Affinity-Based Drug Delivery Systems for Tissue Repair and Regeneration

Injectable Granular Hydrogels Enable Avidity-Controlled Biotherapeutic Delivery

Protein therapeutics represent a rapidly growing class of pharmaceutical agents that hold great promise for the treatment of various diseases such as cancer and autoimmune dysfunction. Conventional systemic delivery approaches, however, result in off-target drug exposure and a short therapeutic half-life, highlighting the need for more localized and controlled delivery. We have developed an affinity-based protein delivery system that uses guest-host complexation between β-cyclodextrin (CD, host) and adamantane (Ad, guest) to enable sustained localized biomolecule presentation. Hydrogels were formed by the copolymerization of methacrylated CD and methacrylated dextran. Extrusion fragmentation of bulk hydrogels yielded shear-thinning and self-healing granular hydrogels (particle diameter = 32.4 ± 16.4 μm) suitable for minimally invasive delivery and with a high host capacity for the retention of guest-modified proteins. Bovine serum albumin (BSA) was controllably conjugated to Ad via EDC chemistry without affecting the affinity of the Ad moiety for CD (KD = 12.0 ± 1.81 μM; isothermal titration calorimetry). The avidity of Ad-BSA conjugates was directly tunable through the number of guest groups attached, resulting in a fourfold increase in the complex half-life (t1/2 = 5.07 ± 1.23 h, surface plasmon resonance) that enabled a fivefold reduction in protein release at 28 days. Furthermore, we demonstrated that the conjugation of Ad to immunomodulatory cytokines (IL-4, IL-10, and IFNγ) did not detrimentally affect cytokine bioactivity and enabled their sustained release. Our strategy of avidity-controlled delivery of protein-based therapeutics is a promising approach for the sustained local presentation of protein therapeutics and can be applied to numerous biomedical applications.

Long-Acting Ocular Injectables: Are We Looking In The Right Direction?

The complex anatomy and physiological barriers of the eye make delivering ocular therapeutics challenging. Generally, effective drug delivery to the eye is hindered by rapid clearance and limited drug bioavailability. Biomaterial-based approaches have emerged to enhance drug delivery to ocular tissues and overcome existing limitations. In this review, some of the most promising long-acting injectables (LAIs) in ocular drug delivery are explored, focusing on novel design strategies to improve therapeutic outcomes. LAIs are designed to enable sustained therapeutic effects, thereby extending local drug residence time and facilitating controlled and targeted drug delivery. Moreover, LAIs can be engineered to enhance drug targeting and penetration across ocular physiological barriers.

Diffusion-Based 3D Bioprinting Strategies

3D bioprinting has enabled the fabrication of tissue-mimetic constructs with freeform designs that include living cells. In the development of new bioprinting techniques, the controlled use of diffusion has become an emerging strategy to tailor the properties and geometry of printed constructs. Specifically, the diffusion of molecules with specialized functions, including crosslinkers, catalysts, growth factors, or viscosity-modulating agents, across the interface of printed constructs will directly affect material properties such as microstructure, stiffness, and biochemistry, all of which can impact cell phenotype. For example, diffusion-induced gelation is employed to generate constructs with multiple materials, dynamic mechanical properties, and perfusable geometries. In general, these diffusion-based bioprinting strategies can be categorized into those based on inward diffusion (i.e., into the printed ink from the surrounding air, solution, or support bath), outward diffusion (i.e., from the printed ink into the surroundings), or diffusion within the printed construct (i.e., from one zone to another). This review provides an overview of recent advances in diffusion-based bioprinting strategies, discusses emerging methods to characterize and predict diffusion in bioprinting, and highlights promising next steps in applying diffusion-based strategies to overcome current limitations in biofabrication.

Quantifying and Modulating Protein Encapsulation in Guanosine-Based Supramolecular Particles

The encapsulation of proteins is an effective way to preserve their structure and enhance their function. One exciting possibility is adjusting the protective agent to match the specific protein's characteristics to influence its properties. In a recent study, we developed a flow cytometry-based method to quantify the encapsulation of small-molecule dyes in colloidal particles made from guanosine derivatives (supramolecular hacky sacks (SHS) particles). We aimed to determine whether this method could quantify protein encapsulation and track changes and if the particles could be tuned to bind to specific proteins. Our results showed that fluorescein isothiocyanate (FITC)-labeled proteins had apparent association constants in the micromolar range with hydrophobicity as the dominant factor enhancing the affinities. Confocal laser scanning microscopy (CLSM) imaging supported these results and provided additional information about the protein distribution within the particles. We also tested the feasibility of tuning the avidin affinity (AVI) for SHS particles with a biotin ligand. We found that increasing the amount of biotin initially enhanced AVI binding, but then reached saturation, which we hypothesize results from noncovalent cross-linking caused by strong biotin/AVI interactions. CLSM images showed that the linker also impacted the AVI distribution within the particles. Our strategy provides an advantage over other methods for quantifying protein encapsulation by being suitable for high-throughput analysis with high reproducibility. We anticipate that future efforts to use lower-affinity ligands would result in better strategies for modulating protein affinity for drug delivery applications.

Interplay between Diffusion and Bond Cleavage Reaction for Determining Release in Polymer-Drug Conjugates

In conjugated polymeric drug delivery systems, both the covalent bond degradation rate and the diffusion of the freely moving drug particles affect the release profile of the formulation. Using Monte Carlo simulations in spherical matrices, the release kinetics resulting from the competition between the reaction and diffusion processes is discussed. For different values of the relative bond cleavage rate, varied over four orders of magnitude, the evolution of (i) the number of bonded drug molecules, (ii) the fraction of the freely moved detached drug within the polymer matrix, and (iii) the resulting fractional release of the drug is presented. The characteristic release time scale is found to increase by several orders of magnitude as the cleavage reaction rate constant decreases. The two extreme rate-limiting cases where either the diffusion or the reaction dominates the release are clearly distinguishable. The crossover between the diffusion-controlled and reaction-controlled regimes is also examined and a simple analytical formula is presented that can describe the full dependence of the release time on the bond cleavage rate constant. This simple relation is provided simply by the sum of the characteristic time for purely diffusional release and the bond cleavage decay time, which equals the inverse of the reaction rate constant.

