PURASORB PLG 8055 is a medical-grade poly(L-lactide-co-glycolide) supplied as white to off-white granules. The product designation denotes an 80:20 molar ratio of L-lactide to glycolide and a nominal inherent viscosity of 0.55 dL/g determined at 0.1 g/dL in chloroform at 25°C in accordance with ISO 1628-1. The copolymer is produced with predominantly carboxylic acid terminal groups, a structural feature that distinguishes the grade from ester-capped copolymers and influences water uptake, autocatalytic hydrolysis, and early-stage strength-loss behaviour. Under the manufacturer’s batch-release system certified to EN ISO 13485:2016, the certificate of analysis reports monomer ratio by nuclear magnetic resonance, residual monomers and residual solvents by gas chromatography, and water content by Karl Fischer titration, with chemical characterization aligned to ISO 10993-18:2020. The grade is intended for conversion by melt processing into bioresorbable implants such as interference screws, suture anchors, and fracture fixation pins, where the resorption profile must be matched to healing timelines rather than left to generic polylactide behaviour.

Unopened vacuum-sealed bags are stored at -20°C in a dry environment. Before opening, the bag is equilibrated to ambient temperature for 4–6 h to prevent condensation on cold granulate. Once opened, the contents should be consumed in a single shift or immediately re-purged with dry nitrogen and vacuum-sealed. Differential scanning calorimetry of the dried granulate at a heating rate of 10 K/min under nitrogen typically places the glass transition temperature between 45°C and 55°C. The material is largely amorphous under standard processing conditions, with no pronounced melting endotherm above 100°C when the copolymer sequence is maintained. Residual water in incoming lots is controlled to a maximum of 0.5 wt%. The lot-specific inherent viscosity midpoint is accompanied by an acceptance window of ±0.05 dL/g; longer chains are not obtained by simply combining lots because melt stability varies with residual monomer and moisture history.

Does Acid Termination Shift the Hydrolytic Degradation Profile When Compared with an Ester-Capped 80:20 Copolymer?

The terminal group chemistry is not a minor packaging detail in PURASORB PLG 8055. Because the chains end in carboxylic acid moieties rather than ester capping groups, water absorption in the first 72 h of immersion produces a locally lower pH inside the polymer matrix, and this accelerates autocatalytic cleavage of the ester backbone. In contrast, an ester-capped 80:20 copolymer of comparable chain length shows slower initial hydrolysis under the same in vitro conditions. The practical consequence is that devices made from acid-capped PURASORB PLG 8055 reach a given loss of inherent viscosity earlier than an ester-capped equivalent, while the overall mass-loss timeline remains governed by the 80:20 monomer ratio. Published head-to-head data for this exact product lot is limited; comparative evaluations should therefore use specimens of identical surface-area-to-volume ratio, immersion in phosphate-buffered saline at pH 7.4 and 37°C, and periodic analysis per ASTM F1635.

The monomer ratio sets the longer-term degradation horizon. A 80:20 L-lactide/glycolide copolymer retains mechanical integrity longer than a 50:50 copolymer under identical test conditions because the lower glycolide content reduces hydrophilicity and slows bulk water diffusion. For load-bearing fixation devices that must carry stress for 8–12 weeks, this slower profile is often selected over faster-resorbing 50:50 grades. Retention interval is not determined solely by the copolymer ratio; part thickness, crystallinity, residual monomer, sterilization history, and implantation-site fluid exchange also shift the curve. These variables are controlled through design verification using ASTM F2502 for creep and stress relaxation when load-bearing devices are assessed.

When Residual Moisture Reaches 0.5 wt%, the Drying Protocol Becomes the Primary Processing Boundary

PURASORB PLG 8055 is hydrolytically labile at melt-processing temperatures, and the most common production failure is moisture-induced viscosity loss during plastication. If Karl Fischer titration of incoming granulate shows water content above 0.5 wt%, the resin must be dried before any melt-processing trial. Vacuum drying at 45°C under ≤50 mbar for 12–24 h is a defined starting condition; drying is terminated when a sample drawn from the bed reads below 250 ppm moisture by ISO 15512. A hopper dryer with dry nitrogen at a dew point of -40°C or lower may be used for continuous operation, but the hopper residence time at temperatures above 50°C should not exceed 2 h to limit hydrolytic chain scission. If granulate is exposed to ambient air at relative humidity above 60% for more than 15 min, re-drying is required because surface moisture re-adsorbs rapidly onto cold granules.

Drying uniformity is also a batch-scale problem. In a vacuum tray oven, the granulate bed should not exceed 5 cm depth; deeper beds produce moisture gradients between top and bottom pellets and cause inconsistent melt viscosity in consecutive shots. A rotary vacuum dryer is used for larger lots, with a jacket temperature of 45°C and rotation at 5–10 rpm. If a lot has been exposed to moisture for an extended period, vacuum drying alone may not restore the original inherent viscosity because hydrolytic chain scission has already occurred; disposition is then based on the remaining inherent viscosity measured by ISO 1628-1, not on additional drying time.

Cold granulate shifted directly from a -20°C freezer to an open feed hopper creates a second moisture barrier: condensation forms on the pellet surface before the material reaches the barrel. The sealed aluminum-laminated bag must be allowed to equilibrate to ambient temperature while still closed, usually for 4–6 h depending on bag mass. This boundary is operational rather than speculative; production sites that skip equilibration often observe intermittent screw feeding, nozzle drool, and a drop in melt viscosity that disappears when Karl Fischer analysis of the hopper feed returns to the 250 ppm limit.

