Publications

Lymph nodes (LNs) dynamically expand in response to immunization, but the relationship between LN expansion and the accompanying adaptive immune response is unclear. Here, we first characterized the LN response across time and length scales to vaccines of distinct strengths. High-frequency ultrasound revealed that a bolus ‘weak’ vaccine induced a short-lived, 2-fold volume expansion, while a biomaterial-based ‘strong’ vaccine elicited an ∼7-fold LN expansion, which was maintained several weeks after vaccination. This latter expansion was associated with altered matrix and mechanical properties of the LN microarchitecture. Strong vaccination resulted in massive immune and stromal cell engagement, dependent on antigen presence in the vaccine, and conventional dendritic cells and inflammatory monocytes upregulated genes involved in antigen presentation and LN enlargement. The degree of LN expansion following therapeutic cancer vaccination strongly correlated with vaccine efficacy, even 100 days post-vaccination, and direct manipulation of LN expansion demonstrated a causative role in immunization outcomes.

Hydrogel-based drug delivery systems typically aim to release drugs locally to tissue in an extended manner. Tissue adhesive alginate-polyacrylamide tough hydrogels are recently demonstrated to serve as an extended-release system for the corticosteroid triamcinolone acetonide. Here, the stimuli-responsive controlled release of triamcinolone acetonide from the alginate-polyacrylamide tough hydrogel drug delivery systems (TADDS) and evolving new approaches to combine alginate-polyacrylamide tough hydrogel with drug-loaded nano and microparticles, generating composite TADDS is described. Stimulation with ultrasound pulses or temperature changes is demonstrated to control the release of triamcinolone acetonide from the TADDS. The incorporation of laponite nanoparticles or PLGA microparticles into the tough hydrogel is shown to further enhance the versatility to control and modulate the release of triamcinolone acetonide. A first technical exploration of a TADDS shelf-life concept is performed using lyophilization, where lyophilized TADDS are physically stable and the bioactive integrity of released triamcinolone acetonide is demonstrated. Given the tunability of properties, the TADDS are a suggested technology platform for controlled drug delivery.

Approved therapies for tendon diseases have not yet changed the clinical practice of symptomatic pain treatment and physiotherapy. This review article summarizes advances in the development of novel drugs, biologic products, and biomaterial therapies for tendon diseases with perspectives for translation of integrated therapies. Shifting from targeting symptom relief toward disease modification and prevention of disease progression may open new avenues for therapies. Deep evidence-based clinical, cellular, and molecular characterization of the underlying pathology of tendon diseases, as well as therapeutic delivery optimization and establishment of multidiscipline interorganizational collaboration platforms, may accelerate the discovery and translation of transformative therapies for tendon diseases.

Tissue adhesives capable of achieving strong and tough adhesion in permeable wet environments are useful in many biomedical applications. However, adhesion generated through covalent bond formation directly with the functional groups of tissues (i.e., -COOH and -NH₂ groups in collagen), or using non-covalent interactions can both be limited by weak, unstable, or slow adhesion. Here, it is shown that by combining pH-responsive bridging chitosan polymer chains and a tough hydrogel dissipative matrix one can achieve unprecedented ultratough adhesion to tissues (>2000 J m⁻²) in 5–10 min without covalent bond formation. The strong non-covalent adhesion is shown to be stable under physiologically relevant conditions and strongly influenced by chitosan molecular weight, molecular weight of polymers in the matrix, and pH. The adhesion mechanism relies primarily on the topological entanglement between the chitosan chains and the permeable adherends. To further expand the applicability of the adhesives, adhesion time can be decreased by dehydrating the hydrogel matrix to facilitate rapid chitosan interpenetration and entanglement (>1000 J m⁻² in ≤1 min). The unprecedented adhesive properties presented in this study open opportunities for new strategies in the development of non-covalent tissue adhesives and numerous bioapplications.

Aging is the largest risk factor for Achilles tendon associated disorders and rupture. Although Achilles tendon macroscale elastic properties are suggested to decline with aging, less is known about the effect of maturity and aging on multiscale viscoelastic properties and their effect on tendon cell behavior. Here, we show dose dependent changes in native multiscale tendon mechanical and structural properties and uncover several nanoindentation properties predicted by tensile mechanics and echogenicity. Alginate hydrogel systems designed to mimic juvenile tendon microscale mechanics revealed that stiffness and viscoelasticity affected Achilles tendon cell aspect ratio and proliferation during aging. This knowledge provides further evidence for the negative impact of maturity and aging on tendon and begins to elucidate how viscoelasticity can control tendon derived cell morphology and expansion.

