Polyanhydride degradation and erosion

Bioresorbable Multilayer Organic-Inorganic Films for Bioelectronic Systems

Bioresorbable electronic devices as temporary biomedical implants represent an emerging class of technology relevant to a range of patient conditions currently addressed with technologies that require surgical explantation after a desired period of use. Obtaining reliable performance and favorable degradation behavior demands materials that can serve as biofluid barriers in encapsulating structures that avoid premature degradation of active electronic components. Here, this work presents a materials design that addresses this need, with properties in water impermeability, mechanical flexibility, and processability that are superior to alternatives. The approach uses multilayer assemblies of alternating films of polyanhydride and silicon oxynitride formed by spin-coating and plasma-enhanced chemical vapor deposition , respectively. Experimental and theoretical studies investigate the effects of material composition and multilayer structure on water barrier performance, water distribution, and degradation behavior. Demonstrations with inductor-capacitor circuits, wireless power transfer systems, and wireless optoelectronic devices illustrate the performance of this materials system as a bioresorbable encapsulating structure.

Polyanhydride Microcapsules Exhibiting a Sharp pH Transition at Physiological Conditions for Instantaneous Triggered Release

Stimulus-responsive microcapsules pose an opportunity to achieve controlled release of the entire load instantaneously upon exposure to an external stimulus. Core-shell microcapsules based on the polyanhydride poly(bis(2-carboxyphenyl)adipate) as a shell were formulated in this work to encapsulate the model active substance pyrene and enable a pH-controlled triggered release. A remarkably narrow triggering pH interval was found where a change in pH from 6.4 to 6.9 allowed for release of the entire core content within seconds. The degradation kinetics of the shell were measured by both spectrophotometric detection of degradation products and mass changes by quartz crystal microbalance with dissipation monitoring and were found to correlate excellently with diffusion coefficients fitted to release measurements at varying pH values. The microcapsules presented in this work allow for an almost instantaneous triggered release even under mild conditions, thanks to the designed core-shell morphology.

Characteristics of Microparticles Based on Resorbable Polyhydroxyalkanoates Loaded with Antibacterial and Cytostatic Drugs

The development of controlled drug delivery systems, in the form of microparticles, is an important area of experimental pharmacology. The success of the design and the quality of the obtained microparticles are determined by the method of manufacture and the properties of the material used as a carrier. The goal is to obtain and characterize microparticles depending on their method of preparation, the chemical composition of the polymer and the load of the drugs. To obtain microparticles, four types of degradable PHAs, differing in their chemical compositions, degrees of crystallinity, molecular weights and temperature characteristics, were used (poly-3-hydroxybutyrate and copolymers 3-hydroxybutyric-co-3-hydroxyvaleric acid, 3-hydroxybutyric-co-4-hydroxybutyric acid, and 3-hydroxybutyric-co-3-hydroxyhexanoic acid). The characteristics of microparticles from PHAs were studied. Good-quality particles with an average particle diameter from 0.8 to 65.0 μm, having satisfactory ζ potential values (from -18 to -50 mV), were obtained. The drug loading content, encapsulation efficiency and in vitro release were characterized. Composite microparticles based on PHAs with additives of polyethylene glycol and polylactide-co-glycolide, and loaded with ceftriaxone and 5-fluorouracil, showed antibacterial and antitumor effects in E. coli and HeLa cultures. The results indicate the high potential of PHAs for the design of modern and efficient drug delivery systems.

Polymer Chemistry Defines Adjuvant Properties and Determines the Immune Response against the Antigen or Vaccine

Activation of the immune system is a needed for designing new antigen/drug delivery systems to develop new therapeutics and for developing animal disease models to study the disease pathogenesis. A weak antigen alone is insufficient to activate the immune system. Sometimes, assistance in the form of polymers is needed to control the release of antigens under in vivo conditions or in the form of an adjuvant to activate the immune system efficiently. Many kinds of polymers from different functional groups are suitable as microbial antigens for inducing therapeutic immune responses against infectious diseases at the preclinical level. The choice of the functionality of polymer varies as per the application type. Polymers from the acid and ester groups are the most common types investigated for protein-based antigens. However, electrostatic interaction-displaying polymers like cationic polymers are the most common type for nucleic acid-based antigens. Metal coordination chemistry is commonly used in polymers designed for cancer immunotherapeutic applications to suppress inflammation and induce a protective immune response. Amide chemistry is widely deployed in polymers used to develop antigen-specific disease models like the experimental autoimmune arthritis murine model.

Aggregation-Inhibiting scFv-Based Therapies Protect Mice against AAV1/2-Induced A53T-α-Synuclein Overexpression

To date, there is no cure for Parkinson's disease (PD). There is a pressing need for anti-neurodegenerative therapeutics that can slow or halt PD progression by targeting underlying disease mechanisms. Specifically, preventing the build-up of alpha-synuclein (αSyn) and its aggregated and mutated forms is a key therapeutic target. In this study, an adeno-associated viral vector loaded with the A53T gene mutation was used to induce rapid αSyn-associated PD pathogenesis in C57BL/6 mice. We tested the ability of a novel therapeutic, a single chain fragment variable (scFv) antibody with specificity only for pathologic forms of αSyn, to protect against αSyn-induced neurodegeneration, after unilateral viral vector injection in the substantia nigra. Additionally, polyanhydride nanoparticles, which provide sustained release of therapeutics with dose-sparing properties, were used as a delivery platform for the scFv. Through bi-weekly behavioral assessments and across multiple post-mortem immunochemical analyses, we found that the scFv-based therapies allowed the mice to recover motor activity and reduce overall αSyn expression in the substantia nigra. In summary, these novel scFv-based therapies, which are specific exclusively for pathological aggregates of αSyn, show early promise in blocking PD progression in a surrogate mouse PD model.

Relationship between mechanical load and surface erosion degradation of a shape memory elastomer poly(glycerol-dodecanoate) for soft tissue implant

Poly(glycerol-dodecanoate) (PGD) has aroused increasing attention in biomedical engineering for its degradability, shape memory and rubber-like mechanical properties, giving it potential to fabricate intelligent implants for soft tissues. Adjustable degradation is important for biodegradable implants and is affected by various factors. The mechanical load has been shown to play an important role in regulating polymer degradation in vivo. An in-depth investigation of PGD degradation under mechanical load is essential for adjusting its degradation behavior after implantation, further guiding to regulate degradation behavior of soft tissue implants made by PGD. In vitro degradation of PGD under different compressive and tensile load has proceeded in this study and describes the relationships by empirical equations. Based on the equations, a continuum damage model is designed to simulate surface erosion degradation of PGD under stress through finite element analysis, which provides a protocol for PGD implants with different geometric structures at varied mechanical conditions and provides solutions for predicting in vivo degradation processes, stress distribution during degradation and optimization of the loaded drug release.

