Non-invasive in vivo characterization of microclimate pH inside in situ forming PLGA implants using multispectral fluorescence imaging

PLGA Implants for Controlled Drug Delivery and Regenerative Medicine: Advances, Challenges, and Clinical Potential

Poly(lactide-co-glycolide) (PLGA) implants have become a cornerstone in drug delivery and regenerative medicine due to their biocompatibility, tunable degradation, and capacity for sustained, localized therapeutic release. Recent innovations in polymer design, fabrication methods, and functional modifications have expanded their utility across diverse clinical domains, including oncology, neurology, orthopedics, and ophthalmology. This review provides a comprehensive analysis of PLGA implant properties, fabrication strategies, and biomedical applications, while addressing key challenges such as burst release, incomplete drug release, manufacturing complexity, and inflammatory responses. Emerging solutions-such as 3D printing, in situ forming systems, predictive modeling, and patient-specific customization-are improving implant performance and clinical translation. Emphasis is placed on scalable production, long-term biocompatibility, and personalized design to support the next generation of precision therapeutics.

EVA implants for controlled drug delivery to the inner ear

This study evaluated the potential of poly(ethylene vinyl acetate) (EVA) copolymers as matrix formers in miniaturised implants, allowing to achieve controlled drug delivery into the inner ear. Due to the blood-cochlea barrier, it is impossible to reliably deliver a drug to this tiny and highly sensitive organ in clinical practice. To overcome this bottleneck, different EVA implants were prepared by hot melt extrusion, altering the vinyl acetate content and implant diameter. Dexamethasone was incorporated as a drug with anti-inflammatory and anti-fibrotic activity. Its release was measured into artificial perilymph, and the systems were thoroughly characterised before and after exposure to the medium by optical and scanning electron microscopy, SEM-EDX analysis, DSC, X-ray powder diffraction, X-ray microtomography and texture analysis. Notably, the resulting drug release rates were much higher than from silicone-based implants of similar size. Furthermore, varying the vinyl acetate content allowed for adjusting the desired release patterns effectively: With decreasing vinyl acetate content, the crystallinity of the copolymer increased, and the release rate decreased. Interestingly, the drug was homogeneously distributed as tiny crystals throughout the polymeric matrices. Upon contact with aqueous fluids, water penetrates the implants and dissolves the drug, which subsequently diffuses out of the device. Importantly, no noteworthy system swelling or shrinking was observed for up to 10 months upon exposure to the release medium, irrespective of the EVA grade. Also, the mechanical properties of the implants can be expected to allow for administration into the inner ear of a patient, being neither too flexible nor too rigid.

Towards in vitro - In vivo correlation models for in situ forming drug implants

In vitro-In vivo correlation (IVIVC) is a main focus of the pharmaceutical industry, academia and the regulatory sectors, as this is an effective modelling tool to predict drug product in vivo performance based on in vitro release data and serve as a surrogate for bioequivalence studies, significantly reducing the need for clinical studies. Till now, IVIVCs have not been successfully developed for in situ forming implants due to the significantly different in vitro and in vivo drug release profiles that are typically achieved for these dosage forms. This is not unexpected considering the unique complexity of the drug release mechanisms of these products. Using risperidone in situ forming implants as a model, the current work focuses on: 1) identification of critical attributes of in vitro release testing methods that may contribute to differences in in vitro and in vivo drug release from in situ forming implants; and 2) optimization of the in vitro release method, with the aim of developing Level A IVIVCs for risperidone implants. Dissolution methods based on a novel Teflon shape controlling adapter along with a water non-dissolvable glass fiber membrane (GF/F) instead of a water dissolvable PVA film (named as GF/F-Teflon adapter and PVA-Teflon adapter, respectively), and an in-house fabricated Glass slide adapter were used to investigate the impact of: the surface-to-volume ratio, water uptake ratio, phase separation rate (measured by NMP release in 24 h post injection in vitro or in vivo), and mechanical pressure on the drug release patterns. The surface-to-volume ratio and water uptake were shown to be more critical in vitro release testing method attributes compared to the phase separation rate and mechanical pressure. The Glass slide adapter-based dissolution method, which allowed for the formation of depots with bio-mimicking surface-to-volume ratios and sufficient water uptake, has the ability to generate bio-relevant degradation profiles as well as in vitro release profiles for risperidone implants. For the first time, a Level A IVIVC (rabbit model) has been successfully developed for in situ forming implants. Release data for implant formulations with slightly different PLGA molecular weights (MWs) were used to develop the IVIVC. The predictability of the model passed external validation using the reference listed drug (RLD), Perseris®. IVIVC could not be developed when formulations with different PLGA molar ratios of lactic acid to glycolic acid (L/G) were included. The present work provides a comprehensive understanding of the impact of the testing method attributes on drug release from in situ forming implants, which is a valuable practice for level A IVIVC development.

Electrospun drug-loaded scaffolds for nervous system repair

Nervous system injuries, encompassing peripheral nerve injury (PNI), spinal cord injury (SCI), and traumatic brain injury (TBI), present significant challenges to patients' wellbeing. Traditional treatment approaches have limitations in addressing the complexity of neural tissue regeneration and require innovative solutions. Among emerging strategies, implantable materials, particularly electrospun drug-loaded scaffolds, have gained attention for their potential to simultaneously provide structural support and controlled release of therapeutic agents. This review provides a thorough exploration of recent developments in the design and application of electrospun drug-loaded scaffolds for nervous system repair. The electrospinning process offers precise control over scaffold characteristics, including mechanical properties, biocompatibility, and topography, crucial for creating a conducive environment for neural tissue regeneration. The large surface area of the resulting fibrous networks enhances biomolecule attachment, influencing cellular behaviors such as adhesion, proliferation, and migration. Polymeric electrospun materials demonstrate versatility in accommodating a spectrum of therapeutics, from small molecules to proteins. This enables tailored interventions to accelerate neuroregeneration and mitigate inflammation at the injury site. A critical aspect of this review is the examination of the interplay between structural properties and pharmacological effects, emphasizing the importance of optimizing both aspects for enhanced therapeutic outcomes. Drawing upon the latest advancements in the field, we discuss the promising outcomes of preclinical studies using electrospun drug-loaded scaffolds for nervous system repair, as well as future perspectives and considerations for their design and implementation. This article is categorized under: Implantable Materials and Surgical Technologies > Nanomaterials and Implants Implantable Materials and Surgical Technologies > Nanotechnology in Tissue Repair and Replacement Therapeutic Approaches and Drug Discovery > Emerging Technologies.