Hydrogel scaffolds in the treatment of spinal cord injury: a review

Spinal cord injury (SCI) is a disease of the central nervous system often caused by accidents, and its prognosis is unsatisfactory, with long-term adverse effects on patients' lives. The key to its treatment lies in the improvement of the microenvironment at the injury and the reconstruction of axons, and tissue repair is a promising therapeutic strategy. Hydrogel is a three-dimensional mesh structure with high water content, which has the advantages of biocompatibility, degradability, and adjustability, and can be used to fill pathological defects by injectable flowing hydrophilic material in situ to accurately adapt to the size and shape of the injury. Hydrogels mimic the natural extracellular matrix for cell colonization, guide axon extension, and act as a biological scaffold, which can be used as an excellent carrier to participate in the treatment of SCI. The addition of different materials to make composite hydrogel scaffolds can further enhance their performance in all aspects. In this paper, we introduce several typical composite hydrogels and review the research progress of hydrogel for SCI to provide a reference for the clinical application of hydrogel therapy for SCI.

Bottom-Up Strategy to Forecast the Drug Location and Release Kinetics in Antitumoral Electrospun Drug Delivery Systems

Electrospun systems are becoming promising devices usable for topical treatments. They are eligible to deliver different therapies, from anti-inflammatory to antitumoral. In the current research, polycaprolactone electrospun membranes loaded with synthetic and commercial antitumoral active substances were produced, underlining how the matrix-filler affinity is a crucial parameter for designing drug delivery devices. Nanofibrous membranes loaded with different percentages of Dacarbazine (the drug of choice for melanoma) and a synthetic derivative of Dacarbazine were produced and compared to membranes loaded with AuM1, a highly active Au-complex with low affinity to the matrix. AFM morphologies showed that the surface profile of nanofibers loaded with affine substances is similar to one of the unloaded systems, thanks to the nature of the matrix-filler interaction. FTIR analyses proved the efficacy of the interaction between the amidic group of the Dacarbazine and the polycaprolactone. In AuM1-loaded membranes, because of the weak matrix-filler interaction, the complex is mainly aggregated in nanometric domains on the nanofiber surface, which manifests a nanometric roughness. Consequently, the release profiles follow a Fickian behavior for the Dacarbazine-based systems, whereas a two-step with a highly prominent burst effect was observed for AuM1 systems. The performed antitumoral tests evidence the high-cytotoxic activity of the electrospun systems against melanoma cell lines, proving that the synthetic substances are more active than the commercial dacarbazine.

Tunable Surface Charge Enables the Electrostatic Adsorption-Controlled Release of Neuroprotective Peptides from a Hydrogel-Nanoparticle Drug Delivery System

We exploit the electrostatic interactions between the positively charged neuroprotective peptide, pituitary adenylate cyclase-activating polypeptide (PACAP), and negatively charged poly(lactic-co-glycolic acid) (PLGA) nanoparticles to control PACAP release from the surface of nanoparticles dispersed in a hyaluronan-methylcellulose (HAMC) hydrogel composite. PACAP is a promising therapeutic for the treatment of neurological disorders, yet it has been difficult to deliver in vivo. Herein, the PACAP release rate was tuned by manipulating peptide adsorption onto the surface of blank nanoparticles by modifying either nanoparticle loading in the hydrogel or nanoparticle surface charge. This peptide-nanoparticle interaction was controlled by the pH-responsive carboxylic acid end terminal groups of PLGA. We further validated this system with the controlled release of a novel stabilized PACAP analog: Ac-[Ala¹⁵, Ala²⁰]PACAP-propylamide, which masks its recognition to peptidases in circulation. Both wild-type and stabilized PACAP released from the vehicle increased the production of neuroprotective Interleukin-6 from cultured primary astrocytes. Using computational fluid dynamics methods, PACAP release from the composite was predicted based on experimentally derived adsorption isotherms, which exhibited similar release profiles to experimental data. This versatile adsorption-based system was used to deliver PACAP locally to the brains of stroke-injured mice over a 10 day period in vivo, highlighting its effectiveness for the controlled release of PACAP to the central nervous system.

Real-time evaluation of a hydrogel delivery vehicle for cancer immunotherapeutics within embedded spheroid cultures

Many protein immunotherapeutics are hindered by transport barriers that prevent the obtainment of minimum effective concentrations (MECs) in solid tumors. Local delivery vehicles with tunable release (infusion) rates for immunotherapeutics are being developed to achieve local and sustained release. To expedite their discovery and translation, in vitro models can identify promising delivery vehicles and immunotherapies that benefit from sustained release by evaluating cancer spheroid killing in real-time. Using displacement affinity release (DAR) within a hydrogel, we tuned the release of a CD133 targeting dual antigen T cell engager (DATE) without the need for further DATE or hydrogel modifications, yielding an injectable vehicle that acts as a tunable infusion pump. To quantify bioactivity benefits, a 3D embedded cancer spheroid model was developed for the evaluation of sustained protein release and combination therapies on T cell mediated spheroid killing. Using automated brightfield and fluorescent microscopy, the size of red fluorescent protein (iRFP670) expressing spheroids were tracked to quantify spheroid growth or killing over time as a function of controlled delivery. We demonstrate that sustained DATE release enhanced T cell mediated killing of embedded glioblastoma spheroids at longer timepoints, killing was further enhanced with the addition of anti-PD1 antibody (αPD1). The multi-cellular embedded spheroid model with automated microscopy demonstrated the benefit of extended bispecific release on T cell mediated killing, which will expedite the identification and translation of delivery vehicles such as DAR for immunotherapeutics.