Characterization of CPH:SA microparticle-based delivery of interleukin-1 alpha for cancer immunotherapy

Background

Interleukin-1 alpha (IL-1α) is a pro-inflammatory cytokine that can activate immune effector cells and trigger anti-tumor immune responses. However, dose-limiting toxicities including cytokine storm and hypotension has limited its use in the clinic as a cancer therapy. We propose that polymeric microparticle (MP)-based delivery of IL-1α will suppress the acute pro-inflammatory side effects by allowing for slow and controlled release of IL-1α systemically, while simultaneously triggering an anti-tumor immune response.

Methods

Polyanhydride copolymers composed of 1,6-bis-(p-carboxyphenoxy)-hexane:sebacic 20:80 (CPH:SA 20:80) was utilized to fabricate MPs. Recombinant IL-1α (rIL-1α) was encapsulated into CPH:SA 20:80 MPs (IL-1α-MPs) and the MPs were characterized by size, charge, loading efficiency, and in-vitro release and activity of IL-1α. IL-1α-MPs were injected intraperitonially into head and neck squamous cell carcinoma (HNSCC)-bearing C57Bl/6 mice and monitored for changes in weight, tumor growth, circulating cytokines/chemokines, hepatic and kidney enzymes, blood pressure, heart rate, and tumor-infiltrating immune cells.

Results

CPH:SA IL-1α-MPs demonstrated sustained release kinetics of IL-1α (100% protein released over 8-10 days) accompanied by minimal weight loss and systemic inflammation compared to rIL-1α-treated mice. Blood pressure measured by radiotelemetry in conscious mice demonstrates that rIL-1α-induced hypotension was prevented in IL-1α-MP-treated mice. Liver and kidney enzymes were within normal range for all control and cytokine-treated mice. Both rIL-1α and IL-1α-MP-treated mice showed similar delays in tumor growth and similar increases in tumor-infiltrating CD3+ T cells, macrophages, and dendritic cells.

Conclusions

CPH:SA-based IL-1α-MPs generated a slow and sustained systemic release of IL-1α resulting in reduced weight loss, systemic inflammation, and hypotension accompanied by an adequate anti-tumor immune response in HNSCC-tumor bearing mice. Therefore, MPs based on CPH:SA formulations may be promising as delivery vehicles for IL-1α to achieve safe, effective, and durable antitumor responses for HNSCC patients.

Polyanhydride Chemistry

Polyanhydrides (PAs) are a class of synthetic biodegradable polymers employed as controlled drug delivery vehicles. They can be synthesized and scaled up from low-cost starting materials. The structure of PAs can be manipulated synthetically to meet desirable characteristics. PAs are biocompatible, biodegradable, and generate nontoxic metabolites upon degradation, which are easily eliminated from the body. The rate of water penetrating into the polyanhydride (PA) matrix is slower than the anhydride bond cleavage. This phenomenon sets PAs as "surface-eroding drug delivery carriers." Consequently, a variety of PA-based drug delivery carriers in the form of solid implants, pasty injectable formulations, microspheres, nanoparticles, etc. have been developed for the sustained release of small molecule drugs, and vaccines, peptide drugs, and nucleic acid-based active agents. The rate of drug delivery is often controlled by the polymer erosion rate, which is influenced by the polymer structure and composition, crystallinity, hydrophobicity, pH of the release medium, device size, configuration, etc. Owing to the above-mentioned interesting physicochemical and mechanical properties of PAs, the present review focuses on the advancements made in the domain of synthetic biodegradable biomedical PAs for therapeutic delivery applications. Various classes of PAs, their structures, their unique characteristics, their physicochemical and mechanical properties, and factors influencing surface erosion are discussed in detail. The review also summarizes various methods involved in the synthesis of PAs and their utility in the biomedical domain as drug, vaccine, and peptide delivery carriers in different formulations are reviewed.

Factors Controlling Degradation of Biologically Relevant Synthetic Polymers in Solution and Solid State

The field of biodegradable synthetic polymers, which is central for regenerative engineering and drug delivery applications, encompasses a multitude of hydrolytically sensitive macromolecular structures and diverse processing approaches. The ideal degradation behavior for a specific life science application must comply with a set of requirements, which include a clinically relevant kinetic profile, adequate biocompatibility, benign degradation products, and controlled structural evolution. Although significant advances have been made in tailoring materials characteristics to satisfy these requirements, the impacts of autocatalytic reactions and microenvironments are often overlooked resulting in uncontrollable and unpredictable outcomes. Therefore, roles of surface versus bulk erosion, in situ microenvironment, and autocatalytic mechanisms should be understood to enable rational design of degradable systems. In an attempt to individually evaluate the physical state and form factors influencing autocatalytic hydrolysis of degradable polymers, this Review follows a hierarchical analysis that starts with hydrolytic degradation of water-soluble polymers before building up to 2D-like materials, such as ultrathin coatings and capsules, and then to solid-state degradation. We argue that chemical reactivity largely governs solution degradation while diffusivity and geometry control the degradation of bulk materials, with thin "2D" materials remaining largely unexplored. Following this classification, this Review explores techniques to analyze degradation in vitro and in vivo and summarizes recent advances toward understanding degradation behavior for traditional and innovative polymer systems. Finally, we highlight challenges encountered in analytical methodology and standardization of results and provide perspective on the future trends in the development of biodegradable polymers.

Preparation and Characterization of Polyanhydride Terminated with Oleic Acid Extracted from Olive Mills Waste

Valorizing the fatty content of agricultural waste in material synthesis is an interesting topic. This work focused on utilizing oleic acid from the solid waste of olive mills in Saudi Arabia to synthesize biodegradable polyanhydrides based on sebacic acid which terminated with different concentrations of fatty acid (10, 30, 50, and 70 wt%), then characterize the final polymer samples and study the effects of termination on polyanhydrides properties, such as molecular weight and degradation profile. The fatty content of the solid waste was extracted, purified, and analyzed prior to and after separating the saturated and unsaturated fractions by urea crystallization, then the microwave-assisted melt polycondensation technique was used in the synthesis of the final polymers. Molecular weights were determined by gel permeation chromatography (GPC), and the degradation profile of the prepared samples was examined by determining the weight loss percentage of the polymer mass and FT-IR scanning for the anhydride bond before and after sample degradation. Results showed a linear degradation profile for most samples with no significant change in the molecular weights due to termination.

Using Compartments to Model Drug Delivery from Biodegradable Polymers

Polymeric drug delivery systems can improve patient compliance, decrease toxicity and prolong therapeutic effects for a wide range of therapeutic treatments, by controlling drug release. Polymer delivery system development can be facilitated by mathematical models. We present here a new compartmental model that will be more familiar to pharmaceutical professionals and equally as effective as common diffusion equation-based models. The compartmental model considers both polymer degradation and drug diffusion to predict drug release. The model is adapted into three different geometries for different polymer delivery scenarios: membranes, fibres and particles. Model parameters are derived in terms of diffusion coefficients. Polymer-drug binding interactions and distributions of fibre/particle diameters are incorporated to the model. The model is validated by comparison to common diffusion equation-based solutions and fitting to experimental data. It is shown how the model for drug release can be incorporated into existing distribution models to predict plasma concentrations of an in vivo administration. A user-friendly Python implementation of the model is available on Github, at https://github.com/spirt-t/compartments_model.