Characterization of Controlled Release Starch-Nimodipine Implant for Antispasmodic and Neuroprotective Therapies in the Brain

Parenteral depot systems can provide a constant release of drugs over a few days to months. Most of the parenteral depot products on the market are based on poly(lactic acid) and poly(lactide-co-glycolide) (PLGA). Studies have shown that acidic monomers of these polymers can lead to nonlinear release profiles or even drug inactivation before release. Therefore, finding alternatives for these polymers is of great importance. Our previous study showed the potential of starch as a natural and biodegradable polymer to form a controlled release system. Subarachnoid hemorrhage (SAH) is a life-threatening type of stroke and a major cause of death and disability in patients. Nimotop® (nimodipine (NMD)) is an FDA-approved drug for treating SAH-induced vasospasms. In addition, NMD has, in contrast to other Ca antagonists, unique neuroprotective effects. The oral administration of NMD is linked to variable absorption and systemic side effects. Therefore, the development of a local parenteral depot formulation is desirable. To avoid the formation of an acidic microenvironment and autocatalytic polymer degradation, we avoided PLGA as a matrix and investigated starch as an alternative. Implants with drug loads of 20 and 40% NMD were prepared by hot melt extrusion (HME) and sterilized with an electron beam. The effects of HME and electron beam on NMD and starch were evaluated with NMR, IR, and Raman spectroscopy. The release profile of NMD from the systems was assessed by high-performance liquid chromatography. Different spectroscopy methods confirmed the stability of NMD during the sterilization process. The homogeneity of the produced system was proven by Raman spectroscopy and scanning electron microscopy images. In vitro release studies demonstrated the sustained release of NMD over more than 3 months from both NMD systems. In summary, homogeneous nimodipine-starch implants were produced and characterized, which can be used for therapeutic purposes in the brain.

3D printed PLGA implants: How the filling density affects drug release

Different types of ibuprofen-loaded, poly (D,L lactic-co-glycolic acid) (PLGA)-based implants were prepared by 3D printing (Droplet Deposition Modeling). The theoretical filling density of the mesh-shaped implants was varied from 10 to 100%. Drug release was measured in agarose gels and in well agitated phosphate buffer pH 7.4. The key properties of the implants (and dynamic changes thereof upon exposure to the release media) were monitored using gravimetric measurements, optical microscopy, Differential Scanning Calorimetry, Gel Permeation Chromatography, and Scanning Electron Microscopy. Interestingly, drug release was similar for implants with 10 and 30% filling density, irrespective of the experimental set-up. In contrast, implants with 100% filling density showed slower release kinetics, and the shape of the release curve was altered in agarose gels. These observations could be explained by the existence (or absence) of a continuous aqueous phase between the polymeric filaments and the "orchestrating role" of substantial system swelling for the control of drug release. At lower filling densities, it is sufficient for the drug to be released from a single filament. In contrast, at high filling densities, the ensemble of filaments acts as a much larger (more or less homogeneous) polymeric matrix, and the average diffusion pathway to be overcome by the drug is much longer. Agarose gel (mimicking living tissue) hinders substantial PLGA swelling and delays the onset of the final rapid drug release phase. This improved mechanistic understanding of the control of drug release from PLGA-based 3D printed implants can help to facilitate the optimization of this type of advanced drug delivery systems.

Self-Boosting Vaccination Based on Pulsatile Antigen Release from Core-Shell Microparticles

Vaccination is among the most effective ways to prevent infectious diseases. Subunit vaccines are safe but usually require multiple booster shots, which may lead to immunity loss and economic consume. In this study, a self-boosting vaccine is developed based on the pulsatile release of antigen from the core-shell microparticle after single-injection immunization. Self-healing technology applied to form an "antigen core" can avoid organic solvents from destroying the spatial structure of the antigen. The "antigen shell" is built-up by self-assemble of the antigen with the opposite charged polypeptide. Primary immunization occurs with the self-assembled film disintegration, and the booster comes with the microparticle degradation. The changing of antigen-specific antibodies after immunization with the core-shell microparticle vaccine is consistent with that caused by the two shots of immunization. The immune effect and safety evaluation results support the translational potential of this self-boosting core-shell microparticle vaccine.

Antibacterial-Anti-Inflammatory-Bone Restoration Procedure Achieved by MIN-Loaded PLGA Microsphere for Efficient Treatment of Periodontitis

The main development process of periodontitis involves periodontal pathogenic bacteria as the initiating factor causing the onset of destructive inflammation, which in turn stimulates the destruction of periodontal tissue. It is difficult to achieve the eradication of periodontitis due to the complex interaction among antibacterial, anti-inflammatory, and bone restoration. Herein, we propose an antibacterial-anti-inflammatory-bone restoration procedural treatment strategy with minocycline (MIN) for the efficient treatment of periodontitis. In brief, MIN was prepared into PLGA microspheres with tunable release behavior using different species of PLGA, respectively. The optimally selected PLGA microspheres (LA:GA with 50:50, 10 kDa, and carboxyl group) had a drug loading of 16.91%, an in vitro release of approximately 30 days, which also had a particle size of approximately 11.8 µm with a smooth appearance and a rounded morphology. The DSC and XRD results showed that the MIN was completely encapsulated in the microspheres as an amorphous state. Cytotoxicity tests demonstrated the safety and biocompatibility of the microspheres (cell viabilities at a concentration of 1-200 μg/mL were greater than 97%), and in vitro bacterial inhibition tests showed that the selected microspheres could achieve effective bacterial inhibition at the initial stage after administration. The favorable anti-inflammatory (low TNF-α and IL-10 levels) and bone restoration effects (BV/TV: 71.8869%; BMD: 0.9782 g/cm³; TB.Th: 0.1366 mm; Tb.N: 6.9318 mm^-1; Tb.Sp: 0.0735 mm) were achieved in a SD rat periodontitis model after administering once a week for four weeks. The MIN-loaded PLGA microspheres were proved to be an efficient and safe treatment for periodontitis by procedural antibacterial, anti-inflammatory, and bone restoration.

Influence of PLGA End Groups on the Release Profile of Dexamethasone from Ocular Implants

The present study deals with the development of dexamethasone (DM)-loaded implants using ester end-capped Resomer RG 502 poly(lactic acid-co-glycolic acid) (PLGA) (502), acid end-capped Resomer RG 502H PLGA (502H), and a 502H:502 mixture (3:1) via hot melt extrusion (HME). The prepared intravitreal implants (20 and 40% DM loaded in each PLGA) were thoroughly investigated to determine the effect of different end-capped PLGA and drug loading on the long-term release profile of DM. The implants were characterized for solid-state active pharmaceutical ingredient (APIs) using DSC and SWAXS, water uptake during stability study, the crystal size of API in the implant matrix using hot-stage polarized light microscopy, and in vitro release profile. The kinetics of PLGA release was thoroughly investigated using quantitative ¹H NMR spectroscopy. The polymorph of DM crystal was found to remain unchanged after the extrusion and stability study. However, around 3 times reduction in API particle size was observed after the HME process. The morphology and content uniformity of the RT-stored samples were found to be comparable to the initial implant samples. Interestingly, the samples (mainly 502H) stored at 40 °C and 75% RH for 30 d demonstrated marked deformation and a change in content uniformity. The rate of DM release was higher in the case of 502H samples with a higher drug loading (40% w/w). Furthermore, a simple digital in vitro DM release profile derived for the formulation containing a 3:1 ratio of 502H and 502 was comparable with the experimental release profile of the respective polymer mixture formulation. The temporal development of pores and/or voids in the course of drug dissolution, evaluated using μCT, was found to be a precursor for the PLGA release. Overall, the release profile of DM was found to be dependent on the PLGA type (independent of subtle changes in the formulation mass and diameter). However, the extent of release was found to be dependent on DM loading. Thus, the present investigation led to a thorough understanding of the physicochemical properties of different end-capped PLGAs and the underlying formulation microstructure on the release profile of a crystalline water-insoluble drug, DM, from the PLGA-based implant.

