizer operated at 500–1,500 bar for microfluidic nanoprecipitation; for batch manufacturing, a probe sonicator at 20–40 W for 60–180 s is used, but probe sonication produces titanium debris and local heating, so process validation must monitor particle size distribution and polydispersity index below 0.2 by dynamic light scattering. The organic solvent is removed by rotary evaporation under reduced pressure at 30–35 °C, and residual acetone or tetrahydrofuran is controlled to ICH Q3C(R8) limits: acetone is Class 3 with a permitted daily exposure of 50 mg/day, while tetrahydrofuran is Class 2 with a permitted daily exposure of 7.2 mg/day and a concentration limit of 720 ppm. The acid-terminated architecture of PDLG 5002A introduces a high density of surface carboxyl groups, which can be used for covalent conjugation of targeting ligands through carbodiimide chemistry, but the same carboxyl groups reduce encapsulation efficiency for weakly basic drugs because they form salts at the polymer–aqueous interface and promote drug leakage into the antisolvent phase. Encapsulation efficiency falls below 40% when the aqueous phase pH is below 4.5 or above 8.0, because ionized polymer end groups increase electrostatic repulsion and reduce the thickness of the polymer shell; the pH must therefore be buffered to 5.5–6.5 with 1–10 mM citrate or acetate buffer. Terminal product is a sterile-filterable nanoparticle dispersion or a lyophilized cake for intravenous injection; the final dispersion must meet USP <788> particulate matter limits for large-volume parenterals, and endotoxin is controlled to USP <85> with a specification of <0.5 EU/mg for parenteral use. Lyophilization requires a cryoprotectant such as trehalose or sucrose at 5–10% w/v, because the low glass transition temperature of PDLG 5002A causes irreversible aggregation during freezing if no cryoprotectant is present.

When PDLG 5002A Is Substituted for an Ester-Terminated Grade in Hot-Melt Extruded Intravitreal Implants

Hot-melt extrusion of an intravitreal implant with PURASORB PDLG 5002A is carried out on a co-rotating twin-screw extruder with an L/D ratio of 20:1 to 40:1, a screw diameter of 11–16 mm for pilot scale, and a strand pelletizer or strand cutter. The formulation addition ratio is 70–90% w/w polymer and 10–30% w/w drug, with a processing temperature of 65–90 °C; the acid-terminated 50:50 grade allows extrusion at the lower end of this range because its low molecular weight reduces melt viscosity, but the low glass transition temperature of 40–50 °C creates a narrow processing window before the polymer softens and sticks to the feed throat. Pre-drying is mandatory: residual moisture must be reduced to <0.1% w/w by vacuum drying at 30 °C for 24–48 h, because hydrolytic chain scission during extrusion increases the acid number and shifts the degradation profile. Screw speed is set to 100–300 rpm with a barrel temperature profile of 65/70/75/80/85/90 °C; torque is monitored continuously, and an increase above 80% of the extruder rated torque indicates either insufficient plasticization or drug–polymer incompatibility. The extrudate is drawn through a 1.0–1.5 mm die, cooled with dry nitrogen, and cut into 1–5 mm rods; after cutting, the implants are inspected for surface roughness, internal voids, and diameter uniformity using a laser micrometer. The terminal product is a preloaded intravitreal implant or a sterile insert for surgical placement, designed to deliver drug over 3–6 months in the vitreous humor. Compliance testing includes USP <71> sterility, USP <85> bacterial endotoxins, USP <788> particulate matter, and ISO 10993-1:2018 biological evaluation for ocular implants. The main process conflict is that the acid-terminated grade has higher moisture sensitivity and lower thermal stability than ester-terminated PLGA; at barrel temperatures above 100 °C, ester exchange and transesterification reactions reduce molecular weight by more than 30% and increase the polydispersity index above 2.0, while at temperatures below 65 °C the melt viscosity exceeds the safe torque limit and the drug may not be homogeneously dispersed. Residual monomer and degradation products are measured by gel permeation chromatography and HPLC, with lactide and glycolide residual levels below 0.5% w/w per the relevant compendial monograph for PLGA parenteral excipients.