Injectable Liposome-based Supramolecular Hydrogels for the Programmable Release of Multiple Protein Drugs

Directing biological functions is at the heart of next-generation biomedical initiatives in tissue and immuno-engineering. However, the ambitious goal of engineering complex biological networks requires the ability to precisely perturb specific signaling pathways at distinct times and places. Using lipid nanotechnology and the principles of supramolecular self-assembly, we developed an injectable liposomal nanocomposite hydrogel platform to precisely control the release of multiple protein drugs. By integrating modular lipid nanotechnology into a hydrogel, we introduced multiple mechanisms of release based on liposome surface chemistry. To validate the utility of this system for multi-protein delivery, we demonstrated synchronized, sustained, and localized release of IgG antibody and IL-12 cytokine in vivo, despite the significant size differences between these two proteins. Overall, liposomal hydrogels are a highly modular platform technology with the ability the mediate orthogonal modes of protein release and the potential to precisely coordinate biological cues both in vitro and in vivo.

Sulfated carboxymethylcellulose-based scaffold mediated delivery of Timp3 alleviates osteoarthritis

Osteoarthritis (OA) is a debilitating progressive joint disease with high incidence and socioeconomic burden. However, no disease-modifying treatment is currently available for OA. Here, we report a sulfated carboxymethylcellulose-based scaffold mediated delivery of tissue inhibitor of metalloprotease 3 (Timp3) as a disease-modifying therapeutic strategy for OA. First, we chemically modified carboxymethylcellulose (CMC) to sulfated carboxymethylcellulose (sCMC) to impart native-like electrostatic interaction-based binding of cationic proteins. We then fabricated cartilage ECM mimicking sCMC-gelatin scaffolds which showed preferential binding and sustained delivery of Timp3. This scaffold-mediated delivery of Timp3 demonstrated a reduction in matrix degradation, protease expression and inflammatory markers in the goat ex vivo OA model leading to enhanced retention of cartilage ECM markers when compared to OA control. Further, similar results were obtained when sCMC-gelatin scaffolds were evaluated using human OA samples, supporting its clinical potential. Overall, the Timp3 loaded sCMC-gelatin scaffold shows potential as a treatment approach for OA.

Using UV-Responsive Nanoparticles to Provide In Situ Control of Growth Factor Delivery and a More Constant Release Profile from a Hydrogel Environment

Nanoparticles are popular delivery vehicles, but their diffusional release results in inconstant drug delivery. Here, we flatten the delivery profile into a more constant, zero-order profile. Brain-derived neurotrophic factor (BDNF) is attached to photoactive titanium dioxide nanoparticles and loaded into a nanofibrous self-assembling peptide (SAP) hydrogel. Different UV exposure conditions show three distinct profiles, including a counterintuitive decrease in release after UV exposure. We propose that the adsorption of the freed growth factor onto the hydrogel nanofibers affects release. Nanoparticles diffuse from the hydrogel readily, carrying the bound growth factor, but the freed growth factor (released from the nanoparticles by UV) instead interacts with─and is released less readily from─the hydrogel. UV shifts growth factor from nanoparticles to the hydrogel, therefore changing the diffusional release. Through midpoint UV exposure, we achieve a flattened delivery profile─unusual for diffusion─by changing in situ the amount of growth factor bound to the diffusing nanoparticles. With nanoparticle diffusion alone, we observed an increasing release profile with 36% of release in the first 6 h and 64% in the second 6 h. With midway UV exposure, this was controlled to 49 and 51%, respectively. The release of an unbound (soluble) control growth factor, glial cell-line derived neurotrophic factor (GDNF), was not affected by UV treatment, demonstrating the potential for independent control of temporal delivery profiles in a multiagent material.

Growth Factor Immobilization Strategies for Musculoskeletal Disorders

PURPOSE OF REVIEW

Tissue regenerative solutions for musculoskeletal disorders have become increasingly important with a growing aged population. Current growth factor treatments often require high dosages with the potential for off-target effects. Growth factor immobilization strategies offer approaches towards alleviating these concerns. This review summarizes current growth factor immobilization techniques (encapsulation, affinity interactions, and covalent binding) and the effects of immobilization on growth factor loading, release, and bioactivity.

RECENT FINDINGS

The breadth of immobilization techniques based on encapsulation, affinity, and covalent binding offer multiple methods to improve the therapeutic efficacy of growth factors by controlling bioactivity and release. Growth factor immobilization strategies have evolved to more complex systems with the capacity to load and release multiple growth factors with spatiotemporal control. The advancements in immobilization strategies allow for development of new, complex musculoskeletal tissue treatment strategies with improved spatiotemporal control of loading, release, and bioactivity.

Peptide hydrogels for affinity-controlled release of therapeutic cargo: Current and potential strategies

The development of devices for the precise and controlled delivery of therapeutics has grown rapidly over the last few decades. Drug delivery materials must provide a depot with delivery profiles that satisfy pharmacodynamic and pharmacokinetic requirements resulting in clinical benefit. Therapeutic efficacy can be limited due to short half-life and poor stability. Thus, to compensate for this, frequent administration and high doses are often required to achieve therapeutic effect, which in turn increases potential side effects and systemic toxicity. This can potentially be mitigated by using materials that can deliver drugs at controlled rates, and material design principles that allow this are continuously evolving. Affinity-based release strategies incorporate a myriad of reversible interactions into a gel network, which have affinities for the therapeutic of interest. Reversible binding to the gel network impacts the release profile of the drug. Such affinity-based interactions can be modulated to control the release profile to meet pharmacokinetic benchmarks. Much work has been done developing affinity-based control in the context of polymer-based materials. However, this strategy has not been widely implemented in peptide-based hydrogels. Herein, we present recent advances in the use of affinity-controlled peptide gel release systems and their associated mechanisms for applications in drug delivery.

