Kenrick Kuwahara

Delivery of demineralized bone matrix powder using a thermogelling chitosan carrier

Demineralized bone matrix (DBM) powder is widely used for bone regeneration due to its osteoinductivity and osteoconductivity. However, difficulties with handling, its tendency to migrate from graft sites, and lack of stability after surgery can sometimes limit the clinical utility of this material. In this work, the possibility of using a thermogelling chitosan carrier to deliver DBM powder was assessed. The DBM-thermogelling putty improved handling and formed a gel-like composite in situ at body temperature within a clinically relevant time period. The properties of the formed composite, including morphology, porosity, mechanical properties, equilibrium swelling as well as degradability, are significantly influenced by the ratio of DBM to thermogelling chitosan. The in vitro study showed that the alkaline phosphatase activity of C2C12 cells encapsulated in the composite was steadily increased with culture time. The in vivo study showed that increased DBM content in the DBM-thermogelling chitosan induced ectopic bone formation in a nude rat model. The diffusion of growth factor from the DBM-thermogelling chitosan as well as the host-implant interactions are discussed.

Enzymatic Crosslinking and Degradation of Gelatin as a Switch for Bone Morphogenetic Protein-2 Activity

Current therapies for tissue regeneration rely on the presence or direct delivery of growth factors to sites of repair. Bone morphogenetic protein-2 (BMP-2), combined with a carrier (usually collagen), is clinically proven to induce new bone formation during spinal fusion and nonunion repair. However, due to BMP-2s short half-life and its diffusive properties, orders of magnitude above physiological levels are required to ensure effectiveness. In addition, a high dose of this multifunctional growth factor is known to induce adverse effects in patients. To circumvent these challenges, we proposed and tested a new approach for BMP-2 delivery, by controlling BMP activity via carrier binding and localized proteolysis. BMP-2 was covalently bound to gelatin through site-specific enzymatic crosslinking using a microbial transglutaminase. Binding of BMP-2 to gelatin can completely switch off BMP-2 activity, as evidenced by loss of its transdifferentiating ability toward C2C12 promyoblasts. When gelatin sequestered BMP-2 is incubated with either microbial collagenase or tissue-derived matrix metalloproteinases, BMP-2 activity is fully restored. The activity of released BMP-2 correlates with the protease activity in a dose- and time-dependent manner. This observation suggests a novel way of delivering BMP-2 and controlling its activity. This improved delivery method, which relies on a physiological feedback, should enhance the known potential of this and other growth factors for tissue repair and regeneration.

The effect of three hemostatic agents on early bone healing in an animal model

BackgroundResorbable bone hemostasis materials, oxidized regenerated cellulose (ORC) and microfibrillar collagen (MFC), remain at the site of application for up to 8 weeks and may impair osteogenesis. Our experimental study compared the effect of a water-soluble alkylene oxide copolymer (AOC) to ORC and MFC versus no hemostatic material on early bone healing.MethodsTwo circular 2.7 mm non-critical defects were made in each tibia of 12 rabbits. Sufficient AOC, ORC or MFC was applied to achieve hemostasis, and effectiveness recorded. An autologous blood clot was applied to control defects. Rabbits were sacrificed at 17 days, tibiae excised and fixed. Bone healing was quantitatively measured by micro-computed tomography (micro-CT) expressed as fractional bone volume, and qualitatively assessed by histological examination of decalcified sections.ResultsHemostasis was immediate after application of MFC and AOC, after 1-2 minutes with ORC, and >5 minutes for control. At 17 days post-surgery, micro-CT analysis showed near-complete healing in control and AOC groups, partial healing in the ORC group and minimal healing in the MFC group. Fractional bone volume was 8 fold greater in the control and AOC groups than in the MFC group (0.42 ± 0.06, 0.40 ± 0.03 vs 0.05 ± 0.01, P < 0.001) and over 1.5-fold greater than in the ORC group (0.25 ± 0.03, P < 0.05). By histology, MFC remained at the application site with minimal healing at the defect margins and early fibrotic tissue within the defect. ORC-treated defects showed partial healing but with early fibrotic tissue in the marrow space. Conversely, control and AOC-treated defects demonstrated newly formed woven bone rich in cellular activity with no evidence of AOC remaining at the application site.ConclusionsEarly healing appeared to be impaired by the presence of MFC and impeded by the presence of ORC. In contrast, AOC did not inhibit bone healing and suggest that AOC may be a better bone hemostatic material for procedures where bony fusion is critical and immediate hemostasis required.

A Passive Refillable Intraocular MEMS Drug Delivery Device

This paper presents the first passive implantable microelectromechanical systems (MEMS) device for targeted intraocular delivery of therapeutic compounds. In particular, this device addresses the treatment of chronic, difficult to reach diseases that affect the retina including retinitis pigmentosa, age-related macular degeneration, diabetic retinopathy, and glaucoma. The device is composed of three structural polymethyldisiloxane (PDMS) layers that are irreversibly bonded without the use of any adhesives. These layers form an integrated drug delivery device consisting of a refillable reservoir, tube, check valve, and suture tabs. This device requires a single implantation surgery and is capable of repeated delivery of multiple drugs. Characterization of the refillable reservoir and check valve performance is presented. Preliminary surgical implantation results of a mechanical test structure are also presented