3D printed PLGA implants: APF DDM vs. FDM

3D Printing offers a considerable potential for personalized medicines. This is especially true for customized biodegradable implants, matching the specific needs of each patient. Poly(lactic-co-glycolic acid) (PLGA) is frequently used as matrix former in biodegradable implants. However, yet relatively little is known on the technologies, which can be used for the 3D printing of PLGA implants. The aim of this study was to compare: (i) Arburg Plastic Freeforming Droplet Deposition Modeling (APF DDM), and (ii) Fused Deposition Modeling (FDM) to print mesh-shaped, ibuprofen-loaded PLGA implants. During APF DDM, individual drug-polymer droplets are deposited, fusing together to form filaments, which build up the implants. During FDM, continuous drug-polymer filaments are deposited to form the meshes. The implants were thoroughly characterized before and after exposure to phosphate buffer pH 7.4 using optical and scanning electron microscopy, GPC, DSC, drug release measurements and monitoring dynamic changes in the systems' dry & wet mass and pH of the bulk fluid. Interestingly, the mesh structures were significantly different, although the device design (composition & theoretical geometry) were the same. This could be explained by the fact that the deposition of individual droplets during APF DDM led to curved and rather thick filaments, resulting in a much lower mesh porosity. In contrast, FDM printing generated straight and thinner filaments: The open spaces between them were much larger and allowed convective mass transport during drug release. Consequently, most of the drug was already released after 4 d, when substantial PLGA set on. In the case of APF DDM printed implants, most of the drug was still entrapped at that time point and substantial polymer swelling transformed the meshes into more or less continuous PLGA gels. Hence, the diffusion pathways became much longer and ibuprofen release was controlled over 2 weeks.

Basic Salt Additives Modulate the Acidic Microenvironment Around In Situ Forming Implants

There is a growing number of protein drugs, yet their limited oral bioavailability requires that patients receive frequent, high dose injections. In situ forming implants (ISFIs) for controlled release of biotherapeutics have the potential to greatly reduce the injection frequency and improve patient compliance. However, protein release from ISFIs is a challenge due to their proclivity for instability. Specifically, factors such as the acidic microclimate within ISFIs can lead to protein aggregation and denaturation. Basic salts have been shown in PLGA microparticle and microcylinder formulations to significantly reduce protein instability by neutralizing this acidic environment. The overall objective of the study was to demonstrate that basic salts can be used with an ISFI system to neutralize the implant acidification. To this end, the basic salts MgCO3 and Mg(OH)2 were added to a protein-releasing ISFI and the effect on drug release, pH, implant swelling, implant diffusivity, and implant erosion were evaluated. Either salt added at 3 wt% neutralized the acidic environment surrounding the implants, keeping the pH at 6.64 ± 0.03 (MgCO₃) and 6.46 ± 0.11 (Mg(OH)₂) after 28 day compared to 3.72 ± 0.05 with no salts added. The salts initially increased solution uptake into the implants but delayed implant degradation and erosion. The 3 wt% Mg(OH)₂ formulation also showed slightly improved drug release with a lower burst and increased slope. We showed that salt additives can be an effective way to modulate the pH in the ISFI environment, which can improve protein stability and ultimately improve the capacity of ISFIs for delivering pH-sensitive biomolecules. Such a platform represents a low-cost method of improving overall patient compliance and reducing the overall healthcare burden.

Mapping in vivo microclimate pH distribution in exenatide-encapsulated PLGA microspheres

The pH inside the aqueous pores of poly(lactic-co-glycolic acid) (PLGA) microspheres, often termed microclimate pH (μpH), has been widely evaluated in vitro and shown to commonly be deleterious to pH-labile encapsulated drug molecules. However, whether the in vitro μpH is representative of the actual in vivo values has long been remained a largely unresolved issue. Herein we quantitatively mapped, for the first time, the in vivo μpH distribution kinetics inside degrading PLGA microspheres by combining two previously validated techniques, a cage implant system and confocal laser scanning microscopy. PLGA (50/50, Mw = 24-38 kDa, acid-end capped and ester-capped) microsphere formulations with and without encapsulating exenatide, a pH-labile peptide that is known to be unstable when pH > 4.5, were administered to rats subcutaneously via cage implants for up to 6 weeks. The results were compared with two different in vitro conditions. Strikingly, the in vivo μpH developed similarly to the low microsphere concentration in vitro condition with 1-μm nylon bags but very different from conventional high microsphere concentration sample-and-separate conditions. Improved maintenance of stable external pH in the release media for the former condition may have been one important factor. Stability of exenatide remaining inside microspheres was evaluated by mass spectrometry and found that it was steadily degraded primarily via pH-dependent acylation with a trend that slightly paralleled the changes in μpH. This methodology may be useful to elucidate pH-triggered instability of PLGA encapsulated drugs in vivo and for improving in vivo-predictive in vitro conditions for assessing general PLGA microsphere performance.

Safety and audiological outcome in a case series of tertiary therapy of sudden hearing loss with a biodegradable drug delivery implant for controlled release of dexamethasone to the inner ear

Background

Intratympanic injections of glucocorticoids have become increasingly common in the treatment of idiopathic sudden sensorineural hearing loss (ISSHL). However, due to their fast elimination, sustained applications have been suggested for local drug delivery to the inner ear.

Materials and methods

The study is based on a retrospective chart review of patients treated for ISSHL at a single tertiary (university) referral center. We included patients who were treated with a solid, biodegradable, poly(D,L-lactic-co-glycolic acid) (PLGA)-based drug delivery system providing sustained delivery of dexamethasone extracochlear into the round window niche (n = 15) or intracochlear into scala tympani (n = 2) for tertiary therapy of ISSHL in patients without serviceable hearing after primary systemic and secondary intratympanic glucocorticoid therapy. We evaluated the feasibility and safety through clinical evaluation, histological examination, and functional tests [pure-tone threshold (PTA), word recognition scores (WRS)].

Results

With adequate surgical preparation of the round window niche, implantation was feasible in all patients. Histologic examination of the material in the round window niche showed signs of resorption without relevant inflammation or foreign body reaction to the implant. In patients where the basal part of scala tympani was assessable during later cochlear implantation, no pathological findings were found. In the patients with extracochlear application, average preoperative PTA was 84.7 dB HL (SD: 20.0) and 76.7 dB HL (SD: 16.7) at follow-up (p = 0.08). The preoperative average maximum WRS was 14.6% (SD: 17.9) and 39.3% (SD: 30.7) at follow-up (p = 0.11). Six patients (40%), however, reached serviceable hearing. The two patients with intracochlear application did not improve.