Translational Applications of Hydrogels

Advances in hydrogel technology have unlocked unique and valuable capabilities that are being applied to a diverse set of translational applications. Hydrogels perform functions relevant to a range of biomedical purposes-they can deliver drugs or cells, regenerate hard and soft tissues, adhere to wet tissues, prevent bleeding, provide contrast during imaging, protect tissues or organs during radiotherapy, and improve the biocompatibility of medical implants. These capabilities make hydrogels useful for many distinct and pressing diseases and medical conditions and even for less conventional areas such as environmental engineering. In this review, we cover the major capabilities of hydrogels, with a focus on the novel benefits of injectable hydrogels, and how they relate to translational applications in medicine and the environment. We pay close attention to how the development of contemporary hydrogels requires extensive interdisciplinary collaboration to accomplish highly specific and complex biological tasks that range from cancer immunotherapy to tissue engineering to vaccination. We complement our discussion of preclinical and clinical development of hydrogels with mechanical design considerations needed for scaling injectable hydrogel technologies for clinical application. We anticipate that readers will gain a more complete picture of the expansive possibilities for hydrogels to make practical and impactful differences across numerous fields and biomedical applications.

In vitro modelling of the physiological and diseased female reproductive system

The maladies affecting the female reproductive tract (FRT) range from infections to endometriosis to carcinomas. In vitro models of the FRT play an increasingly important role in both basic and translational research, since the anatomy and physiology of the FRT of humans and other primates differ significantly from most of the commonly used animal models, including rodents. Using organoid culture to study the FRT has overcome the longstanding hurdle of maintaining epithelial phenotype in culture.  Both ECM-derived and engineered materials have proved critical for maintaining a physiological phenotype of FRT cells in vitro by providing the requisite 3D environment, ligands, and architecture. Advanced materials have also enabled the systematic study of factors contributing to the invasive metastatic processes. Meanwhile, microphysiological devices make it possible to incorporate physical signals such as flow and cyclic exposure to hormones. Going forward, advanced materials compatible with hormones and optimised to support FRT-derived cells' long-term growth, will play a key role in addressing the diverse array of FRT pathologies and lead to impactful new treatments that support the improvement of women's health. STATEMENT OF SIGNIFICANCE: The female reproductive system is a crucial component of the female anatomy. In addition to enabling reproduction, it has wide ranging influence on tissues throughout the body via endocrine signalling. This intrinsic role in regulating normal female biology makes it susceptible to a variety of female-specific diseases. However, the complexity and human-specific features of the reproductive system make it challenging to study. This has spurred the development of human-relevant in vitro models for helping to decipher the complex issues that can affect the reproductive system, including endometriosis, infection, and cancer. In this Review, we cover the current state of in vitro models for studying the female reproductive system, and the key role biomaterials play in enabling their development.

Improvement of wound healing by the development of ECM-inspired biomaterial coatings and controlled protein release

Implant design has evolved from biochemically inert substrates, minimizing cell and protein interaction, towards sophisticated bioactive substrates, modulating the host response and supporting the regeneration of the injured tissue. Important aspects to consider are the control of cell adhesion, the discrimination of bacteria and non-local cells from the desired tissue cell type, and the stimulation of implant integration and wound healing. Here, the extracellular matrix acts as a role model providing us with inspiration for sophisticated designs. Within this scope, small bioactive peptides have proven to be miscellaneously deployable for the mediation of surface, cell and matrix interactions. Combinations of adhesion ligands, proteoglycans, and modulatory proteins should guide multiple aspects of the regeneration process and cooperativity between the different extracellular matrix components, which bears the chance to maximize the therapeutic efficiency and simultaneously lower the doses. Hence, efforts to include multiple of these factors in biomaterial design are well worth. In the following, multifunctional implant coatings based on bioactive peptides are reviewed and concepts to implement strong surface anchoring for stable cell adhesion and a dynamic delivery of modulator proteins are discussed.

Drug-Loaded Hydrogels for Intraocular Lenses with Prophylactic Action against Pseudophakic Cystoid Macular Edema

Pseudophakic cystoid macular edema (PCME), caused by chronic inflammation, is the most common cause of visual impairment in the medium-term after cataract surgery. Therefore, the prophylactic topical administration of combined steroidal and non-steroidal anti-inflammatory drugs is commonly done. Drug-eluting intraocular lenses (IOLs) gained interest as an efficient way to overcome the compliance issues related to the use of ocular drops without the need for additional surgical steps. The incorporation of functional monomers and molecular imprinting were herein applied to design hydrogels suitable as IOLs and able to co-deliver steroidal (dexamethasone sodium phosphate) and non-steroidal (bromfenac sodium) drugs. The incorporation of N-(2-aminopropyl) methacrylamide (APMA) increased the drug uptake and improved the in vitro release kinetics. Imprinting with bromfenac resulted in a decreased drug release due to permanent drug bonding, while imprinting with dexamethasone increased the amount of dexamethasone released after dual-drug loading. The application of a mathematical model to predict the in vivo drug release behavior suggests the feasibility of achieving therapeutic drug concentrations of bromfenac and dexamethasone in the aqueous humor for about 2 and 8 weeks, respectively, which is compatible with the current topical prophylaxis after cataract surgery.

