Three-dimensional printing of clinical scale and personalized calcium phosphate scaffolds for alveolar bone reconstruction.

OBJECTIVE: Alveolar bone defects can be highly variable in their morphology and, as the defect size increases, they become more challenging to treat with currently available therapeutics and biomaterials. This investigation sought to devise a protocol for fabricating customized clinical scale and patient-specific, bioceramic scaffolds for reconstruction of large alveolar bone defects. METHODS: Two types of calcium phosphate (CaP)-based bioceramic scaffolds (alginate/ß-TCP and hydroxyapatite/α-TCP, hereafter referred to as hybrid CaP and Osteoink™, respectively) were designed, 3D printed, and their biocompatibility with alveolar bone marrow stem cells and mechanical properties were determined. Following scaffold optimization, a workflow was developed to use cone beam computed tomographic (CBCT) imaging to design and 3D print, defect-specific bioceramic scaffolds for clinical-scale bone defects. RESULTS: Osteoink™ scaffolds had the highest compressive strength when compared to hybrid CaP with different infill orientation. In cell culture medium, hybrid CaP degradation resulted in decreased pH (6.3) and toxicity to stem cells; however, OsteoInk™ scaffolds maintained a stable pH (7.2) in culture and passed the ISO standard for cytotoxicity. Finally, a clinically feasible laboratory workflow was developed and evaluated using CBCT imaging to engineer customized and defect-specific CaP scaffolds using OsteoInk™. It was determined that printed scaffolds had a high degree of accuracy to fit the respective clinical defects for which they were designed (0.27 mm morphological deviation of printed scaffolds from digital design). SIGNIFICANCE: From patient to patient, large alveolar bone defects are difficult to treat due to high variability in their complex morphologies and architecture. Our findings shows that Osteoink™ is a biocompatible material for 3D printing of clinically acceptable, patient-specific scaffolds with precision-fit for use in alveolar bone reconstructive procedures. Collectively, emerging digital technologies including CBCT imaging, 3D surgical planning, and (bio)printing can be integrated to address this unmet clinical challenge.

Development of Foot Displacement Detection Algorithm for Power Wheelchair Footplate Pressure and Positioning.

Inadvertent lower extremity displacement (ILED) puts the feet of power wheelchair (PWC) users at great risk of traumatic injury. Because disabled individuals may not be aware of a mis-positioned foot, a real-time system for notification can reduce the risk of injury. To test this concept, we developed a prototype system called FootSafe, capable of real-time detection and classification of foot position. The FootSafe system used an array of force-sensing resistors to monitor foot pressures on the PWC footplate. Data were transmitted via Bluetooth to an iOS app which ran a classifier algorithm to notify the user of ILED. In a pilot trial, FootSafe was tested with seven participants seated in a PWC. Data collected from this trial were used to test the accuracy of classification algorithms. A custom figure of merit (FOM) was created to balance the risk of missed positive and false positive. While a machine-learning algorithm (K nearest neighbors, FOM=0.78) outperformed simpler methods, the simplest algorithm, mean footplate pressure, performed similarly (FOM=0.62). In a real-time classification task, these results suggest that foot position can be estimated using relatively few force sensors and simple algorithms running on mobile hardware.Clinical Relevance- Foot collisions or dragging are severe or life-threatening injuries for people with spinal cord injuries. The FootSafe sensor, iOS app, and classifier algorithm can warn the user of a mis-positioned foot to reduce the incidence of injury.

Power Wheelchair Footplate Pressure and Positioning Sensor.

Power wheelchair users are at risk for severe injuries caused by foot mis-position on the footplate. This can lead to collisions or foot dragging which are severe or lifethreatening injuries for people with spinal cord injuries. The foot cannot be safely immobilized due to tilting pressure relief injuries, therefore, the foot can easily fall into a vulnerable position without the user realizing it. To reduce the likelihood of injury, we have developed a sensor for monitoring foot position in real time, as the wheelchair is driven. The sensor uses an array of force-sensing resistors and infrared distance sensors to detect the pressure and location of the foot within the immediate confines of the footplate. Sensor arrays with 23 force sensors and 14 infrared sensors per foot were fabricated on standard printed circuit boards and encapsulated in a durable thermoplastic urethane for environmental resistance. Fabricated sensors transmitted foot pressures and position data at 10 Hz using a Bluetooth Low Energy radio. An iOS app was developed to notify users of vulnerable foot position. Measured results confirmed the functionality of the system over typical foot pressures, and indicated that the device is ready for next-stage clinical trials with spinal cord injured power wheelchair users.