Biocompatibility of implantable synthetic polymeric drug carriers: focus on brain biocompatibility

A review: Carrier-based hydrogels containing bioactive molecules and stem cells for ischemic stroke therapy

Ischemic stroke (IS), a cerebrovascular disease, is the leading cause of physical disability and death worldwide. Tissue plasminogen activator (tPA) and thrombectomy are limited by a narrow therapeutic time window. Although strategies such as drug therapies and cellular therapies have been used in preclinical trials, some important issues in clinical translation have not been addressed: low stem cell survival and drug delivery limited by the blood-brain barrier (BBB). Among the therapeutic options currently sought, carrier-based hydrogels hold great promise for the repair and regeneration of neural tissue in the treatment of ischemic stroke. The advantage lies in the ability to deliver drugs and cells to designated parts of the brain in an injectable manner to enhance therapeutic efficacy. Here, this article provides an overview of the use of carrier-based hydrogels in ischemic stroke therapy and focuses on the use of hydrogel scaffolds containing bioactive molecules and stem cells. In addition to this, we provide a more in-depth summary of the composition, physicochemical properties and physiological functions of the materials themselves. Finally, we also outline the prospects and challenges for clinical translation of hydrogel therapy for IS.

Nanostructured conductive polymers: synthesis and application in biomedicine

Conductive polymers (CPs), distinguished by their sp2-hybridized carbon backbone, offer remarkable electrical conductivity while maintaining the advantageous mechanical flexibility and processing characteristics typical of organic polymers. Compared to their bulk counterparts, nanostructured CPs exhibit unique physicochemical properties, such as large surface areas and shortened charge/mass transport pathways, making them promising candidates for various applications. This mini review explores various synthesis methodologies for nanostructured CPs, including electrospinning, hard templating, and soft templating techniques, while elucidating their advantages and disadvantages. Additionally, the burgeoning biomedical applications of nanostructured CPs are highlighted, including drug delivery, neural electrodes and interfaces, nerve regeneration, and biosensing, demonstrating their potential to significantly advance contemporary biomedical science.

Development and Characterization of PEGylated Poly D,L-Lactic Acid Nanoparticles for Skin Rejuvenation

Recently, various biocompatible and biodegradable materials have garnered significant attention as cosmetic fillers for skin rejuvenation. Among these, poly ε-caprolactone (PCL), poly L-lactic acid (PLLA), poly D,L-lactic acid (PDLLA), and polydioxanone (PDO) microspheres have been developed and commercialized as a dermal filler. However, its irregularly hydrophobic microspheres pose hydration challenges, often causing syringe needle blockages and side effects such as delayed onset nodules and papules after the procedure. In this study, we synthesized a polyethylene glycol-poly D,L-lactic acid (mPEG-PDLLA) copolymer to address the limitations of conventional polymer fillers. Comprehensive characterization of the copolymer was performed using nuclear magnetic resonance spectroscopy, Fourier transform infrared spectroscopy, and differential scanning calorimetry. The mPEG-PDLLA copolymers demonstrated a unimodal size distribution of approximately 121 ± 20 nm in an aqueous solution. The in vitro cytotoxicity and collagen genesis of mPEG-PDLLA copolymers were evaluated using human dermal fibroblast cells. In this study, angiogenesis was observed over time in hairless mice injected with mPEG-PDLLA copolymers, confirming its potential role in enhancing collagen synthesis. To assess the inflammatory response, the expression levels of the genes MMP1 and IL-1β were analyzed. Additionally, gene expression levels such as transforming growth factor-β and collagen types I and III were compared with Rejuran® in animal studies. The newly developed collagen-stimulating PEGylated PDLLA may be a safe and effective option for skin rejuvenation.

Polylactic Acid-Based Polymers Used for Facial Rejuvenation: A Narrative Review

For decades, a diverse range of natural and synthetic materials have been utilized to enhance human tissue and achieve improved aesthetic results. Among these, dermal fillers are some of the most popular treatments. Initially, the primary role of dermal fillers was to restore lost volume. However, with advancements in biomaterial research, a variety of biostimulatory fillers have become essential in aesthetic medicine. One such filler, polylactic acid (PLA), has been extensively used for facial rejuvenation. Upon injection, PLA not only provides immediate volume restoration but also enhances skin quality and appearance while promoting the regeneration of collagen, elastin, and vasculature. This narrative review highlights PLA as a regenerative aesthetic treatment, detailing its physicochemical properties, mechanisms of regeneration stimulation, and clinical applications in facial aesthetics. It represents the cutting-edge foundation upon which further developments can be built to ensure optimal and safe outcomes in treatments using PLA-based collagen stimulators and other similar products for facial rejuvenation. LEVEL OF EVIDENCE V: This journal requires that authors assign a level of evidence to each article. For a full description of these Evidence-Based Medicine ratings, please refer to the Table of Contents or the online Instructions to Authors www.springer.com/00266 .

Microfluidic-Generated Injectable Bulking Agents with Biocompatible Surfaces and Their Mid-term Outcomes in a Rat Model with Anal Sphincter Injury

Bulking agents have gained attention as new, minimally invasive treatments for fecal incontinence. Various materials and surface treatment techniques have been extensively studied to ensure good biocompatibility and long-term stability. Despite significant improvements in biocompatibility, the nonuniform particle size of existing materials has led to other challenges, such as the induction of phagocytosis or reduction of injectability during in vivo tests. This study aimed to conduct a preclinical test of the midterm stability of bulking agents with newly formulated particles with uniform size. To this end, the particles were fabricated using microfluidics, resulting in a narrow size dispersity of less than 5% as the coefficient of variation, which is essentially distinct from conventional bulking agents. The microfluidic fabrication resulted in uniformly sized particles larger than the in vivo migratory limit of 80 μm and in a reduction in maximum injection pressure. Histological staining and microscopic observations confirmed proper positioning of the filler materials in vivo and a negligible immune response for up to 6 months, indicating successful midterm stability.