Conclusion

The extracochlear application of the controlled release system in the round window niche and – based on limited observations - intracochlear implantation into scala tympani appears feasible and safe. Due to the uncontrolled study design, conclusions about the efficacy of the treatment are limited. These observations, however, may encourage the initiation of prospective controlled studies using biodegradable controlled release implants as drug delivery systems for the treatment of inner ear diseases.

Sustained degradation of hyaluronic acid using an in situ forming implant

In pancreatic cancer, excessive hyaluronic acid (HA) in the tumor microenvironment creates a viscous stroma, which reduces systemic drug transport into the tumor and correlates with poor patient prognosis. HA can be degraded through both enzymatic and nonenzymatic methods to improve mass transport properties. Here, we use an in situ forming implant to provide sustained degradation of HA directly at a local, targeted site. We formulated and characterized an implant capable of sustained release of hyaluronidase (HAase) using 15 kDa poly(lactic-co-glycolic) acid and bovine testicular HAase. The implant releases bioactive HAase to degrade the HA through enzymatic hydrolysis at early timepoints. In the first 24 h, 17.9% of the HAase is released, which can reduce the viscosity of a 10 mg/mL HA solution by 94.1% and deplete the HA content within primary human pancreatic tumor samples and ex vivo murine tumors. At later timepoints, as lower quantities of HAase are released (51.4% released in total over 21 d), the degradation of HA is supplemented by the acidic by-products that accumulate as a result of implant degradation. Acidic conditions degrade HA through nonenzymatic methods. This formulation has potential as an intratumoral injection to allow sustained degradation of HA at the pancreatic tumor site.

Controlled release starch-lipid implant for the therapy of severe malaria

Parenteral depot systems can provide a constant release of drugs over a few days to months. Poly-(lactic acid) (PLA) and Poly-(lactide-co-glycolide) (PLGA) are the most commonly used polymers in the production of these systems. Finding alternatives to these polymers is of great importance to avoid certain drawbacks of these polymers (e.g. microacidity) and to increase the selection possibilities. In this study, different types of starch in combination with glycerol monostearate (GMS) were developed and investigated for their physicochemical properties and release characteristics. The noninvasive method of electron paramagnetic resonance (EPR) was used to study the release kinetics and mechanisms of nitroxide model drugs. The studies demonstrated the general suitability of the system composed of high amylose starch and GMS to form a controlled release system. For further characterization of the prepared system, formulations with different proportions of starch and GMS, loaded with the antimalarial agents artesunate or artemether were prepared. The implants were characterized with X-ray powder diffraction (XRPD) and texture analysis. The in vitro release studies demonstrated the sustained release of artemether over 6 days from a starch-based implant which matches desired kinetic for the treatment of severe malaria. In summary, a starch-based implant with appropriate mechanical properties was produced that can be a potential candidate for the treatment of severe malaria.

How agarose gels surrounding PLGA implants limit swelling and slow down drug release

The aim of this study was to better understand to which extent and in which way the presence of an agarose gel (mimicking living tissue) around a PLGA [poly(lactic-co-glycolic acid)] implant affects the resulting drug release kinetics. Ibuprofen-loaded implants were prepared by hot melt extrusion. Drug release was measured upon exposure to phosphate buffer pH 7.4 in Eppendorf tubes, as well as upon inclusion into an agarose gel which was exposed to phosphate buffer pH 7.4 in an Eppendorf tube or in a transwell plate. Dynamic changes in the implants' dry & wet mass and dimensions were monitored gravimetrically and by optical macroscopy. Implant erosion and polymer degradation were observed by SEM and GPC. Different pH indicators were used to measure pH changes in the bulk fluids, gels and within the implants during drug release. Ibuprofen release was bi-phasic in all cases: A zero order release phase (~20% of the dose) was followed by a more rapid, final drug release phase. Interestingly, the presence of the hydrogel delayed the onset of the 2nd release phase. This could be attributed to the sterical hindrance of implant swelling: After a certain lag time, the degrading PLGA matrix becomes sufficiently hydrophilic and mechanically instable to allow for the penetration of substantial amounts of water into the system. This fundamentally changes the conditions for drug release: The latter becomes much more mobile and is more rapidly released. A gel surrounding the implant mechanically hinders system swelling and, thus, slows down drug release. These observations also strengthen the hypothesis of the "orchestrating" role of PLGA swelling for the control of drug release and can help developing more realistic in vitro release set-ups.

An in vitro gel-based system for characterizing and predicting the long-term performance of PLGA in situ forming implants

In situ forming implants are exposed to an extracellular matrix resembling a gel rather than aqueous solution upon subcutaneous administration. The aim of study was to develop a gel-based release testing system for characterizing the long-term in vitro behavior of in situ forming implants. The gel-based system consisted of an agarose gel mimicking the subcutaneous injection site and a receiver layer comprising phosphate buffer. Poly(D,L-lactide-co-glycolide) in situ forming implants containing leuprolide acetate as the model peptide and N-methyl-2-pyrrolidone (NMP), dimethyl sulfoxide (DMSO) or triacetin as co-solvent were investigated. The gel-based release testing system discriminated between the formulations. Accelerated release data obtained at elevated temperatures were able to predict real-time release applying the Arrhenius equation. Monitoring of the microenvironmental pH of the implants was performed by UV-Vis imaging in the gel-based system at 50 °C. A pH drop (from pH 7.4 to 6.7 for the NMP and DMSO implants, to pH 5.5 for the triacetin implants) within the first day was observed, followed by an increase to pH ∼7.4. The gel-based system coupled with UV imaging offered opportunity for detailed evaluation and prediction of the in vitro performance of long-acting injectables, facilitating future development of in situ depot forming delivery systems.

Drug release from in situ forming implants and advances in release testing

In situ forming implants, defined as liquid formulations that generate solid or semisolid depots following administration, have shown a range of advantages in drug delivery. This drug delivery strategy allows localized delivery, sustained drug release over periods of days to months, and is a less invasive option compared to traditional solid implants which typically require surgical implantation. Unfortunately, there are a number of quality control challenges in terms of drug release testing of these delivery systems which is likely to have contributed to the relatively few commercially available in situ forming implant products. This article reviews current marketed in situ forming implant products, FDA guidance on in vitro release testing, and formulation and environmental parameters influencing drug release from in situ forming implants. Formulation considerations for development of biological agents loaded in situ forming implants are also discussed. The advantages and limitations of typically used in vitro release testing methods are summarized. Difficulties in the development of in vitro-in vivo correlations (IVIVCs) for in situ forming implant are discussed. The knowledge presented will be helpful for the development of in situ forming implants, as well as for the development of appropriate in vitro testing methods and IVIVCs.