Recent Progress on Polysaccharide-Based Hydrogels for Controlled Delivery of Therapeutic Biomolecules

A plethora of applications using polysaccharides have been developed in recent years due to their availability as well as their frequent nontoxicity and biodegradability. These polymers are usually obtained from renewable sources or are byproducts of industrial processes, thus, their use is collaborative in waste management and shows promise for an enhanced sustainable circular economy. Regarding the development of novel delivery systems for biotherapeutics, the potential of polysaccharides is attractive for the previously mentioned properties and also for the possibility of chemical modification of their structures, their ability to form matrixes of diverse architectures and mechanical properties, as well as for their ability to maintain bioactivity following incorporation of the biomolecules into the matrix. Biotherapeutics, such as proteins, growth factors, gene vectors, enzymes, hormones, DNA/RNA, and antibodies are currently in use as major therapeutics in a wide range of pathologies. In the present review, we summarize recent progress in the development of polysaccharide-based hydrogels of diverse nature, alone or in combination with other polymers or drug delivery systems, which have been implemented in the delivery of biotherapeutics in the pharmaceutical and biomedical fields.

Heparin-mediated antibiotic delivery from an electrochemically-aligned collagen sheet

BACKGROUND

Implantable medical devices and hardware are prolific in medicine, but hardware associated infections remain a major issue.

OBJECTIVE

To develop and evaluate a novel, biologic antimicrobial coating for medical implants.

METHODS

Electrochemically compacted collagen sheets with and without crosslinked heparin were synthesized per a protocol developed by our group. Sheets were incubated in antibiotic solution (gentamicin or moxifloxacin) overnight, and in vitro activity was assessed with five-day diffusion assays against Pseudomonas aeruginosa. Antibiotic release over time from gentamicin-infused sheets was determined using in vitro elution and high performance liquid chromatography (HPLC).

RESULTS

Collagen-heparin-antibiotic sheets demonstrated larger growth inhibition zones against P. aeruginosa compared to collagen-antibiotic alone sheets. This activity persisted for five days and was not impacted by rinsing sheets prior to evaluation. Rinsed collagen-antibiotic sheets did not produce any inhibition zones. Elution of gentamicin from collagen-heparin-gentamicin sheets was gradual and remained above the minimal inhibitory concentration for gentamicin-sensitive organisms for 29 days. Conversely, collagen-gentamicin sheets eluted their antibiotic load within 24 hours. Overall, heparin-associated sheets demonstrated larger inhibition zones against P. aeruginosa and prolonged elution profile via HPLC.

CONCLUSION

We developed a novel, local antibiotic delivery system that could be used to coat medical implants/hardware in the future and reduce post-operative infections.

Affinity Hydrogels for Protein Delivery

Proteins have been studied as therapeutic agents for treatment of various human diseases. However, the delivery of protein drugs into the body is challenging. In this review, we summarize and highlight progress in developing affinity hydrogels (i.e., hydrogels functionalized with protein-bound ligands) for controlled protein release. Contrary to traditional hydrogels, which release proteins mainly through diffusion, affinity hydrogels stably retain and sustainably release proteins based mainly on diffusion coupled with a binding reaction. These hydrogels can also be modulated to release proteins in response to defined molecules in a triggered manner. Future research efforts may focus on the development of intelligent affinity hydrogels to mimic the properties of human tissues in sensing different environmental stimuli for on-demand release of single or multiple proteins (i.e., biomimetic intelligence for protein delivery).

Conjugated Polymer Nanoparticles Based on Copper Coordination for Real-Time Monitoring of pH-Responsive Drug Delivery

Metal coordination-driven composite systems have excellent stability and pH-responsive ability, making them suitable for specific drug delivery in physiological conditions. In this study, an anionic conjugated polymer PPEIDA with a poly(p-phenylene ethynylene) backbone and iminodiacetic acid (IDA) side chains is used as a drug carrier to construct a class of pH-responsive nanoparticles, PPEIDA-Cu-DOX conjugated polymer nanoparticles (CPNs), by taking advantage of the metal coordination interaction of Cu²⁺ with PPEIDA and the drug doxorubicin (DOX). PPEIDA-Cu-DOX CPNs have high drug loading and encapsulation efficiency (EE), calculated to be 54.30 ± 1.10 and 95.80 ± 0.84%, respectively. Due to the good spectral overlap, Förster resonance energy transfer (FRET) takes place between PPEIDA and the drug DOX, which enables the observation of the loading and the release of DOX from CPNs in an acidic environment by monitoring fluorescence emission changes. Therefore, PPEIDA-Cu-DOX CPNs can also be used in real-time cell imaging to monitor drug release in addition to delivering DOX targeting tumor cells. Compared with free DOX, PPEIDA-Cu-DOX CPNs show a similar inhibition to tumor cells and lower toxicity to normal cells. Our results demonstrate the feasibility and potential of constructing pH-responsive CPNs via metal-ligand coordination interactions for cancer treatment.

Mechanochemical Cellular Membrane Internalization of Nanohydrogels: A Large-Scale Mesoscopic Simulation

By combining large-scale dissipative particle dynamics and steered molecular dynamics simulations, we investigate the mechanochemical cellular internalization pathways of homogeneous and heterogeneous nanohydrogels and demonstrate that membrane internalization is determined by the crosslink density and encapsulation ability of nanohydrogels. The homogeneous nanohydrogels with a high crosslink density and low encapsulation ability behave as soft nanoparticles partially wrapped by the membrane, while those with a low crosslink density and high encapsulation ability permeate into the membrane. Regardless of the crosslink density, the homogeneous nanohydrogels undergo typical dual morphological deformations. The local lipid nanodomains are identified at the contacting region between the membrane and nanohydrogels because of different diffusion behaviors between lipid and receptor molecules during the internalization process. The yolk@shell heterogeneous nanohydrogels present a different mechanochemical cellular internalization pathway. The yolk with strong affinity is directly in contact with the membrane, resulting in partial membrane wrapping, and the contacting area is much reduced when compared to homogenous nanohydrogels, leading to a smaller lipid nanodomain and thus avoiding related cellular toxicity. Our findings provide a critical mechanism understanding of the biological pathways of nanohydrogels and may guide the molecular design of the hydrogel-based materials for controlled release drug delivery, tissue engineering, and cell culture.