Comparison of Printable Biomaterials for Use in Neural Tissue Engineering: An In Vitro Characterization and In Vivo Biocompatibility Assessment

Nervous system traumatic injuries are prevalent in our society, with a significant socioeconomic impact. Due to the highly complex structure of the neural tissue, the treatment of these injuries is still a challenge. Recently, 3D printing has emerged as a promising alternative for producing biomimetic scaffolds, which can lead to the restoration of neural tissue function. The objective of this work was to compare different biomaterials for generating 3D-printed scaffolds for use in neural tissue engineering. For this purpose, four thermoplastic biomaterials, ((polylactic acid) (PLA), polycaprolactone (PCL), Filaflex (FF) (assessed here for the first time for biomedical purposes), and Flexdym (FD)) and gelatin methacrylate (GelMA) hydrogel were subjected to printability and mechanical tests, in vitro cell-biomaterial interaction analyses, and in vivo biocompatibility assessment. The thermoplastics showed superior printing results in terms of resolution and shape fidelity, whereas FD and GelMA revealed great viscoelastic properties. GelMA demonstrated a greater cell viability index after 7 days of in vitro cell culture. Moreover, all groups displayed connective tissue encapsulation, with some inflammatory cells around the scaffolds after 10 days of in vivo implantation. Future studies will determine the usefulness and in vivo therapeutic efficacy of novel neural substitutes based on the use of these 3D-printed scaffolds.

Research advances in Zein-based nano-delivery systems

Zein is the main vegetable protein from maize. In recent years, Zein has been widely used in pharmaceutical, agriculture, food, environmental protection, and other fields because it has excellent biocompatibility and biosafety. However, there is still a lack of systematic review and research on Zein-based nano-delivery systems. This paper systematically reviews preparation and modification methods of Zein-based nano-delivery systems, based on the basic properties of Zein. It discusses the preparation of Zein nanoparticles and the influencing factors in detail, as well as analyzing the advantages and disadvantages of different preparation methods and summarizing modification methods of Zein nanoparticles. This study provides a new idea for the research of Zein-based nano-delivery system and promotes its application.

Synthesis and Physicochemical Characterization of Gelatine-Based Biodegradable Aerogel-like Composites as Possible Scaffolds for Regenerative Medicine

Regenerative medicine is an interdisciplinary field aiming at restoring pathologically damaged tissues and whole organs by cell transplantation in combination with proper supporting scaffolds. Gelatine-based ones are very attractive due to their biocompatibility, rapid biodegradability, and lack of immunogenicity. Gelatine-based composite hydrogels, containing strengthening agents to improve their modest mechanical properties, have been demonstrated to act as extracellular matrices (ECMs), thus playing a critical role in "organ manufacturing". Inspired by the lysyl oxidase (LO)-mediated process of crosslinking, which occurs in nature to reinforce collagen, we have recently developed a versatile protocol to crosslink gelatine B (Gel B) in the presence or absence of LO, using properly synthesized polystyrene- and polyacrylic-based copolymers containing the amine or aldehyde groups needed for crosslinking reactions. Here, following the developed protocol with slight modifications, we have successfully crosslinked Gel B in different conditions, obtaining eight out of nine compounds in high yield (57-99%). The determined crosslinking degree percentage (CP%) evidenced a high CP% for compounds obtained in presence of LO and using the styrenic amine-containing (CP5/DMAA) and acrylic aldehyde-containing (CPMA/DMAA) copolymers as crosslinking agents. ATR-FTIR analyses confirmed the chemical structure of all compounds, while optical microscopy demonstrated cavernous, crater-like, and labyrinth-like morphologies and cavities with a size in the range 15-261 µm. An apparent density in the range 0.10-0.45 g/cm3 confirmed the aerogel-like structure of most samples. Although the best biodegradation profile was observed for the sample obtained using 10% CP5/DMAA (M3), high swelling and absorption properties, high porosity, and good biodegradation profiles were also observed for samples obtained using the 5-10% CP5/DMAA (M4, 5, 6) and 20% CPMA/DMAA (M9) copolymers. Collectively, in this work of synthesis and physicochemical characterization, new aerogel-like composites have been developed and, based on their characteristics, which fit well within the requirements for TE, five candidates (M3, M4, M5, M6, and M9) suitable for future biological experiments on cell adhesion, infiltration and proliferation, to confirm their effective functioning, have been identified.

The design of an RGD in situ sustained delivery system utilizing scallop byssal protein through genetic engineering

Although bioactive peptides enhancing bone healing have demonstrated effectiveness in treating bone defects, in vivo instability poses a challenge to their clinical application. Currently reported peptide delivery systems do not meet the demands of bone tissue repair regarding stability and peptide release efficacy. Herein, the self-assembling recombinant chimeric protein (Sbp5-2RGD) is developed by genetic engineering with cell adhesion peptide RGD as the targeted peptide and a newly discovered scallop byssal-derived protein Sbp5-2 that can assemble into wet stable films as the structural domain. In vitro studies show that the Sbp5-2RGD film exhibits excellent extensibility and biocompatibility. In vitro and in vivo degradation experiments demonstrate that the film remains stable due to the layer-by-layer degradation mode, resulting in sustained delivery of RGD in situ for up to 4 weeks. Consequently, the film can effectively promote osteogenesis, which accelerates bone defect healing and the implants osseointegration. Cell-level studies further show that the film up-regulates the expression of genes and proteins (ALP, OCN, OSX, OPN, RUNX2, VEGF) associated with osteogenesis and angiogenesis. Overall, this novel protein film represents an intelligent platform for peptide immobilization, protection, and release through its self-assembly, dense structure, and degradation mode, providing a therapeutic strategy for bone repair.

Advanced Nano-Drug Delivery Systems in the Treatment of Ischemic Stroke

In recent years, the frequency of strokes has been on the rise year by year and has become the second leading cause of death around the world, which is characterized by a high mortality rate, high recurrence rate, and high disability rate. Ischemic strokes account for a large percentage of strokes. A reperfusion injury in ischemic strokes is a complex cascade of oxidative stress, neuroinflammation, immune infiltration, and mitochondrial damage. Conventional treatments are ineffective, and the presence of the blood-brain barrier (BBB) leads to inefficient drug delivery utilization, so researchers are turning their attention to nano-drug delivery systems. Functionalized nano-drug delivery systems have been widely studied and applied to the study of cerebral ischemic diseases due to their favorable biocompatibility, high efficiency, strong specificity, and specific targeting ability. In this paper, we briefly describe the pathological process of reperfusion injuries in strokes and focus on the therapeutic research progress of nano-drug delivery systems in ischemic strokes, aiming to provide certain references to understand the progress of research on nano-drug delivery systems (NDDSs).