Ovarian Accumulation of Nanoemulsions: Impact of Mice Age and Particle Size

Nanotechnology in the field of drug delivery comes with great benefits due to the unique physicochemical properties of newly developed nanocarriers. However, they may come as well with severe toxicological side effects because of unwanted accumulation in organs outside of their targeted site of actions. Several studies showed an unintended accumulation of various nanocarriers in female sex organs, especially in the ovaries. Some led to inflammation, fibrosis, or decreasing follicle numbers. However, none of these studies investigated ovarian accumulation in context to both reproductive aging and particle size. Besides the influences of particle size, the biodistribution profile may be altered as well by reproductive aging because of reduced capacities of the reticuloendothelial system (RES), changes in sex steroid hormone levels as well as altering ovarian stromal blood flow. This systematic investigation of the biodistribution of intravenously (i.v) injected nanoemulsions revealed significant dependencies on the two parameters particle size and age starting from juvenile prepubescent to senescent mice. Using fluorescent in vivo and ex vivo imaging, prepubescent mice showed nearly no accumulation of nanoemulsion in their uteri and ovaries, but high accumulations in the organs of the RES liver and spleen independently of the particle size. In fertile adult mice, the accumulation increased significantly in the ovaries with an increased particle size of the nanoemulsions by nearly doubling the portion of the average radiant efficiency (PARE) to ~10% of the total measured signal of all excised organs. With reproductive aging and hence loss of fertility in senescent mice, the accumulation decreased again to moderate levels, again independently of the particle size. In conclusion, the ovarian accumulation of these nanocarriers depended on both the age plus the particle size during maturity.

Poly(lactic-co-glycolic acid) microsphere production based on quality by design: a review

Poly(lactic-co-glycolic acid) (PLGA) has garnered increasing attention as a candidate drug delivery polymer owing to its favorable properties, including its excellent biocompatibility, biodegradability, non-toxicity, non-immunogenicity, and mechanical strength. PLAG are specifically used as microspheres for the sustained/controlled and targeted delivery of hydrophilic or hydrophobic drugs, as well as biological therapeutic macromolecules, including peptide and protein drugs. PLGAs with different molecular weights, lactic acid (LA)/glycolic acid (GA) ratios, and end groups exhibit unique release characteristics, which is beneficial for obtaining diverse therapeutic effects. This review aims to analyze the composition of PLGA microspheres, and understand the manufacturing process involved in their production, from a quality by design perspective. Additionally, the key factors affecting PLGA microsphere development are explored as well as the principles involved in the synthesis and degradation of PLGA and its interaction with active drugs. Further, the effects elicited by microcosmic conditions on PLGA macroscopic properties, are analyzed. These conditions include variations in the organic phase (organic solvent, PLGA, and drug concentration), continuous phase (emulsifying ability), emulsifying stage (organic phase and continuous phase interaction, homogenization parameters), and solidification process (relationship between solvent volatilization rate and curing conditions). The challenges in achieving consistency between batches during manufacturing are addressed, and continuous production is discussed as a potential solution. Finally, potential critical quality attributes are introduced, which may facilitate the optimization of process parameters.

Hydrogels Based on Oxidized Cellulose Sulfates and Carboxymethyl Chitosan: Studies on Intrinsic Gel Properties, Stability, and Biocompatibility

Cellulose and chitosan are excellent components for the fabrication of bioactive scaffolds, as they are biocompatible and abundantly available. Their derivatives Ocarboxymethyl chitosan (CMChi) and oxidized cellulose sulfate (oxCS) can form in situ gelling, bioactive hydrogels, due to the formation of imine bonds for crosslinking. Here the influence of the degrees of sulfation (DS), oxidation (DO), and the molecular weight of oxCS on intrinsic and rheological properties of such hydrogels and their ability to support the survival and growth of human-adipose-derived stem cells (hADSC) is investigated. It is found that the pH of the hydrogels is generally slightly acidic, while their network density and E-modulus are found to be dependent on the DS and DO, which makes the properties of hydrogels tunable. Extensive studies show that hydrogels can be stable for up to 14 days and that their stability is largely dependent on the DO, molecular weight, and the components mixing ratio. Cytotoxicity studies of the hydrogel with hADSCs show biocompatible gels in dependence on the molecular weight and degree of oxidation with viable cells up to 14 days. These findings can help to develop specifically tailored hydrogels for tissue engineering applications to replace different types of connective tissue.

Formulation of drug-loaded oligodepsipeptide particles with submicron size

The size of particulate carriers is key to their transport and distribution in biological systems, and needs to be tailored in the higher submicron range to enable follicular uptake for dermal treatment. Oligodepsipeptides are promising nanoparticulate carrier systems as they can be designed to exhibit enhanced interaction with drug molecules. Here, a fabrication scheme for drug-loaded submicron particles from oligo[3-(S)-sec-butylmorpholine-2,5-dione]diol (OBMD) is presented based on an emulsion solvent evaporation method with cosolvent, surfactant, and polymer concentration as variable process parameters. The particle size (300-950 nm) increased with lower surfactant concentration and higher oligomer concentration. The addition of acetone increased the particle size at low surfactant concentration. Particle size remained stable upon the encapsulation of models compounds dexamethasone (DXM) and Nile red (NR), having different physicochemical properties. DXM was released faster compared to NR due to its higher water solubility. Overall, the results indicated that both drug-loading and size control of OBMD submicron particles can be achieved. When applied on porcine ear skin samples, the NR-loaded particles have been shown to allow NR penetration into the hair follicle and the depth reached with the 300 nm particles was comparable to the one reached with the cream formulation. A potential benefit of the particles compared to a cream is their sustained release profile.

Development of mAb-loaded 3D-printed (FDM) implantable devices based on PLGA

The main objective of this work was to explore the feasibility to print monoclonal antibody (mAb)-loaded implantable systems using fused-deposition modelling (FDM) to build complex dosage form designs. Indeed, to our knowledge, this work is the first investigation of mAb-loaded devices using FDM. To make this possible, different steps were developed and optimized. A mAb solution was stabilized using trehalose (TRE), sucrose (SUC), hydroxypropyl-β-cyclodextrin (HP-β-CD), sorbitol or inulin (INU) in order to be spray dried (SD). Printable filaments were then made of poly(lactide-co-glycolide) (PLGA) and mAb powder (15% w/w) using hot melt extrusion (HME). The FDM process was optimized to print these filaments without altering the mAb stability. TRE was selected and associated to L-leucine (LEU) to increase the mAb stability. The stability was then evaluated considering high and low molecular weight species levels. The mAb-based devices were well-stabilized with the selected excipients during both the HME and the FDM processes. The 3D-printed devices showed sustained-release profiles with a low burst effect. The mAb-binding capacity was preserved up to 70% following the whole fabrication process. These promising results demonstrate that FDM could be used to produce mAb-loaded devices with good stability, affinity and sustained-release profiles of the mAb.

