Neurostimulation for Chronic Pain Take Control of Relief Now
Neurostimulation for chronic pain management is a therapy that uses mild electrical pulses to interrupt pain signals traveling to your brain, offering a valuable alternative when other treatments haven’t brought relief. By targeting specific nerves or the spinal cord, it essentially “turns down the volume” on pain without the need for daily medications. Many people find this approach helps them regain control over their daily activities and enjoy a better quality of life, as the device can be adjusted to fit their unique pain patterns. It’s a transformative tool for those seeking long-term, non-drug pain relief.
Decoding Electrical Intervention: The Science Behind Pain Relief
Decoding electrical intervention in neurostimulation for chronic pain management hinges on modulating neural pathways through targeted electrical pulses. Devices deliver specific frequencies and amplitudes to disrupt pain signals traveling from peripheral nerves to the brain, a process known as the gate control theory. By stimulating inhibitory interneurons, the intervention effectively closes the neural “gate” to nociceptive input. Patient outcomes depend critically on precise electrode placement and parameter adjustment, which alters neurotransmitter release such as GABA and endorphins. Long-term efficacy often requires iterative recalibration as neural plasticity shifts the system’s response over months. The science directly translates to user control: individuals can adjust stimulation intensity via a remote unit to match daily fluctuations in pain severity.
How Nerves, Brain Signals, and Pain Perception Intersect
Chronic pain arises when nerves transmit exaggerated electrical signals to the brain, which interprets them as persistent pain. Neurostimulation alters this pathway by delivering mild electrical pulses that disrupt aberrant nerve firing and modulate brain signal processing. This gate control mechanism essentially closes neural “gates” in the spinal cord, preventing pain signals from reaching the brain’s perception centers. By overriding faulty signals, the brain reinterprets incoming data, reducing the sensation of pain without eliminating normal protective sensations.
- Nerve hyperactivity sends constant pain signals to the brain, creating chronic perception.
- Electrical pulses block these signals before they reach brain centers responsible for pain interpretation.
- The brain’s perception shifts as it receives modified, non-painful signals from stimulated nerves.
The Gate Control Theory: A Foundation for Modern Therapies
The Gate Control Theory provides the critical framework for modern neurostimulation. By proposing that non-painful input, such as mild electrical pulses, can close a “gate” in the spinal cord, it blocks pain signals from reaching the brain. This principle is the direct foundation for TENS and spinal cord stimulation devices. Targeting the spinal gate with electrodes effectively overrides chronic pain transmission. This mechanism explains why stimulating large nerve fibers can yield immediate, non-pharmacological relief for conditions like neuropathy. Q: How does The Gate Control Theory guide actual device settings? A: Therapies activate low-threshold touch fibers exclusively to compete with and inhibit pain signals, a direct application of the theory’s core premise.
Key Neuroanatomy Targets: Spinal Cord, Peripheral Nerves, and Cortex
Effective neurostimulation for chronic pain management targets three primary neuroanatomical structures. The spinal cord stimulation (SCS) disrupts pain signals via epidural electrodes placed over the dorsal columns. Peripheral nerve stimulation (PNS) delivers current directly to affected nerves, ideal for localized neuropathic pain. Cortical stimulation, typically targeting the motor cortex, modulates pain processing in the brain for refractory conditions.
| Target | Primary Application | Electrode Placement |
|---|---|---|
| Spinal Cord | Failed back surgery, complex regional pain | Epidural space, dorsal columns |
| Peripheral Nerves | Mononeuropathy, post-surgical pain | Adjacent to specific nerve trunk |
| Cortex | Central pain, post-stroke pain | Epidural/subdural over motor strip |
Selection depends on pain distribution and etiology, with each target offering distinct coverage and surgical risk profiles.
Types of Electrical Therapies for Persistent Pain
For persistent pain, neurostimulation offers targeted electrical therapies. Spinal cord stimulation (SCS) delivers mild pulses via implanted leads to mask pain signals before they reach the brain, effective for failed back surgery syndrome. Peripheral nerve stimulation (PNS) targets specific nerves, ideal for localized neuropathic pain. Dorsal root ganglion (DRG) stimulation provides precise relief for complex regional pain syndrome. Transcutaneous electrical nerve stimulation (TENS) is a non-invasive option using adhesive pads, though its evidence for long-term chronic pain is weaker than implanted systems. Q: Which therapy is best for nerve damage pain? A: PNS or DRG stimulation, as they directly address peripheral and focal neural origins.