Effect of pH on salicylic acid-based poly(anhydride-ester): Implications for polymer degradation and controlled salicylic acid release

Salicylic acid (SA)-based poly(anhydride-esters) (SAPAEs) hydrolytically degrade to release SA in a controlled manner over extended time periods. While these polymers have been well investigated under in vivo conditions, this study is the first detailed, systematic assessment of in vitro polymer degradation over a range of pH values. To investigate the effect of pH conditions on SAPAE degradation, in vitro degradation studies were conducted on SAPAE disks over a wide pH range (2.0, 4.0, 6.0, 7.4, 8.0, 9.0, and 10.0) for 30 days. Several parameters were evaluated, including SA concentrations in the degradation media, polymer mass loss, water uptake in the polymer matrices, and SA solubility at different pH values to substantiate SA release results and characterize the in vitro polymer degradation process. Complete SA release was achieved at more basic conditions (pH 9.0 and 10.0) over 9 days, whereas less than 41% SA was released over the same time period at neutral pH conditions (pH 8.0 and 7.4). By comparison, SA release was minimal in acidic pH conditions. Overall, we present quantitative data of polymer degradation as defined by SA in vitro release, which increased with increasing pH values. More basic conditions promoted polymer degradation, whereas acidic conditions minimized polymer degradation.

Degradable polyprodrugs: design and therapeutic efficiency

Prodrugs are developed to increase the therapeutic properties of drugs and reduce their side effects. Polyprodrugs emerged as highly efficient prodrugs produced by the polymerization of one or several drug monomers. Polyprodrugs can be gradually degraded to release therapeutic agents. The complete degradation of polyprodrugs is an important factor to guarantee the successful disposal of the drug delivery system from the body. The degradation of polyprodrugs and release rate of the drugs can be controlled by the type of covalent bonds linking the monomer drug units in the polymer structure. Therefore, various types of polyprodrugs have been developed based on polyesters, polyanhydrides, polycarbonates, polyurethanes, polyamides, polyketals, polymetallodrugs, polyphosphazenes, and polyimines. Furthermore, the presence of stimuli-responsive groups, such as redox-responsive linkages (disulfide, boronate ester, metal-complex, and oxalate), pH-responsive linkages (ester, imine, hydrazone, acetal, orthoester, P-O and P-N), light-responsive (metal-complex, o-nitrophenyl groups) and enzyme-responsive linkages (ester, peptides) allow for a selective degradation of the polymer backbone in targeted tumors. We envision that new strategies providing a more efficient synergistic therapy will be developed by combining polyprodrugs with gene delivery segments and targeting moieties.

Poly(ester-anhydrides) Derived from Esters of Hydroxy Acid and Cyclic Anhydrides

The alternating architecture and hydrophobic side chains hinder hydrolytic cleavage and anhydride interchange in poly(sebacic acid-ricinoleic acid) (P(SA-RA)), which provides stable polyanhydrides at room temperature. In this report, a series of polyanhydrides were designed to investigate the effect of ester bonds, hydrophobic side chains, phenyl moieties, and their distance from anhydride bonds on their stability and properties. Polyanhydrides with alternating architecture are constructed by the polymerization of ester-diacids prepared from ricinoleic or other hydroxy acids with anhydrides such as succinic, maleic, and phthalic anhydrides. The hydrophobic side chains are designed closer to anhydride bonds to investigate hindrance to hydrolytic cleavage and anhydride interchange. Polyanhydrides were obtained by the activation of ester-diacid using acetic anhydride followed by melt condensation. The reactions were monitored by NMR, Fourier transform infrared (FTIR), and gel permeation chromatography (GPC). The synthesized poly(ester-anhydride)s with a shorter chain length compared to P(SA-RA) were stable at room temperature. The hydrolytic degradation studies reveal that the phenyl moiety present in poly(ricinoleic acid phthalate) (PRAP) and poly(hydroxystearic acid phthalate) (PHSAP) reduces the hydrolysis of anhydride bonds. Poly(hydroxyoctanoic acid succinate) (PHOAS) demonstrates the highest molecular weight of all tested polymers. The results reveal that the presence of hydrophobic side chains, phenyl moieties, and their distance from anhydride bonds significantly improves the stability. These stable polyanhydrides can provide convenience to use in control drug-delivery applications. The in vitro drug release study using ibuprofen shows that polymers with aromatic units such as PRAP and PHSAP establish sustained release, which presents more than 50 and 40% of ibuprofen over a period of 28 days.

Synthesis of Aliphatic Polyanhydrides with Controllable and Reproducible Molecular Weight

Polyanhydrides have been synthesized for decades by melt-polycondensation of diacid monomers and 5 to >10 times mole excess acetic anhydride to diacid monomers to form polymers with a polydispersity ranging from 2.5 to 6 and low reproducibility. Hydrophobic segments in polyanhydrides are beneficial to hinder the characteristic hydrolytic cleavage of an anhydride bond that provides stable polyanhydrides at room temperature. The objective of this work is to synthesize aliphatic polyanhydrides with various hydrophobic segments, controllable and reproducible molecular weight, and low polydispersity that are essential for potential use as drug carriers. A series of polyanhydrides of suberic, azelaic, sebacic, and dodecanedioic acids with controlled molecular weight, reduced polydispersity, and standard deviation of molecular weights, have been synthesized. All synthesized polyanhydrides were thoroughly characterized by NMR, Fourier transform infrared spectroscopy, and gel permeation chromatography. Molecular weights of the synthesized polyanhydrides are highly controllable, depending on the degree of activation of the dicarboxylic acid monomers, i.e., the amount of acetic anhydride used during synthesis. Polyanhydrides have been synthesized in triplicate by melt-polycondensation, using various mole ratios of acetic anhydride to diacids. The standard deviation of the molecular weights of the polyanhydrides is minute when using 1 equivalent of acetic anhydride during the activation of dicarboxylic acids, whereas if excess acetic anhydride is used, the standard deviation is very high. The effect of safe and natural inorganic catalysts, Calcium oxide, Zinc oxide, and Calcium carbonate on polymerization is also studied. As-synthesized poly(sebacic acid) can offer convenience to use in controlled drug delivery applications. In vitro drug release study using Temozolamide (TMZ), a medication used to treat brain tumors such as glioblastoma and anaplastic astrocytoma, shows 14% TMZ release after the first hour and 70% release over one day from the poly(sebacic acid) wafers.