Noninvasive characterization (EPR, μCT, NMR) of 3D PLA electrospun fiber sponges for controlled drug delivery

Highly porous 3D-scaffolds, made from cut, electrospun PLA fibers, are relatively new and promising systems for controlled drug-delivery applications. Because knowledge concerning fundamental processes of drug delivery from those scaffolds is limited, we noninvasively characterized drug-loading and drug-release mechanisms of these polymer-fiber sponges (PFS). We screened simplified PFS-implantation scenarios with EPR and μCT to quantify and 3D-visualize the absorption of model-biofluids and an oil, a possible drug-loading liquid. Saturation of PFS (6 × 8 mm, h x d) is governed by the high hydrophobicity of the material and air-entrapment. It required up to 45 weeks for phosphate-buffered saline and 11 weeks for a more physiological, surface-active protein-solution, indicating the slow fluid-uptake of PFS as an effective mechanism to substantially prolong the release of a drug incorporated within the scaffold. Medium-chain triglycerides, as a good wetting liquid, saturated PFS within seconds, suggesting PFS potential to serve as carrier-vessels for immobilizing hydrophobic drug-solutions to define a liquid's 3D-interface. Oil-retention under mechanical stress was therefore investigated. ¹H NMR permitted insights into PFS-oil interaction, confirming surface-relaxation and restricted diffusion; both did not influence drug release from oil-loaded PFS. Results facilitate better understanding of PFS and their potential use in drug delivery.

Nicardipine Loaded Solid Phospholipid Extrudates for the Prevention of Cerebral Vasospasms: In Vitro Characterization

The aim of the study was to develop nicardipine loaded phospholipid extrudates as an alternative for PLA/PLGA-based implants for the prevention of cerebral vasospasms. Extrudates of different mixtures of saturated and unsaturated phosphatidylcholine (PC) were produced and characterized by DSC, microscopy and texture analysis. Single phospholipid components were identified by ELSD-HPLC. Extrudates of 2 mm diameter were obtained by twin screw extrusion temperatures below 50 °C. The ratio of unsaturated and saturated phosphatidylcholine components determines the physicochemical properties of the extrudates as well as the rate of erosion. Nicardipine loaded phospholipids extrudates released the drug over several weeks in vitro. The phospholipid composition of the remaining extrudate changed during the release, the content of unsaturated phospholipids decreased faster compared to the saturated ones. In conclusion, solid phospholipid extrudates are promising materials for the development of new parenteral controlled release systems.

Silica particles incorporated into PLGA-based in situ-forming implants exploit the dual advantage of sustained release and particulate delivery

Poly (lactic-co-glycolic acid) (PLGA) in situ-forming implants are well-established drug delivery systems for controlled drug release over weeks up to months. To prevent initial burst release, which is still a major issue associated with PLGA-based implants, drugs attached to particulate carriers have been encapsulated. Unfortunately, former studies only investigated the resulting release of the soluble drugs and hence missed the potential offered by particulate drug release. In this study, we developed a system capable of releasing functional drug-carrying particles over a prolonged time. First, we evaluated the feasibility of our approach by encapsulating silica particles of different sizes (500 nm and 1 μm) and surface properties (OH or NH₂ groups) into in situ-forming PLGA implants. In this way, we achieved sustained release of particles over periods ranging from 30 to 70 days. OH-carrying particles were released much more quickly when compared to NH₂-modified particles. We demonstrated that the underlying release mechanisms involve size-dependent diffusion and polymer-particle interactions. Second, particles that carried covalently-attached ovalbumin (OVA) on their surfaces were incorporated into the implant. We demonstrated that OVA was released in association with the particles as functional entities over a period of 30 days. The released particle-drug conjugates maintained their colloidal stability and were efficiently taken up by antigen presenting cells. This system consisting of particles incorporated into PLGA-based in situ-forming implants offers the dual advantage of sustained and particulate release of drugs as a functional unit and has potential for future use in many applications, particularly in single-dose vaccines.

Tabotamp®, Respectively, Surgicel®, Increases the Cell Death of Neuronal and Glial Cells In Vitro

Oxidized regenerated cellulose (ORC) is an approved absorbable hemostat in neurosurgery, and contains 18–21% carboxylic acid groups. This modification leads to a low pH in aqueous solutions. Therefore, the aim of study was to analyze the pH-dependent effects of the ORC Tabotamp^® on astrocytes, Schwann cells, and neuronal cells in vitro to investigate whether Tabotamp^® is a suitable hemostat in cerebral eloquent areas. The ORC-dependent pH value changes were measured with (i) a pH meter, (ii) electron paramagnetic resonance spectroscopy, using pH-sensitive spin probes, and (iii) with fluorescence microscopy. Cell lines from neurons, astrocytes, and Schwann cells, as well as primary astrocytes were incubated with increasing areas of Tabotamp^®. Cytotoxicity was detected using a fluorescence labeled DNA-binding dye. In addition, the wounding extent was analyzed via crystal violet staining of cell layers. The strongest pH reduction (to 2.2) was shown in phosphate buffered saline, whereas culture medium and cerebrospinal fluid demonstrated a higher buffer capacity during Tabotamp^® incubation. In addition, we could detect a distance-dependent pH gradient by fluorescence microscopy. Incubation of Tabotamp^® on cell monolayers led to detachment of covered cells and showed increased cytotoxicity in all tested cell lines and primary cells depending on the covered area. These in vitro results indicate that Tabotamp^® may not be a suitable hemostat in cerebral eloquent areas.

Fundamental insights in PLGA degradation from thin film studies

Poly(lactide-co-glycolide)s are commercially available degradable implant materials, which are typically selected based on specifications given by the manufacturer, one of which is their molecular weight. Here, we address the question whether variations in the chain length and their distribution affect the degradation behavior of Poly[(rac-lactide)-co-glycolide]s (PDLLGA). The hydrolysis was studied in ultrathin films at the air-water interface in order to rule out any morphological effects. We found that both for purely hydrolytic degradation as well as under enzymatic catalysis, the molecular weight has very little effect on the overall degradation kinetics of PDLLGAs. The quantitative analysis suggested a random scission mechanism. The monolayer experiments showed that an acidic micro-pH does not accelerate the degradation of PDLLGAs, in contrast to alkaline conditions. The degradation experiments were combined with interfacial rheology measurements, which showed a drastic decrease of the viscosity at little mass loss. The extrapolated molecular weight behaved similar to the viscosity, dropping to a value near to the solubility limit of PDLLGA oligomers before mass loss set in. This observation suggests a solubility controlled degradation of PDLLGA. Conclusively, the molecular weight affects the degradation of PDLLGA devices mostly in indirect ways, e.g. by determining their morphology and porosity during fabrication. Our study demonstrates the relevance of the presented Langmuir degradation method for the design of controlled release systems.