Calming the Nerves via the Immune Instructive Physiochemical Properties of Self-Assembling Peptide Hydrogels

Current therapies for the devastating damage caused by traumatic brain injuries (TBI) are limited. This is in part due to poor drug efficacy to modulate neuroinflammation, angiogenesis and/or promoting neuroprotection and is the combined result of challenges in getting drugs across the blood brain barrier, in a targeted approach. The negative impact of the injured extracellular matrix (ECM) has been identified as a factor in restricting post-injury plasticity of residual neurons and is shown to reduce the functional integration of grafted cells. Therefore, new strategies are needed to manipulate the extracellular environment at the subacute phase to enhance brain regeneration. In this review, potential strategies are to be discussed for the treatment of TBI by using self-assembling peptide (SAP) hydrogels, fabricated via the rational design of supramolecular peptide scaffolds, as an artificial ECM which under the appropriate conditions yields a supramolecular hydrogel. Sequence selection of the peptides allows the tuning of these hydrogels' physical and biochemical properties such as charge, hydrophobicity, cell adhesiveness, stiffness, factor presentation, degradation profile and responsiveness to (external) stimuli. This review aims to facilitate the development of more intelligent biomaterials in the future to satisfy the parameters, requirements, and opportunities for the effective treatment of TBI.

Synthesizing biomaterials in living organisms

Living organisms fabricate biomacromolecules such as DNA, RNA, and proteins by the self-assembly process. The research on the mechanism of biomacromolecule formation also inspires the exploration of in vivo synthesized biomaterials. By elaborate design, artificial building blocks or precursors can self-assemble or polymerize into functional biomaterials within living organisms. In recent decades, these so-called in vivo synthesized biomaterials have achieved extensive applications in cell-fate manipulation, disease theranostics, bioanalysis, cellular surface engineering, and tissue regeneration. In this review, we classify strategies for in vivo synthesis into non-covalent, covalent, and genetic types. The development of these approaches is based on the chemical principles of supramolecular chemistry and synthetic chemistry, biological cues such as enzymes and microenvironments, and the means of synthetic biology. By summarizing the design principles in detail, some insights into the challenges and opportunities in this field are provided to  enlighten further research.

Intrinsically Disordered Synthetic Polymers in Biomedical Applications

In biology and medicine, intrinsically disordered synthetic polymers bio-mimicking intrinsically disordered proteins, which lack stable three-dimensional structures, possess high structural/conformational flexibility. They are prone to self-organization and can be extremely useful in various biomedical applications. Among such applications, intrinsically disordered synthetic polymers can have potential usage in drug delivery, organ transplantation, artificial organ design, and immune compatibility. The designing of new syntheses and characterization mechanisms is currently required to provide the lacking intrinsically disordered synthetic polymers for biomedical applications bio-mimicked using intrinsically disordered proteins. Here, we present our strategies for designing intrinsically disordered synthetic polymers for biomedical applications based on bio-mimicking intrinsically disordered proteins.

Long-Acting Therapeutic Delivery Systems for the Treatment of Gliomas

Despite the emergence of cutting-edge therapeutic strategies and tremendous progress in research, a complete cure of glioma remains elusive. The heterogenous nature of tumor, immunosuppressive state and presence of blood brain barrier are few of the major obstacles in this regard. Long-acting depot formulations such as injectables and implantables are gaining attention for drug delivery to brain owing to their ease in administration and ability to elute drug locally for extended durations in a controlled manner with minimal toxicity. Hybrid matrices fabricated by incorporating nanoparticulates within such systems help to enhance pharmaceutical advantages. Utilization of long-acting depots as monotherapy or in conjunction with existing strategies rendered significant survival benefits in many preclinical studies and some clinical trials. The discovery of novel targets, immunotherapeutic strategies and alternative drug administration routes are now coupled with several long-acting systems with an ultimate aim to enhance patient survival and prevent glioma recurrences.

4D Printing of Overall Radiopaque Customized Bionic Occlusion Devices

Percutaneous closure of ventricular septal defect (VSD) can effectively occlude abnormal blood flow between ventricles. However, commonly used Nitinol occlusion devices have non-negligible limitations, such as nondegradability leading to life-threatening embolization; limited device size predisposing to displacement and wear; only a few radiopaque markers resulting in inaccurate positioning. Nevertheless, the exploration of customized, biodegradable, and overall radiopaque occluders is still vacant. Here, overall radiopaque, biodegradable, and dynamic reconfigurable 4D printed VSD occluders are developed. Based on wavy bionic structures, various VSD occluders are designed and manufactured to adapt to the position diversity of VSD. The customized configuration, biocompatibility, and biodegradability of the developed 4D printed bionic occluders can eliminate the series of complications caused by traditional occluders. The overall radiopacity of 4D printed VSD occluders is validated ex vivo and in vivo, whereby accurate positioning can be assured. Notably, the preparation strategies for 4D printed occluders are scalable, eliminating the barriers to mass production, and marking a meaningful step in bridging the gap between modeling and clinical application of 4D printed occlusion devices. This work opens attractive perspectives for the rapid manufacturing of customized intelligent medical devices for which overall radiopacity, dynamic reconfigurability, biocompatibility, and biodegradability are sought.

Fabrication of Biodegradable and Biocompatible Functional Polymers for Anti-Infection and Augmenting Wound Repair

The problem of bacteria-induced infections threatens the lives of many patients. Meanwhile, the misuse of antibiotics has led to a significant increase in bacterial resistance. There are two main ways to alleviate the issue: one is to introduce antimicrobial agents to medical devices to get local drug releasing and alleviating systemic toxicity and resistance, and the other is to develop new antimicrobial methods to kill bacteria. New antimicrobial methods include cationic polymers, metal ions, hydrophobic structures to prevent bacterial adhesion, photothermal sterilization, new biocides, etc. Biodegradable biocompatible synthetic polymers have been widely used in the medical field. They are often used in tissue engineering scaffolds as well as wound dressings, where bacterial infections in these medical devices can be serious or even fatal. However, such materials usually do not have inherent antimicrobial properties. They can be used as carriers for drug delivery or compounded with other antimicrobial materials to achieve antimicrobial effects. This review focuses on the antimicrobial behavior, preparation methods, and biocompatibility testing of biodegradable biocompatible synthetic polymers. Degradable biocompatible natural polymers with antimicrobial properties are also briefly described. Finally, the medical applications of these polymeric materials are presented.