Spinal Cord Stimulation: Implanted Devices and Waveform Innovation
Spinal cord stimulation (SCS) relies on implanted devices—a pulse generator and thin leads placed in the epidural space—to deliver electrical pulses that disrupt pain signals. Waveform innovation has transformed efficacy, moving beyond traditional tonic stimulation. Modern systems leverage burst and high-frequency waveforms to reduce paresthesia and target specific pain patterns, offering better relief for back and limb pain. Patients can often switch between waveforms via an external remote, allowing tailored, real-time adjustments without surgical intervention.
Advancements in implanted SCS devices, paired with novel burst and high-frequency waveforms, now enable non-paresthetic, patient-customizable pain relief that directly targets persistent pain pathways.
Peripheral Nerve Stimulation: Targeting Specific Pain Pathways
Peripheral nerve stimulation (PNS) targets specific pain pathways by placing electrodes directly on identified peripheral nerves outside the spine or brain. This approach allows precise modulation of nociceptive signals at their source, such as the occipital, saphenous, or radial nerves, before they reach the central nervous system. Pathway-specific electrostimulation relies on detailed anatomical mapping to disrupt aberrant pain transmission, often enabling therapy for focal neuropathic conditions where spinal cord stimulation is less effective. The procedure typically involves percutaneous lead insertion under ultrasound or fluoroscopic guidance to ensure accurate nerve capture. Unlike generalized systems, PNS offers a highly localized intervention with minimal spread of paresthesia.
Peripheral nerve stimulation precisely modulates identified peripheral nerve pathways to interrupt pain signals at their origin, providing a focal, anatomy-driven therapy for chronic neuropathic conditions.
Transcutaneous Electrical Nerve Stimulation (TENS): Non-Invasive Options
Transcutaneous Electrical Nerve Stimulation (TENS) offers a non-invasive option for chronic pain management by delivering low-voltage electrical currents through electrodes placed on the skin. Users can adjust pulse frequency and intensity to target specific pain pathways, often providing immediate relief for conditions like arthritis or neuropathy. This method carries minimal risk and allows for self-administered sessions at home, making it a practical first-line tool. TENS for persistent pain works by modulating nerve signals, effectively reducing discomfort without medication or needles.
TENS provides a safe, user-controlled, non-invasive electrical therapy that directly manages persistent pain by interrupting pain signals at the skin level.
Deep Brain and Motor Cortex Stimulation for Refractory Cases
For refractory pain unresponsive to less invasive neuromodulation, deep brain and motor cortex stimulation target specific cortical and subcortical structures. Deep brain stimulation (DBS) modulates the periaqueductal gray and thalamic nuclei, interrupting nociceptive transmission in conditions like central post-stroke pain. Motor cortex stimulation (MCS) instead alters thalamocortical dysrhythmia, showing efficacy for neuropathic facial pain and phantom limb pain. Both procedures require precise stereotactic electrode placement and intensive postoperative programming. Candidates must demonstrate a stable psychological profile, as efficacy depends on sustained engagement with therapy. Success rates remain variable; DBS yields about 50% pain reduction in selected patients, while MCS achieves meaningful relief in roughly 60% of appropriate cases.
Patient Selection: Who Gains the Most from These Approaches
Patient selection for neurostimulation hinges on identifying those with specific, refractory pain. The most gains are seen in people with failed back surgery syndrome or complex regional pain syndrome, where nerve signals are clearly misfiring. A strong psychological profile without major untreated depression is key, as the device requires active management. Q: Who gains the least? A: Patients with widespread, non-specific pain or significant untreated drug dependency, as the root cause isn’t a localized nerve issue.
Chronic Pain Conditions That Respond Well: Failed Back, Neuropathy, CRPS
Failed back surgery syndrome (FBSS), peripheral neuropathy, and complex regional pain syndrome (CRPS) rank among the most responsive chronic pain conditions for neurostimulation. In FBSS, epidural spinal cord stimulation targets residual radicular pain after prior surgical intervention. For neuropathy, high-frequency or dorsal root ganglion stimulation often relieves distal burning or numbness when conventional medications fail. CRPS, particularly in a single limb, shows strong outcomes with early neurostimulation, as the therapy directly disrupts maladaptive sympathetic signaling. Success hinges on confirming the pain is neuropathic rather than nociceptive, which these three conditions typically satisfy, making neurostimulation a highly effective neuromodulation target for patients with documented nerve involvement.