E-jet 3D printed drug delivery implants to inhibit growth and metastasis of orthotopic breast cancer

Drug-loaded implants have attracted considerable attention in cancer treatment due to their precise delivery of drugs into cancer tissues. Contrary to injected drug delivery, the application of drug-loaded implants remains underutilized given the requirement for a surgical operation. Nevertheless, drug-loaded implants have several advantages, including a reduction in frequency of drug administration, minimal systemic toxicity, and increased delivery efficacy. Herein, we developed a new, precise, drug delivery device for orthotopic breast cancer therapy able to suppress breast tumor growth and reduce pulmonary metastasis using combination chemotherapy. Poly-lactic-co-glycolic acid scaffolds were fabricated by 3D printing to immobilize 5-fluorouracil and NVP-BEZ235. The implantable scaffolds significantly reduced the required drug dosages and ensured curative drug levels near tumor sites for prolonged period, while drug exposure to normal tissues was minimized. Moreover, long-term drug release was achieved, potentially allowing one-off implantation and, thus, a major reduction in the frequency of drug administration. This drug-loaded scaffold has great potential in anti-tumor treatment, possibly paving the way for precise, effective, and harmless cancer therapy.

Mechanistic explanation of the (up to) 3 release phases of PLGA microparticles: Diprophylline dispersions

The aim of this study was to better understand the root causes for the (up to) 3 drug release phases observed with poly (lactic-co-glycolic acid) (PLGA) microparticles containing diprophylline particles: The 1st release phase ("burst release"), 2nd release phase (with an "about constant release rate") and 3rd release phase (which is again rapid and leads to complete drug exhaust). The behavior of single microparticles was monitored upon exposure to phosphate buffer pH 7.4, in particular with respect to their drug release and swelling behaviors. Diprophylline-loaded PLGA microparticles were prepared with a solid-in-oil-in-water solvent extraction/evaporation method. Tiny drug crystals were rather homogeneously distributed throughout the polymer matrix after manufacturing. Batches with "small" (63 µm), "medium-sized" (113 µm) and "large" (296 µm) microparticles with a practical drug loading of 5-7% were prepared. Importantly, each microparticle releases the drug "in its own way", depending on the exact distribution of the tiny drug crystals within the system. During the burst release, drug crystals with direct surface access rapidly dissolve. During the 2nd release phase tiny drug crystals (often) located in surface near regions which undergo swelling, are likely released. During the 3rd release phase, the entire microparticle undergoes substantial swelling. This results in high quantities of water present throughout the system, which becomes "gel-like". Consequently, the drug crystals dissolve, and the dissolved drug molecules rather rapidly diffuse through the highly swollen polymer gel.

In-situ forming implants for the treatment of periodontal diseases: Simultaneous controlled release of an antiseptic and an anti-inflammatory drug

Different types of in-situ forming implants based on poly(lactic-co-glycolic acid) (PLGA) for the controlled dual release of an antiseptic drug (chlorhexidine) and an anti-inflammatory drug (ibuprofen) were prepared and thoroughly characterized in vitro. N-methyl-pyrrolidone (NMP) was used as water-miscible solvent, acetyltributyl citrate (ATBC) as plasticizer and hydroxypropyl methylcellulose (HPMC) was added to enhance the implants' stickiness/bioadhesion upon formation within the periodontal pocket. Different drug forms exhibiting substantially different solubilities were used: chlorhexidine dihydrochloride and digluconate as well as ibuprofen free acid and lysinate. The initial drug loadings were varied from 1.5 to 16.1%. In vitro drug release, dynamic changes in the pH of the surrounding bulk fluid and in the systems' wet mass as well as polymer degradation were monitored. Importantly, the release of both drugs, chlorhexidine and ibuprofen, could effectively be controlled simultaneously during several weeks. Interestingly, the tremendous differences in the drug forms' solubilities (e.g., factor >5000) did not translate into major differences in the resulting release kinetics. In the case of ibuprofen, this can likely (at least in part) be attributed to significant drug-polymer interactions (ibuprofen acts as a plasticizer for PLGA). In the case of chlorhexidine, the release of the much less soluble dihydrochloride was even faster compared to the more soluble digluconate (when combined with ibuprofen free acid). In the case of ibuprofen, at higher initial drug loadings also limited solubility effects within the implants seem to play a role, in contrast to chlorhexidine. In the latter case, instead, increased system porosity effects likely dominate at higher drug loadings.

Sucrose Acetate Isobutyrate as an In situ Forming Implant for Sustained Release of Local Anesthetics

OBJECTIVE

In this study, an injectable Sucrose Acetate Isobutyrate (SAIB) drug delivery system (SADS) was designed and fabricated for the sustained release of Ropivacaine (RP) to prolong the duration of local anesthesia.

METHODS

By mixing SAIB, RP, and N-methyl-2-pyrrolidone, the SADS was prepared in a sol state with low viscosity before injection. After subcutaneous injection, the pre-gel solution underwent gelation in situ to form a drug-released depot.

RESULT

The in vitro release profiles and in vivo pharmacokinetic analysis indicated that RP-SADS had suitable controlled release properties. Particularly, the RP-SADS significantly reduced the initial burst release after subcutaneous injection in rats.

CONCLUSION

In a pharmacodynamic analysis of rats, the duration of nerve blockade was prolonged by over 3-fold for the RP-SADS formulation compared to RP solution. Additionally, RP-SADS showed good biocompatibility in vitro and in vivo. Thus, the SADS-based depot technology is a safe drug delivery strategy for the sustained release of local anesthetics with long-term analgesia effects.

Controlling and quantifying the stability of amino acid-based cargo within polymeric delivery systems

In recent years, the rapid growth and availability of protein and peptide therapeutics has not only expanded the boundaries of modern science but has also revolutionized the practice of medicine today. The potential of such therapies, however, is greatly limited by the innate instabilities of proteins and peptides, which is further magnified during therapeutic formulation processing, transport, storage, and administration. In this paper, we will consider the unique stability challenges associated with protein/peptide polymeric delivery systems from an engineering approach oriented towards the quantification and modification of amino acid-based cargo stability. While a number of methods have been developed for the purposes of quantifying factors affecting protein and peptide stability, current measurement techniques remain largely limited in scope in regard to polymeric drug delivery systems. This paper will primarily describe the influence of water content, pH, and temperature on protein and peptide stability within polymer-based delivery systems. Moreover, we will review current instrumentation used to quantify factors affecting protein/peptide stability with respect to water content, pH, and temperature. Lastly, we will outline several recommendations to help guide future research efforts to develop methods more specific to quantifying protein/peptide stability within polymer-based delivery systems.

In-situ forming PLGA implants for intraocular dexamethasone delivery

Different types of in-situ forming implants based on poly(lactic-co-glycolic acid) (PLGA) and N-methyl-pyrrolidone (NMP) were prepared for controlled ocular delivery of dexamethasone. The impact of the volume of the release medium, initial drug content, polymer molecular weight and PLGA concentration on the resulting drug release kinetics were studied and explained based on a thorough physico-chemical characterization of the systems. This included for instance the monitoring of dynamic changes in the implants' wet and dry mass, morphology, PLGA polymer molecular weight, pH of the surrounding bulk fluid and water/NMP contents upon exposure to phosphate buffer pH 7.4. Importantly, the systems can be expected to be rather robust with respect to variations in the vitreous humor volumes encountered in vivo. Interestingly, limited drug solubility effects within the implants as well as in the surrounding aqueous medium play an important role for the control of drug release at a drug loading of only 7.5%. Furthermore, the polymer molecular weight and PLGA concentration in the liquid formulations are decisive for how the polymer precipitates during solvent exchange and for the swelling behavior of the systems. These features determine the resulting inner system structure and the conditions for mass transport. Consequently, they affect the degradation and drug release of the in-situ formed implants.