Drug Carriers: A Review on the Most Used Mathematical Models for Drug Release

Carriers are protective transporters of drugs to target cells, facilitating therapy under each points of view, such as fast healing, reducing infective phenomena, and curing illnesses while avoiding side effects. Over the last 60 years, several scientists have studied drug carrier properties, trying to adapt them to the release environment. Drug/Carrier interaction phenomena have been deeply studied, and the release kinetics have been modeled according to the occurring phenomena involved in the system. It is not easy to define models’ advantages and disadvantages, since each of them may fit in a specific situation, considering material interactions, diffusion and erosion phenomena, and, no less important, the behavior of receiving medium. This work represents a critical review on main mathematical models concerning their dependency on physical, chemical, empirical, or semi-empirical variables. A quantitative representation of release profiles has been shown for the most representative models. A final critical comment on the applicability of these models has been presented at the end. A mathematical approach to this topic may help students and researchers approach the wide panorama of models that exist in literature and have been optimized over time. This models list could be of practical inspiration for the development of researchers’ own new models or for the application of proper modifications, with the introduction of new variable dependency.

Bioengineering Strategies for Developing Vaccines against Respiratory Viral Diseases

Respiratory viral pathogens like influenza and coronaviruses such as severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) have caused outbreaks leading to millions of deaths. Vaccinations are, to date, the best and most economical way to control such outbreaks and have been highly successful for several pathogens. Currently used vaccines for respiratory viral pathogens are primarily live attenuated or inactivated and can risk reversion to virulence or confer inadequate immunity. The recent trend of using potent biomolecules like DNA, RNA, and protein antigenic components to synthesize vaccines for diseases has shown promising results. Still, it remains challenging to translate due to their high susceptibility to degradation during storage and after delivery. Advances in bioengineering technology for vaccine design have made it possible to control the physicochemical properties of the vaccines for rapid synthesis, heightened antigen presentation, safer formulations, and more robust immunogenicity. Bioengineering techniques and materials have been used to synthesize several potent vaccines, approved or in trials, against coronavirus disease 2019 (COVID-19) and are being explored for influenza, SARS, and Middle East respiratory syndrome (MERS) vaccines as well. Here, we review bioengineering strategies such as the use of polymeric particles, liposomes, and virus-like particles in vaccine development against influenza and coronaviruses and the feasibility of adopting these technologies for clinical use.

Journey to the Market: The Evolution of Biodegradable Drug Delivery Systems

Biodegradable polymers have been used as carriers in drug delivery systems for more than four decades. Early work used crude natural materials for particle fabrication, whereas more recent work has utilized synthetic polymers. Applications include the macroscale, the microscale, and the nanoscale. Since pioneering work in the 1960’s, an array of products that use biodegradable polymers to encapsulate the desired drug payload have been approved for human use by international regulatory agencies. The commercial success of these products has led to further research in the field aimed at bringing forward new formulation types for improved delivery of various small molecule and biologic drugs. Here, we review recent advances in the development of these materials and we provide insight on their drug delivery application. We also address payload encapsulation and drug release mechanisms from biodegradable formulations and their application in approved therapeutic products.

Functionalized polyanhydride nanoparticles for improved treatment of mitochondrial dysfunction

Parkinson's disease (PD) is a devastating neurodegenerative disease affecting a large proportion of older adults. Exposure to pesticides like rotenone is a leading cause for PD. To reduce disease progression and prolong life expectancy, it is important to target disease mechanisms that contribute to dopaminergic neuronal atrophy, including mitochondrial dysfunction. Achieving targeted mitochondrial delivery is difficult for many therapeutics by themselves, necessitating higher therapeutic doses that could lead to toxicity. To minimize this adverse effect, targeted nano-carriers such as polyanhydride nanoparticles (NPs) can protect therapeutics from degradation and provide sustained release, enabling fewer administrations and lower therapeutic dose. This work expands upon the use of the polyanhydride NP platform for targeted drug delivery by functionalizing the polymer with a derivative of triphenylphosphonium called (3-carboxypropyl) triphenylphosphonium (CPTP) using a novel method that enables longer CPTP persistence on the NPs. The extent to which neurons internalized both nonfunctionalized and functionalized NPs was tested. Next, the efficacy of these nanoformulations in treating rotenone-induced mitochondrial dysfunction in the same cell line was evaluated using a novel neuroprotective drug, mito-metformin. CPTP functionalization significantly improved NP internalization by neuronal cells. This was correlated with significant protection by CPTP-functionalized, mito-metformin encapsulated NPs against rotenone-induced mitochondrial dysfunction. However, nonfunctionalized, mito-metformin encapsulated NPs and soluble mito-metformin administered at the same dose did not significantly protect cells from rotenone-induced toxicity. These results indicate that the targeted NP platform can provide enhanced dose-sparing and potentially reduce the occurrence of systemic side-effects for PD therapeutics.

Thermal Processing of a Degradable Carboxylic Acid-Functionalized Polycarbonate into Scaffolds for Tissue Engineering

Degradable polymers are often desirable for the fabrication of medical implants, but thermal processing of these polymers is a challenge. We describe here how these problems can be addressed by discussing the extrusion of fibers and injection molding of bone pins from a hydrolytically degradable tyrosine-derived polycarbonate. Our initial attempts produced fibers and pins with bubbles, voids, and discoloration, and resulted in the formation of large polymer plugs that seized screws and blocked extruder dies. The material and process parameters that contribute to these issues were investigated by studying the physical and chemical changes that occur during processing. Differential scanning calorimetry (DSC) scans and thermogravimetric analysis combined with IR (TGA-IR) analysis revealed the role of residual moisture and residual solvents that in conjunction with heat cause degradation and crosslinking as indicated by gel permeation chromatography (GPC). Rheology and melt-flow index measurements were useful in characterizing the extent of dependence of polymer viscosity on temperature and molecular weight. With these insights, we could process our polymer into fibers and rods by controlling residual moisture, time and temperature, and by adjusting processing parameters in real-time. The systematic approach described here is applicable to other degradable polymers that are difficult to process.

Principles for Controlling the Shape Recovery and Degradation Behavior of Biodegradable Shape-Memory Polymers in Biomedical Applications

Polymers with the shape memory effect possess tremendous potential for application in diverse fields, including aerospace, textiles, robotics, and biomedicine, because of their mechanical properties (softness and flexibility) and chemical tunability. Biodegradable shape memory polymers (BSMPs) have unique benefits of long-term biocompatibility and formation of zero-waste byproducts as the final degradable products are resorbed or absorbed via metabolism or enzyme digestion processes. In addition to their application toward the prevention of biofilm formation or internal tissue damage caused by permanent implant materials and the subsequent need for secondary surgery, which causes secondary infections and complications, BSMPs have been highlighted for minimally invasive medical applications. The properties of BSMPs, including high tunability, thermomechanical properties, shape memory performance, and degradation rate, can be achieved by controlling the combination and content of the comonomer and crystallinity. In addition, the biodegradable chemistry and kinetics of BSMPs, which can be controlled by combining several biodegradable polymers with different hydrolysis chemistry products, such as anhydrides, esters, and carbonates, strongly affect the hydrolytic activity and erosion property. A wide range of applications including self-expending stents, wound closure, drug release systems, and tissue repair, suggests that the BSMPs can be applied as actuators on the basis of their shape recovery and degradation ability.