Contraindications and Risk Factors to Consider Before Implantation
Before implantation, absolute contraindications include active infection, untreated coagulopathy, or inability to undergo surgery. Relative risk factors involve psychological instability, opioid dependence, or prior failed trials. Implant candidacy requires thorough risk stratification for device migration, lead fracture, or infection. Imaging findings like severe spinal stenosis may preclude safe lead placement. Patients with poorly controlled diabetes or immunosuppression face elevated complication rates. Always verify no alternative therapies are more suitable.
Contraindications and risk factors—including infection, coagulopathy, psychological issues, and anatomical barriers—must be rigorously assessed to prevent complications and ensure safe implantation.
The Psychological Profile: Mood, Coping, and Treatment Compliance
A patient’s psychological profile is critical for predicting neurostimulation success. Those with stable mood, low depression or anxiety, and effective pain coping skills typically achieve better outcomes. In contrast, patients with catastrophizing or poor treatment adherence often struggle. Pre-screening for treatment compliance and coping mechanisms helps identify ideal candidates. How does mood affect neurostimulation results? Negative mood can amplify pain perception and reduce engagement, undermining device efficacy, while positive coping enhances self-management and sustained pain relief.
Clinical Evidence and Outcomes: What Research Reveals
Research reveals that spinal cord stimulation achieves a 50% or greater pain reduction in roughly 60–70% of patients with failed back surgery syndrome, as validated by long-term randomized trials. The SENZA-PNS study documented that peripheral nerve stimulation sustained over 80% pain relief for at least 12 months in chronic mononeuropathy patients. Yet outcomes are deeply individual: response often depends on precise electrode placement and psychological readiness for neuromodulation. A key clinical finding is that outcomes plateau after the first year, with post-hoc analyses showing reduced opioid use in over half of responders without degrading analgesic effect. Real-world evidence confirms that optimal results require monthly programming adjustments during the initial titration phase.
Randomized Trials Versus Observational Data: Weighing Efficacy
Randomized controlled trials (RCTs) for neurostimulation offer high internal validity by minimizing bias through blinding and sham controls, directly proving causal efficacy in pain reduction. However, their strict exclusion criteria often miss real-world patient heterogeneity. Observational data, conversely, captures long-term outcomes and comorbid complexities RCTs cannot, but risks confounding by indication. Weighing these, efficacy is best established via RCTs, while effectiveness—how therapy performs in practice—relies on robust observational evidence. Neither alone suffices; a pragmatic synthesis evaluates RCT results against consistent, high-quality registry data to guide patient selection.
| Aspect | Randomized Trials | Observational Data |
|---|---|---|
| Primary strength | Proves causal efficacy | Reflects real-world use |
| Key limitation | Low external validity | Confounding bias |
| Best for | Initial device approval | Long-term outcome tracking |
Long-Term Success Rates: Sustained Relief and Device Tolerance
Longitudinal studies tracking neurostimulation for chronic pain management report that approximately 50-60% of patients maintain ≥50% pain relief beyond two years, a metric defined as sustained clinical response. Device tolerance, however, declines over time; about 20-30% of recipients elect for explantation by year five, often due to lead migration, infection, or waning efficacy rather than initial failure. paresthesia adaptation—where the brain habituates to stimulation—can reduce relief, requiring program adjustments. Q: What percentage of patients retain adequate relief at five years? A: Research indicates roughly 40-50% of those initially implanted still report meaningful pain reduction at the five-year mark, though revision surgeries are common to maintain this outcome.
Comparative Effectiveness: Stimulation Versus Medication or Surgery
Comparative effectiveness research demonstrates that neurostimulation often yields superior long-term pain relief and functional improvement compared to long-term opioid therapy, which carries significant risks of tolerance and addiction. Unlike surgery, which directly alters anatomy and involves invasive recovery, neurostimulation offers a reversible, adjustable intervention with fewer complications. Studies show that for conditions like failed back surgery syndrome, spinal cord stimulation provides comparable or better outcomes than repeat operations, reducing the need for further invasive procedures. However, medication remains a first-line approach due to lower upfront costs, though stimulation versus medication or surgery favors stimulation when considering sustained efficacy and safety over extended follow-up periods.