Controlled drug release to the inner ear: Concepts, materials, mechanisms, and performance

Progress in drug delivery to the ear has been achieved over the last few years. This review illustrates the main mechanisms of controlled drug release and the resulting geometry- and size-dependent release kinetics. The potency, physicochemical properties, and stability of the drug molecules are key parameters for designing the most suitable drug delivery system. The most important drug delivery systems for the inner ear include solid foams, hydrogels, and different nanoscale drug delivery systems (e.g., nanoparticles, liposomes, lipid nanocapsules, polymersomes). Their main characteristics (i.e., general structure and materials) are discussed, with special attention given to underlining the link between the physicochemical properties (e.g., surface areas, glass transition temperature, microviscosity, size, and shape) and release kinetics. An appropriate characterization of the drug, the excipients used, and the formulated drug delivery systems is necessary to achieve a deeper understanding of the release process and decrease variability originating from the drug delivery system. This task cannot be solved by otologists alone. The interdisciplinary cooperation between otology/neurotology, pharmaceutics, physics, and other disciplines will result in improved drug delivery systems for the inner ear.

Monomer sequence in PLGA microparticles: Effects on acidic microclimates and in vivo inflammatory response

Controlling the backbone architecture of poly(lactic-co-glycolic acid)s (PLGAs) is demonstrated to have a strong influence on the production and release of acidic degradation by-products in microparticle matrices. Previous efforts for controlling the internal and external accumulation of acidity for PLGA microparticles have focused on the addition of excipients including neutralization and anti-inflammatory agents. In this report, we utilize a sequence-control strategy to tailor the microstructure of PLGA. The internal acidic microclimate distributions within sequence-defined and random PLGA microparticles were monitored in vitro using a non-invasive ratiometric two-photon microscopy (TPM) methodology. Sequence-defined PLGAs were found to have minimal changes in pH distribution and lower amounts of percolating acidic by-products. A parallel scanning electron microscopy study further linked external morphological events to internal degradation-induced structural changes. The properties of the sequenced and random copolymers characterized in vitro translated to differences in in vivo behavior. The sequence alternating copolymer, poly LG, had lower granulomatous foreign-body reactions compared to random racemic PLGA with a 50:50 ratio of lactic to glycolic acid.

STATEMENT OF SIGNIFICANCE

This paper demonstrates that changing the monomer sequence in poly(lactic-co-glycolic acid)s (PLGAs) leads to dramatic differences in the rate of degradation and the internal acidic microclimate of microparticles degrading in vitro. We note that the acidic microclimates within these particles were imaged for the first time with two-photon microscopy, which gives an extremely clear and detailed picture of the degradation process. Importantly, we also document that the observed sequence-controlled in vitro processes translate into differences in the in vivo behavior of polymers which have the same L to G composition but differing microstructures. These data, placed in the context of our prior studies on swelling, erosion, and MW loss (Biomaterials2017, 117, 66 and other references cited within the manuscript), provide significant insight not only about sequence effects in PLGAs but into the underlying mechanisms of PLGA degradation in general.

Intended and Unintended Targeting of Polymeric Nanocarriers: The Case of Modified Poly(glycerol adipate) Nanoparticles

Biodegradable nanoparticles based on stearic acid-modified poly(glycerol adipate) (PGAS) are promising carriers for drug delivery. In order to investigate the impact of the particle interface characteristics on the biological fate, PGAS nanoparticles are covalently and noncovalently coated with N-(2-hydroxypropyl) methacrylamide (HPMA) copolymers. HPMA copolymer-modified PGAS nanoparticles have similar particle sizes, but less negative zeta-potentials. Nanoparticles are double labeled with the fluorescent dyes DiR (noncovalently) and DYOMICS-676 (covalently bound to HPMA copolymer), and their biodistribution is investigated noninvasively by multispectral optical imaging. Both covalent and noncovalent coatings cause changes in the pharmacokinetics and biodistribution in healthy and tumor-bearing mice. In addition to the intended tumor accumulation, high signals of both fluorescent dyes are also observed in other organs, including liver, ovaries, adrenal glands, and bone. The unintended accumulation of nanocarriers needs further detailed and systematic investigations, especially with respect to the observed ovarian and adrenal gland accumulation.

Osteosynthesis of a cranio-osteoplasty with a biodegradable magnesium plate system in miniature pigs

Biodegradable magnesium alloys are a new class of implant material suitable for bone surgery. The aim of this study was to investigate plates and screws made of magnesium for osteosynthesis in comparison to titanium in a cranial fracture model. Implants were used for internal fixation of a cranio-osteoplasty in nine minipigs. Computed tomography was conducted repeatedly after surgery. The implants and the adjacent tissues were harvested 10, 20 and 30weeks after surgery and investigated by micro-computed tomography and histological analysis. The surgical procedure and the inserted osteosynthesis material were well tolerated by the animals, and the bone healing of the osteoplasty was undisturbed at all times. The adjacent bone showed formation of lacunas in the magnesium group, resulting in a lower bone-to-implant contact ratio than that of titanium (72 vs. 94% at week 30), but this did not lead to clinical side effects. Radiological measurements showed no reduction in osteosynthesis material volume, but indicated signs of degradation: distinct volumes within the magnesium osteosynthesis group had lower density in micro-computed tomography, and these volumes increased up to 9% at week 30. The histological preparations showed areas of translucency and porosity inside the magnesium, but the outer shape of the osteosynthesis material remained unchanged. No fracture or loosening of the osteosynthesis devices appeared. Soft tissue probes confirmed sufficient biocompatibility. Given their biodegradable capacity, biocompatibility, mechanical strength and visibility on radiographs, osteosynthesis plates made of magnesium alloys are suitable for internal fixation procedures.

STATEMENT OF SIGNIFICANCE

To the best of our knowledge this is the first study that used biodegradable magnesium implants for osteosynthesis in a cranial fracture model. The cranio-osteoplasty in miniature pigs allowed in vivo application of plate and screw osteosynthesis of standard-sized implants and the implementation of surgical procedures similar to those conducted on human beings. The osteosynthesis configuration, size, and mechanical properties of the magnesium implants within this study were comparable to those of titanium-based osteosynthesis materials. The results clearly show that bone healing was undisturbed in all cases and that the biocompatibility to hard- and soft tissue was sufficient. Magnesium implants might help to avoid long-term complications and secondary removal procedures due to their biodegradable properties.