Degradation Behavior, Biocompatibility, Electrochemical Performance, and Circularity Potential of Transient Batteries

Transient technology seeks the development of materials, devices, or systems that undergo controlled degradation processes after a stable operation period, leaving behind harmless residues. To enable externally powered fully transient devices operating for longer periods compared to passive devices, transient batteries are needed. Albeit transient batteries are initially intended for biomedical applications, they represent an effective solution to circumvent the current contaminant leakage into the environment. Transient technology enables a more efficient recycling as it enhances material retrieval rates, limiting both human and environmental exposures to the hazardous pollutants present in conventional batteries. Little efforts are focused to catalog and understand the degradation characteristics of transient batteries. As the energy field is a property-driven science, not only electrochemical performance but also their degradation behavior plays a pivotal role in defining the specific end-use applications. The state-of-the-art transient batteries are critically reviewed with special emphasis on the degradation mechanisms, transiency time, and biocompatibility of the released degradation products. The potential of transient batteries to change the current paradigm that considers batteries as harmful waste is highlighted. Overall, transient batteries are ready for takeoff and hold a promising future to be a frontrunner in the uptake of circular economy concepts.

Polyanhydride nanoparticles stabilize pancreatic cancer antigen MUC4β

Pancreatic cancer (PC) is one of the most lethal malignancies and represents an increasing and challenging threat, especially with an aging population. The identification of immunogenic PC-specific upregulated antigens and an enhanced understanding of the immunosuppressive tumor microenvironment have provided opportunities to enable the immune system to recognize cancer cells. Due to its differential upregulation and functional role in PC, the transmembrane mucin MUC4 is an attractive target for immunotherapy. In the current study we characterized the antigen stability, antigenicity and release kinetics of a MUC4β-nanovaccine to guide further optimization and, in vivo evaluation. Amphiphilic polyanhydride copolymers based on 20 mol % 1,8-bis(p-carboxyphenoxy)-3,6-dioxaoctane and 80 mol % 1,6-bis(p-carboxyphenoxy)hexane were used to synthesize nanoparticles. Structurally stable MUC4β protein was released from the particles in a sustained manner and characterized by gel electrophoresis and fluorescence spectroscopy. Modest levels of protein degradation were observed upon release. The released protein was also analyzed by MUC4β-specific monoclonal antibodies using ELISA and showed no significant loss of epitope availability. Further, mice immunized with multiple formulations of combination vaccines containing MUC4β-loaded nanoparticles generated MUC4β-specific antibody responses. These results indicate that polyanhydride nanoparticles are viable MUC4β vaccine carriers, laying the foundation for evaluation of this platform for PC immunotherapy.

Poly(anhydride-ester) gemcitabine: Synthesis and particle engineering of a high payload hydrolysable polymeric drug for cancer therapy

Gemcitabine (GMT) is a nucleoside analog used in the treatment of a variety of solid tumors. GMT was chemically modified with a hydrolysable linker, and subsequently incorporated into a poly(anhydride-ester) backbone via melt-polymerization, with the active antimetabolite GMT, thus, becoming the repeat unit that makes up this new material, a biodegradable polymer. Characterization of the structure of polymeric GMT (polyGMT) revealed the incorporation of an average 26 molecules of GMT per polymer chain, which corresponds to a drug loading of 58%w/w. The glass transition temperature of the formed polyGMT was determined to be 123 °C. PolyGMT was engineered into nanoparticles (NPs) using a dialysis-based method, with a resulting geometric diameter of 206 ± 38 nm. The particles are easily dispersible and stable in aqueous-based media, with a hydrodynamic diameter of 229 ± 28 nm. The prepared hydrolysable polyGMT NPs demonstrate ultra-long release profile due to the hydrophobic nature of the linker, and as per characteristic erosion behavior of polymers with anhydride-ester bonds. Accelerated in vitro release studies demonstrate the recovery of free GMT upon hydrolysis, with biological activity as assessed by cytotoxicity assays performed in adenocarcinoma human alveolar basal epithelial (A549) and highly metastatic murine osteosarcoma (K7M2) cells lines. The characteristics of polyGMT, including its thermal properties and built in hydrolysable structure, are thus conducive for use in the preparation of drug delivery systems. Engineered structures prepared with polyGMT can maintain their morphology at ambient and physiologically relevant conditions, and free GMT is recovered as the anhydride and ester bonds are hydrolyzed. This work is innovative as for the first time we demonstrate the ability to polymerize GMT in a hydrolysable polymer structure, and engineer NPs of this polymeric chemotherapy. The synthetic strategy allows for tuning of the polymer hydrophobicity and thus potentialize its behavior, including degradation profile, by varying the linker chemistry. Such controlled release hydrolysable polymers with very high drug loading and controlled erosion profiles are relevant as they may offer new opportunities in drug delivery applications for the treatment of malignant neoplasms.

Bioactive Betulin and PEG Based Polyanhydrides for Use in Drug Delivery Systems

In the course of this study, a series of novel, biodegradable polyanhydrides based on betulin disuccinate and dicarboxylic derivatives of poly(ethylene glycol) were prepared by two-step polycondensation. These copolymers can be used as carriers in drug delivery systems, in the form of microspheres. Betulin and its derivatives exhibit a broad spectrum of biological activity, including cytotoxic activity, which makes them promising substances for use as therapeutic agents. Microspheres that were prepared from betulin based polyanhydrides show promising properties for use in application in drug delivery systems, including inhalation systems. The obtained copolymers release the active substance-betulin disuccinate-as a result of hydrolysis under physiological conditions. The use of a poly(ethylene glycol) derivative as a co-monomer increases the solubility and bioavailability of the obtained compounds. Microspheres with diameters in the range of 0.5-25 µm were prepared by emulsion solvent evaporation method and their physicochemical and aerodynamic properties were analyzed. The morphological characteristics of the microspheres depended on the presence of poly(ethylene glycol) (PEG) segment within the structure of polyanhydrides. The porosity of the particles depended on the amount and molecular weight of the PEG used and also on the speed of homogenization. The most porous particles were obtained from polyanhydrides containing 20% wt. of PEG 600 by using a homogenization speed of 18,000 rpm.