The use of percutaneous thermal sensing microchips for non-invasive measurement of body temperature in foals during summer seasons in a subtropical region

Continuous accurate attainment of the body temperature of foals is important to detect early stages of severe heat stress or fever due to a systemic illness. Among a number of methods to measure body temperature, measuring rectal temperature with a digital thermometer is most frequently used due to being relatively fast and simple method. It is also comparatively accurate and correlates well with the core body temperature. However, this method requires restraining the foal for a few seconds to obtain the temperature, and it can be dangerous for the handling person. Percutaneous thermal sensing microchips (PTSMs) are a means of monitoring the body temperature of horses, which offers a non-invasive, hygienic, quick, and accurate way to measure body temperature and provide an identification number for each individual, once it is implanted. This study tested the hypothesis that PTSM has a strong relationship with a conventional body temperature measurement, i.e., measuring rectal temperature with a digital thermometer of foals during summer seasons. Thirty-two foals in three consecutive foaling seasons (2018, 2019, and 2020 season) were implanted a PTSM into the right pectoral muscle, the right splenius muscle, the right gluteal muscle, and the nuchal ligament as early as two weeks after birth. The four PTSM temperatures, rectal temperature, and climate conditions (air temperature, relative humidity, and wet-bulb globe temperature) were obtained simultaneously during the three summer seasons and paired for comparison analysis. Among the PTSM temperatures, the pectoral muscle had the highest correlation and the least differences with rectal temperature. Using PTSM was safe, easy, and reliable for attaining body temperature in foals.

A pH-stable, mucin based nanoparticle system for the co-delivery of hydrophobic and hydrophilic drugs

Biopolymer-based drug carriers are commonly used for the development of safe delivery systems. However, biopolymer-based systems are often highly sensitive to the acidic pH levels in the stomach and release most of their cargo before they have reached their point of destination. Such premature drug release combined with the resulting high dose requirements is not cost-efficient and comes with the risk of unwanted side effects on non-target tissues/organs. This problem can be mitigated by the mucin-based drug carriers developed here, which exhibit good stability at acidic pH levels as proven by dynamic light scattering and enzymatic degradation tests with pepsin. In addition, the mucin-based particles can deliver hydrophobic and hydrophilic drugs simultaneously, which is demonstrated both with experiments performed under in vitro sink conditions and with drug transport tests involving eukaryotic cells as targets. As photo-induced cross-links covalently stabilize those particles, they can release their payload over time in a sustained manner. The drug carrier system introduced here combines good stability with high drug encapsulation efficiency and very good biocompatibility and thus may be valuable for a broad spectrum of applications in biological settings.

The Use of Percutaneous Thermal Sensing Microchips to Measure Body Temperature in Horses during and after Exercise Using Three Different Cool-Down Methods

The frequent monitoring of a horse’s body temperature post strenuous exercise is critical to prevent or alleviate exertional heat illness (EHI) from occurring. Percutaneous thermal sensing microchip (PTSM) technology has the potential to be used as a means of monitoring a horse’s body temperature during and post-exercise. However, the accuracy of the temperature readings obtained, and their relationship to core body temperature are dependent on where they are implanted. This study aimed to document the relationship between core body temperature, and temperature readings obtained using PTSM implanted in different muscles, during exercise and post application of different cool-down methods. PTSMs were implanted into the right pectoral, right gluteal, right splenius muscles, and nuchal ligament. The temperatures were monitored during treadmill exercise, and post application of three different cool-down methods: no water application (Wno), water application only (Wonly), and water application following scraping (Wscraping). Central venous temperature (TCV) and PTSM temperatures from each region were obtained to investigate the optimal body site for microchip implantation. In this study, PTSM technology provided a practical, safe, and quick means of measuring body temperature in horses. However, its temperature readings varied depending on the implantation site. All muscle temperature readings exhibited strong relationships with TCV (r = 0.85~0.92, p < 0.05) after treadmill exercise without human intervention (water application), while the nuchal ligament temperature showed poor relationship with TCV. The relationships between TCV and PTSM temperatures became weaker with water application. Overall, however the pectoral muscle temperature measured by PTSM technology had the most constant relationships with TCV and showed the best potential to act as an alternate means of monitoring body temperature in horses for 50 min post-exercise, when there was no human intervention with cold water application.

Supramolecular Hydrogel Based Post-Surgical Implant System for Hydrophobic Drug Delivery Against Glioma Recurrence

Purpose

The brain, protected by the cranium externally and the blood–brain barrier (BBB) internally, poses challenges in chemotherapy of aggressive brain tumors. Maximal tumor resection followed by radiation and chemotherapy is the standard treatment protocol; however, a substantial number of patients suffer from recurrence. Systemic circulation of drugs causes myelodysplasia and other side effects. To address these caveats, we report facile synthesis of a polyester-based supramolecular hydrogel as a brain biocompatible implant for in situ delivery of hydrophobic drugs.

Methods

Polycaprolactone-diol (PCL) was linked to polyethyleneglycol-diacid (PEG) via an ester bond. In silico modeling indicated micelle-based aggregation of PCL-PEG co-polymer to form a supramolecular hydrogel. Brain biocompatibility was checked in Sprague Dawley rat brain cortex with MRI, motor function test, and histology. Model hydrophobic drugs carmustine and curcumin entrapment propelled glioma cells into apoptosis-based death evaluated by in vitro cytotoxicity assays and Western blot. In vivo post-surgical xenograft glioma model was developed in NOD-SCID mice and evaluated for efficacy to restrict aggressive regrowth of tumors.

Results

20% (w/v) PCL-PEG forms a soft hydrogel that can cover the uneven and large surface area of a tumor resection cavity and maintain brain density. The PCL-PEG hydrogel was biocompatible, and well-tolerated upon implantation in rat brain cortex, for a study period of 12 weeks. We report for the first time the combination of carmustine and curcumin entrapped as model hydrophobic drugs, increasing their bioavailability and yielding synergistic apoptotic effect on glioma cells. Further in vivo study indicated PCL-PEG hydrogel with a dual cargo of carmustine and curcumin restricted aggressive regrowth post-resection significantly compared with control and animals with intravenous drug treatment.

Conclusion

PCL-PEG soft gel-based implant is malleable compared with rigid wafers used as implants, thus providing larger surface area contact. This stable, biocompatible, supramolecular gel without external crosslinking can find wide applications by interchanging formulation of various hydrophobic drugs to ensure and increase site-specific delivery, avoiding systemic circulation.

Medical Applications of Porous Biomaterials: Features of Porosity and Tissue-Specific Implications for Biocompatibility

Porosity is an important material feature commonly employed in implants and tissue scaffolds. The presence of material voids permits the infiltration of cells, mechanical compliance, and outward diffusion of pharmaceutical agents. Various studies have confirmed that porosity indeed promotes favorable tissue responses, including minimal fibrous encapsulation during the foreign body reaction (FBR). However, increased biofilm formation and calcification is also described to arise due to biomaterial porosity. Additionally, the relevance of host responses like the FBR, infection, calcification, and thrombosis are dependent on tissue location and specific tissue microenvironment. In this review, the features of porous materials and the implications of porosity in the context of medical devices is discussed. Common methods to create porous materials are also discussed, as well as the parameters that are used to tune pore features. Responses toward porous biomaterials are also reviewed, including the various stages of the FBR, hemocompatibility, biofilm formation, and calcification. Finally, these host responses are considered in tissue specific locations including the subcutis, bone, cardiovascular system, brain, eye, and female reproductive tract. The effects of porosity across the various tissues of the body is highlighted and the need to consider the tissue context when engineering biomaterials is emphasized.