Procedure Details: From Trial to Permanent System
The procedure begins with a temporary trial, where one or more thin leads are inserted percutaneously into the epidural space and connected to an external stimulator. Over 3–7 days, you adjust stimulation parameters to map coverage of the painful area, with real-time feedback guiding optimal lead placement. If pain relief exceeds 50%, you proceed to the permanent system. The permanent implant involves creating a subcutaneous pocket, typically in the upper buttock or abdomen, to house the implantable pulse generator (IPG). The trial leads are replaced with permanent leads anchored to the spine, then tunneled subcutaneously to the IPG. Trial success directly determines permanent candidacy, with the trial acting as a reversible proof of concept before committing to the surgical implant.
The goal is to achieve stable paresthesia coverage over the pain area before finalizing lead position and IPG programming.
Post-implant, you undergo initial programming to fine-tune settings, with follow-up visits over weeks to optimize efficacy.
Initial Screening and Psychological Evaluation Steps
Initial screening for neurostimulation candidacy begins with a comprehensive medical history review and targeted physical examination to identify organic pain sources. The subsequent psychological evaluation assesses for untreated mood disorders, catastrophizing, or poor coping mechanisms that predict trial failure. Clinicians use validated tools like the MMPI-2 or PHQ-9 to evaluate readiness. A key aim is confirming the patient has realistic expectations and can operate the device. Psychological clearance for stimulator trial requires stable psychosocial function and absence of active substance abuse. The evaluation concludes by teaching the patient about trial logistics and device interaction.
Initial screening verifies pain origin, while psychological evaluation confirms emotional stability and realistic expectations, ensuring the patient is prepared for the neurostimulation trial.
The Temporary Stimulator Trial: Duration and Success Criteria
The temporary stimulator trial typically lasts between three and seven days, during which an externalized lead delivers electrical pulses to the targeted neural pathway. Clinicians define trial success criteria as a documented reduction in baseline pain intensity of at least 50%, often measured via daily pain diaries and functional activity logs. Patients are advised to test various settings and postures to confirm consistent analgesia without paresthesia intolerance. If the predetermined threshold is met and the patient reports improved quality of life, the permanent system is scheduled. Conversely, failure to achieve adequate relief or adverse stimulation effects disqualifies the patient from implantation.
Surgical Implantation of Leads and Pulse Generator
Surgical implantation of leads and pulse generator occurs after a successful trial, typically under sedation or general anesthesia. The leads are placed via a needle or laminotomy, navigating to the targeted epidural space using fluoroscopic guidance. Once optimal paresthesia coverage is confirmed through intraoperative testing, the leads are anchored to fascia to prevent migration. The pulse generator is then positioned in a subcutaneous pocket, usually in the upper buttock or abdomen, with the extension tunneled subcutaneously to connect. Wound closure is layered; the system is activated postoperatively.
Q: How long does the surgical implantation procedure take?
A: The procedure generally lasts one to two hours, depending on lead count and patient anatomy.
Post-Operative Programming and Remote Titration Options
Following implantation, post-operative programming and remote titration options allow clinicians to refine stimulation parameters without requiring in-person visits. The process follows a clear sequence:
- Initial baseline programming establishes stimulation amplitude, frequency, and electrode configuration using a clinician programmer.
- A remote titration system, such as a secure patient controller or smartphone app, enables users to adjust intensity within pre-set safety limits.
- Periodic cloud-based data transmission allows the care team to analyze usage patterns and propose parameter updates.
Fine adjustments via remote titration can extend battery life while maintaining therapeutic coverage. Patients must receive hands-on training to navigate these controls safely.
Managing Potential Complications and Side Effects
Effective management of potential complications with neurostimulation for chronic pain hinges on proactive patient engagement and precise device oversight. Early post-implantation issues like localized infection or hematoma require vigilant wound care and prompt reporting of redness or swelling. Device-specific side effects, such as lead migration causing shocking sensations or loss of coverage, are addressed through routine reprogramming by a specialist. Patients must also monitor for preventing neurological injury by avoiding activities that stress the lead—like sudden twisting or heavy lifting—and promptly reporting any new motor or sensory changes, such as leg weakness. Battery depletion must be tracked via regular recharging or replacement schedules to prevent sudden pain return, ensuring continuous therapy efficacy through careful, collaborative follow-up.