Solvent-cast leuprolide acetate implant rods are prepared from PURASORB PDLG 5002A by dissolving the polymer at 10–20% w/v in a mixture of acetonitrile and water at 90:10 v/v and dispersing or dissolving leuprolide acetate at a drug-to-polymer ratio of 1:4 to 1:7. The solution is cast into cylindrical PTFE or stainless-steel molds with a diameter of 1.0–1.5 mm and a length of 10–20 mm, then dried under a controlled vapor pressure gradient at 25–35 °C for 24–72 h to avoid surface skin formation. The acid-terminated PLGA grade provides a higher carboxylic acid end-group density than ester-terminated grades; this accelerates water uptake in the cast matrix but also creates ion-pair interactions with the basic guanidyl group of leuprolide, which can reduce initial burst from 20–30% to 5–10% in 24 h when the drug is dispersed rather than dissolved. The production process requires residual acetonitrile to be controlled below 410 ppm per ICH Q3C(R8) as a Class 2 solvent with a permitted daily exposure of 4.1 mg/day, measured by headspace GC; residual water is reduced to <0.5% w/w to limit pre-implantation hydrolysis. Sterilization is generally not performed by gamma irradiation because leuprolide acetate is radiation-sensitive; instead, aseptic processing and terminal ethylene oxide or low-temperature hydrogen peroxide gas plasma are used after sealing in foil pouches, with biological indicators and residual gas limits per ISO 11135:2014 or ISO 14937:2009. The terminal product is a single-rod subcutaneous implant for prostate cancer or endometriosis indications, inserted through a trocar needle under local anesthesia; the implant releases drug over 1–3 months by bulk erosion. The critical processing conflict is the narrow solvent evaporation window: if drying temperature exceeds 35 °C, acetonitrile evaporates too quickly and forms a dense polymer skin that traps residual solvent in the core, causing delayed release and implant deformation; if drying temperature is below 25 °C, solvent removal is incomplete and the rod remains tacky, blocking mold ejection and increasing the risk of microbial contamination. Mechanical testing of the dried rods includes three-point bending and tensile strength per ISO 527-2 or ASTM D638 adapted for small-diameter specimens; an acceptable implant rod must not fracture during trocar insertion and must retain dimensional tolerance of ±5% in diameter and ±10% in length.

Microneedle Array Casting Requires Pre-Drying and Demolding Control

Under centrifugation-assisted mold filling, a transdermal microneedle array based on PURASORB PDLG 5002A is fabricated by solvent casting into polydimethylsiloxane (PDMS) molds with pyramidal or conical cavities of 300–900 µm height and 50–300 µm base width. The polymer is dissolved in dichloromethane or a dichloromethane–dimethylformamide mixture at 15–30% w/w; the drug is added at 5–15% w/w relative to polymer, with a preferred drug-to-polymer ratio of 1:10 for small molecules or peptides. The solution is filled into the mold by centrifugation at 3,000–5,000 rpm for 5–15 min to remove air bubbles from the tips, followed by vacuum drying at 25–35 °C for 12–24 h and demolding under controlled relative humidity below 30% RH. The low molecular weight of PDLG 5002A reduces solution viscosity and allows complete filling of sub-100 µm tip cavities at moderate centrifugal force, but the acid-terminated grade absorbs water quickly; if the casting environment exceeds 60% RH, the polymer solution becomes hazy and the resulting microneedles exhibit surface craters and reduced tip sharpness. The terminal product is a transdermal patch or a dissolvable microneedle array for vaccine or peptide delivery; the microneedles penetrate the stratum corneum and release the drug by matrix dissolution and hydrolysis. Compliance testing includes USP <71> sterility, USP <85> endotoxins, ISO 10993-5:2009 cytotoxicity, and ISO 10993-10:2010 skin irritation and sensitization; mechanical integrity is quantified by axial fracture force using a Texture Analyzer equipped with a 5 N load cell, with a minimum tip fracture force of 0.1 N per needle for skin insertion. The addition ratio of PDLG 5002A above 30% w/w increases stiffness but reduces elongation at break below 5%, causing needle tips to snap during insertion; below 15% w/w the polymer matrix does not maintain the pyramidal shape after demolding and the needle height decreases by more than 20%. If polyethylene glycol or glycerol is added as a plasticizer at 5–10% w/w, the elongation increases but the glass transition temperature drops below 25 °C, making the patch storage temperature sensitive; therefore, the formulation must be validated by accelerated stability testing at 25 °C/60% RH and 40 °C/75% RH per ICH Q1A(R2).