Preclinical testing of an anal bulking agent coated with a zwitterionic polymer in a fecal incontinence rat model

Fecal incontinence is a disabling condition in which the passage of fecal material cannot be controlled. Although the condition is not life-threatening, it can seriously reduce the quality of life...

Rationally designed drug delivery systems for the local treatment of resected glioblastoma

Glioblastoma (GBM) is a particularly aggressive brain cancer associated with high recurrence and poor prognosis. The standard of care, surgical resection followed by concomitant radio- and chemotherapy, leads to low survival rates. The local delivery of active agents within the tumor resection cavity has emerged as an attractive means to initiate oncological treatment immediately post-surgery. This complementary approach bypasses the blood-brain barrier, increases the local concentration at the tumor site while reducing or avoiding systemic side effects. This review will provide a global overview on the local treatment for GBM with an emphasis on the lessons learned from past clinical trials. The main parameters to be considered to rationally design fit-of-purpose biomaterials and develop drug delivery systems for local administration in the GBM resection cavity to prevent the tumor recurrence will be described. The intracavitary local treatment of GBM should i) use materials that facilitate translation to the clinic; ii) be characterized by easy GMP effective scaling up and easy-handling application by the neurosurgeons; iii) be adaptable to fill the tumor-resected niche, mold to the resection cavity or adhere to the exposed brain parenchyma; iv) be biocompatible and possess mechanical properties compatible with the brain; v) deliver a therapeutic dose of rationally-designed or repurposed drug compound(s) into the GBM infiltrative margin. Proof of concept with high translational potential will be provided. Finally, future perspectives to facilitate the clinical translation of the local perisurgical treatment of GBM will be discussed.

Recent advances in the development of nanomedicines for the treatment of ischemic stroke

Ischemic stroke is still a serious threat to human life and health, but there are few therapeutic options available to treat stroke because of limited blood-brain penetration. The development of nanotechnology may overcome some of the problems related to traditional drug development. In this review, we focus on the potential applications of nanotechnology in stroke. First, we will discuss the main molecular pathological mechanisms of ischemic stroke to develop a targeted strategy. Second, considering the important role of the blood-brain barrier in stroke treatment, we also delve mechanisms by which the blood-brain barrier protects the brain, and the reasons why the therapeutics must pass through the blood-brain barrier to achieve efficacy. Lastly, we provide a comprehensive review related to the application of nanomaterials to treat stroke, including liposomes, polymers, metal nanoparticles, carbon nanotubes, graphene, black phosphorus, hydrogels and dendrimers. To conclude, we will summarize the challenges and future prospects of nanomedicine-based stroke treatments.

Evaluation of Loco-Regional Skin Toxicity Induced by an In Situ Forming Depot after a Single Subcutaneous Injection at Different Volumes and Flow Rates in Göttingen Minipigs

The present study aims to investigate the loco-regional tolerability and injection parameters (i.e., flow rate and administration volume) of an in situ forming depot (ISFD) in Göttingen minipigs, to secure both the therapeutic procedure and compliance in chronic medical prescriptions. The ISFD BEPO^® technology (MedinCell S.A.) is investigated over 10 days, after a single subcutaneous injection of test item based on a DMSO solution of diblock and triblock polyethylene glycol-polylactic acid copolymers. Injection sites are systematically observed for macroscopic loco-regional skin reactions as well as ultrasound scanning, enabling longitudinal in vivo imaging of the depot. Observations are complemented by histopathological examinations at 72 h and 240 h post-injection. Overall, no treatment-emergent adverse effects are macroscopically or microscopically observed at the subcutaneous injection sites, for the tested injection flow rates of 1 and 8 mL/min and volumes of 0.2 and 1 mL. The histopathology examination confirms an expected foreign body reaction, with an intensity depending on the injected volume. The depot morphology is similar irrespective of the administration flow rates. These results indicate that the ISFD BEPO^® technology can be considered safe when administered subcutaneously in Göttingen minipigs, a human-relevant animal model for subcutaneous administrations, in the tested ranges.

The Development of Design and Manufacture Techniques for Bioresorbable Coronary Artery Stents

Coronary artery disease (CAD) is the leading killer of humans worldwide. Bioresorbable polymeric stents have attracted a great deal of interest because they can treat CAD without producing long-term complications. Bioresorbable polymeric stents (BMSs) have undergone a sustainable revolution in terms of material processing, mechanical performance, biodegradability and manufacture techniques. Biodegradable polymers and copolymers have been widely studied as potential material candidates for bioresorbable stents. It is a great challenge to find a reasonable balance between the mechanical properties and degradation behavior of bioresorbable polymeric stents. Surface modification and drug-coating methods are generally used to improve biocompatibility and drug loading performance, which are decisive factors for the safety and efficacy of bioresorbable stents. Traditional stent manufacture techniques include etching, micro-electro discharge machining, electroforming, die-casting and laser cutting. The rapid development of 3D printing has brought continuous innovation and the wide application of biodegradable materials, which provides a novel technique for the additive manufacture of bioresorbable stents. This review aims to describe the problems regarding and the achievements of biodegradable stents from their birth to the present and discuss potential difficulties and challenges in the future.

An Update on the Routes for the Delivery of Donepezil

Dementia is a significant public health problem in the 21st century. Alzheimer's disease (AD) is an essential factor in dementia. Currently, the drugs used for the treatment of AD are mainly acetylcholine inhibitors (AChEIs). As an AChEI, donepezil (DP) can improve patients' cognitive ability with low side effects and has been accepted by most patients and doctors. For AD patients, the dosage regimen is also crucial due to aging and diseases. Although there are DP oral tablets on the market, there are still many problems to be solved. At present, more and more research is conducted to optimize the route of administration of DP to improve the self-administration of patients. The research fields of DP administration include oral administration, injection administration, intranasal administration, and transdermal administration. This Review is to present the development of different DP administrations and evaluates the advantages and limitations of those works, hoping to optimize the DP dosage regimen for AD patients.