Periadventitial Delivery of Simvastatin-Loaded Microparticles Attenuate Venous Neointimal Hyperplasia Associated With Arteriovenous Fistula

Background

Venous neointimal hyperplasia and venous stenosis (VS) formation can result in a decrease in arteriovenous fistula (AVF) patency in patients with end‐stage renal disease. There are limited therapies that prevent VNH/VS. Systemic delivery of simvastatin has been shown to reduce VNH/VS but local delivery may help decrease the side effects associated with statin use. We determined if microparticles (MP) composed of cyclodextrins loaded with simvastatin (MP‐SV) could reduce VS/VNH using a murine arteriovenous fistula model with chronic kidney disease.

Methods and Results

Male C57BL/6J mice underwent nephrectomy to induce chronic kidney disease. Four weeks later, an arteriovenous fistula was placed and animals were randomized to 3 groups: 20 μL of PBS or 20 μL of PBS with 16.6 mg/mL of either MP or MP‐SV. Animals were euthanized 3 days later and the outflow veins were harvested for quantitative reverse transcriptase–polymerase chain reaction analysis and 28 days later for immunohistochemistical staining with morphometric analysis. Doppler ultrasound was performed weekly. Gene expression of vascular endothelial growth factor‐A (Vegf‐A), matrix metalloproteinase‐9 (Mmp‐9), transforming growth factor beta 1 (Tgf‐β1), and monocyte chemoattractant protein‐1 (Mcp‐1) were significantly decreased in MP‐SV treated vessels compared with controls. There was a significant decrease in the neointimal area, cell proliferation, inflammation, and fibrosis, with an increase in apoptosis and peak velocity in MP‐SV treated outflow veins. MP‐SV treated fibroblasts when exposed to hypoxic injury had decreased gene expression of Vegf‐A and Mmp‐9.

Conclusions

In experimental arteriovenous fistulas, periadventitial delivery of MP‐SV decreased gene expression of Vegf‐A, Mmp‐9, Tgf‐β1 and Mcp‐1, VNH/VS, inflammation, and fibrosis.

Dual-acting therapeutic proteins for intraocular use

Intravitreally injected antibody-based medicines have revolutionised the treatment of retinal disease. Bispecific and dual-functional antibodies and therapeutic proteins have the potential to further increase the efficacy of intraocular medicines.

Williams G, Brocchini S, Awwad S. Injectables and Depots to Prolong Drug Action of Proteins and Peptides

Proteins and peptides have emerged in recent years to treat a wide range of multifaceted diseases such as cancer, diabetes and inflammation. The emergence of polypeptides has yielded advancements in the fields of biopharmaceutical production and formulation. Polypeptides often display poor pharmacokinetics, limited permeability across biological barriers, suboptimal biodistribution, and some proclivity for immunogenicity. Frequent administration of polypeptides is generally required to maintain adequate therapeutic levels, which can limit efficacy and compliance while increasing adverse reactions. Many strategies to increase the duration of action of therapeutic polypeptides have been described with many clinical products having been developed. This review describes approaches to optimise polypeptide delivery organised by the commonly used routes of administration. Future innovations in formulation may hold the key to the continued successful development of proteins and peptides with optimal clinical properties.

Co-delivery of minocycline and paclitaxel from injectable hydrogel for treatment of spinal cord injury

Spinal cord injury (SCI) induces pathological and inflammatory responses that create an inhibitory environment at the site of trauma, resulting in axonal degeneration and functional disability. Combination therapies targeting multiple aspects of the injury, will likely be more effective than single therapies to facilitate tissue regeneration after SCI. In this study, we designed a dual-delivery system consisting of a neuroprotective drug, minocycline hydrochloride (MH), and a neuroregenerative drug, paclitaxel (PTX), to enhance tissue regeneration in a rat hemisection model of SCI. For this purpose, PTX-encapsulated poly (lactic-co-glycolic acid) PLGA microspheres along with MH were incorporated into the alginate hydrogel. A prolonged and sustained release of MH and PTX from the alginate hydrogel was obtained over eight weeks. The obtained hydrogels loaded with a combination of both drugs or each of them alone, along with the blank hydrogel (devoid of any drugs) were injected into the lesion site after SCI (at the acute phase). Histological assessments showed that the dual-drug treatment reduced inflammation after seven days. Moreover, a decrease in the scar tissue, as well as an increase in neuronal regeneration was observed after 28 days in rats treated with dual-drug delivery system. Over time, a fast and sustained functional improvement was achieved in animals that received dual-drug treatment compared with other experimental groups. This study provides a novel dual-drug delivery system that can be developed to test for a variety of SCI models or neurological disorders.

Visible light mediated PVA-tyramine hydrogels for covalent incorporation and tailorable release of functional growth factors

PVA-Tyr hydrogel facilitated covalent incorporation can control release of pristine growth factors while retaining their native bioactivity.

Multi-component supramolecular fibers with elastomeric properties and controlled drug release

Supramolecular fibers fabricated by co-axial electrospinning combine load-bearing properties and sustained drug release of hydrophobic and UPy-modified drugs.