Infection, Lead Migration, and Hardware-Related Issues
When managing a neurostimulation system, watch for signs of device-related infection like redness, swelling, or fever at the implant site—catching it early prevents complications. Lead migration can happen if the electrode shifts from its original position, reducing pain coverage or causing odd sensations; a simple reprogramming or revision might fix it. Hardware issues, such thync as battery depletion or connection failures, often require a checkup to avoid losing therapy benefits. A loose connection can sometimes mimic new back pain, so don’t ignore subtle changes in sensation.
- Monitor the implant site daily for warmth, drainage, or pain that could signal infection.
- If your pain relief suddenly changes or you feel new tingling, report it promptly—lead migration may be the cause.
- Keep track of battery life and note any unexpected stimulator shutdowns to address hardware problems early.
Habituation of Effect: Tolerance and Plateau in Pain Relief
Over time, you might notice your pain relief from neurostimulation feels less effective, which is called habituation of effect. This tolerance or plateau happens because your nervous system adapts to the constant signal. To manage it, your clinician might suggest a simple reset:
- Switch your stimulation program to a different frequency or pulse width.
- Take periodic “stimulation holidays” by turning the device off for a few hours or overnight.
- Adjust electrode positioning slightly to engage new nerve pathways.
These tweaks help prevent the plateau and keep your relief consistent without needing higher intensity.
Strategies to Minimize Shocks, Tingling, or Unwanted Sensations
Minimizing shocks, tingling, or unwanted sensations in neurostimulation hinges on precise programming and patient-device interaction. Clinicians should conduct thorough trial-based mapping of stimulation parameters to identify current amplitudes and frequencies that provide analgesic coverage without inducing paresthesia. Patients must log specific sensation triggers, allowing for targeted pulse-width adjustments.
- Gradually increase amplitude in small increments during session setup to bypass sudden overstimulation.
- Switch to burst or high-frequency stimulation modes when tonic patterns cause persistent tingling.
- Reposition the patient’s body during programming to account for postural changes that alter lead distance from neural targets.
- Utilize multiple independent current control to redirect energy away from dorsal column fibers eliciting unintended shock sensations.
Lifestyle Impact and Day-to-Day Management
Integrating neurostimulation into daily life means adjusting to device maintenance routines like charging or swapping batteries, often at night to avoid interruptions. You’ll need to manage charging schedules to ensure consistent pain relief during waking hours. Remote controls allow on-demand program adjustments for activities—boosting stimulation before a walk or lowering it for sleep. Users often keep a backup charging cable in their car or bag to prevent unexpected downtime during errands. Waterproofing varies by device, so showering habits may require minor changes, like using a waterproof cover. Over time, you learn to toggle between settings seamlessly, making pain management feel like a natural part of your routine rather than a disruptive chore.
Adjusting Daily Activities: Driving, Exercise, and Sleep
Adjusting daily activities is crucial when neurostimulation is used for chronic pain management. Patients must avoid driving during initial device programming or when settings are altered, as sudden stimulation changes can impair reaction time and cause dizziness. Exercise requires careful planning; high-impact or twisting movements may dislodge leads, while low-impact activities like walking or stationary cycling can enhance stimulation efficacy without risking lead migration. Sleep positioning matters: sleeping on the implant site can cause discomfort or disrupt the device, so back or opposite-side sleeping is advised. Adhering to these modifications ensures safe neurostimulation integration into daily routines without compromising pain relief or device function.
Battery Life, Charging Habits, and Replacement Scheduling
Battery life for neurostimulation devices varies by model, typically lasting three to nine years, making charging habits and replacement scheduling critical for consistent pain relief. Rechargeable systems require nightly or bi-weekly charging sessions to avoid therapy interruptions, while non-rechargeable units demand precise surgical replacement planning. Users must log charge cycles to predict degradation, as premature battery failure disrupts stimulation. Scheduling a replacement battery surgery should align with battery depletion trends, avoiding emergency procedures. Adhering to manufacturer guidelines for charge duration and depth preserves battery health, ensuring stable chronic pain management without unplanned downtime.