Modeling the release of food bioactive ingredients from carriers/nanocarriers by the empirical, semiempirical, and mechanistic models

The encapsulation process has been utilized in the field of food technology to enhance the technofunctional properties of food products and the delivery of nutraceutical ingredients via food into the human body. The latter application is very similar to drug delivery systems. The inherent sophisticated nature of release mechanisms requires the utilization of mathematical equations and statistics to predict the release behavior during the time. The science of mathematical modeling of controlled release has gained a tremendous advancement in drug delivery in recent years. Many of these modeling methods could be transferred to food. In order to develop and design enhanced food controlled/targeted bioactive release systems, understanding of the underlying physiological and chemical processes, mechanisms, and principles of release and applying the knowledge gained in the pharmaceutical field to food products is a big challenge. Ideally, by using an appropriate mathematical model, the formulation parameters could be predicted to achieve a specific release behavior. So, designing new products could be optimized. Many papers are dealing with encapsulation approaches and evaluation of the impact of process and the utilized system on release characteristics of encapsulated food bioactives, but still, there is no deep insight into the mathematical release modeling of encapsulated food materials. In this study, information gained from the pharmaceutical field is collected and discussed to investigate the probable application in the food industry.

Scalable microfabrication of drug-loaded core-shell tablets from a single erodible polymer with adjustable release profiles

Oral tablets with tunable release profiles have emerged to enhance the effectiveness of therapies in different clinical conditions. Although the concept of tablets with adjustable release profiles has been studied before, the lack of a fast and scalable production technique has limited their widespread application. In this study, a scalable fabrication method was developed to manufacture controlled-release polyanhydride tablets. A new polymeric core-shell tablet design is also proposed, that in conjunction with a micro-fabrication procedure, allows for achieving tunable release profiles required in personalized medicine in small-size tablets. Utilizing a surface-erodible polymeric carrier in the fabrication of the new tablet design resulted in achieving adjustable release profiles and improvements in the drug-loading capacity of the delivery system which allows for delivering a flexible amount of therapeutics with desirable patterns to patients. The proposed fabrication techniques allow for scalable production of personalized tablets with the high resolution required in precision medicine and hence have a high potential for clinical translation.

Degradable Polymer Films Made from Poly(salicylic-acid-co-sebacic acid) and Poly(sebacic anhydride)/Poly(adipic anhydride) Blends: Degradation Kinetics and Use as Sacrificial Layers for Polymer Multilayer Systems

Two approaches to obtain fast-degrading polymer films based on poly(sebacic anhydride) (PSA) are presented, both of which target polymer films with a lower degree of crystallinity than pure PSA homopolymer: first, thin films were prepared from poly(adipic anhydride)/poly(sebacic anhydride) blends at different ratios, and second, films were made from the copolymer poly(salicylic acid-co-sebacic acid). These films are intended as sacrificial layers for self-regenerating functional coatings, for example to regenerate antimicrobial surface activity. The degradation kinetics of these films were analyzed by surface plasmon resonance spectroscopy (SPR). The results of the blends approach indicate that the blend degradation rate was accelerated only in the initial degradation phase (compared to PSA). The degradation kinetics study of the poly(salicylic-acid-co-sebacic acid) film shows that this copolymer degraded faster than poly(sebacic anhydride) initially, releasing antimicrobial salicylic acid in the process. However, its degradation rate slowed down at a mass loss > 60% and approached the PSA degradation curve at longer degradation times. When tested as sacrificial layer in self-regenerating antimicrobial polymer stacks, it was found that the degradation rate was too low for successful layer shedding.

Systematic Studies on Surface Erosion of Photocrosslinked Polyanhydride Tablets and Data Correlation with Release Kinetic Models

Photocrosslinkable polyanhydrides that undergo surface erosion are suitable materials for controlled-release drug delivery systems. Investigating the impact of different parameters on their erosion behavior is essential before use in drug delivery systems. Although their synthesis is well-established, parameters that may substantially affect the erosion of thiol-ene polyanhydrides including temperature and pH of the media, the geometry of the polymers, and the media shaking rate (the convective force for the polymer erosion), have not yet been studied. This study explores the effects of different environmental and geometric parameters on mass loss (erosion) profiles of polyanhydrides synthesized by thiol-ene photopolymerization. A comparative study on several release kinetic models fitting is also described for a better understanding of the polymer erosion behavior. The results demonstrated that although the temperature was the only parameter that affected the induction period substantially, the mass-loss rate was influenced by the polymer composition, tablet geometry, temperature, pH, and mass transfer (shaking) rate. With regard to geometrical parameters, polymers with the same surface area to volume ratios showed similar mass loss trends despite their various volumes and surface areas. The mass loss of polyanhydride tablets with more complicated geometries than a simple slab was shown to be non-linear, and the kinetic model study indicated the dominant surface erosion mechanism. The results of this study allow for designing and manufacturing efficient delivery systems with a high-predictable drug release required in precision medicine using surface-erodible polyanhydrides.

Drug Delivery and Drug Efficacy from Amorphous Poly(thioether anhydrides)

The correlation between erosion and drug (lidocaine and 6-mercaptopurine, 6-MP) release from amorphous poly(thioether anhydrides), which are synthesized using radical-mediated thiol-ene polymerization, is reported. Cytotoxicity studies of the polymer toward human fibroblast human dermal fibroblasts adult, melanoma A-375, and breast cancer MCF-7 cells are conducted, and drug efficacy of a cancer and autoimmune disease drug (6-MP) when released from the poly(thioether anhydrides) is examined against two cancerous cell types (A-375 and MCF-7). Erosion and drug release studies reveal that lidocaine release is governed by network erosion whereas 6-MP is released by a combination of erosion and diffusion. The cytotoxicity studies show that all three cell types demonstrate high viability, thus cytocompatibility, to poly(thioether anhydrides). Toxicity to the material is dose dependent and comparable to other polyanhydride systems. The 6-MP cancer drug is shown to remain bioactive after encapsulation in the poly(thioether anhydride) matrix and the polymer does not appear to modify the efficacy of the drug.

Functionalization of PEO layer formed on Ti-15Mo for biomedical application

In the present work, deposition of poly(sebacic anhydride) PSBA loaded by amoxicillin, cefazolin, or vancomycin on a previously anodized Ti-15Mo surface is presented. PSBA loaded by the drug was deposited so as not to lose the functionality of the porous oxide layer microstructure. The morphology was evaluated using scanning electron microscopy, surface roughness, and wettability. The drug concentration was evaluated using high-performance liquid chromatography. It was determined that the drugs were loaded into coatings in the range of 35.2-122.87 μg/cm² of Ti sample. The drugs released more than 16% after 0.5 hr of the hybrid coating immersion in artificial saliva. After 3 days, the PSBA coatings were degraded by 51.3 mol %, and after 7 days by 77.8 mol %, which makes it possible to load the material by different, biologically active substances. An antimicrobial investigation of Staphylococcus aureus (DSM 24167) and Staphylococcus epidermidis (ATCC 700296) confirmed the activity of the hybrid layers against the pathogens. Hybrid layer with vancomycin best inhibits the adhesion of the bacteria, whereas coatings with amoxicillin and cefazolin showed a much better bactericidal activity. In this article, the difference in the obtained results is discussed, as well as the possibility of the application of this functional material in biomedicine.