Vascularization strategies for skin tissue engineering

Lack of proper vascularization after skin trauma causes delayed wound healing. This has sparked the development of various tissue engineering strategies to improve vascularization.

Engineered materials for organoid systems

Organoids are 3D cell culture systems that mimic some of the structural and functional characteristics of an organ. Organoid cultures provide the opportunity to study organ-level biology in models that mimic human physiology more closely than 2D cell culture systems or non-primate animal models. Many organoid cultures rely on decellularized extracellular matrices as scaffolds, which are often poorly chemically defined and allow only limited tunability and reproducibility. By contrast, the biochemical and biophysical properties of engineered matrices can be tuned and optimized to support the development and maturation of organoid cultures. In this Review, we highlight how key cell-matrix interactions guiding stem-cell decisions can inform the design of biomaterials for the reproducible generation and control of organoid cultures. We survey natural, synthetic and protein-engineered hydrogels for their applicability to different organoid systems and discuss biochemical and mechanical material properties relevant for organoid formation. Finally, dynamic and cell-responsive material systems are investigated for their future use in organoid research.

Influencing neuroplasticity in stroke treatment with advanced biomaterials-based approaches

Since the early 1990s, we have known that the adult brain is not static and has the capacity to repair itself. The delivery of various therapeutic factors and cells have resulted in some exciting pre-clinical and clinical outcomes in stroke models by targeting post-injury plasticity to enhance recovery. Developing a deeper understanding of the pathways that modulate plasticity will enable us to optimize delivery strategies for therapeutics and achieve more robust effects. Biomaterials are a key tool for the optimization of these potential treatments, owing to their biocompatibility and tunability. In this review, we identify factors and targets that impact plastic processes known to contribute to recovery, discuss the role of biomaterials in enhancing the efficacy of treatment strategies, and suggest combinatorial approaches based on the stage of injury progression.

Recent advances in musculoskeletal local drug delivery

Musculoskeletal disorders are a significant burden on the global economy and public health. Advanced drug delivery plays a key role in the musculoskeletal field and holds the promise of enhancing the repair of degenerated and injured musculoskeletal tissues. Ideally, drug delivery should have the ability to directly deliver therapeutic agents to the diseased/injured sites with a desirable drug level over a period of time. Here, we present a mini-review of the current state-of-the-art research associated with local drug delivery and its use for the treatment of musculoskeletal disorders. First, an overview of drug delivery strategies, with a focus on issues related to musculoskeletal pathology, potential therapeutic strategies, conventional and non-conventional drugs, and various delivery systems, is introduced. Then, we highlight recent advances in the emerging fields of musculoskeletal local drug delivery, involving therapeutic drugs (e.g., genes, small molecule therapeutics, and stem cells), novel delivery vehicles (e.g., 3D printing and tissue engineering techniques), and innovative delivery approaches (e.g., multi-drug delivery and smart stimuli-responsive delivery). The review concludes with future perspectives and associated challenges for developing local drug delivery for musculoskeletal applications. STATEMENT OF SIGNIFICANCE: Three important aspects are highlighted in this manuscript: 1) The advanced musculoskeletal drug delivery is introduced from the aspects ranging from musculoskeletal disorders, potential therapeutic solutions, and various drug delivery systems. 2) The recent advances in the emerging fields of musculoskeletal local drug delivery, involving therapeutic drugs (e.g., genes, small molecule therapeutics, and stem cells), novel delivery vehicles (e.g., 3D printing and tissue engineering technique), and innovative delivery approaches (e.g., multi-drug delivery and smart stimuli-responsive delivery), are highlighted. 3) The challenges and perspectives of future research directions in the development of musculoskeletal local drug delivery are presented.

Programmable hydrogels

Programmable hydrogels are defined as hydrogels that are able to change their properties and functions periodically, reversibly and/or sequentially on demand. They are different from those responsive hydrogels whose changes are passive or cannot be stopped or reversed once started and vice versa. The purpose of this review is to summarize major progress in developing programmable hydrogels from the viewpoints of principles, functions and biomedical applications. The principles are first introduced in three categories including biological, chemical and physical stimulation. With the stimulation, programmable hydrogels can undergo functional changes in dimension, mechanical support, cell attachment and molecular sequestration, which are introduced in the middle of this review. The last section is focused on the introduction and discussion of four biomedical applications including mechanistic studies in mechanobiology, tissue engineering, cell separation and protein delivery.

Nanoparticle-Based Systems for Delivery of Protein Therapeutics to the Spinal Cord

Recent studies have demonstrated that delivery of protein therapeutics to the spinal cord may promote functional axon regeneration, providing a pathway for recovery of certain motor skills. The timeframe for delivery of protein therapeutics, however, must be modulated to prevent bulk release of the therapeutics and minimize the frequency of implantations. This perspective examines both affinity-based and nanoparticle-based strategies for delivery of neurotrophic factors (NFs) to the spinal cord in an effective, safe, and tunable manner.

Self-assembly of affinity-controlled nanoparticles via host-guest interactions for drug delivery

There has been increasing interest in constructing affinity-based drug delivery systems via different non-covalent interactions. Herein we report a host-guest interaction-based strategy to develop effective drug delivery systems using cyclodextrin-containing copolymers. Hydrophilic copolymers with one polyethylene glycol block and another block containing either α-cyclodextrin or β-cyclodextrin were synthesized. Using poly(β-benzyl l-aspartate) and pyrene as model guest compounds, we demonstrated the nanoparticle formation by host-guest interaction-mediated self-assembly. When an antioxidant and anti-inflammatory drug Tempol was used, the formation of well-defined spherical nanoparticles and therapeutic loading can be simultaneously realized. The obtained nanotherapy showed affinity-controlled drug release. In vitro cell culture experiments suggested that the host-guest nanotherapy exhibited desirable antioxidant and anti-inflammatory effects in macrophages. In a mouse model of an inflammatory disease ulcerative colitis, the orally administered host-guest nanoparticle can be effectively accumulated in the inflamed colonic tissue. Oral treatment of mice bearing colitis with the nanotherapy led to significantly improved efficacy in comparison with free drugs. A good in vivo safety profile was also observed for the developed host-guest nanotherapy. Accordingly, these types of affinity nanoparticles based on CD-containing copolymers can function as effective nanoplatforms for targeted treatment of a plethora of diseases.