Battery life dictates rechargeable charging habits or non-rechargeable replacement scheduling; consistent charging and proactive replacement planning prevent therapy gaps in chronic pain management.
Navigating MRI Compatibility and Other Medical Restrictions
Living with a neurostimulator requires careful attention to MRI compatibility and other medical restrictions. Patients must verify their specific device model’s approval for MRI scans; older systems often require full explant before imaging, while newer conditionally-safe devices allow scanning under strict parameters—such as limited body region, field strength, and mode settings. Beyond MRIs, procedures like diathermy, electrocautery, and certain radiation therapies can interfere with lead pathways or damage the implant. Pre-procedure communication with both the pain specialist and treating clinician is essential to confirm device settings, deactivation protocols, and alternative diagnostic options, ensuring safety without disrupting pain management.
Emerging Frontiers and Future Directions in Pain Control
The emerging frontier in neurostimulation for chronic pain management is the shift toward closed-loop, adaptive systems that respond in real time to neural biomarkers of pain. Unlike fixed-parameter devices, these next-generation stimulators can modulate frequency, intensity, and target zones dynamically based on your physiological feedback. A key insight is that
future devices will likely integrate machine learning to predict pain flares before they reach conscious perception, offering preemptive rather than reactive relief.
Simultaneously, the field is advancing into non-invasive ultrasound and optogenetic stimulation, which promise more precise targeting without surgical implantation. For you, this means future protocols may involve brief daily sessions with wearable gear that recalibrates to your specific neural patterns, drastically reducing the need for trial-and-error programming visits.
Closed-Loop Systems: Real-Time Adjustment Based on Neural Feedback
Closed-loop systems represent a paradigm shift by enabling real-time adjustment based on neural feedback for chronic pain. Unlike open-loop devices delivering constant stimulation, these systems continuously monitor spinal or cortical signals and instantly recalibrate parameters—frequency, pulse width, or amplitude—to match the patient’s fluctuating pain levels. This dynamic response prevents overstimulation or under-treatment, often reducing the need for manual reprogramming. Users experience more consistent relief as the device autonomously adapts during movement, posture changes, or pain flares. Practical implementation relies on embedded algorithms analyzing evoked compound action potentials or local field potentials, allowing the system to detect neural signatures of pain before the patient perceives it.
Wireless and Miniaturized Implants: Reducing Invasiveness
Wireless and miniaturized implants are slashing the invasiveness of neurostimulation by ditching bulky batteries and wired leads. Instead of a large pocket under the skin for a power source, these tiny devices are placed directly at the nerve target via a single, small injection or keyhole incision. This shift means drastically smaller surgical wounds, lower infection risks, faster recovery times, and less scarring. As the implants are smaller and more flexible, they also cause less tissue irritation, making them a far more comfortable option for long-term chronic pain management compared to older, clunkier systems. Patients can often get back to their normal routine within a day or two.
Integration with Wearables and Digital Health Platforms
Integration with wearables and digital health platforms enables real-time, bidirectional communication between a neurostimulation device and the patient. A smartwatch or patch can continuously capture biometric data, such as heart rate variability or activity levels, and transmit it to a cloud-based platform. This data is then analyzed to automatically adjust stimulation parameters—like pulse frequency or amplitude—in response to detected pain episodes or movement patterns. Patients can also log symptom flares directly through a companion app, which refines the algorithm over time. This closed-loop system personalizes therapy without requiring manual intervention, improving daily adaptive pain modulation through seamless sensor-driven adjustments.
Potential for Combination Therapies: Stimulation Plus Regenerative Medicine
Combining neurostimulation with regenerative medicine creates a powerful synergy for chronic pain. Stimulation primes the neural environment, enhancing blood flow and reducing inflammation, which directly improves the survival and integration of transplanted cells or growth factors. This synergistic pain repair approach targets the underlying pathology, not just symptoms. For example, spinal cord stimulation applied alongside stem cell injections can guide regenerating neurons to restore proper signaling pathways, potentially reversing neuropathy.
- Stimulation can activate dormant neural stem cells, boosting the effectiveness of injected biomaterials.
- Regenerative agents help rebuild damaged tissue, reducing the electrical energy needed for sustained pain relief.
- Combining modalities may extend pain-free periods far beyond what either therapy achieves alone.
- Personalized protocols could match stimulation frequencies to the specific regenerative growth factors being delivered.