Hydrogels that provide mechanical support and sustainably release therapeutics have been used to treat tendon injuries. However, most hydrogels are insufficiently tough, release drugs in bursts, and require cell infiltration or suturing to integrate with surrounding tissue. Here we report that a hydrogel serving as a high-capacity drug depot and combining a dissipative tough matrix on one side and a chitosan adhesive surface on the other side supports tendon gliding and strong adhesion (larger than 1,000 J m⁻²) to tendon on opposite surfaces of the hydrogel, as we show with porcine and human tendon preparations during cyclic-friction loadings. The hydrogel is biocompatible, strongly adheres to patellar, supraspinatus and Achilles tendons of live rats, boosted healing and reduced scar formation in a rat model of Achilles-tendon rupture, and sustainably released the corticosteroid triamcinolone acetonide in a rat model of patellar tendon injury, reducing inflammation, modulating chemokine secretion, recruiting tendon stem and progenitor cells, and promoting macrophage polarization to the M2 phenotype. Hydrogels with ‘Janus’ surfaces and sustained-drug-release functionality could be designed for a range of biomedical applications.

Operative treatment is assumed to provide superior outcomes to nonoperative (conservative) treatment following Achilles tendon rupture, however, this remains controversial. This study explores the effect of surgical repair on Achilles tendon healing. Rat Achilles tendons (n = 101) were bluntly transected and were randomized into groups receiving repair or non-repair treatments. By 1 week after injury, repaired tendons had inferior mechanical properties, which continued to 3- and 6-week post-injury, evidenced by decreased dynamic modulus and failure stress. Transcriptomics analysis revealed >7000 differentially expressed genes between repaired and non-repaired tendons after 1-week post-injury. While repaired tendons showed enriched inflammatory gene signatures, non-repaired tendons showed increased tenogenic, myogenic, and mechanosensitive gene signatures, with >200-fold enrichment in Tnmd expression. Analysis of gastrocnemius muscle revealed elevated MMP activity in tendons receiving repair treatment, despite no differences in muscle fiber morphology. Transcriptional regulation analysis highlighted that the highest expressed transcription factors in repaired tendons were associated with inflammation (Nfκb, SpI1, RelA, and Stat1), whereas non-repaired tendons expressed markers associated with tissue development and mechano-activation (Smarca1, Bnc2, Znf521, Fbn1, and Gli3). Taken together, these data highlight distinct differences in healing mechanism occurring immediately following injury and provide insights for new therapies to further augment tendons receiving repaired and non-repaired treatments.

Tendinopathy is a debilitating disease that causes as much as 30% of all musculoskeletal consultations. Existing treatments for tendinopathy have variable efficacy, possibly due to incomplete characterization of the underlying pathophysiology. Mechanical load can have both beneficial and detrimental effects on tendon, as the overall tendon response depends on the degree, frequency, timing, and magnitude of the load. The clinical continuum model of tendinopathy offers insight into the late stages of tendinopathy, but it does not capture the subclinical tendinopathic changes that begin before pain or loss of function. Small animal models that use high tendon loading to mimic human tendinopathy may be able to fill this knowledge gap. The goal of this review is to summarize the insights from in-vivo animal studies of mechanically-induced tendinopathy and higher loading regimens into the mechanical, microstructural, and biological features that help characterize the continuum between normal tendon and tendinopathy.

Mechanical stimulation (mechanotherapy) can promote skeletal muscle repair, but a lack of reproducible protocols and mechanistic understanding of the relation between mechanical cues and tissue regeneration limit progress in this field. To address these gaps, we developed a robotic device equipped with real-time force control and compatible with ultrasound imaging for tissue strain analysis. We investigated the hypothesis that specific mechanical loading improves tissue repair by modulating inflammatory responses that regulate skeletal muscle regeneration. We report that cyclic compressive loading within a specific range of forces substantially improves functional recovery of severely injured muscle in mice. This improvement is attributable in part to rapid clearance of neutrophil populations and neutrophil-mediated factors, which otherwise may impede myogenesis. Insights from this work will help advance therapeutic strategies for tissue regeneration broadly.

The development of tough adhesive hydrogels has enabled unprecedented adhesion to wet and moving tissue surfaces throughout the body, but they are typically composed of nondegradable components. Here, a family of degradable tough adhesive hydrogels containing ≈90% water by incorporating covalently networked degradable crosslinkers and hydrolyzable ionically crosslinked main-chain polymers is developed. Mechanical toughness, adhesion, and degradation of these new formulations are tested in both accelerated in vitro conditions and up to 16 weeks in vivo. These degradable tough adhesives are engineered with equivalent mechanical and adhesive properties to nondegradable tough adhesives, capable of achieving stretches >20 times their initial length, fracture energies >6 kJ m⁻², and adhesion energies >1000 J m⁻². All degradable systems show complete degradation within 2 weeks under accelerated aging conditions in vitro and weeks to months in vivo depending on the degradable crosslinker selected. Excellent biocompatibility is observed for all groups after 1, 2, 4, 8, and 16 weeks of implantation, with minimal fibrous encapsulation and no signs of organ toxicity. On-demand removal of the adhesive is achieved with treatment of chemical agents which do not cause damage to underlying skin tissue in mice. The broad versatility of this family of adhesives provides the foundation for numerous in vivo indications.