Effect of tissue microenvironment on fibrous capsule formation to biomaterial-coated implants

Within tissue exposed to the systemic immune system, lymphocytes and fibroblasts act against biomaterials via the development of a fibrous capsule, known as the foreign body reaction (FBR). Inspired by the natural tolerance that the uterine cavity has to foreign bodies, our study explores the role of microenvironment across classical (subcutaneous) and immune privileged (uterine) tissues in the development of the FBR. As a model biomaterial, we used electrospun fibers loaded with sclerosing agents to provoke scar tissue growth. Additionally, we integrated these materials onto an intrauterine device as a platform for intrauterine biomaterial studies. Polyester materials in vitro achieved drug release up to 10 days, greater pro-inflammatory and pro-healing cytokine expression, and the addition of gelatin enabled greater fibroblast attachment. We observed the materials that induced the greatest FBR in the mouse, had no effect when inserted at the utero-tubal junction of non-human primates. These results suggest that the FBR varies across different tissue microenvironments, and a dampened fibrotic response exists in the uterine cavity, possibly due to immune privilege. Further study of immune privileged tissue factors on biomaterials could broaden our understanding of the FBR and inform new methods for achieving biocompatibility in vivo.

Biocompatibility Evolves: Phenomenology to Toxicology to Regeneration

The word "biocompatibility," is inconsistent with the observations of healing for so-called biocompatible biomaterials. The vast majority of the millions of medical implants in humans today, presumably "biocompatible," are walled off by a dense, avascular, crosslinked collagen capsule, hardly suggestive of life or compatibility. In contrast, one is now seeing examples of implant biomaterials that lead to a vascularized reconstruction of localized tissue, a biological reaction different from traditional biocompatible materials that generate a foreign body capsule. Both the encapsulated biomaterials and the reconstructive biomaterials qualify as "biocompatible" by present day measurements of biocompatibility. Yet, this new generation of materials would seem to heal "compatibly" with the living organism, where older biomaterials are isolated from the living organism by the dense capsule. This review/perspective article will explore this biocompatibility etymological conundrum by reviewing the history of the concepts around biocompatibility, today's standard methods for assessing biocompatibility, a contemporary view of the foreign body reaction and finally, a compendium of new biomaterials that heal without the foreign body capsule. A new definition of biocompatibility is offered here to address advances in biomaterials design leading to biomaterials that heal into the body in a facile manner.

Towards a flexible electrochemical biosensor fabricated from biocompatible Bombyx mori silk

In modern days, there is an increasing relevance of and demand for flexible and biocompatible sensors for in-vivo and epidermal applications. One promising strategy is the implementation of biological (natural) polymers, which offer new opportunities for flexible biosensor devices due to their high biocompatibility and adjustable biodegradability. As a proof-of-concept experiment, a biosensor was fabricated by combining thin- (for Pt working- and counter electrode) and thick-film (for Ag/AgCl quasi-reference electrode) technologies: The biosensor consists of a fully bio-based and biodegradable fibroin substrate derived from silk fibroin of the silkworm Bombyx mori combined with immobilized enzyme glucose oxidase. The flexible glucose biosensor is encapsulated by a biocompatible silicon rubber which is certificated for a safe use onto human skin. Characterization of the sensor set-up is exemplarily demonstrated by glucose measurements in buffer and Ringer's solution, while the stability of the quasi-reference electrode has been investigated versus a commercial Ag/AgCl reference electrode. Repeated bending studies validated the mechanical properties of the electrode structures. The cross-sensitivity of the biosensor against ascorbic acid, noradrenaline and adrenaline was investigated, too. Additionally, biocompatibility and degradation tests of the silk fibroin with and without thin-film platinum electrodes were carried out.

Chitosan Membranes Filled with Cyclosporine A as Possible Devices for Local Administration of Drugs in the Treatment of Breast Cancer

The aim of this work is the design, preparation and characterization of membranes based on cyclosporine A (CsA) and chitosan carboxylate (CC) to be used as an implantable subcutaneous medical device for a prolonged therapeutic effect in the treatment of breast cancer. The choice to use CsA is due to literature data that have demonstrated its possible antitumor activity on different types of neoplastic cells. To this end, CsA was bound to CC through an amidation reaction to obtain a prodrug to be dispersed in a chitosan-based polymeric membrane. The reaction intermediates and the final product were characterized by Fourier transform infrared spectroscopy (FT-IR) and proton nuclear magnetic resonance (¹H-NMR). Membranes were analyzed by differential scanning calorimetry (DSC) and scanning electron microscopy (SEM). The data obtained showed the effective formation of the amide bond between CsA and CC and the complete dispersion of CsA inside the polymeric membrane. Furthermore, preliminary tests, conducted on MDA-MB-231, a type of breast cancer cell line, have shown a high reduction in the proliferation of cancer cells. These results indicate the possibility of using the obtained membranes as an interesting strategy for the release of cyclosporin-A in breast cancer patients.

Biomaterials in treatment of Alzheimer's disease

Alzheimer's disease (AD) is a non-recoverable progressive neurodegenerative disorder most prevalent but not limited to the old age population. After all the scientific efforts, there are still many unmet criteria and loopholes in available treatment and diagnostic strategies, limiting their efficacy. The poor drug efficacy is attributed to various biological hurdles, including blood-brain barrier (BBB) and peripheral side effects as most prominent ones and the lack of promising carriers to precisely deliver the drug to the brain by conserving its therapeutic potency. The increasing disease prevalence and unavailability of effective therapy calls for developing a more innovative, convenient and affordable way to treat AD. To fulfill such need, researchers explored various biomaterials to develop potential vectors or other forms to target the bioactives in the brain by preserving their inherent properties, improving the existing lacuna like poor solubility, permeability and bioavailability etc. and minimize the side effect. The unique characteristic properties of biomaterials are used to develop different drug carriers, surface modifying target active ligands, functional carriers, drug conjugate, biosensing probe, diagnostic tool and many more. The nanoparticulate system and other colloidal carriers like hydrogel and biodegradable scaffold can effectively target the drug moieties to the brain. Also, the use of different target-acting ligands and stimuli-responsive carriers assures the site-specificity and controlled release at the desired site by interaction with receptors and various exo- and endogenous stimuli. This review article has highlighted the application of biomaterials for targeting the drug to the brain and as promising diagnostic tools to detect the markers for better AD management. The work particularly focuses on the use of biomaterials as smart drug carriers including pH, thermo, photo, electro and magnetically triggered system; novel drug carriers for brain targeting including polymeric carriers (polymeric nanoparticle, dendrimer and polymeric micelle); lipid carrier (liposome, nanoemulsion, NLC and SLN); inorganic nanoparticles (quantum dots, gold nanoparticles etc.); and other drug vectors (hydrogel, biodegradable scaffold, and carbon nanotube) in treatment of AD. It also highlighted the application of some novel carrier systems and biomaterials as biosensor and other diagnostic tools for early and precise AD diagnosis.