Degradation of Polymer Films on Surfaces: A Model Study with Poly(sebacic anhydride)

There is compelling evidence that the degradation kinetics of thin polymer films differ significantly from those of bulk materials, as interfacial effects become dominant. Therefore, it is crucial to investigate these kinetics separately. Qualitative analytics of thin film degradation exist, e.g. by scanning electron microscopy or atomic force microscopy (AFM), but a quantitative study is so far missing. In this work, poly(sebacic anhydride) (PSA), an aliphatic polyanhydride, is used as a model system for a quantitative degradation study. PSA was spin-coated onto silicon or gold substrates. The degradation of these PSA films was monitored by ellipsometry, surface-plasmon resonance spectroscopy (SPR), and Fourier transform infrared spectroscopy (FTIR). Two kinetic regimes were observed when plotting the relative layer thickness determined by FTIR and SPR against the degradation time. The data obtained by FTIR showed a single process for the rate of ester bond cleavage. Overall, the degradation rate constants of PSA determined by the different methods were consistent. The degradation rate constants of PSA film up to 378 nm thickness were constant. Several thicker free-standing samples studied gravimetrically had a degradation rate constant that was one order of magnitude slower, thus confirming thickness-dependent degradation rate constants.

Novel bioerodable eluting-spacers for radiotherapy applications with in situ dose painting

OBJECTIVE

To investigate feasibility of using bioerodable/bioerodible spacers (BES) over biodegradable spacers (BDS) loaded with gold nanoparticles for radiotherapy applications with in situ dose-painting, and to explore dosimetric impact on dose enhancement ratio of different radioisotopes.

METHODS

Analytical models proposed were based on experimentally reported erosion rate constant (k ₀ = 5. 5E-7 kgm^{- 2}s^{- 1} ) for bioerodible polymeric matrix. An in vivo determined diffusion coefficient (2.2E-8 cm²/s) of 10 nm gold nanoparticles (AuNP) of concentration 7 mg/g was used to estimate diffusion coefficient of other AuNP sizes (2, 5, 14 nm) using the Stoke-Einstein diffusion equation. The corresponding dose enhancement factors (DEF) were used to study dosimetric feasibility of employing AuNP-eluting BPS for radiotherapy applications.

RESULTS

The results showed AuNP release period from BES was significantly shorter (116 h) compared to BDS (more than a month) reported previously. The results also agree with reported Hopfenberg equation for a cylindrical matrix undergoing surface erosion. The DEF at tumour distance 5 mm for Cs-131 (DEF > 2.2) greater than that of I-125 (DEF > 2) and Pd-103 (DEF ≥ 2) could be achieved for AuNP sizes (2, 5, 10, and 14 nm) respectively.

CONCLUSION

Our findings suggested that BES could be used for short-lived radioisotopes like Pd-103 and Cs-131 in comparison to eluting BDS which is feasible for long-lived radioisotopes like I-125.

ADVANCES IN KNOWLEDGE

The study provides scientific basis for development of new generation eluting spacers viable for enhancing localized tumour dose. It concludes that BES gives higher DEF for Cs-131, and good candidate for replacing conventional fiducials/spacers.

Raman Microspectroscopy Study of the Hydrolytic Degradation of Polyanhydride Network Polymers

Raman microspectroscopy was employed in this work to study the degradation of a polyanhydride network polymer synthesized from 4-pentenoic anhydride and pentaerythritol tetrakis(3-mercaptopropionate) monomers in order to illustrate the utility of this method and improve the understanding of the polyanhydride degradation and erosion. Disk-shaped polymer samples were immersed in buffer solutions for different periods of time, and hydrolytic degradation was monitored spatially and temporally via kinetic Raman studies at various depths of penetration into the samples. Erosion, meanwhile, was monitored via mass loss measurements. Dispersive Raman microspectroscopy is shown to be a particularly valuable tool for the study of the hydrolytic degradation of these materials. It confirms that these thiol-ene polyanhydrides are indeed surface eroding, while also revealing that degradation starts to occur at the core of samples on a short time scale (less than 5 h). At any given degradation time, there is a concentration gradient of the unreacted anhydride, with the unreacted anhydride concentration increasing from the outer edge to the center of the polymer samples. Further, the anhydride functionality is found to decrease approximately linearly with degradation time at all depths in the samples, though the degradation rate does appear to increase slightly as degradation occurs.

Recent research and development in synthetic polymer-based drug delivery systems

In recent years, there has been increasing recognition that a number of synthetic polymers which have excellent biodegradability and biocompatibility are materials of pharmaceutical importance in the area of drug delivery technology. The aim of this review is to take a closer look at a few synthetic polymer-based drug delivery systems, specially the aliphatic polyesters, polyamides, polyethers, polyorthoesters, polyanhydrides, polyurethanes, hydrogels and dendritic polymers.

Recent Perspectives in Hot Melt Extrusion-Based Polymeric Formulations for Drug Delivery: Applications and Innovations

Hot melt extrusion (HME), a technology which mixing the advantages of solid dispersion technology and mechanical preparation, is accepted in varied applications in pharmaceutical formulations. When combined with other techniques, such as nanotechnique, three-dimensional printing, and co-extrusion, HME becomes much more multifunctional in the application of drug delivery. While in most cases, polymers employed in HME are responsible for the final property of products. The process of HME together with the selection of materials employed in HME were described briefly. In addition, the applications of HME in drug delivery and its currently status in the pharmaceutical field were also included. Some commercial products produced by HME have met the approval of FDA, indicating the commercial viability of this technique. Although showing great potential in pharmaceutical manufacturing, HME is still challenged by high temperature, shear force, and high input energy. Development of equipment, modifying the parameters, and optimization of polymeric formulations are needed for a safe, effective, and multifunctional hot melt extrusion drug delivery system. Also, wider range of combinations between HME and other techniques may provide guideline for developing multiple applications in drug delivery.

Novel polymeric derivatives of betulin with anticancer activity

In order to provide novel polymeric biomaterials for chemotherapeutic purposes, in this paper we described the synthesis and the characterization of the physicochemical properties of a betulin-based polyanhydride exhibiting anti-cancer effects.

Designing pH-Responsive Biodegradable Polymer Coatings for Controlled Drug Release via Vapor-Based Route

We present the design of a novel pH-responsive drug release system that is achieved by solventless encapsulation of drugs within a microporous membrane using a thin capping layer of biodegradable poly(methacrylic anhydride) (PMAH) coating. The coating was synthesized via a mild vapor polymerization process, namely, initiated chemical vapor deposition, which allowed perfect retention of the anhydride groups during deposition. The synthesized polyanhydride underwent degradation upon exposure to aqueous buffers, resulting in soluble poly(methacrylic acid). The degradation behavior of PMAH is highly pH-dependent, and the degradation rate under pH 10 is 15 times faster than that under pH 1. The release profile of a model drug rifampicin clearly exhibited two stages: the initial stage when the coatings were being degraded but the drugs were well stored and the second stage when drugs were gradually exposed to the medium and released. The drug release also showed strong pH responsiveness where the duration of the initial stage under pH 1 was more than 7 and 3 times longer than that under pH 10 and 7.4, respectively, and the release rates at pH 7.4 and 10 were significantly faster than that at pH 1. The pH-dependent degradation of the encapsulant thus enabled good preservation of drugs under low-pH environment but high drug release efficiency under neutral and alkaline environment, suggesting potential applications in site-specific drug delivery systems.