Heparin-dopamine functionalized graphene foam for sustained release of bone morphogenetic protein-2

The recently developed three-dimensional (3D) graphene foam (GrF) is intriguing for potential bone tissue engineering applications because it provides stem cells with a 3D porous substrate for osteogenic differentiation. However, the nature of graphene's structure lacks functional groups, thus making it difficult for further modification such as immobilization or conjugation of growth factors, which are normally required to promote tissue regeneration. To explore the potential of GrF functionalization and sustained release of therapeutic proteins, we fabricated a modified 3D GrF scaffold with bio-inspired heparin-dopamine (Hepa-Dopa) molecules using a highly scalable chemical vapour deposition method. Our data indicated that Hepa-Dopa modification resulted in significantly higher bone morphogenetic protein-2 (BMP2) binding ability and longer release capacity compared with the untreated scaffolds. Importantly, the heparin-functionalized 3D GrF significantly improved the exogenous BMP2-induced osteogenic differentiation. Therefore, our study, for the first time, indicated that the 3D GrF can be biomimetically functionalized with Hepa-Dopa and be used for sustained release of BMP2, thereby inducing osteogenic differentiation and suggesting promising potential as a new multifunctional carrier for therapeutic proteins and stem cells in bone tissue engineering.

Using biomaterials to modulate chemotactic signaling for central nervous system repair

Chemotaxis enables cellular communication and movement within the body. This review focuses on exploiting chemotaxis as a tool for repair of the central nervous system (CNS) damaged from injury and/or degenerative diseases. Chemokines and factors alone may initiate repair following CNS injury/disease, but exogenous administration may enhance repair and promote regeneration. This review will discuss critical chemotactic molecules and factors that may promote neural regeneration. Additionally, this review highlights how biomaterials can impact the presentation and delivery of chemokines and growth factors to alter the regenerative response.

Endogenous IgG-based affinity-controlled release of TRAIL exerts superior antitumor effects

The inefficiency of recombinant tumor necrosis factor-related apoptosis-inducing ligand (TRAIL)-based clinical regimens has been dominantly attributed to the short half-life of TRAIL. Affinity-controlled release using endogenous long-acting proteins, such as IgG and albumin, as carriers is extremely attractive for improving the pharmacokinetics of TRAIL. Up to now, it is unclear whether IgG-binding is efficient for affinity-controlled release of TRAIL.

Methods: An IgG-binding affibody, IgBD, was genetically fused to the N-terminus of TRAIL to produce IgBD-TRAIL.The IgG-binding ability, cytotoxicity, serum half-life, and in vivo antitumor effect of IgBD-TRAIL were compared with that of TRAIL. In addition, an albumin-binding affibody, ABD, was fused to TRAIL to produce ABD-TRAIL. The cytototoxicity, serum half-life, and antitumor effect of IgBD-TRAIL and ABD-TRAIL were compared.

Results: IgBD fusion endowed TRAIL with high affinity (nM) for IgG without interference with its cytotoxicity. The serum half-life of IgBD-TRAIL is 50-60 times longer than that of TRAIL and the tumor uptake of IgBD-TRAIL at 8-24 h post-injection was 4-7-fold that of TRAIL. In vivo antitumor effect of IgBD-TRAIL was at least 10 times greater than that of TRAIL. Owing to the high affinity (nM) for albumin, the serum half-life of ABD-TRAIL was 80-90 times greater than that of TRAIL. However, after binding to albumin, the cytotoxicity of ABD-TRAIL was reduced more than 10 times. In contrast, binding to IgG had little impact on the cytotoxicity of IgBD-TRAIL. Consequently, intravenously injected IgBD-TRAIL showed antitumor effects superior to those of ABD-TRAIL.

Conclusions: Endogenous long-acting proteins, particularly IgG-based affinity-controlled release, prolonged the serum half-life as well as significantly enhanced the antitumor effect of TRAIL. IgBD-mediated endogenous IgG binding might be a novel approach for the affinity-controlled release of other protein drugs.

Systems for localized release to mimic paracrine cell communication in vitro

Paracrine cell communication plays a pivotal role for signal exchange between proximal cells in vivo. However, this localized, gradient type release of mediators at very low concentrations (pg/ml), relevant during physiological and pathological processes, is rarely reflected within in vitro approaches. This review gives an overview on state-of-the-art approaches, which transfer the paracrine cell-to-cell communication into in vitro cell culture model setups. The traditional methods like trans-well assays and more advanced microfluidic approaches are included. The review focusses on systems for localized release, mostly based on microparticles, which tightly mimic the paracrine interaction between single cells in 3D microenvironments. Approaches based on single microparticles, with the main focus on affinity-controlled storage and release of cytokines, are reviewed and their importance for understanding paracrine communication is highlighted. Various methods to study the cytokine release and their advantages and disadvantages are discussed. Basic principles of the release characteristics, like diffusion mechanisms, are quantitatively described, including the formation of resulting gradients around the local sources. In vitro cell experiments using such localized microparticle release systems in approaches to increase understanding of stem cell behavior within their niches and regulation of wound healing are highlighted as examples of successful localized release systems for mimicking paracrine cell communication.