Poly(lactic-co-glycolic Acid) Nanoparticle Encapsulated 17β-Estradiol Improves Spatial Memory and Increases Uterine Stimulation in Middle-Aged Ovariectomized Rats

Hormone therapy that contains 17β-estradiol (E2) is used commonly for treatment of symptoms associated with menopause. E2 treatment has been shown to improve cognitive function following the decrease in ovarian hormones that is characteristic of menopause. However, once in circulation, the majority of E2 is bound to serum hormone binding globulin or albumin, becoming biologically inactive. Thus, therapeutic efficacy of E2 stands to benefit from increased bioavailability via sustained release of the hormone. Here, we focus on the encapsulation of E2 within polymeric nanoparticles composed of poly(lactic-co-glycolic) acid (PLGA). PLGA agent encapsulation offers several delivery advantages, including improved bioavailability and sustained biological activity of encapsulated agents. We hypothesized that delivery of E2 from PLGA nanoparticles would enhance the beneficial cognitive effects of E2 relative to free E2 or non-hormone loaded nanoparticle controls in a rat model of menopause. To test this hypothesis, spatial learning and memory were assessed in middle-aged ovariectomized rats receiving weekly subcutaneous treatment of either oil-control, free (oil-solubilized) E2, blank (non-hormone loaded) PLGA, or E2-loaded PLGA. Unexpectedly, learning and memory differed significantly between the two vehicle control groups. E2-loaded PLGA nanoparticles improved learning and memory relative to its control, while learning and memory were not different between free E2 and its vehicle control. These results suggest that delivery of E2 from PLGA nanoparticles offered cognitive benefit. However, when evaluating peripheral burden, E2-loaded PLGA was found to increase uterine stimulation compared to free E2, which is an undesired outcome, as estrogen exposure increases uterine cancer risk. In sum, a weekly E2 treatment regimen of E2 from PLGA nanoparticles increased cognitive efficacy and was accompanied with an adverse impact on the periphery, effects that may be due to the improved agent bioavailability and sustained biological activity offered by PLGA nanoparticle encapsulation. These findings underscore the risk of non-specific enhancement of E2 delivery and provide a basic framework for the study and development of E2's efficacy as a cognitive therapeutic with the aid of customizable polymeric nano-carriers.

Controlled radical polymerization of hydrophilic and zwitterionic brush-like polymers from silk fibroin surfaces

Bombyx mori silk fibroin is a fibrous protein whose tunable properties and biocompatibility have resulted in its utility in a wide-variety of applications, including as drug delivery vehicles, wound dressings, and tissue engineering scaffolds. Control of protein and cell attachment is vital to the performance of biomaterials, but silk fibroin is mostly hydrophobic and interacts nonspecifically with cells and proteins. Silk functionalised with hydrophilic polymers reduces attachment, but the low number of reactive sites makes achieving a uniform conjugation a persistent challenge. This work presents a new approach to grow brush-like polymers from the surface of degradable silk films, where the films were enriched with hydroxyl groups, functionalised with an initiator, and finally reacted with acrylate monomers using atom transfer radical polymerisation. Two different routes to hydroxyl enrichment were investigated, one involving reaction with ethylene oxide (EO) and the other using a two-step photo-catalysed oxidation reaction. Both routes increased surface hydrophilicity, and hydrophilic monomers containing either uncharged (poly(ethylene glycol), PEG) pendant groups or zwitterionic pendant groups were polymerised from the surfaces. The initial processing of the films to induce beta sheet structures was found to impact the success of the polymerizations. Compared to the EO modified or unmodified silk surfaces, the oxidation reaction resulted in more polymer conjugation and the surfaces appear more uniform. Mesenchymal stem cell and protein attachment were the lowest on polymers grown from oxidised surfaces. PEG-containing brush-like polymers displayed lower protein attachment than surfaces conjugated with PEG using a previously reported "grafting to" method, but polymers containing zwitterionic side chains displayed both the lowest contact angles and the lowest cell and protein attachment. This finding may arise from the interactions of the zwitterionic pendant groups through their permanent dipoles and is an important finding because PEG is susceptible to oxidative damage that can reduce efficacy over time. These modified silk materials with lower cell and protein attachments are envisioned to find utility when enhanced diffusion around surfaces is required, such as in drug delivery implants.

Modular design of a hybrid hydrogel for protease-triggered enhancement of drug delivery to regulate TNF-α production by pro-inflammatory macrophages

Systemic drug administration has conventionally been prescribed to alleviate persistent local inflammation which is prevalent in chronic diseases. However, this approach is associated with drug-induced toxicity, particularly when the dosage exceeds that necessitated by pathological conditions of diseased tissues. Herein, we developed a modular hybrid hydrogel which could be triggered to release an anti-inflammatory drug upon exposure to elevated protease activity associated with inflammatory diseases. Modular design of the hybrid hydrogel enabled independent optimization of its protease-cleavable and drug-loaded subdomains to facilitate hydrogel formation, cleavability by matrix-metalloprotease-9 (MMP-9), and tuning drug release rate. In vitro study demonstrated the protease-triggered enhancement of drug release from the hybrid hydrogel system for effective inhibition of TNF-α production by pro-inflammatory macrophages and suggested its potential to mitigate drug-induced cytotoxicity. Using non-invasive imaging to monitor the activity of reactive oxygen species in biomaterial-induced host response, we confirmed that the hybrid hydrogel and its constituent materials did not induce adverse immune response after 5 days following their subcutaneous injection in immuno-competent mice. We subsequently incorporated this hybrid hydrogel onto a commercial wound dressing which could release the drug upon exposure to MMP-9. Together, our findings suggested that this hybrid hydrogel might be a versatile platform for on-demand drug delivery via either injectable or topical application to modulate inflammation in chronic diseases.