Melt processing on a reciprocating-screw injection moulding machine with a screw L/D of 20:1 to 25:1 and a general-purpose low-shear metering geometry has been used to convert PURASORB PLG 8055 into small orthopaedic implants. The nozzle melt temperature is maintained between 180°C and 210°C, and the mould is held at 20–40°C. Injection pressures in the range of 80–140 MPa are typical for thin-wall geometries; pack/hold pressure is limited to 50–70% of the injection pressure to avoid overpacking and residual stress. Total residence time in the barrel above 210°C should not exceed 10 min; longer exposure produces transesterification, discoloration, and a measurable drop in inherent viscosity. On a co-rotating twin-screw extruder with an L/D of 40:1, screw speed is typically set between 150 rpm and 250 rpm, and the temperature profile is zoned from 170°C at the feed throat to 200°C at the die. The extruder vent is maintained under vacuum to strip residual moisture and low-molecular-weight volatiles, but the vacuum port must not be so deep that it draws melt into the vent. For this specific grade, published production-scale data is limited; the settings above are to be verified by process qualification.

If the melt temperature is set below 180°C, the grade may not homogenize sufficiently in the nozzle, producing visible flow lines and shrinkage anisotropy in small parts. If the melt is raised above 210°C, the risk shifts from incomplete filling to degradation; early signs are translucent amber discoloration and a reduction in inherent viscosity of more than 0.05 dL/g after a single pass. Batch-to-batch variation on a production line is usually traced to residual moisture or monomer content before molecular weight variation. When a lot exhibits lower melt viscosity at the same barrel settings, Karl Fischer analysis of the hopper feed and gas chromatography of the raw granulate are performed before adjusting the temperature profile. The melt viscosity of PURASORB PLG 8055 is intrinsically lower than that of a 1.0 dL/g grade, which is why the 0.55 dL/g material is preferred for injection moulding of small parts where thin flow paths and short cycle times are required.

Incoming-Release Specifications and Compliance Markers for PURASORB PLG 8055

The parameters in Table 1 are used as incoming-release markers for medical device polymer receipts; the manufacturer’s certificate of analysis remains the lot-specific source. Test methods are selected to align with chemical characterization expected under ISO 10993-1:2018 and ISO 10993-18:2020.

Biocompatibility of the finished device is not established by the polymer specification alone. The manufacturer supplies the polymer with a pre-screening suitability statement aligned to ISO 10993-1, but the device manufacturer must perform cytotoxicity, sensitization, irritation, and implantation testing on the final sterilized device according to ISO 10993-5, ISO 10993-10, and ISO 10993-6. Leachables evaluation under ISO 10993-18:2020 may include residual lactide, glycolide, and oligomeric degradation products; the analytical reporting threshold should be justified by the intended contact duration and tissue contact type.

The principal differences between PURASORB PLG 8055 and other resorbable polyester grades lie in three independent variables: chain terminal group, lactide/glycolide ratio, and inherent viscosity. Table 2 summarizes the operational consequences. The comparisons are qualitative unless lot-specific test data are generated under the same conditions; published data for the exact product lot is limited, and the table is to be read as a differentiation framework rather than a degradation prediction.

When the design requires load-bearing fixation lasting beyond 12 weeks, the 80:20 grade is preferred over 50:50 under identical implant geometry and sterilization route. For matrices where rapid mass loss is desired, the 50:50 D,L-lactide/glycolide grade remains the typical benchmark. The acid-capped terminal group in PURASORB PLG 8055 should not be confused with lower molecular weight; acid capping alters degradation rate at constant chain length rather than simply reducing melt viscosity. Within the PURASORB portfolio, the PLG prefix denotes L-lactide-based copolymers, while PDLG grades contain D,L-lactide and are more amorphous. The stereochemical difference changes degradation behaviour and solvent-based processing characteristics; for melt processing, both classes can be run on similar equipment, but drying and storage limits must be verified for the specific grade.

Terminal sterilization must be incorporated into device design verification because aliphatic polyesters are sensitive to ionizing radiation, heat, and moisture. Ethylene oxide processing under ISO 11135:2014 is the least hydrolytically aggressive terminal method for this polymer class, but the finished device must be assessed for residual ethylene oxide, ethylene chlorohydrin, and ethylene glycol according to ISO 10993-7:2008. Gamma irradiation under ISO 11137 is possible only if dose-setting establishes that the absorbed dose does not reduce inherent viscosity below the device design limit; absorbed doses above 25 kGy are typically associated with measurable chain scission in aliphatic polyesters, although the exact dose-response for this lot is not published. Steam sterilization is not recommended because the combination of heat and water accelerates hydrolysis. Dry-heat sterilization above the glass transition temperature is also not recommended because it can cause dimensional distortion and melt fusion of pellets. Package format must include a desiccant and an oxygen absorber when ethylene oxide is used, because residual moisture after sterilization can shorten the usable shelf life of the polymer.

Reprocessing of devices is not recommended. Any regrind inclusion changes molar mass distribution and degradation predictability; the manufacturer’s medical-grade supply is not intended for direct substitution of virgin granulate by runners, sprues, or rejected parts. If regrind is used under controlled conditions, the maximum addition level must be established by verification of inherent viscosity and residual monomer content, not assumed from standard thermoplastics practice.