Amphiphilic block copolymer NPs obtained by coupling ricinoleic acid/sebacic acids and mPEG: Synthesis, characterization, and controlled release of paclitaxel

Currently, nanoparticles (NPs) made of amphiphilic block copolymer are still an essential part of drug delivery system. Here, we report a novel amphiphilic block copolymer and paclitaxel (PTX)-loaded copolymer NPs for the controlled delivery of PTX. The block copolymer was synthesized via melt polycondensation method of methoxy poly(ethylene glycol) (mPEG), sebacic acid (SA) and ricinoleic acid (RA). A series of characterization approaches such as Fourier Transform Infrared Spectroscopy (FTIR), ¹Hydrogen-Nuclear Magnetic Resonance (¹H-NMR), Differential Scanning Calorimetry (DSC), X-Ray Diffraction (XRD) and Gel Permeation Chromatography (GPC) applied have shown that the amphiphilic block copolymer was prepared as designed. NPs prepared by nanoprecipitation method consist of mPEG segments as the hydrophilic shell and RA-SA segments as the hydrophobic core, hydrophobic PTX was encapsulated as model drug. Subsequently, Transmission Electron Microscopy (TEM) analysis indicated that the spherical NPs have effective mean diameters ranging from 100 to 400 nm. Dynamic Light Scattering (DLS) analysis also revealed the controllable NPs diameter by modulating the mass ratio of RA to SA and drug loading amount (DLA). Besides, biphasic profile with zero order drug release was observed in general in vitro release behaviors of PTX from NPs. Further investigation confirmed that the release behaviors depend on the crystallinity of hydrophobic RA-SA segments. Results above suggest that NPs with amphiphlic block copolymer mPEG-b-P(RA-SA)-b-mPEG have a remarkable potential as a carrier for hydrophobic drug delivery in cancer therapy.

Recent Advances in Polyanhydride Based Biomaterials

This review focusses on recent developments of polyanhydrides, a class of degradable synthetic biopolymers. Polyanhydrides have been used as carriers for controlled delivery of drugs. A polyanhydride copolymer of carboxyphenoxy propane and sebacic acid has been used in Gliadel brain tumor implants for the controlled delivery of carmustine or bis-chloroethylnitrosourea. They are easy and inexpensive to synthesize (especially scale up). However, polyanhydrides possess a short shelf-life. Hydrolytic cleavage and anhydride interchanges lower their molecular weights during storage. One of the highlights in recent developments of polyanhydride chemistry is the discovery of alternating copolymers having extended shelf-life. Other highlights include their applications in biomedical electronics, vaccine delivery, and nano/micro particulate delivery systems. This review examines approaches for polyanhydride synthesis followed by their recent developments in biomedical applications.

A Fully Biodegradable Battery for Self-Powered Transient Implants

Biodegradable transient devices represent an emerging type of electronics that could play an essential role in medical therapeutic/diagnostic processes, such as wound healing and tissue regeneration. The associated biodegradable power sources, however, remain as a major challenge toward future clinical applications, as the demonstrated electrical stimulation and sensing functions are limited by wired external power or wireless energy harvesters via near-field coupling. Here, materials' strategies and fabrication schemes that enable a high-performance fully biodegradable magnesium-molybdenum trioxide battery as an alternative approach for an in vivo on-board power supply are reported. The battery can deliver a stable high output voltage as well as prolonged lifetime that could satisfy requirements of representative implantable electronics. The battery is fully biodegradable and demonstrates desirable biocompatibility. The battery system provides a promising solution to advanced energy harvesters for self-powered transient bioresorbable implants as well as eco-friendly electronics.

Reinforcement of polymeric nanoassemblies for ultra-high drug loadings, modulation of stiffness and release kinetics, and sustained therapeutic efficacy

The optimization of current polymeric nanoparticle therapies is restricted by low drug loadings and limited tunability of core properties. To overcome these shortcomings, a novel self-association approach is utilized to fabricate a dual-loaded poly(1,2-glycerol carbonate)-graft-succinic acid-paclitaxel (PGC-PTX) conjugate nanoparticle (NP) in which the physical entrapment of free paclitaxel (PTX) affords unprecedented ultra-high drug loadings >100 wt%, modulation of mechanical stiffness, and tunable release kinetics. Despite high incorporation of free PTX (up to 50 wt%), the dual-loaded PGC-PTX nanocarriers (i.e., PGC-PTX + PTX NPs) exhibit controlled and sustained drug release over 15 days, without burst release effects. Importantly, optimization of drug/material efficiency concomitantly affords improved in vitro efficacy. In vivo, PGC-PTX + PTX NPs are safely administered at doses exceeding the median lethal dose of standard PTX, while a single high dose significantly extends survival relative to weekly PTX administrations in a murine model of peritoneal carcinomatosis.

Zwitterionic Polyester-Based Nanoparticles with Tunable Size, Polymer Molecular Weight, and Degradation Time

Biodegradable polymer nanoparticles are an important class of materials used in several applications for their unique characteristics. In particular, the ones stabilized by zwitterionic materials are gaining increased interest in medicine as alternative to the more common ones based on poly(ethylene glycol) thanks to their superior stability and ability to avoid both the accelerated blood clearance and allergic reactions. In this work, a novel class of zwitterionic based NPs has been produced, and a method to independently control the nanoparticle size, degradation time, and polymer molecular weight has been developed and demonstrated. This has been possible by the synthesis and the fine-tuning of zwitterionic amphiphilic block copolymers obtained via the combination of ring-opening polymerization and reversible addition-fragmentation chain transfer polymerization. The final results showed that when two block copolymers contain the same number of caprolactone units, the one with longer oligoester lateral chains degrades faster. This phenomenon is in sharp contrast with the one seen so far for the common linear polyester systems where longer chains result in longer degradation times, and it can be used to better tailor the degradation behavior of the nanoparticles.

Unlocking the Potential of Poly(Ortho Ester)s: A General Catalytic Approach to the Synthesis of Surface-Erodible Materials

Poly(ortho ester)s (POEs) are well-known for their surface-eroding properties and hence present unique opportunities for controlled-release and tissue-engineering applications. Their development and wide-spread investigation has, however, been severely limited by challenging synthetic requirements that incorporate unstable intermediates and are therefore highly irreproducible. Herein, the first catalytic method for the synthesis of POEs using air- and moisture-stable vinyl acetal precursors is presented. The synthesis of a range of POE structures is demonstrated, including those that are extremely difficult to achieve by other synthetic methods. Furthermore, application of this chemistry permits efficient installation of functional groups through ortho ester linkages on an aliphatic polycarbonate.