Medical device: molding, BLE, validation

From MVP to Medical Device: Technical Solutions for Casting, BLE Control, and International Validation

The development of a medical device has moved beyond a hobby project: the first 25 units of the housing have been produced using vacuum casting, the mobile app version on React Native with iOS and Android support has been completed, and a two-week field validation in the United States has been successfully carried out—including testing of the 'Biolumos Mini' in Ohio. This article describes the technical solutions, architectural trade-offs, and engineering challenges encountered during the transition from prototype to a certifiable product.

Vacuum Casting as an Intermediate Production Stage

For the batch of 25 housings, FDM printing was abandoned: unstable geometry, poor repeatability, and rough surfaces made the parts unsuitable for demonstration to potential partners and clinical users. The choice fell on vacuum (cold) casting—a technology that balances rapid prototyping with the quality of mass-produced items.

The process consists of three phases:

• Creation of a master model using a photopolymer 3D printer (SLA/DLP)—high precision and minimal shrinkage;
• Casting of a silicone mold: lifespan of 20–30 cycles, requiring manual cleaning and wall-thickness control;
• Injection of a two-component polyurethane followed by vacuum chamber processing (bubble removal), thermal cycling, and manual finishing.

The material used mimics ABS in terms of rigidity, heat resistance, and machinability—but without the shrinkage and internal stresses typical of FDM. The surface after casting does not require sanding or painting, which is critical for medical devices: the absence of additional coatings reduces the risk of degradation and ensures biocompatibility.

The cost per part increased by 3.2 times compared with printing, but post-processing time decreased by 78%. For an MVP, this is justified: stable geometry allows for reproducible testing of electromagnetic compatibility (EMC), mechanical stress on fasteners, and sealing integrity of the housing.

Mobile App Architecture: React Native + BLE Stack with Fault-Tolerant Control

The app is built on React Native 0.74, using react-native-ble-plx (v4.6.0) as the primary BLE driver. The architecture is divided into three layers: UI logic, connection management service, and a native adapter for platform-specific features.

Key technical solutions include:

• Automatic reconnection upon BLE session disconnection: implemented through a combination of scanForPeripheralsWithServices() and connectToDevice() with exponential backoff (from 500 ms to 5 s);
• Caching device parameters in AsyncStorage with subsequent synchronization upon connection establishment;
• Handling firmware version conflicts: if the firmware version is < 2.1.0, the app blocks access to manual control mode and displays a warning;
• Support for two types of BLE services: one for control commands (UUID 0000fff0-0000-1000-8000-00805f9b34fb), the other for telemetry transmission (board temperature, battery charge, MAC address).

On iOS, manual configuration of Info.plist was required: keys such as NSBluetoothAlwaysUsageDescription, NSLocationWhenInUseUsageDescription, and UIBackgroundModes with bluetooth-central were added. On Android, the ACCESS_FINE_LOCATION permission was requested at runtime, and android.permission.BODY_SENSORS was declared for proper background scanning.

For debugging, react-native-debugger with a custom plugin is used, which logs all BLE packets in HEX + ASCII format and builds a timeline of connection/disconnection events.

Field Validation in the USA: From Ergonomics to Therapeutic Effect

In December 2025, two versions of the device were tested in Ohio: the main MVP and the simplified 'Biolumos Mini'. The goal was not marketing demonstration, but data collection on three metrics: usability (assessed via the System Usability Scale), adherence (frequency of use over 14 days), and preliminary efficacy (subjective assessment of effect on a 5-point scale).

Participants—12 individuals aged 42–68, all diagnosed with chronic pain conditions (osteoarthritis, fibromyalgia). Testing conditions: home use without medical supervision, daily reporting via the in-app journal.

Key observations:

• The 'Mini' achieved 92% adherence compared to 63% for the main MVP (reason: ease of switching on/off and no need for synchronization);
• The main device received an ergonomics score of 4.1/5, but 7 out of 12 participants noted discomfort when attaching it for prolonged use (>20 minutes);
• The therapeutic effect was rated higher when using the 10 Hz pulsed mode with vibration (average score 4.4/5) than with continuous illumination (3.2/5);
• 100% of participants noted that the app interface was 'intuitively understandable,' but 8 out of 12 requested the ability to export the log to CSV.

These findings formed the basis for refining the mechanical design and expanding the app's functionality—specifically, implementing automatic log export and modular mounting.

What Matters

• Vacuum casting is not an alternative to injection molding, but an intermediate step that allows producing 20–30 parts with certification-acceptable geometry and surface quality without investing in tooling.
• With proper architecture (separating BLE logic from the UI), React Native ensures 92% code consistency between iOS and Android, but requires manual handling of platform-specific permissions and background execution.
• Field validation in the USA showed that for home medical devices, adherence is just as critical as effectiveness—and it can be improved by radically simplifying the UX and eliminating mandatory synchronization.
• To enter the U.S. market, FDA 510(k) clearance is required, which necessitates documentation according to ISO 13485, IEC 62304 (software lifecycle), and IEC 60601-1 (electrical safety). Prototypes sent to Ohio are not considered 'clinical devices' in the legal sense—they are classified as 'research-use-only'.
• The mobile app must comply with HIPAA—even if data is not transmitted to a server: local log storage requires AES-256 encryption and key protection via Keychain (iOS) and Keystore (Android).

Roadmap: From MVP to Certified Product

The next six months will focus on three areas:

1. Clinical Validation

• Partnership with two university clinics (U.S. and EU) for a randomized controlled trial (RCT) with n=45 per group;
• Development of an evaluation protocol: primary endpoint—change in VAS pain scale after 4 weeks; secondary—usage frequency and sleep quality (assessed via actigraphy);
• Preparation of documentation for the ethics committee: Informed Consent Form, Investigator Brochure, Clinical Study Report template.

2. Certification and Compliance

• Audit of software development processes according to IEC 62304 Class B;
• EMC testing in an accredited laboratory (EN 60601-1-2:2015);
• Biological evaluation of housing materials according to ISO 10993-1 (cytotoxicity, sensitization, irritation);
• Preparation of technical dossier for CE Marking (Class IIa) and FDA 510(k).

3. Technical Development

• Porting the firmware to FreeRTOS with task prioritization: BLE stack (priority 5), sensor acquisition (priority 4), LED/vibration control (priority 3), watchdog (priority 1);
• Implementation of OTA updates via BLE DFU (Device Firmware Upgrade) with ECDSA-P256 signature;
• Adding a 'Clinical Mode' to the app: disabling all user functions, enabling timestamped logging with GPS coordinates (for RCT).

Transitioning from MVP to a regulatory-approved product is not about scaling up, but rethinking every component—from the choice of housing material to the firmware architecture. Every decision must be documented, reproducible, and backed by data—otherwise no regulatory authority will accept it.

— Editorial Team