Blockade of macrophage adhesion to CD200-treated polystyrene culture surface

CD200 is an anti-inflammatory transmembrane glycoprotein in the immunoglobulin superfamily. The interaction of CD200 and its receptor CD200R has shown to inhibit inflammatory response of myeloid cells to foreign materials. The purpose of this study is to create a CD200 immobilized biomaterial surface through polydopamine coating to suppress macrophage cell adhesion and reduce inflammatory cytokine secretion accordingly by macrophages. In this study, tissue-culture treated polystyrene (TCPS) surface was modified with biotin through polydopamine coating. Purified CD200-streptavidin fusion protein was then immobilized onto the biotinylated TCPS surface through the high affinity between biotin and streptavidin. Mouse J774A.1 macrophages were seeded on CD200-immobilized TCPS surface to evaluate the effect of CD200 on preventing macrophage attachment. The effects of CD200-immobilized TCPS surface on pro-inflammatory cytokine secretion from J774A.1 macrophages were measured by enzyme-linked immunosorbent assay. As a result, CD200-immobilized TCPS surface suppressed macrophage attachment for up to 9 hr. The level of IL-6 and TNF-α secreted from J774A.1 macrophages interacted with CD200-coated TCPS surface was reduced by 36.3% and 32.4%, respectively.

Resorbable bacterial cellulose membranes with strontium release for guided bone regeneration

Hybrid materials, based on bacterial cellulose (BC) and hydroxyapatite (HA), have been investigated for guided bone regeneration (GBR). However, for some GBR, degradability in the physiological environment is an essential requirement. The present study aimed to explore the use of oxidized bacterial cellulose (OxBC) membranes, associated with strontium apatite, for GBR applications. BC membranes were produced by fermentation and purified, before oxidizing and mineralizing by immersing in strontium chloride solution and sodium bibasic phosphate for 5 cycles. The hybrid materials (BC/HA/Sr, BC/SrAp, OxBC/HA/Sr and OxBC/SrAp) were characterized for biodegradability and bioactivity and for their physicochemical and morphological properties. In vitro cytotoxicity and hemolytic properties of the materials were also investigated. In vivo biocompatibility was analyzed by performing histopathological evaluation at 1, 3 and 9 weeks in mices. Results showed that the samples presented different strontium release profiles and that oxidation enhances degradation under physiological conditions. All the hybrid materials were bioactive. Cell viability assay indicated that the materials are non-cytotoxic and in vivo studies showed low inflammatory response and increased connective tissue repair, as well as degradation in most of the materials, especially the oxidized membranes. This study confirms the potential use of bacterial cellulose-derived hybrid membranes for GBR.

Neurorestoration Approach by Biomaterials in Ischemic Stroke

Ischemic stroke (IS) is the leading cause of disability in the western world, assuming a high socio-economic cost. One of the most used strategies in the last decade has been biomaterials, which have been initially used with a structural support function. They have been perfected, different compounds have been combined, and they have been used together with cell therapy or controlled release chemical compounds. This double function has driven them as potential candidates for the chronic treatment of IS. In fact, the most developed are in different phases of clinical trial. In this review, we will show the ischemic scenario and address the most important criteria to achieve a successful neuroreparation from the point of view of biomaterials. The spontaneous processes that are activated and how to enhance them is one of the keys that contribute to the success of the therapeutic approach. In addition, the different routes of administration and how they affect the design of biomaterials are analyzed. Future perspectives show where this broad scientific field is heading, which advances every day with the help of technology and advanced therapies.

Keratinous materials: Structures and functions in biomedical applications

Keratins are a family of fibrous proteins anticipated to possess wide-ranging biomedical applications due to their abundance, physicochemical properties and intrinsic biological activity. This review mainly focuses on the biomaterials derived from three major sources of keratins; namely human hair, wool and feather, that have effective applications in tissue engineering, wound healing and drug delivery. This article offers five viewpoints regarding keratin i) an introduction to keratin protein extraction and keratin-based scaffold fabrication methods ii) applications in nerve and bone tissue engineering iii) a review on the keratin dressings applied to different types of wounds to facilitate wound healing and thereby repair the skin iv) the utilization of keratinous materials as a carrier system for therapeutics with a controlled manner v) a discussion regarding the main challenges for using keratin in biomedical applications as well as its future prospects.

Traumatic Brain Injuries: Pathophysiology and Potential Therapeutic Targets

Traumatic brain injury (TBI) remains one of the leading causes of morbidity and mortality amongst civilians and military personnel globally. Despite advances in our knowledge of the complex pathophysiology of TBI, the underlying mechanisms are yet to be fully elucidated. While initial brain insult involves acute and irreversible primary damage to the parenchyma, the ensuing secondary brain injuries often progress slowly over months to years, hence providing a window for therapeutic interventions. To date, hallmark events during delayed secondary CNS damage include Wallerian degeneration of axons, mitochondrial dysfunction, excitotoxicity, oxidative stress and apoptotic cell death of neurons and glia. Extensive research has been directed to the identification of druggable targets associated with these processes. Furthermore, tremendous effort has been put forth to improve the bioavailability of therapeutics to CNS by devising strategies for efficient, specific and controlled delivery of bioactive agents to cellular targets. Here, we give an overview of the pathophysiology of TBI and the underlying molecular mechanisms, followed by an update on novel therapeutic targets and agents. Recent development of various approaches of drug delivery to the CNS is also discussed.

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.

Time-of-flight secondary ion mass spectrometry three-dimensional imaging of surface modifications in poly(caprolactone) scaffold pores

Scaffolds composed of synthetic polymers such as poly(caprolactone) (PCL) are widely used for the support and repair of tissues in biomedicine. Pores are common features in scaffolds as they facilitate cell penetration. Various surface modifications can be performed to promote key biological responses to these scaffolds. However, verifying the chemistry of these materials post surface modification is problematic due to the combination of three-dimensional (3D) topography and surface sensitivity. Time-of-flight secondary ion mass spectrometry (ToF-SIMS) is commonly used to correlate surface chemistry with cell response. In this study, 3D imaging mass spectrometry analysis of surface modified synthetic polymer scaffolds is demonstrated using PCL porous scaffold, a pore filling polymer sample preparation, and 3D imaging ToF-SIMS. We apply a simple sample preparation procedure, filling the scaffold pores with a poly(vinyl alcohol)/glycerol mixture to remove topographic influence on image quality. This filling method allows the scaffold (PCL) and filler secondary ions to be reconstructed into a 3D chemical image of the pore. Furthermore, we show that surface modifications in the pores of synthetic polymer scaffolds can be mapped in 3D. Imaging of "dry" and "wet" surface modifications is demonstrated as well as a comparison of surface modifications with relatively strong ToF-SIMS peaks (fluorocarbon films [FC]) and to more biologically relevant surface modification of a protein (bovine serum albumin [BSA]). We demonstrate that surface modifications can be imaged in 3D showing that characteristic secondary ions associated with FC and BSA are associated with C3 F8 plasma treatment and BSA, respectively within the pore.